Association between culling reasons and lactation curve components in Holstein cows

The lactation curve expresses the pattern of milk production throughout the lactation period. Such a curve provides insights to assist in designing proper management strategies. Culling dairy cows directly influences the farm economy and animal welfare. The lactation curve components (LCC) of culled Holstein cows, compared with those of retained cows, have not been studied. This study aims to investigate the LCC in culled Holstein cows compared with those retained unculled in the same herd. This research included 27,297 complete lactation records for Holstein cows described as retained or culled for low milk yield, reproductive disorders, udder problems, metabolic disorders, locomotive problems, endemic diseases, respiratory diseases and unknown reasons. The incomplete gamma function was fitted to estimate LCC, as represented by initial milk yield (IMY), the rate of milk increase to peak, the rate of milk decline after peak, peak yield (PY), time to reach peak and persistency. The general linear model was applied to analyse the effects of stayability class (retained/culled) on LCC. Cows culled for reproductive disorders showed no significant differences in LCC compared to retained cows, but they spent more days in milk (54.9 weeks) than retained cows (48.9 weeks). Except for those with reproductive disorders, all culled cows exhibited shorter lactation lengths, higher rates of milk decline after peak, shorter times to attain PY and lower persistence than retained cows. In addition, cows culled for metabolic disorders exhibited higher initial milk (35 kg) and peak milk yields (44.2 kg) than the retained cows and those culled for other reasons. In conclusion, by linking culling causes to milk production trends, this research equips farmers to identify risks earlier, such as tracking milk decline onset and adapting management to retain healthier, high-value cows longer. This strategy could reduce costs, enhance milk output and improve herd welfare on dairy farms.