Section A. Physiology of dairy cattle: I. Reproduction and lactation

Abstract

Some years ago the annual wastage of cows in dairy herds in Britain was estimated by Wright(1) to be approximately 22%, and of this about one-quarter was due to sterility. Recent figures(2) from Shropshire, Staffordshire and Warwickshire suggest that this position has not changed in the past few years. Thus in forty-eight herds containing 1925 cows there were 620 disposals in the 12 months ending September 1940. 23% of the disposals were due to sterility. The annual losses from bovine sterility in Britain have been calculated to be equivalent to £7,000,000 in milk alone. This fact is cited by Day(3) in a concise article on the control of sterility in which he discusses various factors which contribute to the problem. Some of these factors, such as contagious abortion and trichomonas infection, are pathological, but many others are functional or physiological. The present review is concerned only with the latter. Mackintosh (4), in an article on breeding and rearing to maintain the milk supply, summarizes for the practical dairy farmer many of the methods by which the incidence of functional sterility can be reduced. Both Day and Mackintosh emphasize the importance of pregnancy diagnosis, of detecting the short winter oestrus and of testing the fertility of the bull. They also mention that hormone therapy can frequently be used to great advantage for inducing oestrus. Knowledge of these factors and how best to deal with them has greatly increased during the past few years as a result of the work carried out in many research stations throughout the world.