Dystocia or difficult parturition has long been known to increase the likelihood of neonatal death among calves. Beef researchers (Woodward and Clark, 1959; Laster and Gregory, 1973) were among the first to document this relationship and found dystocia to be a leading cause of mortality among newborns. Sale of livestock is the primary source of income for beef breeders and increasing income through the reduction of mortality rates was the primary impetus for evaluating beef sires for dystocia. Using bulls that sired easy calving progeny on heifers and other cows in which dystocia was likely to be a problem was expectecf to decrease mortality. While a dairyman's primary income is not usually from livestock sales, dystocia and calf mortality reduce income. Dairy researchers in severaf countries (Bar-Anan et. al. 1976 (Israel); Philipsson, 1976a (Sweden); Poliak and Freeman, 1976 (USA); Cady, 1977 (USA); Cady and Burnside, 1982b (Canada)) found a positive relationship between dystocia and high mortality rates.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 7. Symposia (1), , 139–144, 1982
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