Dairy Sheep Symposium - the Department of Animal Sciences ...

Little research has been done on the composition of fatty acids of sheep milk, but the diet
seems important on this regard. Casoli et al. (1989) reported that sheep milk fat contains high
percentages of palmitic and oleic acid, while essential fatty acids, linoleic acid and linolenic acid
are low. Volatile fatty acids range from 15 to 30 % and are more saturated than unsaturated.
Casoli et al. (1989) and Rossi and Pulina (1991) also reported that nutrition affects the fatty acid
composition of the fat in the milk. If the ewes are underfed and mobilize their body reserves, the
proportions of high molecular weight fatty acids are increased. In particular, there is an increase
in oleic acid, which derives from stearic acid after the action of a mammary desaturase. So, the
ratio C18/C10 in the milk provides an indication of the nutritional status of the animal. Ewes
generally mobilise body reserves for the first 4-5 weeks of lactation (Pulina 1990). The presence
of unsaturated fatty acids in the milk could generate processing problems which, however, would
not be detected in European sheep dairy systems as for the first 4-5 weeks of lactation the milk is
consumed by the lambs. Processing problems in the first few weeks of lactation have been
reported by sheep dairy manufacturers in Australia, where the ewes are separated from the lambs
and milked soon after birth. The hypothesis that these processing problems in early lactation
may be due to the presence of unsaturated fatty acids in the milk is currently being investigated
by researchers at the University of Western Australia.
The fatty acid composition of the fat in the milk also can be modified by feeding protected
fat, as demonstrated by the work of Pulina et al. 1990b, Sklan (1992) and Chiofalo et al. (1993)
who observed significant increases in long chain fatty acids, especially unsaturated fatty acids, in
ewes fed protected fat.
Pulina (1990) observed that improving the quality of the diet can reduce the somatic cell
count in the milk, especially toward the end of lactation (Pulina et al. 1992). This is probably
due to an improved functionality of the rumen which results in the combined effect of increasing
production, resulting in a dilution of the somatic cells and of slowing down mammary cell
turnover. Somatic cell counts can increase in sheep grazing green pasture due to excessive
nitrogen intake (Cuccurru et al. 1994). The use of regulators of rumen fermentations such as
Flavomycin (Hoechst Ltd) may result in reductions in the somatic cell count (Pulina and Rassu
1991b).
Nutrition has a limited effect on the microbiological characteristics of sheep milk, which are
mainly attributable to hygienic conditions during milking. However, dietary imbalances (excess
carbohydrates, excess nitrogen, insufficient fibre) causing anomalous fermentations in the rumen
or the hind gut can provoke the output of highly contaminating faeces because of their low
consistency and high content of microbial cells (Bertoni 1992). Also selenium deficiency can
compromise the anti-oxidant properties of the mammary tissue and cause an increase in the
somatic cell count of the milk (Ronchi et al. 1994).
The use of silage can also increase the number of spore-forming bacteria, especially
Clostridium spp, in the milk (Manfredini et al. 1987; Cavani et al. 1991), which could affect the
keeping properties of the cheese.