General Introduction
The Australian dairy sheep industry is relatively small, primarily relying on natural grass grazing, resulting in a low contribution of sheep milk to national production, with only 500 thousand litres annually compared to 9 billion litres from dairy cows Key challenges hindering industry growth include the absence of specialized breeds, limited local sheep milk products, and pre-weaning lamb mortality Despite these obstacles, there is a rising market demand for sheep milk products that exceeds local supply, which could lead to significant growth in the Australian dairy sheep sector.
Chronic diseases are the leading cause of death globally, responsible for 41 million fatalities, which represents 71% of all reported deaths (WHO, 2018) A significant contributor to these diseases is an unhealthy diet, particularly one low in omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) Omega-3 polyunsaturated fatty acids, characterized by two or more double bonds with the first double bond located on the third carbon from the methyl end, play a crucial role in health.
n-3 polyunsaturated fatty acids (PUFAs) include short-chain (SC) varieties like α-linolenic acid (ALA) and stearidonic acid (SDA), as well as long-chain (≥C20) n-3 PUFAs such as eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and the less researched docosapentaenoic acid (DPA) While previous research has primarily concentrated on EPA and DHA, DPA's structural similarities and potential health benefits have been overlooked, partly due to the lack of commercially available pure DPA for clinical studies This study encompasses EPA, DHA, and DPA under the term n-3 LC-PUFA.
Despite the recognized importance of fish and seafood as primary sources of n-3 LC-PUFA, many people still do not consume enough seafood, leading to a low intake of n-3 PUFA in their diets (Simopoulos, 2011) This issue is particularly evident in traditional diets of Western countries, where regular consumption of fish and marine products is often lacking (Cordain et al.).
The rising cost of seafood, coupled with other influencing factors, has significantly contributed to a notable trend in dietary choices (Kennedy et al., 2012) In contrast, milk and its processed products are recognized for their low levels of n-3 LC-PUFA content (Shingfield et al.).
Dairy foods have been a crucial part of human diets for over 8,000 years, serving as significant sources of energy, protein, fat, and essential microelements such as calcium, vitamin D, and potassium In 2015, global milk and dairy product consumption reached 111.3 kg per capita, with an anticipated increase of about 12.5% by 2025 This rising demand has prompted numerous studies aimed at enhancing the beneficial n-3 PUFA and n-3 LC-PUFA content in milk and its processed products, primarily sourced from cows and sheep.
Nutritional manipulation has been the primary method for modifying milk fatty acids (FA) due to concerns about lactose intolerance in some individuals and the high levels of short to medium chain fats in milk from small ruminants Dietary FA account for half of the C16 and all long-chain FA in milk, including all n-3 PUFA and n-3 LC-PUFA Lipid supplementation is an effective strategy for enhancing milk fat composition and increasing dietary energy.
Incorporating oil seeds and vegetable oil into dairy animal diets significantly boosts ALA content, while using rumen-protected marine-derived oil is the most effective method to enhance EPA, DHA, and DPA levels in dairy products However, a key challenge in this nutritional strategy is ruminal biohydrogenation, where dietary polyunsaturated fatty acids (PUFAs) are converted into monounsaturated and saturated fatty acids due to microbial activity in the rumen.
In addition, the biosynthetic pathway of these FA from the precursor ALA seems to be limited (Nguyen et al., 2018)
Current research on the impact of dietary supplementation with oil-infused pellets from canola, flaxseed, rice bran, and safflower on milk production and fatty acid composition in grazing dairy ewes, particularly within Australia's pasture-based production system, is limited Canola, the largest oilseed crop in Australia, is rich in alpha-linolenic acid (ALA) and has an optimal n-6 to n-3 polyunsaturated fatty acid (PUFA) ratio of 2:1 Studies have explored the use of canola oil-infused pellets as supplements for lambs and dairy cows in both pasture and feedlot systems Flaxseed oil, recognized as the richest plant oil source of ALA, contains up to 59.3% ALA in its fatty acid profile, making it a popular choice for enhancing the fatty acid profile of dairy products when fed to ruminants Conversely, rice bran and safflower oil are primarily composed of linoleic acid (18:2n-6, LA).
2006; Matthaus et al., 2015) than ALA The LA content of rice bran oil varies widely from 28.0-53.4% depending on the refining process (physical or chemical) (Gopala Krishna et al.,
Research has explored the impact of rice bran supplementation on the performance and fatty acid composition in ruminants, particularly in lambs and dairy cattle However, there is limited investigation into its effects on dairy sheep.
Safflower, cultivated in more than 60 countries, is a highly sustainable annual oilseed crop Its rich content of polyunsaturated and monounsaturated fats makes it a popular supplement for ruminants.
Fatty acids (FAs), especially linoleic acid (LA), make up to 77% of total fatty acids (Matthaus et al., 2015) Despite this significant presence, there is limited research on the effectiveness of LA as a dietary supplement for enhancing milk production, composition, and fatty acid content in lactating sheep.
This thesis investigates the impact of various dietary omega-3 oil supplements on the performance, yield, composition, fatty acid profile, and quality of milk and cheese from dairy ewes in a pasture-based system The primary research question focuses on how supplementing grazing dairy ewes with rumen-protected oil pellets or those infused with oils from canola, rice bran, flaxseed, or safflower, along with their interactions with sire breed, affects these outcomes.
• Animal performance traits of feed intake, lactation and body condition score
• Enhancing the concentration of milk and cheese n-3 LC-PUFA
• Enhancing cheese eating quality and consumer acceptability
The thesis has been structured into the following chapters:
Chapter 2: Literature Review provides a thorough examination of the Australian dairy sheep industry, highlighting the nutritional benefits of sheep milk and the significance of body condition score in managing dairy sheep It explores the factors influencing lactation and cheese flavor, alongside recent studies focused on enhancing n-3 LC-PUFA levels in dairy products Through a critical analysis of the existing literature, knowledge gaps were identified, which subsequently guided the formulation of the research objectives addressed in this thesis.
Chapter 3 assesses how canola, rice bran, flaxseed, safflower, and rumen-protected oil-infused supplements, along with their interactions with sire breed, influence the lactation performance, milk composition, and body condition score of dairy ewes during mid-lactation while grazing on low-quality pastures.
Chapter 4: Uncovers the relationship between canola, rice bran, flaxseed, safflower, and rumen protected oil-infused diets and the concentration of n-3 LC-PUFA in milk from grazing ewes
Literature Review
Dairy sheep industry background
As of 2018, the Food and Agriculture Organization (FAOSTAT) reported that there are around 200 million dairy sheep globally, representing 21.3% of the total sheep population In 2017, sheep milk production reached 10 million tonnes, accounting for 1.3% of the world's total milk output Asia leads in both the number of dairy sheep and total milk yield Projections indicate a 26% increase in global dairy sheep production, equating to approximately 2.7 million tonnes over the next decade Additionally, cheese remains the primary processed product derived from sheep milk, with a global production of 680 thousand tonnes in 2014.
Table 2.1 Worldwide sheep milk products(Source: FAOSTA (2018)
Items Unit World Asia Africa Europe America Year
Fresh milk Million tonnes 10.4 5.02 2.44 2.85 0.097 2017 Cheese Thousand tonnes 680.3 273.3 57.4 34.2 7.84 2014 Butter and ghee Thousand tonnes 63.3 61.0 2.3 - - 2014
The Australian dairy sheep industry, established since 1906, remains relatively small compared to the meat and wool sectors, with only 5,500 out of 72 million sheep used for milking across 13 commercial farms Despite the potential of 250,000 milking ewes to produce 8,000 tonnes of milk products for the domestic market, current production is limited to 550,000 litres annually Approximately 60% of this milk is processed into yoghurt, while the remainder is used for cheese Dairy ewes, like their meat and wool counterparts, are primarily raised on extensive grazing systems with low-quality pastures, leading to low productivity Efforts to enhance the industry included the introduction of East Friesian and Awassi breeds in the 1990s, but data on their milk production remains insufficient for producers to improve farm gate value.
Sheep milk
Sheep milk is a more nutrient-dense option compared to cow and goat milk, offering higher levels of fat, protein, and essential minerals, especially calcium (Park et al., 2007; Balthazar et al., 2017).
Milk fat is a crucial element that determines the nutritional and energetic values of milk, with sheep milk containing twice the fat content of goat and cow milk This results in a higher energy value of 105 calories per 100 ml for sheep milk, compared to 69 and 70 calories per 100 ml for cow and goat milk, respectively Additionally, the size of milk fat globules in sheep (3.6 µm) and goats (3.0 µm) is smaller than that in cows (4 µm), facilitating easier access for lipolytic enzymes and enhancing digestibility for consumers These characteristics of fat globules also provide technical benefits, such as reducing phase separation during frozen storage in cheese production Sheep milk, like goat and cow milk, primarily consists of saturated fatty acids.
Sheep milk contains a higher proportion of polyunsaturated fatty acids (PUFA) at 4.82% compared to cow and goat milk, which have 4.05% and 3.70%, respectively (Gantner et al., 2015; Markiewicz-Keszycka et al., 2013) Additionally, sheep milk boasts a greater concentration of conjugated linoleic acid (CLA) at 1.08%, surpassing the levels found in goat and cow milk (1.01% and 0.65%, respectively) The notably lower ratio of n-6 PUFA to n-3 PUFA in sheep milk enhances its appeal for reducing the risk of chronic diseases, making it a more desirable choice than cow and goat milk (Simopoulos, 2002; Zymon et al., 2014).
Sheep milk offers a higher protein content (5.8%) compared to cow milk (3.3%), with 80% of this protein being casein, which is advantageous for cheesemakers due to its positive correlation with cheese yield The casein micelles in sheep milk are rich in calcium, facilitating rennet coagulation without the need for added CaCl2 This higher mineralization allows cheesemakers to produce sufficient curd using less rennet while maintaining the same coagulation time as cow milk Additionally, sheep milk's elevated protein concentration and lower allergic sensitization make it an excellent alternative protein source for those allergic to cow milk.
Sheep milk is a superior source of vitamins and essential minerals when compared to goat and cow milk It contains significantly higher levels of calcium and phosphorus, which are crucial for the growth and maintenance of skeletal structure.
Figure 2.1 Fat (a), protein (b), lactose (c), solids-non-fat (SNF) (d), casein (e), albumin and globulin (f) percentage of milks from cow, goat, sheep and human (Park et al., 2007)
A standard serving of sheep milk (494 mg of calcium per 250 ml) provides nearly half of the daily recommended intake of 1000 mg of calcium for adults, according to NHMRC (2013) Research indicates that high protein intake can enhance calcium absorption (Kerstetter et al., 2011), making sheep milk, which is rich in both calcium and protein, an effective dietary calcium supplement.
Table 2.2 Mineral and vitamin contents in sheep, goat and cow milk (Sources: Park et al.,
Items Unit Sheep Goat Cow
2.2.2 Factors affecting milk yield and composition
Approximately 180 sheep breeds are capable of producing milk for human consumption, but only a few, such as the East Friesian (EF) and Awassi, are recognized as primary dairy breeds The East Friesian, developed in northern Germany and the Netherlands, is renowned for its high milk production; however, its use in harsh environments with excessive heat and humidity is limited Consequently, EF is often utilized in crossbreeding programs to enhance the milk production and prolificacy of local breeds Following EF in milk production capacity, the Awassi breed is the most widespread dairy sheep globally, thanks to its adaptability to various environmental conditions.
Table 2.3 Average lactation length, milk yield and composition of common sheep breeds used for milk production (Sources: Haenlein, 2007; Park et al., 2017)
Heritability estimates for key milk traits indicate moderate values for milk, fat, and protein yields (approximately 0.25-0.30), while fat and protein content show higher heritability (0.50 to 0.60) (Park et al., 2017) Genetic improvement programs, primarily based on pure breed selection, have been predominantly implemented in Europe, where milk, fat, and protein yields are critical selection criteria for breeders (Barillet, 2007; Carta et al., 2009) For example, genetic programs for the Lacaune breed in France have resulted in annual increases of 0.12% in fat content and 0.14% in protein content, alongside a genetic gain of 5 liters in milk production (Astruc et al., 2002).
Table 2.4 Heritabilities and genetic correlations for lactating traits of different breeds (Source:
Trait Milk yield Fat yield Protein yield Fat (%) Protein (%) Milk yield 0.20 to 0.32 0.77 to 0.89 0.88 to 0.94 -0.43 to -0.56 -0.46 to -0.64 Fat yield 0.16 to 0.26 0.82 to 0.93 0.02 to 0.25 -0.36 to -0.12 Protein yield 0.18 to 0.28 -0.18 to -0.28 0.01 to -0.15
2.2.2.2 Dietary nutrients for improving milk production and composition
The synthesis of milk components is primarily influenced by secretory cells in the mammary gland, which utilize precursors from dietary nutrients To enhance milk production and its components, modifying dietary nutrition strategies is the most effective method.
Most sheep milk is primarily utilized for cheese production, as highlighted by Balthazar et al (2017) The yield of cheese is significantly influenced by the concentrations of milk fat and protein, according to Pellegrini et al (1997) This review focuses on how dietary nutrients impact the yields and contents of milk fat and protein.
Dietary nutrient composition and milk yield
Milk production in dairy ewes is primarily influenced by voluntary feed intake, particularly the energy intake necessary to support the high energy content of sheep milk Enhancing the energy and nutritional quality of the diet for lactating ewes is crucial for boosting milk production Fat supplementation has proven to be an effective method for increasing milk yield and improving milk composition for human health benefits Different types and dosages of oil supplements have led to notable variations in the performance of dairy ewes.
Dietary nutrient composition and milk protein content
Milk protein content is influenced by various nutritional factors, but changes are less significant compared to milk fat concentration in both dairy cows and sheep A positive correlation exists between dietary energy concentration and milk protein content, particularly when energy sources are soluble carbohydrates This relationship is attributed to increased bacterial protein and improved nitrogen utilization in the rumen, as most microbial energy comes from carbohydrate fermentation Additionally, similar to dairy cows, higher dietary crude protein content negatively affects milk protein percentage in dairy sheep, as excess crude protein can surpass microbial needs, leading to increased urinary nitrogen and reduced microbial protein synthesis.
Table 2.5 Effect of lipid supplementation on milk yield and composition a
Diet MY Fat FY Protein PY References
SO + 8 g/ kg DM of Marine Algae
SO + 16 g/ kg DM of Marine Algae
SO + 24 g/ kg DM of Marine Algae
2018) a Milk yield (MY, g/day), fat (g/100 g milk), fat yield (FY, g/day), protein (g/100 g milk), protein yield (PY, g/day)
Research by Gonzalez et al (1982) and Purroy and Jaime (1995) indicates that the protein content and yield of milk can be affected by various protein sources, likely due to differences in rumen undegraded crude protein (CP) in dietary protein (Pulina et al., 2006) Additionally, lipid supplementation has led to inconsistent findings regarding milk protein concentration.
2.5) The wide range of inclusion rates, dietary components, feeding regimes might have led to these contrasting outcomes
Dietary nutrients and milk fat content
Milk fat content is highly responsive to changes in dietary nutrition Key factors affecting both the yield and concentration of milk fat include energy balance, the intake and source of neutral detergent fiber, and the use of dietary fat supplements.
Milk fat content in dairy cows and sheep is negatively correlated with their dietary nutrition levels Undernutrition frequently occurs in extensive or semi-intensive grazing systems for dairy ewes, leading to adverse effects on their health and productivity.
Body condition score as an essential management tool for dairy sheep producers 17 2.4 Enhancing omega-3 long-chain polyunsaturated fatty acid content of dairy-derived
Body condition score (BCS) is a vital health management tool used to estimate body fat and energy reserves, as well as assess animal welfare (Caldeira et al., 2007; Morgan-Davies et al., 2008; Caroprese et al., 2009; Phythian et al., 2011) Standardized in the 1960s for dairy sheep (Russel et al., 1969), BCS is determined through subjective palpation of the backbone and ribs, with scores ranging from 1 to 5 Ewes with BCS scores below 2 are considered thin and emaciated, indicating inadequate nutrition during early lactation.
4 and above are considered obese and probably over-fed (Caroprese et al., 2009)
Body condition score (BCS) is a valuable predictor of body weight in sheep breeds, aiding producers in estimating the necessary feed volume and quality to fulfill ewes' nutrient requirements Research by Kenyon et al (2014) supports the positive correlation between BCS and reproductive traits in ewes across various sheep breeds, highlighting its significance in sheep management.
Research indicates that the optimal body condition score (BCS) for ewes at breeding is between 2.5 and 3.0 to maximize pregnancy rates Additionally, higher BCS scores during mid-pregnancy are associated with improved lamb survival rates in subsequent winters While the relationship between BCS and milk production has primarily been studied in dairy cows, findings show that a one-point increase in BCS during the dry period can lead to an additional 545.5 kg of milk in the first 120 days of lactation Understanding BCS and its impact on animal performance can enable sheep producers to enhance productivity through effective nutritional management at various production stages.
Table 2.6 Description of body condition scoring of sheep (Source: Western Australian
The bones form a sharp narrow ridge Each vertebra can be easily felt as a bone under the skin There is only a very small eye muscle
The ends of short ribs are distinctly shaped, resembling a square When you run your fingers 1 cm apart along the surface, you can easily feel the fingernail-like structure beneath the skin with minimal covering.
The bones form a narrow ridge but the points are rounded with muscle It is easy to press between each bone
The ends of short ribs are rounded and can be easily pressed between with fingers spread 0.5 cm apart, resembling the shape of finger tips Although they are covered with flesh, it is simple to press underneath and between the ribs.
The vertebrae are only slightly elevated above a full eye muscle It is possible to feel each rounded bone but not to press between them
The ends of short ribs are rounded and packed with muscle, making them distinct when pressed together with four fingers While the rounded ends are easily felt, the space between them remains less pronounced, highlighting the muscle coverage and fullness of the ribs.
It is possible to feel most vertebrae with pressure The back bone is a smooth slightly raised ridge above full eye muscles and the skin floats over it
Feeling or sensing one or two short ribs is challenging, as they can only be pressed under with difficulty The sensation resembles the texture of the side of the palm, where perhaps only one end can be detected.
The spine may only be felt (if at all) by pressing down firmly between the fat covered eye muscles A bustle of fat may appear over the tail
Feeling the ends of the short ribs is nearly impossible due to the thick layer of meat and fat that fills the triangular area between the long ribs and the hip bone.
2.4 Enhancing omega-3 long-chain polyunsaturated fatty acid content of dairy-derived foods for human consumption
2.4.1 Role of Omega 3 long chain polyunsaturated fatty acid
Omega-3 polyunsaturated fatty acids (n-3 PUFA) are essential fatty acids that humans cannot synthesize and must obtain from their diet Key n-3 PUFA include α-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and docosapentaenoic acid (DPA), which are vital for reducing the risk of chronic diseases Seafood, particularly fish oil, is the primary source of these fatty acids, but the low consumption of seafood in many diets highlights the need to enhance n-3 PUFA content in other food groups, such as dairy products Despite the high consumption of milk, it is typically low in n-3 PUFA, prompting research into increasing these fatty acids in dairy through nutritional manipulation The challenge lies in ruminal biohydrogenation, where dietary PUFA are converted into less beneficial fatty acids by rumen microbes Incorporating oil seeds and vegetable oils in dairy animal diets can boost ALA levels, while rumen-protected marine-derived supplements effectively increase EPA, DHA, and DPA concentrations in dairy products Further research is needed to understand the biosynthesis of n-3 LC-PUFA from ALA and the genetic factors influencing lipid metabolism in ruminants.
2.4.2 Structure of omega-3 LC-PUFA
Omega-3 polyunsaturated fatty acids (n-3 PUFA) are characterized by having more than two double bonds, with the first double bond located on the third carbon from the methyl end The primary types of n-3 PUFA include shorter chain (SC, ≤C18) variants such as α-linolenic acid (ALA, 18:3n-3) and stearidonic acid (SDA, 18:4n-3), as well as long-chain (≥C20) n-3 PUFA, which encompasses eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), and the less extensively researched docosapentaenoic acid (DPA, 22:5n-3) (Nichols et al., 2010).
Figure 2.2 The structure of common omega-3 polyunsaturated fatty acids Adapted from
2.4.3 Metabolic pathways, human health benefits and recommended intake of n-3 PUFA 2.4.3.1 Dietary n-3 PUFA intake recommendations
Dietary intake recommendations for n-3 long-chain polyunsaturated fatty acids (LC-PUFA) vary significantly among organizations and are influenced by factors such as age, gender, and individual consumption purposes (Nichols et al., 2010; Nguyen et al., 2018) According to the National Health and Medical Research Council (NHMRC) guidelines (NHMRC, 2006), adequate daily intakes are set at 1.3 g of alpha-linolenic acid (ALA) and 160 mg of total EPA+DPA+DHA for men, while women should aim for 0.8 g of ALA and 90 mg of total EPA+DPA+DHA.
PUFAs are considered sufficient to prevent deficiency symptoms in adults, but they are not optimal To reduce the risk of chronic diseases, the NHMRC recommends daily intakes of total n-3 LC-PUFA of 430 mg for women and 610 mg for men Additionally, the FAO and WHO suggest a sufficient daily intake of EPA and DHA to mitigate the risk of coronary heart disease.
The recommended intake of EPA and DHA is 250 mg per day for adult males and non-pregnant, non-lactating adult females, while lactating and pregnant women should consume 300 mg For patients with hypertriglyceridemia, the American Heart Association suggests a higher intake of 2 to 4 g per day Additionally, a review by Nguyen et al (2018) indicates that the general recommendation for n-3 LC-PUFA to prevent cardiovascular disease is approximately 500 mg per day, which corresponds to two or three servings of fish weekly.
2.4.3.2 Metabolic pathways for the biosynthesis and dietary sources of n-3 PUFA
Mammals, including humans, cannot synthesize n-3 polyunsaturated fatty acids (PUFAs) due to the absence of delta-12 and delta-15 desaturase enzymes, necessitating their intake through food or supplements (Lee et al., 2016) The synthesis of n-3 long-chain PUFAs in the human body begins with the conversion of alpha-linolenic acid (ALA) to stearidonic acid (SDA), with ALA primarily sourced from green plant tissues and oils, particularly flaxseed/linseed and canola oil (Baker et al.).
Table 2.7 Common food sources of ALA (18:3n-3, as gram per serving)
Data from Office of Dietary Supplements, National Institute of Health (NIH), USA Tbsp denotes tablespoon
There are two recognised biosynthesis pathways for n-3 LC-PUFA (Figure 2.3), including the presently accepted pathway (Sprecher, 2002) and conventional metabolic pathway (Park et al.,
In the biosynthesis of n-3 long-chain polyunsaturated fatty acids (LC-PUFAs), two primary pathways exist: one involves the production of docosahexaenoic acid (DHA) from docosapentaenoic acid (DPA) through sequential desaturation, elongation, and β-oxidation, while the other pathway directly converts DPA to DHA via the delta-4 desaturase enzyme The existence of delta-4 desaturase, which supports the conventional metabolic pathway for n-3 LC-PUFA biosynthesis, was first evidenced by Park et al (2015) Although further research is necessary to elucidate the specific biosynthetic pathway in humans, existing studies indicate a very low conversion rate of alpha-linolenic acid (ALA) to n-3 LC-PUFAs.
Nutritional aspect of sheep cheese and factors driving cheese eating quality
2.5.1 Nutritional aspects of sheep cheese
Sheep cheese, like cow and goat cheese, is primarily composed of fat and protein The concentration of these nutrients can vary significantly among different sheep breeds, largely influenced by the raw milk's composition and the cheese processing methods used (Raynal-Ljutovac et al., 2008).
Table 2.13 Major nutritional properties of sheep cheese (%) (Source: Raynal-Ljutovac et al
Cheese Breed Age of cheese Total solids Fat Protein
Ruminant dairy products high in saturated fatty acids (SFA) are linked to cardiovascular diseases, with studies showing a positive correlation between milk and cheese consumption and coronary heart disease Notably, the specific types of cheese and their animal sources were not addressed in these analyses However, research indicates that consuming sheep cheese for three weeks can significantly elevate plasma levels of beneficial fatty acids while reducing low-density lipoprotein (LDL) levels by 7% in individuals with mild hypercholesterolemia This reduction in LDL is associated with a decreased risk of major vascular diseases Sheep cheese, produced under similar conditions, boasts higher levels of healthy fatty acids, such as conjugated linoleic acid (CLA) and total n-3 polyunsaturated fatty acids (PUFA), compared to cow and goat cheeses Additionally, sheep cheese has a lower palmitic acid content, which is known to correlate positively with coronary heart disease risk.
2.5.2 Factors driving cheese eating quality
Cheese quality is significantly influenced by its appearance, flavor, and texture, which are crucial factors in consumer choice Flavor, defined by its organoleptic properties, is the most vital quality attribute, arising from a complex array of sapid and aromatic compounds These compounds develop through biochemical and microbiological processes during cheese production Various factors, such as milk supply, coagulants, starter cultures, non-starter lactic acid bacteria, cheese composition, and ripening temperature, along with their intricate interactions, play a critical role in determining cheese quality This complexity often leads to challenges in consistently producing premium-quality cheese.
The flavor of cheese is fundamentally influenced by the quality of raw milk, which is determined by total somatic cell count (SCC) and chemical composition, both of which are affected by the characteristics and diet of the animals A high SCC negatively impacts cheese quality, with optimal milk for cheese making recommended to have less than 300,000/ml of SCC The composition of milk, particularly its casein, fat, and calcium content, significantly affects cheese yield, texture, and overall quality Genetic and non-genetic factors influencing milk composition can therefore indirectly affect cheese quality Research has shown that cheese made from Cinisara cows exhibits a smoother texture and a sweeter, more acidic taste compared to cheese from Brown cows, which tends to be more bitter and salty.
Research indicates that pasture-based diets for dairy cows enhance the yellow density of ripened cheese, improving its eating quality (Kilcawley et al., 2018) Additionally, varying levels of concentrate supplementation can alter the sensory properties of cheese (Bovolenta et al., 2009) While studies have explored the impact of lipid supplementation on fatty acid changes and cheese quality, findings remain limited Najera et al (2017) and Vargas-Bello-Perez et al (2015a,b) found that rapeseed oilcake and various vegetable oil supplements had a neutral effect on cheese sensory attributes in sheep and cows Conversely, Sympoura et al (2009) showed that feeding cows extruded linseed can modify odor compounds in cheese The composition of milk fatty acids likely influences cheese sensory attributes, as volatile flavor compounds responsible for cheese flavor originate from these fatty acids (McSweeney, 2004).
Breed Stage of lactation Plane of nutrition Animal health
GDL Starter culture Secondary/adjunct culture Rennet
Natural creaming Centrifugal Milk powder Rate of lysis
Figure 2.7 Factors affect cheese quality, adapted from (Fox et al., 2000)
Justification and Research Objectives of the study
Effective feeding programs in animal production must prioritize the nutritional needs of animals to ensure optimal growth, performance, and product quality Key factors to consider include feed availability, nutrient costs, and the overall health and wellbeing of the animals Additionally, it is crucial that commercial feed supplementation does not adversely affect consumer ethics, eating quality, or product acceptability.
Research indicates that the nutritional quality of feeds significantly influences sheep milk production, composition, and fatty acid profile, which in turn affects the value of cheese products However, there are notable gaps in understanding the effects of plant oil supplementation on dairy sheep and their products, particularly in Australian pasture-based systems This study aims to compare various plant-derived oils as supplementary feed sources and assess their integration into dairy sheep milk and cheese for commercial production The research objectives focus on addressing these critical knowledge gaps.
This study aims to assess the effects of various plant-based oils and rumen-protected EPA + DHA dietary supplements on the performance of grazing dairy sheep Key performance indicators include body conformation, feed intake, milk yield, milk composition, and the fatty acid profiles of both milk and cheese.
To examine cheese eating quality and consumer acceptability of products from dairy sheep supplemented with different types of oils
Chapter 3: Supplementing dairy ewes grazing low quality pastures with plant-derived and rumen-protected oils containing EPA + DHA pellets increases body condition score and milk, fat, and protein yields
Abstract
The Australian dairy sheep industry, primarily reliant on natural grass grazing, faces productivity limitations This study investigated the effects of various plant oil-infused and rumen-protected polyunsaturated fats on lactation traits and body condition scores (BCS) of ewes on low-quality pastures It was hypothesized that supplementing diets with plant-derived oils would enhance milk production and composition without affecting BCS Sixty mid-lactation ewes, balanced by sire breed and other factors, were supplemented with different treatments, including control pellets and those infused with canola oil, rice bran oil, flaxseed oil, safflower oil, and rumen-protected marine oil The results indicated that the rumen-protected marine oil significantly improved milk, fat, and protein yields by approximately 30%, 13%, and 31%, respectively Additionally, canola oil, rice bran oil, and safflower oil also led to increased milk production Breed played a crucial role in performance, with crossbred Awassi x East Friesian ewes yielding more milk than purebred Awassi This research supports the use of oil-infused pellets as effective supplements for enhancing production in dairy sheep grazing on low-quality pastures.
Introduction
Sheep milk is nutritionally superior to cow milk, yet its contribution to Australia's national milk production remains minimal, with only 13 commercial farms producing 550,000 litres annually compared to 9 billion litres from dairy cows Factors such as diet, breed, age, management practices, health, and environment significantly influence milk yield and composition Dietary fat supplementation is an effective strategy to enhance milk yield and modify its composition, particularly through plant-derived oils that increase energy density and boost n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) in dairy products High n-3 LC-PUFA consumption is linked to reduced risks of various diseases, including Alzheimer's However, while fat supplements can improve milk yield, they often lead to decreased milk fat and protein content, negatively impacting producers' income since milk is traded based on total solids Consequently, the use of dietary fats to enhance sheep milk yield in Australia is limited, primarily applied during dry seasons to support lactating animals when pasture quality is low.
Current research on the impact of dietary supplementation with rice bran, canola, and safflower oils on milk yield and composition has primarily focused on dairy cows and goats, with no studies conducted on dairy ewes While the effects of flaxseed supplementation on dairy ewes have been explored, these studies utilized either whole or extruded flaxseed Furthermore, there is a significant lack of research investigating the effects of different dietary supplements on lactation and liveweight traits in grazing dairy ewes of various genetic backgrounds under consistent management and feeding conditions.
This study aimed to address knowledge gaps by evaluating the lactation performance, milk composition, and body condition score of dairy ewes in mid-lactation grazing on low-quality pastures, supplemented with canola, rice bran, flaxseed, safflower, and rumen-protected oil-infused pellets It was hypothesized that the inclusion of various plant-derived and marine oils would yield distinct effects on milk yield, milk composition, and body condition score in grazing dairy ewes.
Materials and Methods
3.3.1 Animal Management and Experimental Design
The use of animals and procedures performed in this study were all approved by the University of Tasmania Animal Ethics Committee (Permit No A0015657)
A study was conducted involving sixty lactating Awassi and crossbred Awassi-East Friesian ewes in mid-lactation at Grandvewe Cheeses Farm in Tasmania, Australia Over a 10-week feeding trial, the ewes had unrestricted access to local natural velvet tussock grass, hay, and water while being kept in the same paddock The ewes were divided into six dietary treatment groups, ensuring balance in liveweight, breed, parity, body condition score (BCS), and milk yield across the groups.
The study involved feeding ewes different types of wheat-based pellets, including a control group without oil and groups infused with various oils: canola (CO), rice bran (RBO), flaxseed (FSO), safflower (SFO), and rumen protected EPA + DHA (RPO) All treatments were designed to be isocaloric and isonitrogenous Each ewe received 1 kg/day of the supplemented pellets during milking time in the milking parlour, following a two-week adjustment period and an eight-week experimental phase.
During the initial two weeks of the adjustment period, commercial pellets were gradually replaced by experimental diets (CO, RBO, FSO, SFO, and RPO) at a rate of 100 g/day, reaching a total of 1 kg/day by day 10 Ewes were milked every morning at 0600 hours, with individual milk yields electronically recorded using De Laval’s Alpro Herd Management System software version 6.54.
Table 3.1 Ingredient composition of the experimental pellets a
Items Control CO RBO FSO SFO RPO
Rice bran oil, ml/kg - - 50 - - -
Sodium bicarbonate 6.25 6.25 6.25 6.25 6.25 6.25 a Canola oil (CO), rice bran oil (RBO), flaxseed oil (FSO), safflower oil (SFO), rumen-protected oil (RPO)
3.3.2 Feed intake and body condition score
Daily measurements of offered pellets and residuals were taken to assess feed intake Weekly feed samples were collected and preserved at -20 °C for later chemical analysis Body condition score (BCS) was consistently evaluated weekly on a scale of 1-5 by the same evaluator to maintain consistency and repeatability (Kenyon et al., 2014).
Table 3.2 Nutrient compositions a of basal and experimental diets b
Pasture Hay Control CO RBO FSO SFO RPO
The study presents the metabolizable energy (ME) values in MJ/kg dry matter (DM) for various feed components, including canola oil (CO), rice bran oil (RBO), flaxseed oil (FSO), safflower oil (SFO), and rumen-protected oil (RPO) The ME values range from 7.1 to 12.2 MJ/kg DM, highlighting the nutritional significance of these oils in animal diets Additionally, the analysis includes key parameters such as organic matter (OM), acid detergent fibre (ADF), neutral detergent fibre (NDF), ether extract (EE), and crude protein (CP), which are essential for understanding the overall feed quality and energy content.
Weekly milk samples were collected from each animal during daily milkings at 0600hrs and stored in labeled plastic vials with bronopol blue preservative at 4 °C before being sent to TasHerd Pty Ltd in Hadspen, Tasmania, for compositional analysis The analysis utilized Fourier Transformed Infrared spectrometry technology, specifically the Bentley Fourier Transform Spectrometer, to quantify milk composition This system incorporates Bentley Flow Cytometry to measure somatic cell count, while the spectrometer assesses milk fat, protein, and lactose according to the official laboratory analysis method (AOAC, 1990) Additionally, the equation from Mavrogenis and Papachristoforou (1988) was employed to calculate Fat-corrected milk (FCM).
6% FCM=M (0.453+0.091F), where “F” is the percentage of fat and “M” is milk yield (kg)
3.3.4 Chemical analysis of experimental and basal diets
Samples of the basal and experimental diets were dried at 65 °C in a fan-forced oven and ground through a 1 mm sieve Dry matter (DM) content was assessed by heating the ground samples at 150 °C for 24 hours to eliminate moisture Ash content was determined by combusting the samples in a furnace at 600 °C for 8 hours Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were quantified using an ANKOM220 fibre analyser, while ether extract was measured with an ANKOM XT15 fat/oil extractor The crude protein percentage was calculated from the nitrogen content, determined using a Thermo Finnigan EA 1112 Series Flash Elemental Analyser.
MA, USA) Table 2 shows the nutritional composition of the experimental diets
Data analysis was conducted using the Statistical Analysis System (SAS, 2009), beginning with descriptive summary statistics to identify data entry errors and outliers through means, standard errors, and minimum and maximum values The General Linear Model (PROC GLM) was employed to assess the effects of different oil supplementation, sire breed, week of supplementation, and their interactions as fixed effects, while feed intake, milk yield, milk composition, and body condition score served as dependent variables A significance threshold of P < 0.05 was established, with differences between means determined using Duncan’s multiple range and Turkey’s probability pairwise comparison tests The final statistical model utilized for the analysis was specified accordingly.
The equation \( Y_{ijk} = \alpha + SB_i + D_j + W_k + (SBD)_{ij} + (SBW)_{ik} + (DW)_{jk} + e_{ijk} \) represents a statistical model where \( Y_{ijk} \) is the dependent variable, \( \alpha \) denotes the overall mean, and \( SB \), \( D \), and \( W \) indicate the fixed effects of sire breed, diet, and week of supplementation, respectively The terms in brackets signify second-order interactions, while \( e_{ijk} \) represents the error term in the model.
Results
The study's findings indicate that dietary treatments had a significant impact on the feed intake of grazing dairy ewes (P