Abstract
Calving and subsequent breeding information were obtained on 1889 Hereford and Angus cows bred to bulls representing the Hereford, Angus, Jersey, South Devon, Limousin, Simmental and Charolais breeds. The influence of sire breed, dam breed, dam age, calf sex and calf birth weight on the occurrence of dystocia and the effects of dystocia on subsequent reproductive performance were examined. Sire breed, dam breed, dam age and calf sex were significant (P<.005) sources of variation associated with dystocia when birth weight was not included in the analysis. The regression of birth weight on calving difficulty was a significant (P<.005) source of variation and calving difficulty increased 2.30 ± 0.21% for each kilogram increase in birth weight. When birth weight was held constant in the analysis, dam age was the only main effect significantly (P<.005) associated with percent calving difficulty. Calves sired by Charolais, Simmental, Limousin and South Devon bulls experienced significantly (P<.01) more calving difficulty (30.90±2.41, 32.66±3.09, 30.78±3.19 and 32.34±5.19%) than those sired by Hereford, Angus and Jersey bulls (15.78+-2.27, 9.90±2.55 and 6.46±3.61%). Percent calving difficulty was higher (P<.05) in Hereford-than in Jersey-sired calves. No significant differences in percent calving difficulty were found among the Charolais-, Simmental-, Limousin- and South Devon-sired calves nor between the Angus- and Jersey-sired calves. Dystocia in 2-year-old cows was 36.03±2.96% higher than in 3-year-olds and 44.62± 2.99% higher than in 4 and 5-year-olds. Percent dystocia was 8.59±3.39% higher (P<.05) in 3-year-old than in 4- and 5-year-old cows. Hereford cows had more (P<.005) calving difficulty than Angus cows, 34.78±3.19 compared to 27.02±3.13%. Dystocia was not significantly different between crossbred and straightbred calves, but crossbred calves were 1.55±0.26 kg heavier at birth than straightbreds. Male calves were heavier (P<.005) at birth than female calves, 35.12±1.82 compared to 32.10±1.81 kg, and experienced more (P<.005) dystocia, 28.40±1.71 compared to 16.98±1.70%. There was a higher percentage of calving difficulty in male births than in female births for all ages of cows, but the magnitude of the differences between sexes was greater in 2-year-old cows than in the other age groups. Dystocia had a signicant (P<.005) effect on the percentage of cows detected in estrus during the 45-day AI period, conception rate to AI and total conception rate. Fewer (14.4%) cows experiencing dystocia were detected in estrus during the AI period than those with no dystocia. In all cows, dystocia resulted in a 15.6% lower conception rate to AI and a 15.9% lower overall conception rate. The 2-year-old cows had a lower estrus detection rate, a lower conception rate during the AI period and a longer interval from calving to first breeding and from calving to conception than the 3-, 4- and 5-year-old cows. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science