Seasonal variation in the reproductive capacity of the bull

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Abstract
Seasonal variation in the reproductive capacity of the bull was studied during a 27-month experimental period at the Experimental Station. There are a total of 1049 ejaculates for this period. Supplementary data for other periods on the Experimental Station and for two other large farms practising artificial insemination are also included.Highly significant individual and monthly differences were noted during the experimental period for the density and motility of the sperm, the pH of the semen and for the percentage of ejaculations performed. The seasonal variation in semen is marked, but there is considerable variation in different years between bulls and between farms in the periods of maximal and minimal types of semen and in seasonal trends.The relationship between such variation and climatic and nutritional conditions is discussed. There appears to be a basic seasonal rhythm in bull semen associated with climatic factors, warmer conditions causing stimulation and vice versa. Nutritional factors may, however, modify this rhythm. The relationship between seasonal variations in semen quality and fertility is discussed.

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