Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2014
Publication Date: 4/1/2015
Citation: Cooper, T.A., Wiggans, G.R., Van Raden, P.M. 2015. Short communication: Analysis of genomic predictor population for Holstein dairy cattle in the United States – Effects of sex and age. Journal of Dairy Science. 98(4):2785-2788.
Interpretive Summary: The objective of this study was to evaluate the increase in reliability from inclusion of cow and bull information and the impact of historic bulls in the US evaluation system. Cow information increased reliability by 0.4 points when predicting young bulls and 1.5 points when predicting young cows. Removing bulls born before 1996 decreased gains by 0.4 points. Cows contribute a small amount to genomic reliability because bulls have already provided the majority of the benefit that is attainable. Historic bulls also contribute a small amount to reliability due to linkage decay between the current population and ancestral population.
Technical Abstract: The number of females genotyped in the US has increased to 12,650 per month, comprising 74% of the total genotypes received in 2013. Concerns of increased computing time of the ever-growing predictor population set and linkage decay between the ancestral population and the current animals have arisen. The objective of this study was to evaluate the increase in reliability from inclusion of cow and bull traditional information and the impact of removing historic bulls from the predictor population in the US genomic evaluation system. Cutoff studies to determine gains in reliability due to the addition or removal of genomic information were compared for two sets of predictor populations. The first group included three sets: cows only, bulls only and both. The second set included four groups: all bulls, and removal of bulls born before 1996, 2001, and 2005. The addition of cow information to that of bulls increased genomic reliability by 0.4 percentage points across all traits when predicting young bulls and 1.5 points across all traits when predicting young cows. Over all traits, removing bulls born before 1996 decreased gains in genomic reliability by 0.4 points. The use of cow information only in the predictor population can be used for genomic predictions. However, the addition of cow data to data from the large number of high reliability bulls in the US system has only a small benefit. For Holstein, cows contribute a small amount to genomic reliability of predictions because bulls have already provided the majority of the benefit that is attainable from genomics. However, the use of cow information only in the predictor population can be used for genomic predictions. Also, if bull genotypes are limited, they become more valuable. Historic bulls contribute only a small amount to genomic reliability of predictions due to linkage decay between the current validation population and the ancestral population. Although cows and historic bulls contribute only a small amount to the US genomic evaluation system, the plateau of gains achievable has not yet been reached.