Some aspects of the comparative efficiency of wool production of Corriedale sheep unselected for fleece weight

Abstract

Two groups of sheep, one of 22 rams and one of 22 ewes each approximately balanced for birth status, were housed and pen-fed individually such that fleece body weight increased only slightly over three consecutive 28 day experimental periods. Thus net efficiency and maintenance wool production parameters were determined.

Although the sex and birth status comparisons are confounded with the two family lines involved, it is considered that this does not affect the sex and birth status effects. The data are characterised by significant sex x birth status interactions for the wool production parameters (net efficiency, experimental fleece production and wool growth rate), in which the effect of birth status is greater for the ewes than for the rams.

The periodic wool growth rate data indicate a phase difference in the annual rhythm between the sexes, the ewes approaching the minimum production level which the rams have achieved. This renders a sex comparison invalid. It is concluded that these rams and ewes may produce wool at a similar net efficiency when compared at equivalent phases of the cycle. This greater wool growth rate of the ewes, due largely to a greater fibre diameter, is balanced by the smaller wool bearing surface area and results in an experimental fleece production similar to that of the rams.

Twin-born animals tend to be handicapped in net efficiency and experimental fleece production. The lack of significance of the handicap may be due to compensatory growth of the twins.

Net efficiency is predicted with a high degree of accuracy from wool growth rate, experimental fleece production and fleece weight index calculated from the experimental data. However, sulphur content of the wool bears only a small, but positive relationship to net efficiency and wool production parameters. The effects of sex and birth status on sulphur content are small. Similarly, there is no relationship of net efficiency or the wool production parameters with the follicle parameters of S/P ratio, primary follicle density and total follicle density.

Despite low coefficients of variation in body weight and feed intake data, there is a large variation in the wool production parameters, suggesting a potential for considerable improvements in such an unselected flock in response to culling for wool production.