Genetic correlations between female fertility and post-weaning growth and feed efficiency traits in multi-breed beef cattle

With selection in beef cattle now incorporating feed efficiency, knowing the relationship with other traits is needed. Genetic relationships were estimated with an animal model in ASReml with a three generation pedigree inclusive of 2,882 animals. Multi-breed data from two Ontario beef research farms with fertility traits were available on 1,366 females and post-weaning traits, including feed efficiency on 1,297 individuals. Estimates of heritability for fertility traits were low to moderate ranging from 0.03 ± 0.01 for pregnancy rate to 0.21 ± 0.02 for gestation length and post weaning traits were moderate to high with feed conversion ratio at 0.22 ± 0.06 to mid-metabolic weight at 0.89 ± 0.01. Both dry matter intake and mid-metabolic weight were genetically correlated with most fertility traits from -0.52 to 0.34. The genetic correlation between average daily gain and days to calving was moderately negative (-0.33 ± 0.16) as was residual feed intake with days to calving (-0.34 ± 0.17). Bigger cows with more feed intake and faster growth were more fertile, and residual feed intake had an unfavourable genetic correlation with days to calving, indicating programs to select for feed efficiency should include fertility simultaneously in a selection index.