Sources of variation in the birth weight of Ayrshire calves

Authors

• Vappu Kossila Department of Animal Husbandry, University of Helsinki
• Pirkko Taskinen Department of Animal Husbandry, University of Helsinki

DOI: https://doi.org/10.23986/afsci.71738

Abstract

Sources of variation in the birth weights of 225 single Ayrshire calves, born to regular cows (calving interval less than 15 months) in the dairy herd of the Viik Experimental Farm, were studied. The mean birth weight (35.2 kg) of 111 male calves was significantly (P<0.005) higher than that (33.4 kg) of 114 females. The relative birth weight calculated as a percentage from the live weight of the dam was 7.05 % in males and 6.55 % in females, on an average. The smallest calves were born in July-September (32.3 kg) and the heaviest in April-June (35.5 kg), this seasonal trend being significant (P<0.001). However, the relative birth weight of combined sexes remained constant throughout the year. The number of the dam’s calvings affected significantly the birth weight, which was low at the first calving (32.0 kg) and also at the 6th or subsequent calvings (33.6 kg). Maximum birth weight of males (39.2 kg) was attained at the 5th calving and that of females (36.1 kg) at the 3rd calving. The relative birth weight was highest in the males (7.44 %) at first calving and lowest in the females (5.93 %) at the 6th or subsequent calvings. The relationships between the birth weight of the calf (X1), the live weight of the dam (X2), the number of services per gestation resulting in the birth of the calf (X3), the number of days dry prior to parturition (X4), and the level of fat corrected milk (FCM) yield during the lactation period subsequent to calving (X5), were investigated by means of calculating the coefficients of simple and partial correlations. The live weight of the dam was the only variable which significantly affected the birth weight of the calf (r12.345 = 0.4022, P< 0.001, N = 225), the length of the dry period had a slight positive effect (r14.235 = 0.1235). The correlations obtained separately for males were mostly of similar order as those obtained for females. Regression equations demonstrating the relationship between the birth weight of the calf and the live weight of the dam, are given. Due to strong feeding of the cows, it is believed that the birth weights of the calves in the dairy herd of the Viik Experimental Farm are somewhat larger if compared with the overall values of the Ayrshire breed in Finland.