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Genetic selection for calving ease

published: August 23rd 2018
source: Beef Cattle Browsing

The most important factor affecting calving difficulty is birth weight of the calf in relation to size of the dam. Genetics influences birth weight. Birth weight was one of the four traits (along with weaning weight, yearling weight, and maternal ability which is often called “milk”) originally evaluated with Expected Progeny Difference (EPD), an estimate of genetic transmitting potential. Birth Weight EPD includes records not only from an individual but also from relatives and progeny. So, if Birth Weight EPD is available for an individual it should be used in genetic selection instead of the individual’s actual birth weight, which can be highly influenced by non-genetic factors.

Birth Weight EPD is just an indicator of calving ease. As breed genetic evaluation programs evolved, EPD was developed for actual calving ease. EPD for calving ease includes the effect of birth weight and so should be used instead of Birth Weight EPD. And when EPD for calving ease is available, it should be used alone without considering Birth Weight EPD.

Most breed associations report two estimates of calving ease. One is Direct Calving Ease EPD. It should be thought of as a factor of the calf, i. e., how easily is the calf born. This is the EPD that should be considered in predicting ease of birth of a sire’s calves. The other is Maternal Calving Ease EPD, i. e., how easily a female gives birth. In sire selection, Maternal Calving Ease predicts calving ease of a sire’s daughters.

Direct and Maternal Calving Ease are different traits. Just because a sire has a desirable Direct Calving Ease EPD does not mean his daughters will necessarily be easy calving. This is a common misconception. In fact, most research shows a negative genetic relationship, ranging in magnitude from low to medium depending on the particular study. So, if you are selecting terminal sires (with no replacement heifers to be saved) you should concentrate only on Direct Calving Ease EPD. But if you save heifers, you should consider both Direct and Maternal Calving Ease. You can find sires with desirable EPD for both Direct and Maternal, but it will not be as easy as when looking for Direct alone.