Test and animal factors associated with probability of being the ‘22’ genotype.

Estimated parameters from the final selected logistic regression model for the probability of an animal possessing the ‘22’ genotype (p22 ∼ Age + a2 + breed). Odds ratios are presented to two significant figures, along with 95% confidence intervals. Significant effects at the 95% level are highlighted in bold. The selected model shows no significant evidence of a lack of fit (p-value = 0.51). Predictive ability of the selected models was assessed using the receiver-operating-characteristic (ROC) curve, which has an area under the curve of 0.68. Breed effects are measured relative to the Holstein Breed (HOL) that is the most represented breed within the study population. For breed codes, see Table 1.