Milk quality in Merino and Corriedale ewes

Abstract

Comparisons have been made of the milk quality of ewes of two strains of Merino, strong-wool (S) and medium-wool Peppin (B), and of two breeds, strong-wool Merino and Corriedale (C). The strains were compared in two ways – for ewes suckling single lambs and for ewes suckling a pair of twins containing one lamb of each strain, and the breeds were compared for ewes suckling single lambs. The strain comparisons were made in 1960–61 and the breed comparison in 1961–62.

Ewes of the S and B strains during the first 10 weeks of lactation had milk with mean fat percentages of 6.0 and 6.5 respectively when suckling singles, and 6.4 and 7.2 when suckling twins. The corresponding percentages for solids-not-fat (S.N.F.) for the period 45–72 days after parturition were 9.5 and 9.3 for singles, 9.9 and 10.2 for twins. The C breed and the S strain yielded milk with respective mean fat percentages of 8.6 and 9.4, and mean S.N.F. of 10.1 and 10.6, during the first 20 days of lactation. The only statistically significant difference among these breed and strain comparisons was the breed difference in S.N.F.

In Merino ewes suckling twins the fat percentage was higher than in those suckling singles over 10 weeks of lactation (6.8 v. 6.2), while the percentage of S.N.F. for the period 45–72 days after parturition was also higher (10.1 v. 9.4). The difference in fat was not significant, but the difference in S.N.F. was. When adjusted for the higher amount of whole milk produced by ewes suckling twins, the relative amounts of fat and S.N.F. secreted become 116 : 100 and 112 : 100. There is thus a suggestion that the extra sucking stimulus which leads to a greater production of whole milk also increases the secretion of fat and S.N.F.

When the 10-week lactation period was divided into three subperiods, the fat percentages showed a significant increase with time since parturition for Merino ewes suckling singles (5.7 : 5.8 : 7.2) or twins (5.7 : 6.8 : 7.9). Even when these figures were adjusted for amount of whole milk, the relative total amounts of fat secreted were 100 : 105 : 102 and 100 : 111 : 104.

Lamb growth rate was no more highly correlated with the constituents of milk quality than with the total amount of whole milk.

No important differences in milk quality were found between the genetic groups examined, but these were all related, the Corriedale breed being half Merino. The possibility remains that breeds differing more widely in their genetic background might also differ in milk quality.