Abstract #63

# 63
Relationships between daughter phenotypes and sire PTA for production and fertility traits in US organic Holstein cows.
Lydia C. Hardie*1, Isaac W. Haagen1, Longfei Han1, Brad J. Heins2, Dorthea D. Fitzsimmons3, Chad D. Dechow1, 1Pennsylvania State University, University Park, PA, 2University of Minnesota, Minneapolis, MN, 3Alfred State University, Alfred, NY.

The objective of this study was to evaluate the relationship between daughter performance on US organic farms with sire predicted transmitting ability (PTA) estimated through national evaluations. Production and fertility data were collected from 3,002 Holstein cows housed on 9 commercial organic farms across the US. Only records from the year of organic certification through 2017 were used, and for a cow to be included in the data set, her first parturition must have occurred during or after the year of organic certification. Daughters belonged to 513 sires with the most commonly used sire having 185 daughters. We regressed 1,560 daughter records of 305-d mature equivalent (ME305) milk, fat, and protein yield on sire PTA for milk, fat, protein, respectively, and we regressed 1,624 records of average lactation SCS, on sire PTA for SCS. For analyses of fertility, we regressed 5,432 daughter phenotypes for days open on sire PTA for daughter pregnancy rate (DPR) and cow conception rate. Fixed class effects of age group at parturition within lactation group (lactations 1, 2, 3, ≥ 4) and random effects of herd-year-season and cow were included in all models. Analyses were performed in SAS using mixed linear models. Regression coefficients on sire PTA were 0.87 ± 0.15, 0.62 ± 0.15, 0.86 ± 0.16 for ME305 milk, fat, and protein, respectively, and 1.43 ± 0.25 for SCS. Expectations for these coefficients were 1. The regression coefficients for days open on sire PTA for cow conception rate and DPR were −1.38 ± 0.38 and −1.72 ± 0.45 d per unit PTA, respectively. Nationally, the expectation is 4 fewer days open per unit PTA of DPR. Overall, regression coefficients were smaller in magnitude than expected indicating that the genetic variation of Holstein sires is not fully expressed on these farms, with the exception of the regression on SCS. However, regression coefficients carried the expected sign, suggesting that use of sire PTAs estimated through national evaluations should foster genetic improvement for production and fertility on US organic farms.

Key Words: regression, organic, genetics