Ileal and total tract digestibility in growing pigs fed cassava root meal diets with inclusion of fresh, dry and ensiled sweet potato (ipomoea batatas l (lam )) leaves

114 2004 127–139Ileal and total tract digestibility in growing pigs fed cassava root meal diets with inclusion of fresh, dry and ensiled sweet potato Ipomoea batatas L.. Box 7024, S-750

114 (2004) 127–139

Ileal and total tract digestibility in growing pigs fed cassava root meal diets with inclusion

of fresh, dry and ensiled sweet potato

(Ipomoea batatas L (Lam.)) leaves

Le Van Ana, Tran Thi Thu Honga, Jan Erik Lindbergb,∗

aHue University of Agriculture and Forestry, 24 Phung Hung St., Hue City, Vietnam, Sweden

bDepartment of Animal Nutrition and Management, Swedish University of Agricultural Sciences,

P.O Box 7024, S-750 07 Uppsala, Sweden

Received 20 May 2003; received in revised form 5 November 2003; accepted 15 December 2003

Abstract

Ileal and total tract digestibility in growing pigs fed cassava root meal (CRM) based diets with inclusion of fresh, dry and ensiled sweet potato leaves was studied in a 4 × 4 Latin square design Four diets were formulated with CRM and casein (CAS), fresh sweet potato leaves (FSP), dry sweet potato leaves (DSP) and ensiled sweet potato leaves (ESP) The control diet (CAS) contained 100 g casein per kg DM The experimental diets FSP, DSP, and ESP contained 350, 350 and 400 g DM

of fresh, dry and ensiled sweet potato leaves per kg DM diet, respectively Leaves were separated manually from stems and only the leaf part was used

The daily feed intakes of dry matter (DM) and dietary components were significantly different between diets (P < 0.05) There was no difference in ileal apparent digestibility of OM between diets (P > 0.05), while the total tract apparent digestibility of OM and crude protein (CP) was higher on diet CAS than on diets FSP, DSP and ESP (P < 0.05) The ileal apparent digestibility of

CP and essential amino acids (EAA), except for arginine, threonine and tyrosine, were higher for diet CAS than for diets FSP, DSP and ESP (P < 0.05) The ileal digestibility of NDF and the total tract digestibility of crude fibre (CF) were lower for diet CAS than for diets FSP, DSP and ESP (P < 0.05)

Abbreviations:AA, amino acids; ADF, acid detergent fibre; CAS, casein diet; CF, crude fibre; CP, crude protein; CRM, cassava root meal; DM, dry matter; DSP, dry sweet potato leaf diet; EAA, essential amino acids;

EE, ether extract; ESP, ensiled sweet potato leaf diet; FSP, fresh sweet potato leaf diet; NDF, neutral detergent fibre; NEAA, non-essential amino acids; OM, organic matter

∗ Corresponding author Tel.: +46-18-672102; fax: +46-18-67-2995.

E-mail address:jan-eric.lindberg@huv.slu.se (J.E Lindberg).

0377-8401/$ – see front matter © 2004 Elsevier B.V All rights reserved.

doi:10.1016/j.anifeedsci.2003.12.007

There were no differences (P > 0.05) in digestibility of OM, CP, CF, NDF, ADF and most EAA among sweet potato leaf diets However, there was a tendency (P = 0.064) of a lower ileal apparent digestibility of lysine in the dried and ensiled sweet potato leaves

It was concluded that, sweet potato leaves have the potential to improve dietary protein and amino acid supply in low fibre diets for pigs Further, the optimum strategy for preserving sweet potato leaves can be decided on from consideration of the prevailing climatic conditions, as the general nutritional properties were similar for fresh, sun-dried and ensiled sweet potato leaves

© 2004 Elsevier B.V All rights reserved

Keywords:Amino acids; Fibre; Digestibility; Sweet potato leaves; Pigs

1 Introduction

In Vietnam, pig production is increasing annually at a rate of about 4.5%, with a total

of 22 million pigs produced in 2001 (Statistical Yearbook, 2002) In addition to providing protein for human consumption, pig production is important as it is the main source of cash income of resource-poor farmers in rural areas and provides manure for cropping Farmers in the rural areas of Vietnam, account for over 75% of the total pig production in the country However, there is a shortage of suitable homegrown feed resources, in particular feedtuffs with an acceptable protein content and quality, for the growing pig population Commercial feeds are partly based on imported feedtuffs and are too expensive to be used

by resource-poor farmers Thus, commercial feeds are mainly used in the large-scale of industrial pig production located around the major cities in the country

Sweet potato (Ipomoea batatas L (Lam)) is the third most common crop in Vietnam

after rice and maize, and has high biomass yields of both tubers and vines (An et al., 2003) Traditionally, sweet potato was used as human food when rice was not sufficient, although

at present it is commonly used as feed for farm livestock, especially pigs The tubers have

a high carbohydrate content while the leaves are rich in protein, and both tubers and vines can be used as animal feed (Woolfe, 1992) The vines include the leaf and stem, with a crude protein content in the leaves of 260–330 g kg− 1DM compared with 100–140 g kg− 1

DM in the stems (Woolfe, 1992; Ishida et al., 2000; An et al., 2003) It has been shown that the leaves makes up approximately half of the sweet potato vines biomass (Woolfe, 1992; An et al., 2003) Thus, if the leaves could be separated from the stems a considerable improvement with respect to the dietary protein and amino acid supply would be expected (An et al., 2003)

Earlier studies have indicated that vegetative plant parts may have nutritional properties that should allow them to be used in diets for pigs This applies to temperate forages (Lindberg and Andersson, 1998; Reverter et al., 1999) as well as to tropical green biomass (Phuc et al., 2001).Phuc and Lindberg (2000)showed that cassava leaves, leucaena leaves and groundnut foliage could be used to improve the dietary protein and amino acid supply

to growing pigs under tropical conditions However, as indicated from studies on lucerne, the nutritional properties of lucerne leaf meal (Lindberg and Cortova, 1995; Reverter and Lindberg, 1998) is superior to that of the whole plant (Lindberg and Andersson, 1998; Reverter et al., 1999) Dominguez and Ly (1997)also concluded that the proportion of

sweet potato vines in diets for pigs should be kept low to avoid negative effects on nutrient digestibility, and they called for new methods to improve the digestibility of this potentially valuable feed resource

This study was conducted to determine the ileal and total tract digestibility in growing pigs

of nutrients, in particular crude protein and amino acids, in sweet potato leaves which had been separated from the stems Also, the influence of preservation method on the digestibility was evaluated by feeding the sweet potato leaves in fresh, dried and ensiled form

2 Materials and methods

2.1 Animals

Four 13-weeks old crossbred (Large White × Mong Cai) castrated male pigs from the same litter, with an average body weight of 25.4 ± 0.6 kg were used The pigs were vacci-nated against pasteurellosis and hog cholera, surgically fitted with a post-valve T-caecum cannula (Van Leeuwen et al., 1991) and kept for 2 weeks to recover from surgery before the experimental diets were introduced Pigs were kept individually in metabolism cages and had free access to water from nipple drinkers The experiment was conducted in the period March and April 2002 during which time outdoor temperatures ranged from 22 to 28◦C

2.2 Diets and feeding

Sweet potato leaves were harvested at 60 days after planting, with subsequent harvests at 20-day intervals The vines were separated into leaf and stem and only the leaf part was used

in this experiment Fresh sweet potato leaves were harvested daily from the field and were chopped into 1–2 cm long pieces prior to feeding Dried sweet potato leaves were made by chopping the leaves into 2–3 cm long pieces, which were spread out on concrete out-doors

in the sun for 2–3 days The dried leaves were collected and milled through a 1 mm screen, stored in a dry place, and mixed with CRM at the time of feeding For ensiling, sweet potato leaves were chopped into small pieces 2–3 cm long and spread out on the floor overnight for wilting to reduce the moisture content Cassava root meal was used as additive at 60 g kg− 1

of the wilted weight of the leaves and also common salt (NaCl) was added at 5 g kg−1of the wilted weight of the leaves The silage was kept in sealed air-tight plastic bags with

a capacity of 30 kg and was stored for 21 days prior to feeding The ensiled sweet potato leaves were removed from the plastic bags twice daily and were mixed with CRM at the time of feeding

In the casein diet (CAS) protein was supplied by casein and in the other three diets fresh sweet potato leaves (FSP), dried sweet potato leaves (DSP) and ensiled sweet potato leaves (ESP) were included as the sole protein sources (Table 1) The four diets were based on CRM and contain formulated to 120 g crude protein kg−1DM (Table 2) Soybean oil was added

at a level of 40 g kg−1to the FSP, DSP and ESP diets (Table 2) to equalize the calculated content of metabolisable energy of the diets Chromium oxide was used as a digesta flow marker and was added at 5 g kg−1 DM weight of the diets A vitamin and micromineral mixture was added at 5 g kg− 1(Table 2)

Table 1

Dry matter (DM, g kg −1 material), organic matter (OM), crude protein (CP), ether extract (EE), crude fibre (CF), NDF, ADF (g kg −1 DM) and metabolisable energy (ME, MJ kg −1 DM) contents of ingredients

SPL: sweet potato leaves.

Daily feed allowance was 4 kg 100 kg−1of body weight for each individual animal, and was adjusted at the start of each experimental period The pigs were fed two times per day

at 06.00 and 18.00 h, with the daily allowance equally divided between the two meals Food refusals and spillage were recorded, and were used to correct the food intake data

Table 2

Ingredients, analysed chemical composition (g kg −1 DM), calculated metabolisable energy content (ME,

MJ kg −1 DM) and daily intake (g per day) of the diets

Ingredients

Chemical composition

Metabolisable energy (ME) c 13.2 13.2 13.2 13.2

Mean daily intake

a CAS: casein diet as control; FSP: fresh sweet potato leaf diet; DSP: dried sweet potato leaf diet; ESP: ensiled sweet potato leaf diet.

b Premix composition per kg: 2400 mg retinol; 4.32 mg cholecalciferol; 15,000 mg ␣-tocopherol; 5000 mg phytylmenaquirone; 2000 mg thiamin; 15,000 mg riboflavin; 25,000 mg calcium pantothenate; 30,000 mg niacin;

30 mg cyanocobalamin; 2000 mg folic acid; 100 mg choline; 100 mg Fe; 115 mg Zn; 40 mg Cu; 0.15 mg Co; 0.6 mg I; 0.3 mg Se.

c The calculated ME values were reached by addition of soyabean oil, which was mixed with the other diet ingredients at the time of feeding To FSP, DSP and ESP were added 40 g of soyabean oil per kg DM of diet.

2.3 Experimental design

The experiment was designed as a 4 × 4 Latin square and lasted for a total of 48 days Each of the four experimental periods was 12 days and comprised 5 days of adaptation to each diet, 4 days of collection of faeces, followed by 1 day of collection of ileal digesta, 1 day rest and a second day of collection of ileal digesta

2.4 Digesta, faeces collection and calculations

For the determination of ileal digestibility, a total of 12 digesta samples from each pig was taken during the 2 days of collection in each experimental period On each day of collection, samples were taken after every 2 h during the 12 h period between the morning and afternoon feedings, giving six samples per day of collection At each sample collection, digesta were quantitatively collected for 1 h in a container through a soft plastic tubing connected to the ileal cannula The digesta were frequently removed from the tube and container and transferred to a bigger container where they were kept on ice during sam-pling The samples were then kept frozen at −18◦C For total tract digestibility, faeces were collected four times per day and kept in a freezer at −18◦C Finally, prior to chemical anal-ysis, individual samples of ileal digesta and faeces were thawed and pooled within pigs and periods

The digestibility of the diets at each sampling site was calculated using the indicator technique (Sauer et al., 2000) according to the equation:

CADD=1 − (DCF×ID)

(DCD×IF) where is CADDthe coefficient of apparent digestibility of dietary component in the assay diet; DCF the dietary component concentration in ileal digesta or faeces (g kg−1); IDthe indicator concentration in the assay diet (g kg−1); DCD: dietary component concentration

in the assay diet (g kg−1); If the indicator concentration in ileal digesta or faeces (g kg−1) The coefficient of apparent ileal digestibility of CP and amino acids in sweet potato leaves (CIADSPL) was estimated by difference from the values of the assay diets (CIADD) and those of the cassava root meal (CIADCRM)

CIADSPL=CIADD−(CIADCRM×PCRM)

PSPL where is CIADSPLthe coefficient of apparent ileal digestibility of CP and amino acids in sweet potato leaf in the assay diet; CIADDthe coefficient of apparent ileal digestibility of

CP and amino acids in the assay diet; CIADCRMthe coefficient of apparent ileal digestibility

of CP and amino acids of cassava root meal; PCRMthe proportion of CP and amino acids

coming from cassava root meal in the assay diet; PSPL: proportion of CP and amino acids coming from sweet potato leaves in the assay diet

The coefficient of apparent ileal digestibility of CP and amino acids in cassava root meal (CIADCRM) was estimated by difference from values of the control diet (CIADCAS) by using the coefficient of ileal standardized digestibility (CISDC) for CP and amino acids in

casein (Pedersen and Boisen, 2002) according to the equations:

CIADCRM=CISDC−CIADCAS

PCRM where is CIADCRMthe coefficient of apparent ileal digestibility of CP and amino acids of cassava root meal, CISDCthe coefficient of ileal standardized digestibility of CP or amino acids in casein; CIADCAS the coefficient of apparent ileal digestibility of CP and amino

acids in the control diet; PCRMthe proportion of CP and amino acids coming from cassava root meal in the assay diet

2.5 Chemical analysis

Food, digesta and faecal samples were dried at 60◦C for 24 h and milled through a 1 mm screen before analysis All analyses were performed on dried samples, except for nitrogen (N) in ileal digesta and faeces, which was determined on fresh samples Dry matter (DM; method 930.15), ash (method 942.05), crude protein (CP, N × 6.25; method 988.05) and crude fibre (CF; method 978.10) were determined in dry samples according to standard AOAC methods (AOAC, 1990) Neutral detergent fibre (NDF) was analysed according to

Robertson and Van Soest (1977), with addition of sodium sulfite and alpha amylase Acid de-tergent fibre (ADF) was analysed according toGoering and Van Soest (1970) NDF and ADF values were expressed without residual ash Chromium was determined by atomic absorp-tion spectrometry after ashing according toFenton and Fenton (1979) Amino acids were analysed according toSpackman et al (1958)on an ion-exchange column using a HPLC

2.6 Statistical analysis

Analysis of variance was performed according to a 4 × 4 Latin square arrangement, using the General Linear Model ofMinitab Statistical Software Version 12.2 (1998) Tukey pair-wise comparisons were used to determine differences between treatment means at

P <0.05

3 Results

3.1 Intake

The chemical composition of the ingredients is presented inTable 1and of the experi-mental diets inTable 2 The CP content of fresh and dried sweet potato leaves was similar, while a lower value was found in ensiled sweet potato leaves Also, the content of amino acids differed between fresh, dried and ensiled sweet potato leaves (Table 3) Thus, the proportion of total EAA in ensiled sweet potato leaves was 0.95 of that in fresh leaves Further, the contents of arginine (0.95), histidine (0.82), lysine (0.87), methionine (0.82), cystine (0.69), tyrosine (0.91) and glycine (0.66) were lower in the ensiled than in the fresh material Also, in the sun-dried sweet potato leaves the contents of histidine (0.89), lysine (0.92), cystine (0.95), tyrosine (0.96) and glycine (0.86) were lower than in the fresh mate-rial There was no difference in CF content between fresh, dried and ensiled sweet potato

Table 3

Amino acid composition of the fresh, dried and ensiled sweet potato leaves (g/16 g N)

Essential amino acids (EAA)

Non-essential amino acids (NEAA)

leaves The highest contents of NDF and ADF were found in fresh and lowest in ensiled sweet potato leaves

All experimental diets had the same levels of CP and ME However the CF, NDF and ADF content was lowest in diet CAS There was no difference of CF, NDF and ADF between FSP, DSP and ESP diets

Due to differences in DM intake (Table 2) and chemical composition of the diets, the daily intakes of CP (Table 2) and of OM, CF, NDF, ADF and AA were different (data not shown) between diets (P < 0.05) Diets CAS and DSP showed similar intakes of DM, CP and OM, as did diets FSP and ESP (P > 0.05) The lowest daily intakes of CF, ADF and NDF were recorded for diet CAS (P < 0.05) The NDF and ADF intakes were not different between diets FSP and ESP (P > 0.05), and were lower than those on diet DSP (P < 0.01)

3.2 Ileal and total tract apparent digestibility of nutrients

There were no differences (P > 0.05) in the coefficients of ileal apparent digestibility (CIAD) of OM among diets (Table 4) However, the CIAD of CP was higher (P < 0.05) and the CIAD of NDF was lower (P < 0.05) on diet CAS than on diets FSP, DSP and ESP There were no differences between sweet potato diets (P > 0.05) in the CIAD of OM, CP and NDF

The coefficient of total tract apparent digestibility (CTTAD) of OM and CP were higher (P < 0.05) and the CTTAD of CF was lower (P < 0.05) on diet CAS than on diets FSP,

Table 4

Ileal and total tract apparent digestibility coefficients of nutrients in the experimental diets

Ileal

Total tract

a, b, c Values within row with different letters were significantly different (P < 0.05).

a CAS: casein diet as control; FSP: fresh sweet potato leaf diet; DSP: dried sweet potato leaf diet; ESP: ensiled sweet potato leaf diet.

DSP and ESP There were no differences between diets in CTTAD of NDF and ADF, and

no differences between sweet potato diets (P > 0.05) in CTTAD of OM, CP, CF, NDF and ADF

The CIAD of most amino acids was lower in the diets which contained protein from sweet potato leaves than from casein (P < 0.05), except for threonine, alanine and glycine (Table 5) There were no differences in the CIAD of most of the amino acids between the sweet potato leaf diets (P > 0.05)

The estimated CIAD and CTTAD of CP, CF, NDF, ADF and EAA in sweet potato leaves are presented inTable 6 There were no differences in CIAD or CTTAD between fresh, dried and ensiled sweet potato leaves (P > 0.05) However, the CIAD for lysine tended (P = 0.064) to be higher in fresh than in dried and ensiled sweet potato leaves

4 Discussion

The CP and CF contents of the fresh sweet potato leaves used in the present study were

in good agreement with earlier reports in the literature (Woolfe, 1992; Ishida et al., 2000;

An et al., 2003) The content of CP in fresh sweet potato leaves was comparable to values reported for cassava and leucaena leaves (Phuc and Lindberg, 2001), while that of CF and NDF was lower than in cassava leaves, leucaena leaves and groundnut foliage (Phuc and Lindberg, 2000) Also, the content of amino acids in fresh sweet potato leaves was similar to values reported byAn et al (2003), in a study including several varieties grown in Vietnam

In general, the content of EAA in fresh sweet potato leaves was similar to levels found

in other tropical foliages (Phuc et al., 2001) However, the content of lysine was lower in fresh sweet potato leaves than in cassava and leucaena leaves (Phuc and Lindberg, 2001) The content of EAA in ensiled sweet potato leaves was lower than in the dried material,

in agreement with studies on cassava leaves (Phuc and Lindberg, 2001) The sun-drying of

Table 5

Apparent ileal digestibility coefficients of amino acids in the experimental diets

Essential amino acids

Non-essential amino acids

a, b, c Values within row with different letters were significantly different (P < 0.05).

a CAS: casein diet as control; FSP: fresh sweet potato leaf diet; DSP: dried sweet potato leaf diet; ESP: ensiled sweet potato leaf diet.

sweet potato leaves did not affect the total content of EAA, although ensiling resulted in a reduction of the CP, NDF and ADF contents compared with the fresh material Also, the content of amino acids was affected by the ensiling process (reduced content of arginine, histidine, lysine, methionine, cystine, tyrosine and glycine) and also by sun-drying (reduced content of histidine, lysine, cystine, tyrosine and glycine) This is in agreement with a study where the contents of arginine, histidine, lysine and methionine were found to be lower in ensiled than in sun-dried cassava leaves (Phuc and Lindberg, 2001) The reduction in CP content in sweet potato silage could be due to microbial decomposition to ammonia during the ensiling process (An and Lindberg, 2004) Also, the change in AA content in ensiled sweet potato leaves can be explained by microbial activities during the ensiling process (McDonald et al., 1991) However, the reduced content of AA in sun-dried sweet potato leaves can be due to the action of endogenous plant enzymes during the initial phase of the drying process The lower content of NDF in sweet potato silage could be a result of losses

in the chemical analysis caused by solubilisation of fibre constituents in the acid conditions prevailing in the ensiled product.Man and Wiktorsson (2002) also reported a decrease

in NDF content of 8 and 4% after ensiling cassava top and gliricidia leaves, respectively

Morrison (1979)reported that approximately 10–20% of the hemicellulose was solubilized during 150 day ensiling of forages

The daily intakes of DM were lower (−13%) on the diets with FSP and ESP than on diets CAS and DSP Thus, the ensiling of sweet potato leaves did not have a negative influence

Table 6

Estimated ileal and total tract digestibility coefficients of nutrients in sweet potato leaves

Ileal digestibility

Total tract digestibility

Ileal AA digestibility

on the palatability compared with the fresh material The reduction in DM intake suggests that the way of presenting the foliage to the pigs may be of importance in maintaining a high daily feed intake Apparently, the reduction in water content by sun-drying and the subsequent reduction in particle size by milling helped to maintain feed intake at similar levels as in the control diet in the present study In contrast, in an earlier study on sun-dried and ensiled cassava leaves (Phuc and Lindberg, 2000), where the daily DM feed allowance was similar (4 kg 100 kg− 1), feed intake was unaffected by the preservation method In the latter study, the diet was given as a wet mash in the proportion 1:1 (w/w), while in the present study no water was added to the diet in connection with feeding

The CIAD and CTTAD of OM in the cassava root meal based control diet was similar

to previously published values for similar diets (Phuc and Lindberg, 2000) However, the CIAD of CP, and the CTTAD of CP and OM were higher in the present study This can be explained by the lower digestibility values of soya bean meal, which was used as a protein source in the study byPhuc and Lindberg (2000), than that of casein (Martins et al., 2001) used in the present study The CIAD for CP in the control diet was in agreement with values reported byPeiniau et al (1996)feeding diets based on cassava starch, supplemented with casein, to weaned pigs

When sweet potato leaves were included in the diet, the CIAD and CTTAD of CP and the CTTAD of OM were reduced This can be explained by the increase in fibre content

of the diets and was in agreement with studies on inclusion of tropical foliages (Phuc and Lindberg, 2000), as well as inclusion of temperate forages (Lindberg and Andersson, 1998)