Date of this Version
Calf deaths caused by dystocia (calving difficulty) result in a $600 million annual loss to U.S. beef producers (Bellows and Short, 1994). Therefore, methods to reduce dystocia must be investigated, understood, and utilized to decrease the incidence and degree of calving difficulty. A review of early research was presented at the 1989 Range Beef Cow Symposium at Rapid City (Deutscher, 1989) indicating the major cause of dystocia in first calf heifers was a disproportion between the size of calf at birth (birth weight) and the cow's birth canal (pelvic area). A pelvic area/ birth weight ratio developed in Nebraska was suggested as a method to estimate the size of calf a heifer could deliver without assistance.
At the 1993 Range Beef Cow Symposium in Cheyenne, Dr. R. A. Bellows presented an extensive overview of research conducted at Miles City on numerous factors affecting calving difficulty. He concluded the following: 1) high calf birth weights were the main cause of dystocia, 2) dam pelvic area must be adequate to deliver calf, 3) selection for pelvic size will increase frame size and calf birth weight, 4) low nutrition will not reduce dystocia, 5) maternal uterine environment affects calf birth weight, 6) exercise during gestation did not affect dystocia, 7) early obstetrical assistance increased calf survival and dam subsequent pregnancy rate, and 8) hormones of calf and dam are involved in calving difficulty.
This paper will not review all the above factors but instead will try to expand on the most important and will summarize the latest research on dystocia. It will also recommend some strategies for selection and management of heifers and bulls to reduce calving difficulty.