Short communication: a genetic study of mortality in Danish Jersey heifer calves

The aim of this study was to estimate genetic parameters for mortality of Jersey heifer calves during the first 6 mo after birth, calculate the genetic trend of the trait, and estimate breeding values of widely used Jersey sires. More than 260,000 heifer calves were included in the study. The mortality traits included in the analysis were defined as mortality in 8 different periods from 24h after birth to age 180 d (d 1-14, d 15-30, d 31-60, d 61-90, d 91-120, d 121-150, and d 151-180) and mortality over the entire period. A linear model was used for estimation of genetic parameters, breeding values of sires, and genetic trend. Fixed effects included in the model were herd-year class, month of birth, parity of mother, and whether the calf was sold to another farm in the first 6 mo. Both direct and maternal genetic effects were included in the model; however, the maternal genetic effect was very small and not significant. The mortality rate was highest in the first month after birth (7.8%). Total mortality in the first 180 d was 12.5%. Direct heritabilities of mortality were quite low, ranging from 0.002 to 0.03 on the observable scale and 0.025 to 0.076 on the underlying scale. Maternal heritabilities were even lower. The genetic correlation between mortality from d 1 to 14 and d 1 to 180 was estimated to be 0.88, although by definition, these 2 traits share the same observations for many records. No clear genetic trend existed over the last 20 yr; however, considerable genetic variation exists. The best and the worst sires differed by about 8% in their estimated breeding values of mortality in the first 180 d. Based on the results obtained in this study, genetic selection for reducing calf mortality should be possible.