Effects of Seasonal Climatic Changes on Certain Physiological Reactions, Semen Production and Fertility of Dairy Bulls

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Abstract
During recent years the practice of artificial insemination of dairy cattle has spread rapidly into the Gulf Coast area of the United States and also into other subtropical and tropical areas of the world having a similar warm, humid climate. Since most of the bulls used in these programs have been of the European breeds developed in temperate areas there is a need for knowledge of the effects of such a climate on the thermoregulatory mechanisms, semen characteristics, and fertility of such bulls. The opinion that certain breeds are better adapted to southern conditions than are others has been expressed frequently, but few careful studies of breed reactions and seasonal fertility have been carried out. Gaalaas (6), Seath (12), and Seath and Miller (13, 14) have reported studies which indicated that air temperatures of 90 ° F. or above cause marked increases in body temperatures and respiration rates of lactating cows, whereas relative humidity did not show such a relationship. Anderson (1) has reviewed much of the literature concerned with seasonal effects on the bull, indicating that high environmental temperatures tend to have a detrimental effect on semen production and fertility of bulls of the European breeds. Dordick (4) has summarized data from several southern and northern ex- periment stations and found that the fertility of bulls in the southern area was lower than that of animals maintained at northern stations, with the greatest effect on semen quality and f~rtility being shown during the months of July, August, and September. He cited the high southern summer temperatures and humidities as the probable cause of these differences. Seasonal studies of the fertility of dairy cattle conducted in the northern and central portions of the United States (7, 8, 9, 10, 16) generally have shown a tendency for maximum fertility in the spring, followed by low fertility either in late summer or during ~ the fall and winter months. This study was undertaken in order to evaluate the effects of climatic condi- tions of the Gulf Coast area on dairy bulls and their fertility and also to de- termine whether or not there are major differences in breed responses to such conditions. METHODS

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