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A large amount of wool on the face (face cover) of Merino sheep has been regarded as a fault by Australian sheep breeders as it has been associated with poor reproduction rates. Fail & Dun (1956) and Drinan & Dun (1967) reported that the degree of face cover was negatively correlated with fertility, but Young, Turner & Dolling (1963) found no evidence of a genetic association. In a review of these factors, Turner & Young (1969) commented that degree of face cover had been related to reduced reproduction rates in various breeds of sheep in Australia, New Zealand and the United States but not in the Soviet Union. The degree of face cover of individual ewes changes with season, and during pregnancy and lactation, with pregnant and lactating ewes showing less face cover than their non-pregnant contemporaries in the same flock (Mullaney, 1965). Physiological status of the ewe could therefore influence phenotypic assessment and may have contributed to the conflict of opinion on the importance of face cover as a criterion of selection. In the course of experiments on diluents for ram semen involving the artificial insemination (AI) of fine-wool Merinos (Saxony strain), we were able to make observations on semen production and factors associated with oestrus and fertility, and relate these to the degree of face cover of ewes and rams. AI is potentially a valuable technique for investigations aimed at identifying genetic factors determining reproductive efficiency. The libido and semen characteristics of rams and the occurrence and intensity of oestrus of ewes can be observed, the number of spermatozoa inseminated per ewe is controlled, and each sire is identified but the animals are not free to exercise any mating preferences. In the experiments reported here, most of the ewes in each flo;k were inseminated in a period of 17 days so that seasonal or nutritional effects would have been minimal. Some of the semen treatments applied in these experiments reduced the fertilizing capacity of the spermatozoa (Martin & Watson, 1976) but, as semen treatments were applied to split ejaculates from individual rams and ewes were randomized to treatments following the methods described by Entwistle & Martin (1972), the analyses relating face cover to fertility were not biassed by the effects of semen treatments.

Fertility of Merino sheep classified according to degree of development of face wool and bred by artificial insemination