Breeding Considerations for Minimising Difficult Calving
Factors influencing calving difficulty in beef herds are examined using two data sources. The first set of data was from two breed populations maintained by the University of Alberta at its experimental beef breeding ranch and the second was obtained from the Canadian Charolais Association ‘Conception to Consumer’ progeny testing programme.
Age of dam, which was closely related to weight of dam, was an important factor in calving difficulty. Most of the problem was associated with 2 and 3-year-old heifers in the University herds. Breed differences in calving difficulty were apparent in the University herds with 27% of Hereford births requiring assistance compared with 15% of the Synthetics. Two-year-old Hereford heifers received assistance in 59% of their calvings, 3-year-olds in 23% while the comparable figures for the Synthetics were 41% and 6% respectively.
In the Charolais progeny testing programme sire/breed ranking for increasing calving difficulty was; Chianina, Limousin, Charolais. Regressing calving assistance on sire progeny average birth weight indicated from 1 to 40% increase in calving difficulty for an increase of 1 kg in birth weight of calves.
Calf weight as a percentage of cow weight seemed to show promise for explaining variation in calving difficulty. Calf weight, cow weight and calf weight as a percentage of cow weight explained 20 – 30% of the variance in calving difficulty. Possible breeding methods for alleviating calving difficulty are discussed.
KeywordsBirth Weight Gestation Length Beef Herd Calve Difficulty Critical Percentage
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