Some Factors Affecting Reproduction in Beef Cattle

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Abstract
The effects of breed of dam, calving period, age of dam, weight change from fall to spring and weight change from spring to fall on calving rate were evaluated using data obtained from an extensive beef cattle crossbreeding project at the Louisiana Agricultural Experiment Station, Baton Rouge. Estimates of the effect of heterosis on calf crop were calculated. A total of 2,035 matings over a 10-yr. period were covered in this study. Sires of six breeds —Angus, Brahman, Brangus, Charolais, Hereford, and Shorthorn—were mated with Angus, Brahman, Brangus, and Hereford dams. No straightbred Charolais and Shorthorn dams were included. Consequently, only 20 different crossbred-dam groups were available. Brangus were considered as straightbred. Previous calving period, weight change from fall to spring prior to the breeding season, and weight change from spring to fall of the breeding season all had highly significant effects upon subsequent calving percent. Breed of dam also significantly influenced calving percent. The average calving rate for all cows was 77.15%. All crossbred cows excelled straightbred cows in calf production with the exception of the Shorthorn × Angus cross. Purebred cows averaged 63.3% while cross-bred cows averaged 79.9% calving rate. Brahman-Hereford crosses exhibited the greatest effect of heterosis (27.4%) followed by the Brangus-Hereford (18.8%) and Brahman-Angus (17.1%) crosses. Among straight-bred cows, the Brahman (65.2%) and Brangus (66.9%) had higher calving rates than cows of the Angus (61.2%) and Hereford (59.8%) breeds. Charolais×Angus (94.3%) and Charolais × Hereford (97.5%) cows displayed the highest calving rates followed by Hereford×Brahman (90.5%) cows. All of the British×British crossbred cows except the Shorthorn × Hereford cross were below the crossbred average in calving rate. Cows which were dry during the breeding season had a lower calving percent (58.6%) than cows which were lactating (83.4%). This indicated that dry cows were more difficult to settle than lactating cows. The genetic or permanent environmental effect which caused the cows to be dry may be causing them not to settle in the subsequent breeding season. Analysis did not show a breed by calving period interaction. Cows which more nearly maintained their weight during the winter had higher conception rates during the subsequent breeding season than those that lost weight. Cows which were gaining during the breeding season had an increased calving rate. Age of dam did not affect calving rate. Copyright © 1968. American Society of Animal Science . Copyright 1968 by American Society of Animal Science

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