Traits associated with fitness such as aspects of reproduction (for a review see Lamberson and Thomas, 1984) and lamb survival (Wiener, Woolliams and Macleod, 1983) are seriously affected by inbreeding. Homeostatic control is an important component of fitness in animals. In an experiment reported by Wiener, Woolliams and Slee (1988) and Slee, Wiener and Woolliams (1988), inbred (I) rams were far less able to resist acute cold than outbred (O) rams. The opportunity was taken in this same experiment to examine the effects of inbreeding, plane of nutrition (high (H) or low (L)) and exposures to acute cold and heat on aspects of semen quality.

Earlier reports have shown that inbred sheep were smaller than outbreds although they grew at a similar rate (Wiener, Woolliams and Slee, 1988a), that both the effects of inbreeding and of nutrition affected cold resistance and heat tolerance (Slee, Wiener and Woolliams, 1988) and that all these factors influenced semen quality (Wiener, Woolliams and Slee, 1988b). The present report deals with a number of constituents in the blood of the same experimental animals.