Genetic analysis of association among juvenile growth and female reproductive traits in Canadian Angus cattle

The purpose of this research was to determine the genetic association between juvenile growth and female reproductive efficiency traits in beef cattle. Analyses of three data sets of calving records from 1984 to 2001 in five Angus herds were based on REML type mixed model methodology using a four trait model (n = 6,886 animals in the pedigree, Study I) for birth weight (BW), weaning weight (WW), yearling weight (YW) and first calving date (CD1), a five trait model (n = 7,171, Study II) for BW, WW, YW, calving date (CD) and calving interval (CI), and single trait models (n = 6,864, Study III) for BW, WW and YW and stayability of cows to three years of age (Stay3, a binomial trait).; The results from four- and five trait animal models revealed that the estimates of direct heritability (h2) for BW, WW and YW were ranged from 0.44 to 0.80 (Study I and II), and that for WW and YW in the Study III were relatively lower. The maternal heritability (m2) estimates for BW, WW and YW in all three studies were between 0.10 and 0.25. The h 2 estimates of CD1 (Study I), CD and CI (Study II) were 0.16, 0.25 and 0.10, respectively. The estimates of genetic correlations, both direct (ra) and maternal (rm), among growth traits were positive and of a moderate to high magnitude (Study I and II). Direct-maternal genetic correlation (ram) of each of the juvenile growth traits was negative indicating the antagonistic genetic relationship between animal's genetic potential for the trait and that for the mothering ability for the same trait (Study I and II). The ra estimate between CD1 and WW was 0.27, indicating their unfavorable genetic association, while the corresponding estimates between BW and CD1, and between YW and CD1 were negligible. The ra estimates of BW, WW and YW with CD were -0.19, -0.31 and -0.21, respectively, and those with CI were -0.23, -0.38 and -0.65, respectively, indicating their favorable genetic relationships. The ram estimates of trait CD with maternal genetic effects for BW, WW and YW were -0.02, -0.18 and -0.36, respectively. In contrast, the ram estimates of CI with maternal genetic effects for BW and WW were zero and 0.07, respectively. Corresponding estimate between CI and maternal genetic effects for YW was 0.51, and possibly not consequential due to low heritabilities of both the traits. The results from the analyses of genetic trends (Study II) suggested that multiple traits played a role in the selection process. The culling rate of cows in their herds as indicated by their hazard function was highest at three years of age, and heritability for Stay3 was 0.38, demonstrating merit in genetic improvement. However, the EBVs for Stay3 were not significantly correlated with the direct or maternal EBVs for any of the three growth traits studied, except that maternal EBVs for WW and direct EBVs for Stay3 were positively correlated (P < 0.10).