The Effect of Exposure to High Ambient Temperature on Spermatogenesis in the Dairy Bull

The effects of seasonal influences on reproductive activity in domestic animals have been reviewed in detail by Anderson (4), and seasonal variations in reproductive activity in the dairy bull have been reported by several investigators (1, 2,3,5,7,12).Recently, Weeth and Herman (13) have reported a seasonal variation in the motility and longevity of dairy bull semen, indicating a mid-summer maximum followed by a sharp decline in September and then a significant increase in October, suggesting a delayed detrimental effect of high environmental temperature.Mercier and Salisbury (8) reported a low level of sperm production during June and July in five Holstein and five Guernsey bulls, accompanied by lower than average levels of fertility for these 2 months.Subsequent studies by Mercier and Salisbury (9, 10) indicate that hours of daylight are a predominant factor in seasonal variations in fertility.Erb and Waldo (6) observed a relationship between season and non-return rates in bulls used for artificial breeding.The rates were lowest in January, February, March and April and gradually increased to the highest level in September, October and November.This study was initiated in conjunction with investigations of heat tolerance to determine some of the basic factors involved in seasonal variations in reproductive activity and to determine the effects of high environmental temperatures on spermatogenesis in the dairy bull.This report represents the progress of these investiga£ions to date. EXPERIMENTALMaintenance conditions.This study was conducted using two experimental chambers, A and B, equipped to handle two animals each.These chambers were insulated rooms in which temperature and humidity could be controlled and maintained at specified conditions over extended periods.Eight 100-watt daylight fluorescent bulbs were installed in each chamber.These lights were on from approximately six to six each day throughout the, experiment.Four Guernsey bulls were used.Bulls A-1 and A-2 were assigned to chamber A; bulls B-1 and B-2 were assigned to chamber B. A-1 and B-1 were obtained from private herds in western North Carolina and were 34 and 28 months old, respectivelY.A-2 and B-2 were from the College herd and were 24 and 19 months old, respectively.The bulls were tied in individual stalls within the chambers.They were fed hay and a grain mix twice daily and had free access to water from individual drinking cups.