Longevity, lifetime production and stayability in beef cattle

Genetic parameters for longevity given a specific opportunity (L:O), measured as months between first calving and disposal, lifetime production measured as number of calves born (NB), number weaned (NW), and cumulative weaning weight (CW), stayability to six different specified ages (ST), stayability to calving (SC), stayability to weaning (SW) and survival (years) were estimated using records of 2019 Hereford cows collected from 1964 to 1979 from a selection experiment with three lines selected for weaning weight (WWL), yearling weight (YWL), and an index of yearling weight and muscle score (IXL), and a control line (CTL). Analyses were performed with (1) a generalized linear mixed model for binary data with a probit link and with a penalized quasi-likelihood function (for stayability traits) and with (2) a linear mixed model using REML for L:O, NB, NW, CW and stayability traits. Survival was analyzed using a Weibull model. Estimates of heritability for L:O ranged from 0.05 to 0.15; for NB, from 0.08 to 0.16; for NW from 0.05 to 0.16; and for CW from 0.06 to 0.16. Estimates of heritability for ST with threshold and linear models ranged from 0.09 to 0.30; and 0.05 to 0.19, respectively and from 0.09 to 0.35 transformed to an underlying normal scale. Estimates for SC with threshold and linear models ranged from 0.29 to 0.38 and from 0.19 to 0.25, respectively and from 0.30 to 0.40 transformed to an underlying normal scale. Estimates for SW with the threshold and linear models ranged from 0.21 to 0.47 and from 0.12 to 0.26, respectively, and from 0.21 to 0.50 transformed to an underlying normal scale. The estimate of heritability for survival was 0.06 and 0.15 on the original scale (years). Estimates of genetic change by line for all traits were close to zero and differences between selected lines and CTL were not significant (P \u3e 0.05) for any trait. Selection for any of these traits could be successful, but would be relatively slow for L:O, NB, NW, CW and longevity from survival analysis due to low heritability and extended generation interval. Genetic trends for LJO, NB, NW, CW, ST, SC, SW, and survival indicate that successful selection for weights at relatively young weaning or yearling ages had little impact on these traits