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Seasonal Changes in Fertility of Dairy Bulls in Northwestern Washington¹

State College of Washington, Department of Dairy Husbandry, Pullman

ABSTRACT

The per cent 60- to 90-day non-returns to 93,113 first- and second-service inseminations for Guernsey, Jersey and Holstein bulls used for artificial breeding purposes in northwestern Washington over a 6-yr. period were tabulated for this study. Monthly variation was highly significant, with January showing the lowest and September the highest average non-return rates. Non-return rate was lowest during January, February, March and April and gradually increased to the highest level in September, October and November. This pattern of breeding efficiency essentially parallels the results Mercier and Salisbury (7, 8, 9) observed from data collected in New York and eastern Canada.

Monthly correlations of sperm concentration, initial motility, motility after 30-min. incubation at 45° C., and drop in motility during incubation with non-return rates revealed great variation in the relationships from one period of the year to the next. Only 591 semen samples collected during 1 yr. were involved, but the data strongly suggest that the value of semen quality measurements cannot be accurately estimated during experimental periods of less than 1 yr.

¹ Scientific paper no. 1062, Washington Agricultural Experiment Stations, The State College of Washington, Pullman.

² Manager, Northwest Co-op Breeders, Mt. Vernon, Wash.