Recent results of the long-term milk study on Dairy Campus within the Customized lactation project show that extending the voluntary waiting time after calving until insemination (VWP) from 50 to 200 days resulted in less yield for milk and calves, but also in less costs for feed and inseminations.
Between 2017 and 2020, the researchers conducted a field trial on Dairy Campus with 154 cows assigned to a VWP of 50, 125 or 200 days. This resulted in an average calving interval of 380, 452 or 498 days. This study showed that milk production for heifers was the same for the 3 groups. The older cows with a VWP of 200 days realized less milk per day between calving, but became pregnant more quickly after the end of the VWP. The recent report shows that this lower milk production is indeed related to lower milk yield, but also lower feed costs, and the longer lactation results in lower costs for inseminations and a lower yield of calves.
Less dry cow therapy use
The study also looked at the effect on udder health. For both multi-calf and first-calf cows, the length of the VWP had no effect on the number of cases of clinical mastitis per lactation or per year. However, multiple-calf cows with a VWP of 125 days had on average a higher somatic cell count than multiple-calf cows with a VWP of 50 days. A higher cell count was not observed in the group with a VWP of 200 days. On an annual basis, extending the VWP resulted in a lower dry-setter use in multiple-calf cows. In the first 6 weeks of the following lactation, somatic cell count was higher for cows after a VWP of 200 days than for cows with a VWP of 50 days, which may be related to the lower dry-setter use in this group.
Colostrum and calves
Extending the VWP from 50 to 125 or 200 days had no consequences for the colostrum quality after the next calving moment. There was no difference in birth weight of the heifer calves, but there was a tendency for less growth in calves from cows with a VWP of 200 days, compared to VWP of 50 or 125 days. Due to the difference in lactation length between the VWP groups, the calves were born in different seasons, which may also contribute to the difference in growth.
Within the 'Customized lactation' project, the researchers also examined the discharge figures of 11 dairy farms that deliberately extend lactations. A longer calving interval was associated with a longer lifespan and with a longer last lactation on these farms. High cell count/mastitis was the most common discharge reason for all calving interval lengths, but the second reason was low production in animals with a calving interval <400 days, and 'Fertility' in animals with a calving interval >400 days.
The 'Customized Lactation' project is financed by ZuivelNL and the Ministry of Agriculture, Nature Management and Food Quality. CRV contributes to the practical translation and delivery of data. Parallel to the trial on Dairy Campus, there is also a network of livestock farmers involved in 'Persistant milking'.