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Bennet Cassell
Extension Dairy Scientist, Genetics and Management
(540) 231-4762, email: bcassell@vt.edu
First-ever genetic evaluations for stillbirth percentages in Holsteins will be published this August. Stillbirth rates for Holsteins average between 7 and 8% across all parities, and are highest (over 10%) in first calf heifers. Replacement heifers are an economic asset to dairy farms, so loss at birth of one of every twelve heifer calves is cash down the drain. Most calves lost are born dead, but the genetic evaluations also include calves that die within 48 hours of birth. Heritabilities of stillbirths are low, 3% or less, but there are important bull to bull differences in stillbirth rates of progeny, especially for extreme bulls. The new genetic evaluations will allow producers to identify and discriminate against those “outliers”. Genetic control of stillbirths is expressed through genes a sire passes to his calves as well as through the genes expressed when his daughters give birth. Service sire and maternal grandsire genetic evaluations will be published using the same procedures that are used for genetic evaluations for calving difficulty. USDA combines service sire and maternal grandsire evaluations for both stillbirths and calving difficulty into a composite called Calving Ability. This composite receives a negative weight (lower percentages are favorable for both calving ease and stillbirths) in Net Merit, and is as important in the index as udder composite. Producers do not need to practice additional selection against bulls with unfavorable calving ability composites if they use Net Merit for sire selection. If a well constructed index is not used for selection, be cautious not to place too much emphasis on stillbirths at the expense of other important traits. That said, genetic evaluations for stillbirths will help dairy breeders begin to eliminate unfavorable genes for this trait from the Holstein breed.