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Estimation of genetic parameters for stayability in organic Holsteins.

L. C. Hardie




Estimation of genetic parameters for stayability in organic Holsteins.
L. C. Hardie*1, B. J. Heins2, C. D. Dechow1. 1The Pennsylvania State University University Park, PA, 2University of Minnesota, West Central and Outreach Center Morris, MN.

The objective of this study was to estimate genetic parameters for stayability of organic Holsteins and determine genetic relationships with other traits. Stayability (1 = remained in herd to a given parity, 0 = left) was generated for parity 1 through 5 for cows from 16 USDA certified organic farms. Animals with a Holstein sire and no other breed for 3 generations were included. All models included fixed herd-year-season of birth and pedigree completeness and the random effect of animal. Heritabilities for parity 1 (n = 27,630 with 66% staying in the herd from birth to parity 1), 2 (82% staying from parity 1 to 2; n = 12,766) and 3 (78% staying from parity 2 to 3; n = 6,978) were estimated using univariate threshold models. Genetic correlations among them were estimated with bivariate linear models. An across-parity analysis used records (n = 101,201 from 27,630 animals) for individual parities up to 5; the fixed effect of parity and random effect of permanent environment were added. Approximate genetic correlations between stayability and nationally evaluated traits were extrapolated from PTA correlations for bulls with accuracy of PTA stayability greater than 0.35. Heritability estimates for stayability to first, second, and third parities were 0.10 � 0.01, 0.07 � 0.02, and 0.07 � 0.03, respectively. The across-parity heritability estimate was 0.12 � 0.01 and repeatability was 0.61 � 0.004. The genetic correlations for stayability to parity 1 and 2, 1 and 3, and 2 and 3 were 0.80 � 0.08, 0.60 � 0.22, and 0.81 � 0.19, respectively. Genetic correlations between stayability and most key traits were positive, but less so for heifers (Table 1). In conclusion, there is a genetic component to stayability that remains consistent across parities such that it can serve to mitigate selection bias in genetic analyses with sparse recording of production traits.Table 1. Approximate genetic correlations with stayability

TraitAll paritiesTo parity 1Parity 1 to 2
Productive Life0.54*0.33*0.73*
Milk Yield0.29*0.060.26*
Daughter Pregnancy Rate0.12*−0.100.30*
Heifer Conception Rate0.16*0.120.17
Early First Calving0.21*−0.23*0.42*
*Differs from 0, P < 0.05.

Keywords: organic, herd-life, heritability.