The effects of inbreeding on four families of Peppin Merinos. III. The influence of crude pituitary extract on inbred lambs

Abstract

Treatment of inbred lambs with crude pituitary extract produced a highly significant increase in griwth rate over the first 10 weeks when compared with untreated inbred lambs. Continued treatment from 10 to 23 weeks of age did not cause any further change in growth rate. Differences between treated and untreated lambs in body weight and size were maintained long after cessation of treatment. Wool production was significantly increased during, but not after, the treatment period. At 12 months of age (7 months' fleece), treated and untreated groups did not differ significantly in wool production, mean fibre weight, mean fibre length, or total fibre number. The ratio of secondary to primary follicles did not differ significantly at any stage. Similar treatment produced no detectable response in non-inbred lambs. It is suggested that the effect of inbreeding is partially derived from a reduction in pituitary activity. Treatment of inbred lambs caused a decrease in the variances of body weight and size and an increase in the variance of wool production. This may be explained by differences between different tissues in their hormone requirements for maximum response, and would suggest that the effects of inbreeding on the variance of any character depend on the physiological paths through which the effect is produced.