In addition to being the greatest cause of baby calf mortality, calving difficulty markedly reduces reproductive performance during the next breeding season. Cattle suffering from calving difficulty have been reported (Brinks, et al. 1973) to have pregnancy rates decreased by 14% and those that did become pregnant to calve 13 days later at the next calving. Results from a Montana study (Doornbos, et al., 1984) showed that heifers receiving assistance in early stage 2 of parturition returned to heat earlier in the post-calving period and had higher pregnancy rates than heifers receiving traditionally accepted obstetric assistance. In this study, heifers were either assisted about one hour after the fetal membranes (water bag) appeared (EARLY) or were assisted only if calving was not completed within two hours of the appearance of the water bag (LATE).
Heifers that were allowed to endure a prolonged labor (LATE) had a 17% lower rate of cycling at the start of the next breeding season. In addition, the rebreeding percentage was 20% lower than the counterparts (EARLY) that were given assistance in the first hour of labor. First calf heifers should deliver the calf in about one hour. The starting time is the first appearance of the water bag and ends with complete delivery of the calf. Mature cows, that have calved previously, should proceed much faster and should deliver the calf in about a half hour. The calves weaned the following year from cows that endured the long delivery weaned 46 pounds lighter than calves from cows with earlier re-breeding dates due to a shorter stage 2 of parturition.
Always check to be certain that cervical dilation has been completed, before you start to pull the calf. If you are uncertain about whether cervical dilation has taken place or if the calf is in a deliverable position, call your large animal veterinarian immediately. Prolonged deliveries of baby calves (in excess of 1.5 or 2 hours) often result in weakened calves and reduced rebreeding performance in young cows!