A STUDY OF DIETARY PROTEIN FOR GROWING CALIFORNIAN RABBITS IN THE MEKONG DELTA OF VIETNAM

And the last experiment was to determine the optimum ME level in diets of growing Californian rabbits under feeding conditions in the Mekong Delta of Vietnam.. 64 4.2 Experiment 2: Effec

MINISTRY OF EDUCATION AND TRAINING

CAN THO UNIVERSITY

TRUONG THANH TRUNG

A STUDY OF DIETARY PROTEIN FOR GROWING CALIFORNIAN RABBITS IN THE MEKONG DELTA OF VIETNAM

DOCTORAL THESIS IN ANIMAL SCIENCE

2017

MINISTRY OF EDUCATION AND TRAINING

CAN THO UNIVERSITY

TRUONG THANH TRUNG

A STUDY OF DIETARY PROTEIN FOR GROWING CALIFORNIAN RABBITS IN THE MEKONG DELTA OF VIETNAM

DOCTORAL THESIS IN ANIMAL SCIENCE

SCIENTIFIC SUPERVISOR

ASSOCIATE PROFESSOR NGUYEN THI KIM DONG

2017

ACKNOWLEDGMENT

I would like to thank to lectures at Department of Animal Science, Can Tho University who gave me useful knowledge and encouraged me during the course

I want to express particular appreciation to my supervisors, Association Professor Dr Nguyen Thi Kim Dong and Professor Dr Nguyen Van Thu, Department of Animal Science, Can Tho University, Vietnam, for all your support, advice and explanation throughout the research, also for their reading and correcting my thesis papers I learnt a lot of useful knowledge and real life experience from them

My thanks are extended to my classmates for sharing knowledge and experience in class Many thanks to my friends in rabbit farm in Can Tho University for their help and encouragement to me

Last but not least, special thanks to my parents, younger brother, sisters, aunt and my girlfriend for their love and moral support

I would like to thank all the people who contributed to this study

Truong Thanh Trung

ABSTRACT

This thesis is based on five experiments that were conducted at the experimental farm in Cantho City to evaluate protein utilization of growing Californian rabbits in the Mekong Delta of Vietnam The first experiment was

to identify the nutritional values of some common feedstuffs for feeding rabbits in the Mekong Delta The second was to determine the optimum level

of crude protein in diets of growing Californian rabbits The third was to compare and choose appropriate protein sources in diets of growing Californian rabbits The fourth was to find out optimum level of lysine and threonine in diets for growing Californian rabbits And the last experiment was

to determine the optimum ME level in diets of growing Californian rabbits under feeding conditions in the Mekong Delta of Vietnam

The results showed that in the first experiment, almost essential and

non-essential amino acid components of water spinach and Psophocarpus

scandens were higher than those of Operculina turpethum and para grass

Sweet potato vine and water spinach leaves were good feedstuffs with high CP values and proportional fiber components Soybean had low values of essential amino acids and non-essential amino acids than those of fish meal, feather meal and blood meal with the exception of methionine, glutamic and arginine concentrations

In the second experiment, the CP intake increased (P<0.05) while the

NDF, ADF and EE intakes decrease (P<0.05) among treatments The daily

weight gain were significantly different (P<0.05) among treatments with the higher values (22.4, 23.3 and 23.2 g/day) for the CP19, CP21 and CP23 treatments The carcass, thigh meat and lean meat weights were significantly higher (P<0.05) for the animals fed the 19, 21 and 23% CP treatments and the highest profit was obtained for the CP21 treatment

In the third experiment, intakes of DM, OM, CP, EE, NDF, ADF and

ME of the soybean extraction meal (SEM) and water spinach leaves meal (WLM) treatments were significantly higher (P<0.05) than those the other treatments The digestible DM, OM, CP, EE, CF, NDF and ADF were significantly higher (P<0.05) for the SEM and WLM treatments as compared

to the feather meal (FEM) and blood meal (BM) treatments Daily weight gain was significantly different (P<0.05) among treatments with the highest value for the SEM treatment (22.8 g/day) and the lowest value for the FEM treatment (14.9 g/day) The carcass weight and carcass percentage of the SEM and WLM treatments were significantly (P<0.05) higher than those of the FEM and BM, while the higher profit was found for the WLM and SEM treatments (3.07 and 2.63 USD/rabbit), respectively

In the fourth trial, almost amino acid digestibility of rabbits were significantly higher (P<0.05) for the 0.95-Lys treatment as compared to the 0.85-Lys and 1.05-Lys treatments In term of threonine treatments, digestibility coefficients of almost amino acids were significantly different (P<0.05) with the higher values for the 0.75-Thr treatment Daily weight gain

of rabbit in the 0.95-Lys and the 0.75-Thr treatments (22.4 and 22.2 g/day, respectively) were significantly higher (P<0.05) than that of the 0.85-Lys and the 1.05-Lys treatments and the 0.65-Thr treatments, respectively The carcass, lean meat and thigh weights of rabbit in the 0.95-Lys treatments were significantly higher (P<0.05) than others lysine treatments The carcass, lean meat and thigh weights were also significantly different (P<0.05) between threonine treatments and the higher results were found for the 0.75-Thr treatment

In the fifth experiment, the DM and CP intakes were not significantly different among treatments being from 69.4-74.5 and 13.2-14.2 gDM/rabbit/day, respectively The digestible DM, OM and CP were not significantly different (P>0.05) among treatments being 39.9-45.4, 35.8-41.3 and 7.65-9.06 g/rabbit/day, respectively Daily weight gain was significantly different (P<0.05) among treatments with the highest value (24.5 g/day) for the ME11.5 treatment The carcass, lean meat and thigh meat weights were significantly different (P<0.05) among treatments with the highest values in the ME11.5 treatment (1.374, 1.049 and 412 g, respectively)

It was concluded that the combination among locally available feedstuffs in the Mekong Delta of Vietnam could formulate balanced nutrient diets for Californian growing rabbits The diets contained 19% CP, 0.95% Lysine and 0.75% Threonine and 11.5 MJME/kgDM should be fed on growing Californian rabbits for improving growth performance, nutrient digestibilities, carcass quality and economic returns Soybean extraction meal should be used in the Californian rabbit diets, as a protein supplement source due to its appetite and high nutrient digestibility

Keywords: carcass quality, income, nitrogen, nutrient digestibility, rodents

DECLARATION

I assure that this thesis is a scientific work that was implemented by myself All the figures and results presented in the thesis are true and not published in any previous theses

Author

Truong Thanh Trung

CONTENT

Page

Chapter 1 Introduction 1

1.1 Problem statement 1

1.2 Research objectives 3

1.3 Key findings 3

1.4 Sciential and practical values 3

Chapter II Literature review 5

2.1 Californian rabbits 5

2.1.1 History 5

2.1.2 Appearance 5

2.1.3 Temperament 5

2.1.4 Californian rabbits in Vietnam 6

2.2 The Understanding of Protein digestion on rabbit 7

2.2.1 Some features of the protein sources using in rabbit diets 7

2.2.2 Some characteristics of rabbit diets in Mekong Delta Vietnam 9

2.2.3 Balance of protein and amino acid 10

2.2.4 Crude protein and total amino acids 11

2.2.5 Faecal digestibility 12

2.2.6 Ileal digestibility 13

2.2.7 Nitrogen metabolism in the caecum 19

2.2.8 Protein digestion in young rabbits 21

2.3 Soft faeces and protein digestibility 22

2.4 The enhanced objectives for protein nutrition in rabbits 26

2.4.1 A documented context 26

2.4.2 The relation between nitrogen and microbial growth 29

2.4.3 The interaction of nitrogen ileal flow and intestinal health 31

2.4.4 The trend of using protein in rabbit diets 35

Chapter III Materials and methods 38

3.1 Location and time 38

3.2 Animals and housing 39

3.3 Feed and feeding 39

3.4 Experimental design 45

3.5 Sampling procedure for nutrient digestibility 49

3.6 Chemical analyses 49

3.7 Measurements 49

3.8 Statistical analysis 50

Chapter IV Results and discussion 51

4.1 Experiment 1: Nutrient evaluation with emphasis on amino acid values of the common feedstuffs for rabbits in the Mekong delta, Vietnam 51

4.1.1 Nutrient composition of natural plants for feeding rabbits 51

4.1.2 Nutrient composition of agricultural and industrial by-products for feeding rabbits

54 4.1.3 Nutrient composition of protein and energy supplemental feed ingredients for feeding rabbits 58

4.1.4 Summary 64

4.2 Experiment 2: Effects of dietary crude protein levels on growth rate, meat production, digestible nutrients and economic return of Californian rabbits in Mekong Delta Vietnam 65

4.2.1 Feed and nutrient intakes 65

4.2.2 Daily weight gain and economic returns 66

4.2.3 Carcass and meat nutrients 67

4.2.4 Nutrient digestibility and nitrogen retention 68

4.2.5 Summary 69

4.3 Experiment 3: Effect of different protein sources in the diets on feed intake, nutrient digestibility, growth and carcass value of Californian rabbits in the Mekong Delta Vietnam 70

4.3.1 Feed and nutrient intakes 70

4.3.2 Growth performance and economic returns 71

4.3.3 Carcass values and meat nutrients 72

4.3.4 Nutrient digestion and nitrogen retention 73

4.3.5 Summary 75

4.4 Experiment 4: Effect of lysine and threonine levels in the diets on feed intake, nutrient digestibility, growth and carcass value of Californian rabbits in the Mekong Delta, Vietnam 76

4.4.1 Feed and nutrient intakes 76

4.4.2 Growth performance and economic returns 78

4.4.3 Carcass values and meat quality of experimental rabbits 80

4.4.4 Nutrient digestion and nitrogen retention 81

4.4.5 Summary 83

4.5 Experiment 5: A response of feed utilization, nutrient digestibility, growth and carcass value of Californian rabbits to dietary metabolizable energy 84

4.5.1 Feed and nutrient intakes 84

4.5.2 Growth performance and economic returns 85

4.5.3 Carcass values and meat nutrients 86

4.5.4 Nutrient digestion and nitrogen retention 87

4.5.5 Summary 89

Chapter V Conclusion and recommendations 90

References 92

Appendices 109

LIST OF FIGURES

Page Figure 2.1 Relative value of some protein sources in rabbit diets in relation to soybean meal (100) using different nitrogen units (total versus apparent (app.)

faecal digestible 11

Figure 2.2 Apparent (a) and true (b) ileal amino acid digestibility of soybean meal with respect to its crude protein digestibility 15

Figure 2.3 Relationship between faecal crude protein (CP) digestibility and amino acid true ileal digestibility 17

Figure 2.4 Caecal nitrogen metabolism 20

Figure 2.5 Effect of the crude protein (CP) concentration of the caecal contents on the CP of soft faeces 23

Figure 2.6 Contribution of soft faeces to the total intake of crude protein and some amino acids 26

Figure 2.7 Relationship between mortality (%) and the DP/DE ratio in the growing period ………31

Figure 2.8 Effect of ileal flux of crude protein on mortality from 25 to 60 days of age 33

Figure 2.9 Relationship between average daily gain (g/d) and the DP/DE ratio in the growing period 36

Figure 3.1 Cages were used in the nutrient digestibility experiment 39

Figure 3.2 Operculina turpethum 43

Figure 3.3 Water spinach 43

Figure 3.4 Psophocarpus scandens 43

Figure 3.5 Para grass 43

Figure 3.6 Sweet potato vines 43

Figure 3.7 Water spinach leaves 43

Figure 3.8 Soybean extraction meal 43

Figure 3.9 Soya waste 43

Figure 3.10 Soybean meal 44

Figure 3.11 Fish meal 44

Figure 3.12 Feather meal 44

Figure 3.13 Blood meal 44

Figure 3.14 Maize 44

Figure 3.15 Broken rice 44

Figure 3.16 Sweet potato tuber 44

Figure 3.17 Amino acids were used in the study 45

Figure 3.18 Rabbits for slaughtering 50

Figure 3.19 Experimental rabbit carcass 50

Figure 3.20 Rabbit thigh 50

Figure 3.21 Rabbit thigh meat 50

Figure 3.22 Rabbit lean meat 50

Figure 4.1 DM, CP and ME concentration of para grass, water spinach, Psophocarpus scandens and Operculina turpethum 52

Figure 4.2 Lysine, Threonine and Methionine concentration of para grass, water spinach, Psophocarpus scandens and Operculina turpethum 54

Figure 4.3 CP, NDF and ME concentration of sweet potato vines, water spinach leaves, soybean extraction meal and soya waste 56

Figure 4.4 Lysine, Threonine and Methionine concentration of sweet potato vines, water spinach leaves, soybean extraction meal and soya waste 57

Figure 4.5 DM, CP and ME concentration of soybean, fish meal, feather meal and blood meal 61

Figure 4.6 Lysine, Threonine and Methionine concentration of soybean, fish meal, feather meal and blood meal 62

Figure 4.7 DM, CP and ME concentration of maize, broken rice and sweet potato tuber 63

Figure 4.8 Lysine, Threonine and Methionine concentration of maize, broken rice and sweet potato tuber 64

Figure 4.9 Effect of CP intake on daily gain of rabbits in the experiment 67

Figure 4.10 Effect of ME concentration in diets on daily weight gain of rabbits in the experiment 86

LIST OF TABLES

Page Table 2.1 Proportions of the different types of proteins in total protein of cereal and legume grains 8 Table 2.2 Amino acid composition (g/16 g nitrogen) of wheat proteins 8 Table 2.3 Crude protein (g/kg dry matter) of leaves and stems of lucerne hay and the amino acid composition (as a proportion of total amino acids) of leaf protein from fresh lucerne 9 Table 2.4 Dietary composition of growing rabbit diets in Mekong delta Vietnam 9

Table 2.5 The invitro OMD (%) by using rabbit caecum fluid of some

common feeds for rabbit production in the Mekong delta Vietnam 10 Table 2.6 Prediction equations for apparent faecal digestible protein (DP, g/kgDM) from chemical composition (g/kgDM) for different groups of feed ingredients 12 Table 2.7 Amino acid composition (g/16 g nitrogen) of endogenous flow at the ileal and faecal levels 14 Table 2.8 Total and digestible protein and amino acid content (g/kg dry matter) using different units for the most important sources 18 Table 2.9 Effect of age on apparent ileal crude protein (CP) digestibility and the distribution of protein apparently digested 22 Table 2.10 Protein and amino acid recommendations according to several authors (as-fed basis) 27 Table 2.11 Ileal balance in adult rabbits fed alfalfa based diets 30 Table 2.12 Effect of the level of protein in isofibrous diets (30% NDF) on pathogenic flora and mortality in early (25 d) weaned rabbits … 32

Table 2.13 Effect of level and type of dietary CP on intestinal health and ileal CP flow 34

Table 3.1 Chemical composition and metabolism energy concentration of feeds used in experiment 2 (%DM) 40 Table 3.2 Chemical composition (% DM) and metabolism energy concentration of feeds used in experiment 3 41 Table 3.3 Chemical composition and metabolism energy concentration of feeds used in experiment 4 (% DM, with the exception of DM as fed basic) 42

Table 3.4 Chemical composition and metabolism energy concentration of feeds in experiment 5 (%DM) 42 Table 3.5 Dietary feed ingredients and metabolism energy concentration of the experiment 2 45 Table 3.6 Feed ingredients composition, chemical composition and metabolism energy concentration of diets in the Exp 3 (% DM) 46 Table 3.7 Feed ingredients composition, dietary chemical composition and metabolism energy concentration in the experiment 4 (% DM) 47 Table 3.8 Feed ingredients composition, dietary chemical composition and metabolism energy concentration in the experiment 5 (% DM) 48 Table 4.1 Nutrient composition of natural grasses for feeding rabbits (Mean ±

SD, n=3) 51 Table 4.2 Nutrient composition of agricultural and industrial by-products for feeding rabbits 54 Table 4.3 Nutrient composition of protein and energy supplemental feed ingredients for feeding rabbits (Mean ± SD, n=3) 58 Table 4.4 The feed, nutrient and metabolizable energy (ME) intakes of rabbits 65 Table 4.5 Daily weight gain, feed conversion ratio and economic returns of experimental rabbits 66 Table 4.6 Carcass and meat quality of rabbits in the experiment 67 Table 4.7 Nutrient intakes, digestible nutrients, and nitrogen retention of experimental rabbits 68 Table 4.8 The feed, nutrient and metabolizable energy (ME) intakes of rabbits 70 Table 4.9 Final live weight, daily weight gain (DWG) and economic returns of experimental rabbits 71 Table 4.10 Carcass values, internal organs and meat quality of rabbits in the experiment 72 Table 4.11 Nutrient intakes, digestible nutrients and nitrogen retention of rabbits in the nutrients digestibility trial 73 Table 4.12 Feed and nutrient intakes of experimental rabbits 76 Table 4.13 Amino acid intakes of experimental rabbits (g/rabbit/day) 77

Table 4.14 Final live weight, daily weight gain (DWG) and economic returns

of experimental rabbits 78 Table 4.15 Carcass values, internal organs and meat quality of rabbits in the experiment 80 Table 4.16 Nutrient intakes, digestible nutrients and nitrogen retention of rabbits in the nutrient digestibility trial 81 Table 4.17 Amino acids intake of rabbits in the nutrient digestibility trial (g/day)

82

Table 4.18 Amino acids digestibility of experimental rabbits (%) 82 Table 4.19 The feed and nutrient intakes of rabbits in the experiment 84 Table 4.20 Body weight, daily weight gain, feed conversion ratio and economic returns of experimental rabbits 85 Table 4.21 Carcass values, internal organs and meat quality of rabbits in the experiment 86 Table 4.22 Nutrient intakes, digestible nutrients and nitrogen retention of experimental rabbits 88

LIST OF ABBREVIATION

ADF: Acid detergent fiber

AID: Apparent ileal CP digestibility

AOAC: Association of Official Agricultural Chemists

CF: Crude fiber

CP: Crude protein

CPD: Apparent faecal CP digestibility

DM: Dry matter

DWG: Daily weight gain

EE: Ether extract

FCR: Feed conversion ratio

FW: Final live weight

INRA: National Institute for Agricultural Research of France IW: Initial live weight

ME: Metabolizable energy

N: Nitrogen

NDF: Neutral detergent fiber

NI: Nitrogen intake

NIAS: National Institute of Animal Science of Vietnam

CHAPTER I INTRODUCTION

1.1 Problem statement

In recent years, rabbit production has increased considerably in

Vietnam because of increasing human consumption Local rabbits are

popularly raised in the Mekong delta due to a good adaptation to the local climate and feeds; however, its productivity is very low Californian rabbits have been imported into Vietnam to upgrade rabbit production since 1980 In 2000s, rabbit producers in the Mekong delta of Vietnam raised Californian rabbits by feeding locally available feed resources In initial period, growth and reproductive performances of Californian rabbits were low and unstable

In recent years, Californian rabbits have been adapted to local feeding

conditions, thus its productivity has been enhanced Studies on Californain rabbits was rare, even in the world In 2000-2012, World Rabbit Science Association published 230 papers including 2 papers research on Pure

Californian rabbits, 52 papers for pure New Zealand White rabbits, 35 papers for Californian crossbred rabbits and 141 papers for local rabbits There were

508 papers that were published in Livestock Research for Rural Development Journal from 1989 to 2016 In which, there was no study on pure Californian rabbits It had 23 papers for Californian crossbred rabbits, 93 papers for pure New Zealand White rabbits and 392 papers for local rabbits Shortly, studing

on nutritional requirements of pure Californian rabbits has been rarely It is necessary to study on feed utilization of pure Californin rabbits in local

conditions for enhacing rabbit production

Rabbit producers fed natural grasses, wild vegetables and

agro-industrial byproducts for both growing and reproductive rabbits The diets for rabbits usually contain high proportion of fiber and low protein Protein is needed for growth, reproduction and health of rabbits, and it can be obtained from both plant and animal sources Protein is an important component for life processes, effects on growth performance, and carcass yield of rabbits The nutritive value of a protein feed source is determined not only by its amino acid composition, but also by its digestibility of ingested protein The main factors involved in protein digestibility of rabbits are chemical structure,

properties, and accessibility to enzyme activity (McDonald et al., 2010)

Rabbits could also utilize more protein resources from microbial activity in caecum by the coprophagy In recent years, dietary supplementation of protein and amino acids had the major and traditional objective to meet rabbit

requirements for production (Carabano et al., 2008)

Recent studies in rabbit nutrition have increased the number of criteria included in the nutritional recommendations, especially for fibrous and amino acids components (Gidenne and Fortun, 2003) The most important practical advance was the recommended nutritional needs of growing rabbits for the most frequent limiting amino acids (lysine, methionine and threonine) It is noted that current recommendations are higher for lysine and threonine

(Carabano et al., 2008) There is a lot of studies on lysine, methionine and

interaction between them on rabbit nutrient requirements, however, researches

on interaction between lysine and threonine are rarely Of all amino acids, lysine is the only one to play a metabolic role almost exclusively to add body protein that is for meat deposition Lysine is generally related to protein

synthesis (Champe and Harvey, 1997) Threonine is an amino acid that is used

in the biosynthesis of protein Threonine also aids in the production of

antibodies to strengthen the immune system Threonine is necessary for

creating glycine and serine, two amino acids required to produce collagen, muscle tissue and elastin (Hawwa, 2013)

Metabolizable energy (ME) was used by growing rabbits for productive functions as maintenance and growth Several factors would affect the ME requirement in rabbits including body size, age, gender and breed, vital and productive functions, and feeding environment (De Blas and Wiseman, 2010) Several authors have studied the optimal dietary crude protein, amino acids

and metabolizable energy levels for growing rabbits (Carabano et al., 2008)

but their studies mainly used commercial pellets for feeding rabbits Rabbits can be achieved optimum growing performance by supplying a balanced diet

of protein, amino acid, fiber and energy Diet quality has been a major limiting factor of rabbit production in the Mekong Delta of Vietnam, especially

Californian rabbit diets To formulate appropriately rabbit diets, it is necessary

to know the nutritional composition of the feedstuffs to be used However, there is limitary information on the chemical composition of feedstuffs for rabbit diets, especially amino acid components The researches on suitable protein sources for growing Californian rabbits were not yet implemented The studies on nutrient requirements, forage feeding and diet digestibility of

Californian rabbits under feeding conditions in the Mekong Delta of Vietnam are still limited, especially crude protein levels, lysine and threonine and

metabolizable levels in diets

1.2 Research objectives

The objectives of this study were:

- To enhance knowledge of the nutritional values of some popular

feedstuffs for feeding rabbits in the Mekong Delta of Vietnam

- To identify optimal levels of crude protein in diets for the Californian

Key findings of this study were:

- Supplying the nutritional values, especially amino acid compostion, of the popular feeds for rabbits in the Mekong Delta of Vietnam

- Identifying appropriate protein source in the diets for growing Californian rabbits in the Mekong Delta of Vietnam

- Determining optimal levels of crude protein, lysine and threonine, metabolizable energy in the diets for Californian rabbits under feeding conditions in the Mekong delta of Vietnam

1.4 Sciential and practical considerations

Sciential consideration

This thesis supplies the scientific knowledge about nutrient

compositions of some common feedstuffs in the Mekong Delta for feeding Californian rabbits with emphasis to amino acid values Finding a better

protein source in rabbit diets in the Mekong Delta of Vietnam is very

informative for scientists who study on rabbits This thesis researched on the protein utilization of Californian rabbits by systematic method and found the optimal levels of crude protein, lysine and threonine, metabolizable energy in diets It is profitably scientific information for further studies on Californian rabbits in the Mekong Delta of Vietnam

Practical consideration

The findings of this study can be applied in the practice for feeding Californian rabbits to enhance productivity and economic returns for rabbit producers in the Mekong Delta of Vietnam

CHAPTER II LITERATURE REVIEW

2.1 Californian rabbits-introduction

The Californian rabbits is a medium to large domestic animals that is the result of a Himalayan crossbred with a Chinchilla, before making kits to a New Zealand white, developed in Southern California in the early years of the 1920s George West, breeder who are seeking an animal that has good

coverage as well as a high quality of meat At the initial time, Californian failed to arouse the interest of American fanciers and it was not until the 1930s when it became popular Today, Californian is one of the most common meat production rabbit in the world (Pets4home, 2010)

2.1.1 History

The Californian rabbit was originally developed by George West in Southern California such as meat and feather production animal The country has experienced a boom in rabbit breeding to meet the needs of a hungry population, and Californian was intended to help meet the growing demand for food By putting together a Himalayan and a standard Chinchilla, West was partway to achieve their goals By breeding the New Zealand White, he finally realized his ambition of creating a new rabbit that had great muscle cover and lovely body, silky soft fur (Pets4home, 2010)

2.1.2 Appearance

Californian's main color is white with dark brown markings on the nose, tail, feet and ears The average live weight is 3.5 to 4.75 kg for adult Californian rabbit ears is big, which was held up, and is a moderate to large-sized animals The coat is silky and soft and white, with a dark brown almost ear, tail, nose and feet This unusual colors make Californian look very similar

to its ancestors of the Himalaya The breed is well rounded and compact, with

a short neck It is muscular, plump and firm The nose markings continue below the jaw and up towards the eyes, while the leg markings run well up the limbs towards the body and the nails and feet are dark Ears up from base to tip the tail is also a dark chocolate brown (Pets4home, 2010)

remember though, that is a prey animal, any rabbit can pale and may show fear Any rabbit producers should learn how to pick up and keep a rabbit correctly, if the rabbit feels unsafe or uncomfortable, they will struggle

Rabbits are much stronger than they appear and have powerful hind legs If they struggle while being held, they can cause injury to themselves or their keeper As a first breed developed in warmer climates, Californian is known for not thrive at low temperatures (Pets4home, 2010)

Figure 2.1 Californian rabbit

2.1.4 Californian rabbits in Vietnam

Rabbit meat production has been more developed recently in Vietnam due to suitable production conditions such as low investment, labor saving, good income and low risks Local rabbits are mainly raised because of their good adaptation to the local conditions, however, productivity is very low Thanks to National Institute of Animal Science of Vietnam, Californian

rabbits have been imported two times in 1980 and 2000 from Hungary to upgrade rabbit production Up to now they have adapted to Vietnamese

ecological condition in the North Vietnam (Binh et al., 2008) The

performance of Californian rabbits in the North Vietnam has achieved 5.12 kg for adult female and 5.65 kg for adult male Body live weights at birth, at 30 days and at 3 months were 64.0, 707 and 2.840 g, respectively Feed

conversion ratio from 1 month to 3 month was 5.05 kgDM/kg weight gain

(Binh et al., 2008) In 2000s, rabbit producers in the Mekong delta of Vietnam

raised Californian rabbits by using locally available feed resources In initial period, growing and reproductive performance of Californian rabbits were low and unstable In recent years, Californian rabbits have been adapted to local feeding conditions, thus its productivity was enhanced Californain rabbits

become an important breed for rabbit production in the Mekong Delta of Vietnam

2.2 The Understanding of Protein digestion on rabbit

2.2.1 Some features of the protein sources using in rabbit diets

Proteins, as we know, are macromolecules which are made up of long amino acids chains linked by peptide bonds to form a polypeptide chain The polypeptide chains are folded in three dimensions to form a characteristics tertiary structure for each protein The chain structure of each amino acid (size and electric charge) decides its properties Nutrition experts consider eight of them (isoleucine, leucine, lysine, methionine, phenylalanine,

threonine, tryptophan and valine) essential since their carbon skeletons cannot

be synthesized in higher animals (De Blas and Wiseman, 2010)

A protein’s nutritive value is determined by both its amino acid

composition and its digestibility proportion of ingested protein digested in the gut and absorbed as free amino acids It is chemical structure and properties (the insoluble proteins are more resistant to digestion) and accessibility to enzyme activity that involved in protein digestibility in rabbits, as in other non-ruminant species (De Blas and Wiseman, 2010)

There are two major classes of plant proteins: seed and leaf proteins The main seed proteins are a part of the reserve material needed for the

development of the future plant’s embryo Therefore, the cereal endosperm holds around 0.7 of total cereal protein; the rest is in the germ and in the outer bran The proportions of the different types of proteins (Table 2.1) are

divergent between cereals: the soluble albumins and globulins derive from the cell’s cytoplasm, and the insoluble prolamins and glutelins are storage

proteins Since the bran includes the aleuronic layer of endosperm (inner bran), its proportions of both crude protein (CP) and cell walls are higher than those of the whole grain The storage proteins’s nonessential amino acids (especially glutamic acid and proline) are richer and their lysine and threonine are lower in comparison to cytoplasmic proteins (Table 2.2) Consequently, cereals’ amino acid composition depends on the relative proportions of the various types of proteins While protein from cereals represents about 0.13 of the total protein of rabbit diets, it is about 0.2 for cereal byproducts, mainly wheat bran (De Blas and Wiseman, 2010)

Table 2.1 Proportions of the different types of proteins in total protein of cereal and legume grains

Cytoplasmic or soluble protein

salt-Storage or insoluble protein

Sources: Boulter and Derbyshire, 1978; Larkins, 1981; Miflin and Shewry, 1981

In general, proportions of albumins and globulins in the grains of

legumes and oil seeds are higher than in cereal grains Therefore, the proteins

of legumes’ essential amino acids (especially lysine) are richer and these

proteins should be more digestible than those of cereals The value of these seeds, however, is limited by the presence of various antinutritive factors (e.g trypsin inhibitors, lectins or tannins) when they are used unprocessed The mostly used protein concentrates in rabbit diets in Europe are soybean and sunflower meals whose inclusion levels are 80–90 g/kg comprising from 0.35

to 0.4 of total dietary protein (De Blas and Wiseman, 2010)

Table 2.2 Amino acid composition (g/16 g nitrogen) of wheat proteins

Source: Bushuk and Wrigley, 1974

The leave is where the proteins of forage plants are concentrated (Table 2.3) Unlike grains’ storage proteins, leaf proteins are concerned with the

growth and biochemical functions of the cells The amino acid composition of

plant leaf proteins varies within narrow limits (Makoni et al., 1993) and this is

due to their enzymatic nature Even though a comparatively small fraction of insoluble protein remains tightly bound to the cell wall’s cellulose, leaf

proteins’ major portion are separated from the cell wall Lucerne hay (0.90 of

diets; Villamide et al., 2009) with inclusion levels from 200 to 400 g/kg is the

forage most extensively used in rabbit diets Lucerne protein hence represents

at least 0.25 of the dietary protein Lucerne hay’s protein content is very

variable as it mainly depends on the maturation state and drying process

Therefore, INRA (2002) tables classify dehydrated Lucerne into four groups according to protein content (from <160 to 220–250 g/kg) (De Blas and

Wiseman, 2010)

Table 2.3 Crude protein (g/kg dry matter) of leaves and stems of lucerne hay and the amino acid composition (as a proportion of total amino acids) of leaf protein from fresh lucerne

Cytoplasmic proteinb

Chloroplast membraneb

a Alvir et al (1987), b Makoni et al (1993) The ratio of cytoplasmic to chloroplast protein was 0.25:0.75

of total leaf protein

2.2.2 Some characteristics of rabbit diets in the Mekong Delta of Vietnam

In the Mekong delta of Vietnam, rabbits are fed locally available feed resources including natural grasses, wild vegetables and agro-industrial

byproducts Natural and wild feeds were naturally available almost all the year round in the Mekong Delta Locally available forages could be provided major

part of protein and fiber requirement of rabbits The in vitro organic matter

digestibility (% OMD) by using rabbit caecum fluid of these feeds gave good results and it showed that they had well-potential feed for rabbit production (table 2.5) However, feeding only forages would not satisfy nutrients for

growth and reproductive performance, thus supplementation of protein and energy feed sources was needed Rabbit producers only utilize the local

feedstuffs for feeding rabbits but they do not concern about dietary nutrient requirement Dietary composition of growing rabbits in the Mekong delta of Vietnam was shown in table 2.4

Table 2.4 Dietary composition of growing rabbits in the Mekong delta of Vietnam

Source: Chau & Thu., 2014

Chau & Thu (2014) conducted a research on current status of rabbit

production in the Mekong Delta of Vietnam They concluded that forage sources such as natural grasses, sweet potato vines and water spinach were often used as basal diets, while brewery waste, soya waste and concentrates were used as supplemental feeds for rabbit production The dietary crude protein (13.9-14.1%) for growing rabbits was low as compared to the crude protein requirement of the temperature rabbits (15-19%) The nutrient intakes per day (58.4 gDM, 7.84 gCP and 680 kJME) and growth rate (13.2

g/rabbit/day) of growing rabbits were lower than domestic data reported 24.5 g/rabbit/day) Rabbit production in the Mekong Delta has advantages of easy sale, yearly available feed sources and adaptable breeds but due to

(16.7-limited knowledge on nutritional techniques, the production has not achieved

to its potential They also recommended that more studies on nutrient

requirements and local feeds for rabbits should be considered to serve for extension activities in raising rabbits

Table 2.5 The invitro OMD (%) by using rabbit caecum fluid of some common

feeds for rabbit production in the Mekong delta of Vietnam

Nutural grasses 0 24 48 96

Operculina turpethum (Bìm bìm) 52.3 68.1 72.3 72.8

Commelina communis (Rau trai) 53.1 65.0 73.3 77.3

Phyllanthus urinaria (Cây chó đẻ) 62.3 65.9 72.4 76.1

Eichhornia crassipes (Lục bình) 51.8 52.0 56.1 58.4

Brachiaria mutica (Cỏ lông tây) 23.1 40.4 49.4 53.5

Eleusine indica (Cỏ mần trầu) 29.2 45.6 50.6 57.5

Psophocarpus scandens (cỏ đậu) 50.4 64.8 69.4 71.2

Brassica oleracea (Lá bông cải) 58.1 70.8 74.0 77.6

Brassica oleracea (Lá bắp cải) 50.9 71.1 89.0 91.0

Source: Thu & Dong., 2011

2.2.3 Balance of protein and amino acid

The different feedstuffs’ capability to satisfy the protein and amino acid requirement of rabbits depends on the nitrogen unit used (Carabano et al., 2000) The relative value of sunflower meal, wheat, wheat shorts, and Lucerne hay in relation with soybean meal using different units (total CP or

methionine, apparent digestible faecal or ileal, and true digestible ileal

contents of both protein and methionine) is shown in Figure 2.1 Therefore, Lucerne hay could represent 0.21 of the soybean meal value if it is judged as apparent digestible faecal CP and 0.42 if it is mentioned in the same breath as

a crude methionine source (Fig.2.1) In the same manner, 0.71 and in 1.46 are the corresponding values for sunflower meal As a result, a proper definition

of the nitrogen unit both in rabbit requirements and feedstuff evaluation will allow an increase in the accuracy of diet formulation, lowering the risks of intestinal pathologies like epizootic rabbit enteropathy (Carabano et al., 2008) and environmental pollution (Maertens el al., 2005)

Fig.2.1 Relative value of some protein sources in rabbit diets in relation to soybean meal (100) using different nitrogen units (total versus apparent (app.) faecal digestible versus

app ileal digestible versus true ileal digestible crude protein (CP) or methionine (met)

contents) Adapted from data of Llorente et al (2006, 2007a)

2.2.4 Crude protein and total amino acids

The most common units which are used to express nitrogen

requirements and the nutritive value of feedstuffs are CP and amino acid contents The main advantage from this is the large quantity of available

information since one can directly determine feedstuff evaluation in the

laboratory and extrapolate it between animal species Even so, when carrying

out experiments designed to determine rabbits’ amino acid requirements, scientists observed a different apparent faecal digestibility of amino acids, depending on whether they came from conventional feeds (from 0.64 to 0.80,

on average) or had a synthetic origin (from 0.93 to 1.0) (Taboada et al., 1994, 1996; de Blas et al., 1998) These results highlight the significance of using digestible instead of total units to express both protein and amino acid

requirements for rabbits

experimental diets were assessed The validation error of the prediction lowers

a little (from 0.045 to 0.043) as dietary CP is included in the equation with a positive sign It seems that protein digestibility varies more in accordance to type of feed ingredient than to the composition of the chemicals (de Blas et al.,

1979, 1984) In the information mentioned above, a bad relationship of

Lucerne hay content (r= -0.22) or of the ratio of dietary protein from Lucerne hay (r= -0.27) with CPD observed although this relationship shows positive signs for sunflower meal content (r = 0.22)

Some equations to anticipate the DP of dissimilar groups of feed

ingredients (Table 2.6) were put forward by Villamide and Frage (1998)

Table 2.6 Prediction equations for apparent faecal digestible protein (DP, g/kgDM) from chemical composition (g/kgDM) for different groups of feed ingredients

Fibrous by-products 11 DP = 8.73 + 0.716 CP – 0.184 ADL 0.964 3.16

to 0.967 for fibrous by-products and protein focuses, respectively), the best single predictor for every group is the CP content A rise in the CP content of

a feedstuff raises its CPD since the proportional contribution of endogenous nitrogen to faecal nitrogen is lowered Similarly, the form of proteins of

feedstuffs having a great content of CP (legume feeds, Lucerne leaves) is broadly less resistant to digestion The judgment of the ratio of the indigestible nitrogen content of feeds can be done because of the determination of the ratio

of nitrogen bound to acid detergent fiber containing heart-damaged protein and nitrogen associated with lignin Actually, a really bad correspondence between CPD and nitrogen linked to acid detergent fiber has been studied in both diets (r= -0.87, n = 8; Martinez and Fernández, 1980) and feedstuffs (r = -0.95, n = 11; Villamide and Fraga, 1998) Even so, this analysis is still

incapable to gain more homogeneous and representative data which enable an accurate CPD prediction of the main ingredients included in rabbit diets since

it is not often carried out in the testing of rabbits

Information concerning amino acids’ digestibility is even more limited Both the content and the digestibility of most amino acids are affected by the type of Lucerne hay (Garcia et al (1995b) A positive correspondence

between protein and amino acid digestibility is obvious, yet a difference of 0.07 between extreme CPD values exists while a change of 0.14 is obtained for lysine Even so, another issue appears in an attempt to anticipate the amino acid digestibility of feeds If the amino acids disappearing from the large intestine have not been reused through soft feces, not all of them are used for protein synthesis

2.2.6 Ileal digestibility

The final part of the digestive tract in which scientists can absorb the amino acids is the ileum As a result, the digestibility of ileal is thought to estimate more precisely the actual availability of amino acids for animal

protein synthesis both in rabbits (Carabano et al., 2000) and in other ruminant species

In Ileal and faecal digesta, there are significant amounts of protein of endogenous origin (3.8 and 2.5 g/100g dry matter DM intake at the ileal and

faecal level, respectively; Garciaet al., 2004; Llorente et al., 2005) originating

from digestive secretions, epithelial cells and mucins or microorganism This endogenous protein accounts for about 0.64 of the total nitrogen flow at both the ileal and the faecal levels In addition to varying with the DM amount of food, the relative importance of endogenous protein varies with the type of

diet and protein origin Therefore, the endogenous protein at the ileal level accounts for 0.65 and 0.55, respectively, of the total ileal change in diets with the same amount of food and resembling chemical ingredient based on peas and soybean hulls

Table 2.7 shows the ingredient of endogenous protein of amino acid at the ileal and faecal level More concentrations of several non-essential

(glutamic acid, glycine, and serine) amino acids exist in the endogenous

protein than in the faecal ones The dissimilar ingredient of endogenous

secretions can explain these differences as compared to those of microbial origin Consequently, a correction for endogenous losses must be carried out

to make a more reliable definition of digestible protein and amino acids of feedstuffs As soon as this correction is finished, a new unit appears and is referred to as ‘true’ (TID) instead of ‘appearent’ (AID) ileal digestibility Fig 2.2 shows the variation in every amino acid digestibility in

relation with the CP ileal digestibility (AID or TID) for soybean meal Several amino acids like glycine and threonine are dramatically less digestible than protein (0.14 and 0.06 respectively for AID and TID), while others like

methionine and isoleucine are more digestible (0.06 for AID and 0.05 for TID) Thus, major errors happens when using the same digestibility value for all amino acids especially when apparent values are used since the endogenous correction causes a drop in the variation of amino acid digestibility in relation with protein digestibility

Table 2.7 Amino acid composition (g/16 g nitrogen) of endogenous flow at the ileal and faecal levels

Essential amino acids

Fig 2.2 Apparent (a) and true (b) ileal amino acid digestibility of soybean meal with

respect to its crude protein digestibility ( Source: Llorente et al., 2006)

The aim of the studies carried out with cannulation is to evaluate rabbit diets’ chief sources of protein (Garcia et al., 2005; Llorente et al., 2005, 2006, 2007a) Table 2.6 presents total ileal (apparent and true) and faecal (apparent) digestible contents of CP and of most limiting amino acids from these raw materials Since feedstuffs having very little CP content have not been

assessed because of little influence on dietary nitrogen and too many mistakes associated with its development, total CP averages of 205 g/kg DM Lysine, methionine, and threonine account for 0.05, 0.015, and 0.036 of the total CP of these feed composition at a usual level TID of CP is quite high (average 0.81) though the apparent ileal values (average 0.66) are 0.15 lower because of the great importance of endogenous losses at the ileal level This influence plays special major role for threonine and lysine digestibility in the development of cereals (0.38 and 0.22 as average higher TID than AID of threonine and

lysine, respectively) Though at a different ratio for each amino acid, obvious faecal digestibility of CP indicates intermediate values (average 0.76),

showing that protein has disappeared in the large intestine (about 0.1)

Threonine appears to disappear by a great amount (0.12 as average) than lysine (0.01) and methionine, appearing to be more digestible at the ileal than faecal level for 11 out of 15 feedstuffs AID values are essential to estimate the total ileal change coming to the caecum (indigestible plus endogenous nitrogen), which should be used for microbial development The caecum microbial activity produces a number of changes in the amino acid ingredients

of digesta, and as a result, a problematic interpretation is caused by the faecal amino acid balance (Garcia et al., 2005) However, values for CP faecal

digestibility of feed composition calculated in cannulation fits with average dietary values defined in developing rabbits (0.73, n = 164; Villamide et al., 2009)

Major dissimilarities appear among feedstuffs both in protein and in amino acid digestibility (from 0.4 to 0.9) and are mainly related to the CP content (r = 0.91, 0.81, and 0.61 for CPD, AID and TID, respectively) and the type of protein (concentratesversusforagesorfibrous byproducts) Pigs have a larger amount of the AIDs of CP and threonine for dissimilar feedstuffs than rabbits (INRA, 2002) while lysine and methionine AID values are nearly the same Nevertheless, values of both CP and limiting amino acid TID are of a larger amount for almost every feedstuff than the standard ileal digestibility as defined in pigs because of the more major importance of endogenous protein

in rabbits

Because of the use of semi-purified diets provided to cannulated

animals, endogenous determinations and analysis of amino acid, TID

determination takes lots of time and money As a result, there has been an attempt to predict TIDs from easier and cheaper ways Encouraging outcomes

have appeared with the use of an in vitro way (Llorente et al., 2007b) evolved

for pigs and creating an adaptation to rabbits (Ramos at al., 1992) In spite of

the higher in vitro CP digestibility than the corresponding invivo values

(0.225, 0.119 and 0.58 on average for AID, CPDand TID, respectively), the precision of their prediction is higher Actually, the coefficients of change for

amino acid TID prediction are lower than 0.057 even as the in vitro CP

digestibility is considered a predictor The same process has taken place with

the use of in vivo CPD as predictor to estimate ileal digestibility of different

feed composition from the faecal figure The predicted relationships for the three major amino acids are shown in Figure 2.3

The effect of the use of ileal digestible units in practical formulation is not clearly defined due to the fact that rabbit requirements have not been determined Even so, in a study of formulation using ileal digestible threonine

instead of total threonine, the amount of money for the diet is lowered

decreased (by 3.3% and 2.8% for AID and TID, respectively) and the

inclusion of concentration and cereal by-products instead of forages was preferred (Carabano et al., 2009) That many fibrous sources in little amounts

in rabbit diets take place has a limited effect on protein formulation

irrespective disregarding the unit used on account of the very low content of protein and amino acid

Fig.2.3 Relationship between faecal crude protein (CP) digestibility and amino

acid true ileal digestibility

Table 2.8 Total and digestible protein and amino acid content (g/kg dry matter) using different units for the most important sources of protein

in rabbit diets

2.2.7 Nitrogen metabolism in the caecum

Residues of intestinal digestion and the urea recycled through the blood are potential substrates that allow caecal bacteria to obtain energy and nitrogen for growth At the end of the ileum, fiber is the main component of the digesta (about 0.70 of total DM), while nitrogen is second in importance (about 0.15

of total DM) However, these figures may be poor indicators of the

contribution of each component to microbial growth Taking into account the low fermentability of the fiber (0.30 for neutral detergent fiber digestibility) and the high content of endogenous substances in nitrogen residues (about 0.64), both components may contribute equally to maintain the resident

intestinal microbiota There is very little information about the quantitative utilization of nitrogen by caecal microbiota However, early qualitative studies suggest that the caecal microbiota is able to utilize the nitrogen that enters the caecum and transform it into other nitrogen-containing components such as

microbial protein and ammonia Several studies (Yoshida et al., 1968, 1971,

1972; Rerat, 1978), where germfree animals have been compared with

conventional ones, have observed that the caecal content of germfree rabbits is enriched in different nitrogenous compounds such as urea, free amino acids, peptides and other nitrogen sources of endogenous origin (mucoproteins, pancreatic enzymes or desquamated cells) On the other hand, in conventional animals the caecum contains more ammonia and true protein (enriched in essential amino acids) and lower quantities (up to ten fold) of endogenous components Further studies focusing on the characterization of the caecal

microbiota (Emaldi et al., 1979; Forsythe and Parker, 1985a) have confirmed

that the enzymatic capacity of bacteria might be able to hydrolyze digesta that reaches the caeca These bacteria are in decreasing order of importance,

ammonia-users, ureolytic species, proteolytic species, pectinolytic species, xylanolytic species and cellulolytic species Similar to in the rumen, 0.57 of

viable counts are ammonia-users, being Bacillus species, Staphylococcus species and Bacteroides vulgates, with Clostridium clostridioforme the main

ureolytic bacteria Furthermore, some of the most frequent isolated caecal

bacteria, Bacteroides species, are the most active genera in mucin digestion (Hill, 1986; Sirotek et al., 2003), one of the non protein components of the

endogenous nitrogen that enters the caecum

Figure 2.4 shows a tentative scheme of caecal nitrogen metabolism The proteolytic activity of caecal bacteria results in volatile fatty acids (VFAs)

as energy yielding compounds and ammonia production for growth Hoover and Heitmann (1975) observed that 0.95–0.98 of labelled C14-alanine infused

into the caecum was located in VFAs, with a small proportion in other amino acids These labelled VFAs appear rapidly in the blood, showing a maximum

at 0.5 h post-infusion However, the activity of labelled amino acids was

negligible or undetected in the blood, suggesting that amino acids are only

minimally absorbed, if at all, in the last segments of the intestinal tract A

similar conclusion has been obtained by using labelled lysine in animals that

have been prevented from caecotrophy (Belenguer et al., 2005)

Ammonia produced from protein and urea hydrolysis is partially used

by caecal bacteria as the main substrate for protein synthesis (Hoover and

Heitmann, 1975; Forsythe and Parker, 1985a,b) and another portion is

absorbed in the caecal wall, contributing to urea production (0.27 of total urea; Forsythe and Parker, 1985c) The extent of these processes has not yet been totally quantified; however, the characteristics of the diet affect total ammonia caecal concentration and the incorporation of ammonia nitrogen into microbial protein

Figure 2.4 Caecal nitrogen metabolism

An increment in caecal ammonia concentration has been related by

different authors (Carabano et al., 1988, 1989, 1997; Fraga et al., 1991; Ferreira et al., 1996; Garcia et al., 1995a, 2000, 2002; Nicodemus et al., 2002)

Motta-to the dietary DE: DP ratio (Fig 3.5) When the protein intake exceeds

nutritional requirements, urea recycling from the blood to the caecum may be increased, leading to an elevation in the caecal ammonia concentration

According to Forsythe and Parker (1985c) the contribution of urea-nitrogen to the caecal ammonia pool is around 0.25 of caecal ammonia turnover

Other dietary factors can affect the caecal ammonia concentration The presence of condensed tannins or other phenolic components may decrease the proteolytic capacity of caecal microorganisms, as occurs in the rumen

(Waghorn et al., 1987) This may in part explain the low caecal ammonia

values obtained in diets that contain grape pomace or olive leaves

(Motta-Ferreira et al., 1996; Garcia et al., 2000)

The efficacy of synthesis of microbial protein from ammonia seems to

be more related to the characteristics of dietary carbohydrates than to

nitrogenous composition The caecal ammonia concentration in the rabbit fed

a balanced diet is in the range of 4.5–6 mmol/l ammonia, which seems

adequate for appropriate protein microbial synthesis when compared with the ammonia concentration of the rumen However, the availability of energy in the caecum could be the limiting factor for bacterial growth Inclusion in the diet of increasing levels of fiber or sources of fiber with high lignification decreases VFA production and the protein concentration in the caecum

(strongly related to microbial protein; Carabano et al., 1988; Fraga et al.,

1991) On the other hand, the inclusion of more fermentable fiber (linked to pectins or hemicelluloses) or fiber with a high proportion of fine particles (<0.3 mm in diameter) improves both total and microbial nitrogen in the soft

faeces (Garcia et al., 2000)

The final result of bacterial activity in the caecum is a substantial

change in the amino acid composition of the protein that enters the caecum

from the ileum According to Garcia et al., (2005) the bacterial activity leads

to an enrichment in lysine (0.072 g/day; 0.63 of the ileal flow), methionine (0.026 g/day; 0.95 of the ileal flow) and threonine (0.059 g/day; 0.40 of the ileal flow) when comparing total excretion in hard and soft faeces with

apparent ileal flow Furthermore, the enrichment of these essential amino acids was higher in diets where the faeces contained a higher proportion of

microbial protein

2.2.8 Protein digestion in young rabbits

In the last 10 years, the protein digestion research in young rabbits has gained more relevance on account of its effect on intestinal health (Carabano

et al., 2009) Important gaps in knowledge in several particular parts cause difficulties to the interpretation of results even though data has become greater concerning the precious decade Methodological sides in relation with

markers, sample collection and analysis (Gallois et al., 2008), design of diets,

or endogenous losses might interpret several contrast results The enzymatic

ability to digest protein at the ileal level appears to be higher than that for

several nutritive substances Even though the enzymatic capacity for the

digestion of protein around weaning might have limitation, the AID of CP in

young rabbits (from 21 to 35 days) shows similar or even higher figures in

comparison with that of elder animals (42 – 45 days) (Table 2.9)

Table 2.9 Effect of age on apparent ileal crude protein (CP) digestibility and the

distribution of protein apparently digested in the digestive tract of rabbits

digestibility (AID)

Apparent faecal CP digestibility (CPD)

Apparent caecal

CP digestibility

Ratio AID:CPD

These differences could be interpreted by the insufficiency of stability

in the amount of food (feed and caecotrophy) and caecal contents or a lower

importance of endogenous losses Actually, only 0.71 of the total digested

protein is digested at the ileum in young rabbits as soon as the mean values of AID are compared to faecal ones This figure is not as high as those stated in

adult animals, varying from 0.82 to 0.90 for forages or concentrates,

respectively (Table 2.7)

Young rabbit’s digestion of protein is limited not only for forages

Differences in ileal digestibility among sources of protein were found with the same faecal digestibility by Gutierrez et al (2003) There is an agreement

between the low digestion of protein at the ileum, a greater energy limitation

in the caecum (more little ratio of VFAs) and a higher caecal ammonia

concentration seen in the youngest as compared to adult rabbits (Garciaet al.,

2002; Gidenne and Fortun-Lamothe,2002; Nicodemus et al., 2002)

2.3 Soft faeces and protein digestibility

Protein reutilization is the major influence of soft faeces Many pieces

of information on the chemical ingredient of soft faeces suggest that the

ingredient is identical to that of the caecal contents In the comparison

between the protein concentration of soft faeces and that of the caecal contents

of rabbits and in employing the same methodology, scientists obtained the

question below (Fig 2.5):

Y = 100.88 + 0.689 (±0.8) X, R2 = 0.712, P<0.001, n = 31,

where Y = CP (g/kgDM) of soft faeces, and X = CP (g/kgDM) of caecal contents

Fig 2.5 Effect of the crude protein (CP) concentration of the caecal contents on the

CP of soft faeces (Sources: Carabaño et al., 1988, 1989, 1997; Fraga et al., 1991; García et

al., 1995a; Motta-Ferreira et al., 1996)

In these research, the CP concentration of caecal contents fluctuated from 190 to 340 g/kg and the corresponding CP concentration in soft faeces from 230 to 335 g/kg This makes a suggestion that the mucosal envelope’s nitrogen content covering the contents of caecal in the last parts of the large intestine to form the last soft faeces might be approximately 55 g/kg The endogenous nitrogen amount secreted every day as the mucosal envelope is approximately 0.05 g/day (taking an average soft faeces production of 20 g DM/day, with 280 g CP/kg DM) Similarly, the relationship of the crude fiber content of the soft faeces and caecal contents is high (r = 0.90) even though the crude fiver of soft faeces is 8 per cent more little than that of the caecal

contents (Carabano et al., 1988)

Age, physiological status, diet and faeces collection method are the factors with which the amount of soft faeces excretion varies The use of information from 36 diets provided to rabbits of which weight is 2.0 kg, where

a wooden collar was made at 08.00 h and destroyed 24 h later, and with diets where the neutral detergent fiber content changed from 230 to 550 g/kg

(Carabanoet al., 1988, 1989, 1997; Garciaet al., 1995a, 2000; Motta-Ferreira et

al., 1996; Nicodemus 2000; Nicodemuset al., 2006), the excretion of soft faece changed from 15 to 32 g DM/ day, having an average value of 21.3 gDM/day (that is about 10 g DM/kg live weight) In contrast, a continuous and good relationship (r = 0.64) between the amount of hard and soft faeces excreted from 28 to 133 days of age was reported by Gidenne and Lebas (1987)

In accordance to the chemical ingredients of the diet and the

composition of the feed ingredients contained in diets, the contribution of soft faeces to the total CP amount of food changes from 0.104 to 0.286 (with the use of the mentioned studies) Low digestible diets increasing the flow of indigestible protein to the caecum is combined with the highest values (Motta-Ferreira et al., 1996) while the lowest values are in relation with diets

providing small amounts of protein to the caecum (Garcia et al., 2000) In practical diets, the source of protein from the soft faeces is normally 0.18 of the total CP amount of food

The values for production of soft faeces gained in growing rabbits are lower (around 35 gDM/day) than in lactating does fed conventional diets (Lorente et al., 1988; Nicodemus et al., 1999), but the contribution of soft faeces to the total CP amount of food (around 0.16) is kept in the same range due to the higher amount of food of the does This means the contribution of microbial lysine to tissue lysine in lactating does predicted by the use of millk and liver lysine enrichments is 0.23 and 0.19 respectively (Abecia et al.,

2007) These values are similar to those obtained in growing rabbits with the use of liver enrichment (o.23) (Belenguer et al., 2005)

Therefore, it is the ingestion of soft faeces that improves the obvious faecal digestibility, especially the digestibility of protein In the prevention against coprophagy, DM digestibility drops a little by about 0 – 0.17

However, CP digestibility drops by 0.04 to 0.72 This drop is higher as the dietary protein originates from forage than from mixed or non-forage diets (Fraga and de Blas, 1977; Fraga et al., 1984; Raharjo et al., 1990; Sakaguchi et al., 1992; Merino, 1994) Nevertheless, in these researches, the CPD of rabbits which do not practice caecotrophy has been worked out with the inclusion of the sum of nitrogen of hard and soft faeces when nitrogen excreted The

obvious digestibility of protein was lower in animals which do not practice caecotrophy than in those which practice it on account of the higher ratio of nitrogen excreted As soon as the soft faeces nitrofen was taken out from the balance, this discrepancy disappeared (Merino, 1994) and coprophagy had no influence on either the ileal digestibility of DM (0.537 versus 0.572) or the ileal digestibility of CP (0.723 versus 0.721) in cannulated adult females

(Merino and Carabano, 2003)

On the contrary, soft faeces’ ingestion raises the ileal flow of DM (by 0.31), nitrogen (by 0.18) and the endogenous ratio of the most major limiting indispensable amino acids (arginine, lysine, phenylalanine and threonine) (Garciaet al., 2004) This regular increase in the endogenous ileal nitrogen flow is caused by the rise in the DM amount of food when two variables are closely related (Garcia et al., 2004)

As a result, the soft faeces’ ingestion allows rabbits to use part of the amino acids not to be absorbed out of the ileum for the synthesis of microbial protein Actually, caecotrophy makes contribution to recycling 0.36 of the total protein excreted (soft plus hard faeces) chiefly originating from bacteria (around 0.67; Garciaet al., 2005) Additionally, this protein provides an ideal source of the most commonly limiting amino acids (methionine, lysine and threonine), as has been in the reports of some authors (Proto, 1976;

Nicodemus et al., 1999; Garciaet al., 2004, 2005) Nevertheless, the microbial content of the amino acid composition of soft faeces has an influence on it It

is also affected by the dissimilarities in the digestibility of dietary amino acids and the contribution of nitrogen of endogenous sources (especially that of the mucosal envelope) The enrichment contained in these important amino acids

of soft faeces is higher as animals are fed on diets raising the synthesis of microbial nitrogen (Garcia et al., 2005)

In lactating does fed on diets that satisfy all of the essential nutrient

requirements, Nicodemus et al (1999) through his observation found that the

contributions of some of the essential amino acids (methionine, lysine,

threonine, isoleuine and valine) are higher than the CP contribution of soft faeces to nutrient intake (0.15; see Fig 2.6) The difference, however, took place mostly in the case of threonine, recognized as the third most limiting amino acids in rabbits The major outcomes of digestive processes defining the amino acid composition of soft faeces concerning diet composition are the rise

in the methionine to cysteine proportion as a result of the quite high value of this proportion in bacterial protein and the drop in arginine, histidine, and phenylalanine Consequently, the amino acid source from soft faeces of

conventional diets does not appear to be enough to change the dietary amino acid pattern in order to satisfy the vital amino acid requirements of rabbits

In understanding nitrogen digestion of rabbits, scientists have achieved many advances permitting the adaptation of rabbit nutrition to satisfy

commercial alternatives, laws on environment, and so on Nevertheless, there