Improving the Accuracy of Genomic Selection for Lactation Anoestrous Interval in Brahman Cattle

Lactation anoestrous interval (time from the beginning of the annual mating period to the identification of the cows’ first subsequent corpus luteum by ultrasound scanning) was measured in 898 Brahman females. Previous analyses, including genomic prediction, were performed using a trait defined in cows which successfully weaned a calf (as 3 year olds) from their first mating (LAI: n = 629). The current study expanded this dataset by including an additional 269 records for cows from the same experiment, whose first calf was weaned from their second annual mating, increasing the number of records for the new trait (LAI12) to 898. Heritability for LAI12 (0.43 ± 0.13) was consistent with the previous estimate for LAI (0.51 ± 0.18). A genome wide association study identified more significant SNPs at the P < 0.01 level for LAI12 (n = 16,886) than were previously identified for LAI (n = 597). Importantly, a five-fold cross-validation analysis showed that the accuracy of genomic EBVs was increased from 0.14 to 0.24. Expanding the definition of lactation anoestrous interval to that described for LAI12 identified more significant SNPs associated with the trait and increased the accuracy of the associated genomic EBVs for lactation anoestrous interval.