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A feasibility study to implement genetic and genomic evaluations for twinning in Holstein cattle.

A. Sewalem




A feasibility study to implement genetic and genomic evaluations for twinning in Holstein cattle.
A. Sewalem*, M. McClure, K. Olson. ABS Global DeForest, WI.

Twin births are detrimental for dairy producers due to their association with several unfavorable effects, including increased reproductive disorder, culling risk, abortions, and calving interval. The aims of this study were to (A) assess the incidence of twinning and evaluate its risk factors; (B) examine this trait's association with other traits of economic importance; (C) to develop genetic and genomic evaluations for twinning. The data included Holstein calving records from 2000 to 2019, comprising 1,804 herds with 14M calving records from 25,868 AI sires. The 2018 overall twinning rate was 4.2% which represented a 9.94% increase from 2010. Twinning rate increased with parity with rates of 1.16%, 4.73%, and 7.86% for parities 1, 2, and 3+, respectively, and AI sires' overall twinning rate ranged from 0 to 13.89%. A genetic evaluation of twinning was carried out using a single-trait linear sire model which included the fixed effects of parity and herd-year-season with random effects of sire and the residual. The sire evaluation results were expressed as an estimated transmitting ability (ETA) representing the expected twinning rate differences among daughters with the average ETA set to 100 and std of 5. The ETAs had a normal distribution ranging from 75 to 115. Traditional evaluation results for twinning were de-regressed and used as pseudo-phenotypes to predict the direct genomic values for animals with 43K SNP genotypes. No markers with large effects were observed. Twinning had statistically significant but low correlations with numerous production and fertility traits which indicate that a direct twinning breeding value is needed to make any significant impact on the trait. In conclusion, this study showed large variation in the predicted twinning breeding values indicating that the implementation of genetic and genomic evaluation for twining will help producers make breeding decisions to reduce their herd's economic risk from twin births.

Keywords: twinning, genetic and genomic evaluations.