Genomic Evaluation for Resistance to Fertility Disorders in Canadian Dairy Breeds
Genomic evaluation was developed for resistance to fertility disorders in Canadian Ayrshire, Holstein and Jersey breeds, with the first official release in December 2020. The evaluation model includes the following traits: CO = Cystic Ovaries, MET = Metritis, and RP = Retained Placenta. All traits are scored as 0 (no case) or 1 (at least one case) in the period from calving to 305 d, 150 d, and 14 d after calving, for CO, MET and RP, respectively. First and later lactation traits are treated as different but correlated traits. Observations from lactations >2 are repeated records of lactation 2. The model is a multiple-trait (6 traits) linear animal model. Genomic information is utilized in additive relationships among animals via single-step method implemented in the MiX99 software. Genetic parameters were estimated using a subset (N= 76,082) of Holstein data. Heritability for fertility disorders ranged from 0.02 to 0.03. Genetic correlation between fertility disorders expressed in first and later lactation cows were between 0.55 (CO) and 0.70 (MET). This confirmed that disease resistance to fertility disorders are genetically different traits in first and later parities. Resistance to CO was genetically uncorrelated with resistance to 2 other disorders within and across parities (correlations did not statistically differ from 0). MET and RP were moderately genetically correlated (0.44 to 0.54). Estimated genomic breeding values for all traits are reversed in sign. Three additional evaluations are created by combining proofs for first and later lactation for a given disorder with equal weights. All proofs are expressed as RBV (mean = 100 and SD = 5, for base bulls).
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