An extended lactation and thus a longer calving interval seems to have virtually no influence on the fertility of dairy cows. This is the surprising result of the "Customized Lactation" project, which follows a network of 14 dairy farmers who opt for a deliberately extended lactation. The number of inseminations required per gestation was also comparable to that of unconsciously extended lactations at approximately 1.9.
Less health risks
Most farmers in the network choose to extend the lactation of (part of) the dairy herd from the idea that cows then have less risk of health problems. Because there are relatively fewer calvings with the associated risks, they expect fewer sick animals. Moreover, it can be difficult, with a short lactation length, to put animals dry that still give a relatively large amount of milk. In addition, livestock farmers attach value to the labor saving of fewer calves, both around the calving itself, and the care of the newborn calf.
The chosen strategy to wait longer with insemination after calving varies within this practice network. Some dairy farmers choose to inseminate the entire flock later, others apply it specifically to the heifers, or start insemination when the daily production falls below a certain level.
Longer recovery does not lead to better fertility
The expectation was that the fertility of cows will increase when you wait longer before insemination, thus giving the cow a better chance to recover from the negative energy balance at the beginning of lactation. However, based on the data from the network companies, this turned out not to be the case. The fertility of the cows did not differ between animals where the first insemination took place early after calving (within 12 weeks after calving) compared to animals where the first insemination was delayed (sometimes even more than 36 weeks after calving). The number of inseminations required was comparable, with approximately 1.9 inseminations per gestation. The selection policy of the dairy farmers may have contributed to this because especially animals with lower production (and better energy balances) were inseminated early, while higher productive animals had to wait longer.
Do lower costs offset the lower returns?
The persistence and 305-day production of the cows with a longer calving interval appeared indeed higher. The high-yielding cows were thus often correctly selected for an extended lactation length. Nevertheless, the average milk production per day over the entire lactation with a longer calving interval was not always highest in the cows with the longest calving interval. More research is needed to see whether this reduction in the average daily production (and milk money) can be compensated by reduced labor, feed or medical costs.
Practical trial Dairy Campus
Parallel to the practice network, an experiment is running at Dairy Campus with 150 cows and three different insemination times: from 50, 125 or 200 days after calving. Data on fertility and production from this field trial will only become available in the course of 2020.