Effect of voluntary waiting period length on milk yield, fertility, and culling in high-yielding, second-parity cows.

The substantial increase in milk yield capacity in modern dairy herds has led to growing interest in extending the voluntary waiting period, the time from calving to first insemination, as a strategy to prolong the calving interval. However, the effects of an extended voluntary waiting period on fertility and milk production vary, particularly between primiparous and multiparous cows. This study evaluated the effect of an extended voluntary waiting period, compared with a conventional one, on fertility, milk production, and culling in second-parity cows from 12 high-yielding commercial herds. Cows were distributed, based on odd or even ear tag numbers, and allocated into either a 50- or 140-d voluntary waiting period. Data including calving records, fertility metrics, monthly milk yields, and culling rates were collected from the Swedish official milk recording scheme. Out of 819 cows enrolled, 590 completed a third calving. The protocol extended the interval from calving to first insemination by 60 d, which resulted in a 46-d increase in the calving interval (12.5 mo vs. 14.0 mo). Daily milk yields did not differ between groups and averaged 34 kg ECM per day between 2 consecutive calvings and 40 kg ECM per lactating day. Although average milk yield at the last test milking before dry-off tended to be lower in cows with an extended voluntary waiting period compared with those on a conventional one (LSM 32.5 ± 0.96 kg ECM vs. 33.7 ± 1.01 kg ECM), dry period length remained unaffected. Total milk yield in the first 100 d of the third lactation did not differ between treatments. Fertility outcomes were improved in the extended voluntary waiting period group compared with the conventional group, as indicated by a higher pregnancy proportion at first service (LSM 0.62 ± 0.050 vs. 0.46 ± 0.046), fewer inseminations per born calf (LSM 1.61 ± 0.131 vs. 2.02 ± 0.137), and shorter insemination period (LSM 20.8 ± 4.8 d vs. 35.6 ± 4.3 d). The voluntary waiting period did not influence culling rates. These findings indicate that a voluntary waiting period of 140 d may be a viable alternative to the conventional 50-d duration, without compromising milk production and fertility in second-parity cows from high-yielding herds.