Dairy Sheep Symposium - the Department of Animal Sciences ...
Dairy Sheep Symposium - the Department of Animal Sciences ... Dairy Sheep Symposium - the Department of Animal Sciences ...
This is often done by cheese makers with milk that does not clot (Alais 1974; Losi et al. 1982). Cheese makers also control the temperature and the rennet concentration at which the clotting takes place. On the other hand, cheese makers have little or no control over the composition and quality of the milk that reaches the cheese factory. The milk received should be of high microbiological quality, free of antibiotics and have a composition within acceptable limits. However, this does not always occur, despite the fact that often the payment for the milk is based on its quality (Pulina 1990). Also researchers have identified animals that produce milk that does not clot and is therefore unsuitable for cheese making in both dairy cows (Losi et al. 1982) and sheep (Casoli et al. 1992). Antibiotics Cheese maker Microbes Cheese making process (coagulation temperature, addition of Calcium, starter cultures, cutting time, cutting size, cooking, salting, etc) Milk Somatic cells Clotting properties Composition (protein, fat, total solids) Cheese outcome (quantity & quality) Figure 1. Factors affecting the outcome of sheep milk cheese at the cheese factory level. Cheese makers receive milk with certain characteristics, and have little power to change them. These include the gross composition of the milk (protein, fat, total solids), the presence of microbes (desirable or not), the possible presence of antibiotics that can disturb the starter cultures and the presence of somatic cells that come from the animals. Cheese makers can modify these characteristics only to a limited extent, but their methods of cheese making have a great influence on cheese outcome. High protein, fat and total solids concentrations in the milk are associated with high yields in the resulting dairy products (Chapman 1981; Storry et al. 1983). As a consequence, the milk of sheep has a higher yield of dairy products than the milk of cows and goats because it has higher concentrations of protein, fat and total solids (Ucci 1945; Casu and Marcialis 1966; Anifantakis 1986, 1990). Therefore any factor that affects the composition of the milk, will affect the yield and quality (chemical composition, texture and flavour) of dairy products obtained from the milk. Factors affecting the quality of sheep milk As shown in Figure 1, the cheese maker at the cheese factory receives milk of a certain composition and can do very little to change it. In Figure 2 the factors that affect sheep milk quality at the farm level are shown, and it is apparent that the farmer too has little control over some of these factors. However, the farmer has some control over the environmental factors that affect the quality of sheep milk.
Sheep Genetic factors breed and genotype Physiological factors •Age & parity • Weight • Lambs •Stage of lactation • Health Milk Composition (protein, fat, total solids) Somatic cells Microbes Antibiotics Farmer In the dairy Milking techniques Milking interval Stripping Management Nutrition Shearing Breeding out of season Use of hormones & medicines Figure 2. Factors affecting the outcome of cheese at the farm level. Some of these factors can be controlled by the farmer only to a certain extent (eg the genotype of sheep milked). Others depend exclusively on the sheep (eg age and parity, stage of lactation and number of lambs). Others are totally controlled by the farmer (nutrition, shearing, breeding and use of chemicals). Somatic cell count The somatic cell count is correlated with the health of the animal (Ruiu and Pulina 1992). Therefore the somatic cell count and the microbiological quality of the milk are correlated. Only 10% the somatic cells are mammary gland cells (eosinophils, epithelial cells), normally secreted together with the milk as a result of cellular turnover in the mammary gland. The remaining 90% of the somatic cells are blood cells (macrophages, leucocytes, lymphocytes). These normally contribute to the immune defence of the mammary gland, but their number increases considerably in the case of inflammatory or pathological processes within the mammary gland (Ranucci and Morgante 1994; Morgante et al. 1994). The health of the sheep in general, and of the mammary glands in particular, influence both the quantity and the quality of the milk produced. The most common pathology of the mammary gland in sheep dairies is mastitis, an inflammation of the udder caused by infection of the mammary tissue. Mastitis is economically important for sheep dairies because it reduces milk production and causes qualitative changes in milk composition which alter the processing performance of the milk and the qualitative characteristics of the dairy products obtained. This is due to a decreased synthetic capacity of the mammary secretory cells and to an increased permeability of the mammary epithelium that causes the passage of blood components directly into the milk (Ranucci and Morgante 1994; Harmon 1995).
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<strong>Sheep</strong><br />
Genetic factors<br />
breed and genotype<br />
Physiological factors<br />
•Age & parity<br />
• Weight<br />
• Lambs<br />
•Stage <strong>of</strong> lactation<br />
• Health<br />
Milk<br />
Composition<br />
(protein, fat, total solids)<br />
Somatic cells<br />
Microbes<br />
Antibiotics<br />
Farmer<br />
In <strong>the</strong> dairy<br />
Milking techniques<br />
Milking interval<br />
Stripping<br />
Management<br />
Nutrition<br />
Shearing<br />
Breeding out <strong>of</strong> season<br />
Use <strong>of</strong> hormones &<br />
medicines<br />
Figure 2. Factors affecting <strong>the</strong> outcome <strong>of</strong> cheese at <strong>the</strong> farm level. Some <strong>of</strong> <strong>the</strong>se factors can be controlled by <strong>the</strong><br />
farmer only to a certain extent (eg <strong>the</strong> genotype <strong>of</strong> sheep milked). O<strong>the</strong>rs depend exclusively on <strong>the</strong> sheep<br />
(eg age and parity, stage <strong>of</strong> lactation and number <strong>of</strong> lambs). O<strong>the</strong>rs are totally controlled by <strong>the</strong> farmer<br />
(nutrition, shearing, breeding and use <strong>of</strong> chemicals).<br />
Somatic cell count<br />
The somatic cell count is correlated with <strong>the</strong> health <strong>of</strong> <strong>the</strong> animal (Ruiu and Pulina 1992).<br />
Therefore <strong>the</strong> somatic cell count and <strong>the</strong> microbiological quality <strong>of</strong> <strong>the</strong> milk are correlated. Only<br />
10% <strong>the</strong> somatic cells are mammary gland cells (eosinophils, epi<strong>the</strong>lial cells), normally secreted<br />
toge<strong>the</strong>r with <strong>the</strong> milk as a result <strong>of</strong> cellular turnover in <strong>the</strong> mammary gland. The remaining<br />
90% <strong>of</strong> <strong>the</strong> somatic cells are blood cells (macrophages, leucocytes, lymphocytes). These normally<br />
contribute to <strong>the</strong> immune defence <strong>of</strong> <strong>the</strong> mammary gland, but <strong>the</strong>ir number increases<br />
considerably in <strong>the</strong> case <strong>of</strong> inflammatory or pathological processes within <strong>the</strong> mammary gland<br />
(Ranucci and Morgante 1994; Morgante et al. 1994).<br />
The health <strong>of</strong> <strong>the</strong> sheep in general, and <strong>of</strong> <strong>the</strong> mammary glands in particular, influence both<br />
<strong>the</strong> quantity and <strong>the</strong> quality <strong>of</strong> <strong>the</strong> milk produced. The most common pathology <strong>of</strong> <strong>the</strong> mammary<br />
gland in sheep dairies is mastitis, an inflammation <strong>of</strong> <strong>the</strong> udder caused by infection <strong>of</strong> <strong>the</strong> mammary<br />
tissue. Mastitis is economically important for sheep dairies because it reduces milk production<br />
and causes qualitative changes in milk composition which alter <strong>the</strong> processing performance<br />
<strong>of</strong> <strong>the</strong> milk and <strong>the</strong> qualitative characteristics <strong>of</strong> <strong>the</strong> dairy products obtained. This is due<br />
to a decreased syn<strong>the</strong>tic capacity <strong>of</strong> <strong>the</strong> mammary secretory cells and to an increased permeability<br />
<strong>of</strong> <strong>the</strong> mammary epi<strong>the</strong>lium that causes <strong>the</strong> passage <strong>of</strong> blood components directly into <strong>the</strong><br />
milk (Ranucci and Morgante 1994; Harmon 1995).
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