Previous articles entitled “Using cow-calf health and production data: Pregnancy percentage” and “Using cow-calf health and production data: When are cows getting bred?” discuss methods of measuring reproductive efficiency such as pregnancy percentage and distribution of breeding dates. Calving percent and calf death loss are also measures of reproductive efficiency in a cow-calf herd.
Calving percentage is calculated by dividing the number of cows that give birth to a live calf by the number of cows exposed to a bull for breeding. If this value is lower than other similar operations, or past performance, consideration should be given to factors that influence the maintenance of pregnancy such as the nutritional management of the pregnant cow, and potential disease resulting in embryonic loss. Similar to pregnancy percentage, the calving percentage alone does not inform on when the calves are born. The calves may all be born within a 60-day time frame, or they may be spread out over 6 months. It is useful to look at the distribution of calving dates as the final indicator of when conception is occurring within the breeding season. Calculating breeding dates from estimated gestation lengths obtained during pregnancy checking is inherently dependent on the accuracy of the estimated age of the fetus. Determining the age of the fetus by rectal palpation or ultrasound becomes more difficult as pregnancy progresses, making the estimated breeding dates less accurate. Calving dates however are a much more reliable method of determining when the cow conceived. For mature cows, 283 days is good estimate of gestation length, although it can range from 279 to 287 days.1 Heifers may experience gestation lengths on the short end of the range when carrying their first calf.
Calf death loss is the number of calves that die prior to weaning divided by the number of live calves born. Abnormally high calf death loss compared to other similar operations may indicate issues with nutrition, infectious disease, biosecurity, or all three. Accurate calf death loss data includes age of calf at death, age of dam, and reason for death. According to the National Animal Health Monitoring Service 2007-2008 National Beef study, for calves less than 3 weeks of age, the most common cause of death was calving-related problems.2 Many calving-related problems can be prevented by good management of the calving season. This begins by using bulls with reasonable birthweight EPD’s. The ideal calf birthweight depends on size of cows, breed, etc., but in general, the target birthweight should be as large as can be achieved without creating calving difficulties (i.e. dystocia). Excessively small calves are often less vigorous, may be more at risk for disease, and often do not grow well. Managing the calving season well includes ensuring cattle can calve in a reasonably clean environment, and being available to intervene in cases of difficult delivery.
Evaluating calving percentage and calf death loss can help the cow-calf producer and their veterinarian identify areas where management, nutrition, or disease prevention could be improved, in order to improve the overall reproductive performance of the cow-calf herd.
- Pregnant cows, timing of pregnancy, open cows, and pregnancy rate. University of Nebraska-Lincoln Institute of Agriculture and Natural Resources. https://beef.unl.edu/faq/pregnant-cows
- Mortality of Calves and Cattle on U.S. Beef Cow-calf Operations. National Animal Health Monitoring Service: 2007-2008 Beef study. USDA APHIS CEAH VS. May 2010.