Sex ratios have been the subject of numerous investigations, particularly in studies with humans. In general, however, the literature relating to sex ratio in sheep is limited (Chapman & Lush, 1932; Henning, 1939; Rasmussen, 1940; Karam, 1957). Population studies have generally been based on an expected sex ratio of 0\m=.\5, and any factor causing marked divergence from this ratio is important. Although the proportion of entire males used in domestic animal populations in very much smaller than

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... for females, production from castrated males is a significant proportion of the total production of wool and meat from sheep. Hence, studies of population dynamics and flock structure need to take account of factors causing variation in sex ratios. This paper examines the influence of some factors, breed and strain, age of