Estimation of genetic parameters for health and survival in a population of Ontario Holstein calves
This thesis is an investigation of the genetic parameters for health and survival using 1,588 Holstein heifer calves sired by 252 bulls. Calves were enrolled from January to December 2008 from 16 farms in South-western Ontario. Single trait and bi-variate animal models were used to estimate genetic parameters for requiring treatment for illness and for survival. A Weibull proportional hazards model was used to determine relative risk ratio of mortality, including important fixed effects affecting the risk of mortality. This study confirmed that calf survival is a trait of low heritability (0.056), as is the predisposition of a calf to require treatment (0.069). Negative genetic correlations between requiring treatment and survival show that calves that do not require treatment are genetically predisposed to survive. Body size traits (weight and height) were confirmed to be moderately heritable. Higher peri-natal and pre-weaning weight was genetically, and favorably, correlated with healthier calves.