摘要或動機

Successful calving is measured by the safe delivery of a healthy calf. Any factors that\r
cause dystocia (difficult calving) are undesirable; as it will result in weak or dead calves, stress\r
dams and a decrease in profit to the rancher. The most often identified reason for dystocia are\r
calves that are too large at birth. Ranchers frequently use sires that will result in calves with\r
small birth weights that will be born easy. This is especially true when breeding first calving\r
heifers. The selection for small calves at birth results not only in less growth in the uterus but\r
also less growth after birth, which means less beef to sell. This means ranchers try to balance\r
reasonable growth and reasonable calf size when selecting their sires. Much data has been\r
published on birth weight and its selection.