Seasonal Variations in Hours of Daylight Associated with Fertility Level of Cattle under Natural Breeding Conditions

Abstract

Summary In a study of three herds of cattle located at different latitudes in Eastern Canada, the lowest per cent of successful services was obtained during winter and spring and the highest during summer and fall. The differences in fertility level between herds were not significant statistically but those between seasons were significant at the 5 per cent level of probability. The average monthly conception rate of the three herds was significantly correlated with the monthly average length of daylight, there being a lag of approximately 1 to 2 months before the maximum effect was reached. Temperature changes had no measurable direct effect on fertility level under the existing conditions. The authors believe that at high latitudes variations in length of daylight measurably influence the fertility level in cattle.