Six to 10 percent of all calves born in beef cow herds in the U.S. die at or soon after birth. About half of those deaths are due to calving difficulty (dystocia). This multi-million dollar annual loss is second only to losses from failing to conceive.
Calving difficulty has received much more attention in recent years, primarily because of the mating of larger European breeds of bulls to British breeds of cow. Increased calving problems are also being encountered within purebred breeds, as genetically large bulls are often mated to cows of only average size.
The purpose of this guide is to acquaint cattle producers with calving management principles that will help minimize calf loss in their herds.
Factors causing calving difficulty
About 80 percent of all calves lost at birth are anatomically normal. Most of them die because of injuries or suffocation resulting from difficult or delayed parturition (calving). Factors contributing to calving problems fall into three main categories — calf effects, cow effects and fetal position at birth.
Heavy birth weights account for most of the problems related to the calf. Birth weights are influenced by breed of the sire, bull within a breed, sex of the calf, age of the cow and, to a slight degree, nutrition of the cow. Shape of the calf may also have a small effect on calving problems.
Several factors associated with the cow influence dystocia, the major ones being her age and pelvic size.
First-calf heifers require more assistance in calving than do cows, because they are usually structurally smaller.
Pelvic area (birth canal) increases as the female develops to maturity. Thus, a higher proportion of calving difficulty in 2- or 3-year-old cows is due to smaller pelvic openings. Heifers and cows with small pelvic areas are likely to require assistance at calving. However, even heifers with a large pelvic area may need help delivering large calves.
The calf’s birth weight and cow’s pelvic area have a combined effect on dystocia. Many heifers giving birth to calves weighing more than 80 pounds will have difficulty, even if they have large pelvic areas. Two-year-old heifers tend to have either a pelvis too small or a calf too large to allow them to deliver without assistance. Therefore, calving problems could be reduced by decreasing birth weight through bull selection and/or increasing pelvic area by selecting the larger, more growthy heifers.
Fetal position at birth
About 5 percent of the calves at birth are in abnormal positions, such as forelegs or head turned back, breech, rear end position, sideways or rotated, etc. (Figure 1). This requires the assistance of a veterinarian or an experienced herdsman to position the fetus correctly prior to delivery. If fetal position cannot be corrected, the veterinarian may have to perform a caesarean section.