More rumination, better cows: Exploring genetic parameters of daily rumination time in Holstein dairy cows around first calving

Several studies have indicated that rumination could be used as a metric to monitor dairy cows' performance, condition, and health status. Along with applications in cow management, there may be scope to use rumination data in breeding programs. However, the genetics of rumination around first calving and the relationships with other key traits have not been studied. Therefore, the main objectives of this study were to estimate genetic parameters for daily rumination time (DRT) in Holstein Friesian cows around first calving and genetic correlations with 2 production traits, 3 reproduction traits, and disease frequency. Between April 2020 and January 2024, DRT records were collected from 3,517 Holstein Friesian heifers wearing accelerometer-based collars. Six DRT traits were derived, corresponding to part-periods of the study, namely precalving from -60 to -1 d relative to calving (d 0 = day of first calving), postcalving from 0 to 60 d, precalving1 from -60 to -31 d, precalving2 from -30 to -1 d, postcalving1 from 0 to 15 d, and postcalving2 from 16 to 60 d. Genetic parameters of DRT were estimated based on a random regression test-day model, and approximate genetic correlations were assessed. Daily heritabilities before and after parturition ranged from 0.06 to 0.62, with higher values during -30 to -1 d and lower values during 0 to 15 d. Average heritabilities of precalving1 to postcalving2, calculated based on daily estimates, ranged from 0.07 ± 0.01 (0 to 15 d) to 0.32 ± 0.15 (-30 to -1 d), and their approximate genetic correlations ranged from 0.57 ± 0.07 (precalving1 and postcalving1) to 0.89 ± 0.08 (precalving1 and precalving2). Low to moderate approximate genetic correlations were found for precalving1 to postcalving2 with the average daily milk yield in the first week and month after first calving (-0.09 to 0.36), first calving ease (-0.52 to 0.15), interval from first calving to first insemination (-0.02 to -0.15), interval from first to last insemination in primiparous cows (-0.03 to -0.17), and disease frequency during 0 to 60 d (-0.05 to -0.34). Cows with higher DRT, particularly from 0 to 60 d, tended to have greater milk yield, better fertility status, and higher disease resistance. These findings indicate that there is scope to use DRT records around first calving in breeding programs to select better cows. Also, DRT patterns before calving may be used to assess the potential calving difficulties of heifers, which would facilitate farm management.