Genomic evaluation of health traits in dairy cattle

There is growing interest from dairy producers in traits related to health and fitness of cattle, which often have low heritabilities but high economic values. Traits with low heritability can be improved by genetic selection, but large numbers of daughter records are required to produce predicted transmitting abilities with high reliability. Producer-recorded health event data collected from on-farm computer systems were used to estimate variance components and compute traditional predicted transmitting abilities (PTA) for several health traits (digestive problems, displaced abomasum, ketosis, lameness, mastitis, metritis, reproductive problems, and retained placenta) using single-trait threshold sire models. Heritabilities ranged from 0.01 for lameness to 0.30 for displaced abomasum using only first lactation data. Results were similar when only first lactation or first through fifth parity data were used. Multiple trait models also were used to estimate genetic correlations among those traits, which ranged from -0.29 (ketosis, lameness) to +0.81 (displaced abomasum, ketosis). Only three traits (displaced abomasum, mastitis, metritis) had 300 or more bulls with traditional reliabilities of at least 0.50. A multiple-trait sire threshold model was used to compute genomic PTA for 2,649 genotyped bulls. The increase in reliability from including the genomic data ranged from 0.38 (displaced abomasum) to 0.48 (lameness). These results suggest that enough data may exist in on-farm computer systems to enable the routine calculation of genetic and genomic evaluations for the most common health disorders in US Holstein cattle.