Genetic Evaluation for Resistance to Metabolic Diseases in Canadian Dairy Breeds

Abstract

Genetic evaluation was developed for resistance to metabolic disease traits in Canadian Ayrshire, Holstein and Jersey breeds, with the first official release scheduled for December 2016. The model is a 9-trait animal linear model including producer-recorded data on clinical ketosis (CK) and displaced abomasum (DA), sub-clinical ketosis (SCK) defined as a level of milk β-hydroxybutyrate, and 2 indictor traits: fat to protein ratio (F:P) and first lactation body condition score (BCS) from the conformation classification.  First and later (up to the 5^th) lactations are considered as different (but correlated) traits.  Genetic parameters were estimated using a subset (records on 35,575 cows) of the Holstein data. Heritabilities for CK and DA ranged from 0.02 to 0.06. Higher heritabilities were estimated for SCK and indicator traits, from 0.08 (SCK in later lactations) to 0.30 (BCS). Genetic correlations of clinical disease traits between first and later lactations were strong (0.70 for CK and 0.79 for DA), correlations for SCK and F:P were 0.50 and 0.70, respectively.  First lactation CK was strongly correlated with DA (0.77) and SCK (0.68); lower correlations were estimated with BCS (-0.56) and F:P (0.42). Genetic links between DA in first and lactations and indicator traits were weaker.  EBVs for CK, DA and SCK are published as relative breeding values, with a mean of 100 and standard deviation of 5, where higher values are desirable. The overall Metabolic Disease Resistance (MDR) index includes SCK, CK and DA, with weights of 50%, 25% and 25%, respectively, and the component EBVs are the averages of first and later lactation EBV for each trait. The MDR index is standardized in the same way as EBVs for individual metabolic disease traits.