Cow characteristics associated with lactation performance of cows with customized lactation lengths on commercial dairy farms

Around calving, dairy cows have an increased risk for health issues. Some dairy farmers extend the voluntary waiting period (VWP) to extend the calving interval (CInt) and herewith reduce the frequency of calvings. Moreover, farmers customize the length of the VWP for individual cows based on cow characteristics before insemination. In an earlier experimental study, models were developed where parity, peak yield, and milk yield (MY) and fat content in the week before insemination were associated with MY end lactation and MY per day of CInt (MY/CInt). The current study aimed to evaluate these models on dairy farms. Over 3,000 complete lactations of Holstein Friesian cows between 2014 and 2019 from 13 farms were grouped by parity (1 or 2+) and calving to first service interval (CFSI; < 84 d, 84-140 d, 140-196 d, 196-252 d, and ≥ 252 d). Lactation curves were fitted with a mixed model by using a Wilmink curve with a negative gestation effect to derive MY end lactation and MY/CInt. Parity, CFSI, their interaction and MY before successful insemination affected MY end lactation (R2=0.54). A similar model was created for MY/CInt with addition of peak yield and fat content before successful insemination (R2=0.87). When including farm as fixed effect in the final models, these R2 were 0.79 and 0.89 respectively, indicating an additional effect of farm on MY end lactation. Overall, a greater MY before insemination was associated with a greater MY end lactation, and a greater peak yield and MY before insemination and a lower fat content before insemination were associated with a greater MY/CInt, indicating that cows with these characteristics may be suitable for an extended VWP.