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

Casoli et al. (1989) reviewed the milk composition in 12 breeds of sheep and reported a high
variation in the concentration of fat, which varied from 4.6% in the Iraqi Kurdi sheep to 12.6%
in Dorset ewes milked in America. Protein concentration was less variable, and it varied from
4.8% in the Grade Precoce to 7.2% in the Armenian Corriedale.
In Australia, few comparisons have been made between milk composition of different breeds.
Moore (1966a, 1966b) compared the production and composition of milk of 2 strains of the
Merino with those of Corriedale ewes, and found no significant difference between the yields of
milk and the concentrations of fat and solids-non-fat. Bencini and Purvis (1990) and Bencini et
al. (1992) observed no difference in the composition of milk from two different strains of Merino
and from Awassi x Merino and Merino ewes, and concluded that nutrition probably plays a
more important role in determining the composition of milk. This is also supported by the
studies of Geenty (1979), who compared the yield and composition of Romney, Corriedale,
Dorset, Romney x Dorset and Dorset x Romney ewes in New Zealand and found no difference
in milk composition between these breeds.
The genotype of the sheep may also affect the clotting properties of the milk through different
genetic variants of the casein fractions (Feagan et al. 1972; McLean 1984; McLean 1987;
McLean et al. 1984; McLean et al. 1987). For dairy cows the presence of certain casein genotypes
can affect the composition of the milk (Aleandri et al. 1990), and Italian researchers have
identified individual cows carrying particular genetic variants of the κ-Casein which make the
milk unsuitable for Parmesan cheese making due to poor coagulation (Morini et al. 1975, 1979;
Mariani et al. 1976, 1979; Losi et al. 1979, 1982; Losi and Mariani 1984).
In European dairy sheep, polymorphism of the casein has been reported by Lyster (1972),
Arave et al. (1973), Davoli et al. (1985), Russo et al. (1981), Chiofalo et al. (1982), Bolla et al.
(1985; 1986) and Manfredini et al. (1987). The αs1 casein variant, named Welsh, the frequency
of which varies from 2.2% (Chiofalo and Micari 1987) to 22% (Caroli et al. 1989) provokes a
reduction in casein content and a worsening of milk clotting properties in homozygous animals
and to a lesser extent, in heterozygous animals (Piredda et al. 1993).
In Australian sheep, Thomas et al. (1989) reported the existence of genetic variants of the
casein, but it is still not clear whether these genetic variants have an effect on clotting properties
and cheese outcome.
Few studies have been conducted on renneting times, coagulation patterns, rate of curd
formation and curd firmness of sheep milk (Askar et al. 1984; Manfredini et al. 1987; Casoli et
al. 1992; Bencini 1993, Delacroix-Buchet et al. 1994; Bencini and Johnston 1997).
Despite the reported differences in composition of the milk between different breeds of
sheep, Italian researchers have shown that there was no difference in cheese making performance
of milk between the breeds Sarda, Comisana, Massese and Delle Langhe (Chiofalo et al. 1989;
Casoli et al. 1990; Ubertalle et al. 1991).
In France, Delacroix-Buchet et al. (1994) have calculated the coefficients of genetic repeatability
in the Lacaune breed for renneting time (0.57) rate of curd formation (0.48) and curd
consistency (0.53). They concluded that since these repeatability values were similar to the
repeatability for milk production (circa 0.5) family type selection would be needed to achieve
genetic progress.