Effects of dry period length on milk production, health, fertility, and quality of colostrum in dairy cows. Invited review

In terms of milk production, the dry period (DP) is a non-productive time. In addition, the risk of mastitis increases when cows with daily milk yield >12.5kg are dried off, which is often the case when the DP is set to 55-60 days. References on the positive effects of a shortened DP on the metabolic health at the start of lactation and the subsequent reproductive performance were the motive of this review. Completely foregoing or shortening the DP produces a decrease in milk yield during the following lactation. This decrease is particularly pronounced for cows at the beginning of the second lactation. It is thought that this may be due in part to different involution and proliferation processes of the mammary glands in primiparous and multiparous animals. The majority of the scientific papers suggest that shortening the DP has a positive rather than a negative effect on udder health. The quality of the colostrum is also unaffected; but if there is no drying off, the colostrum will be diluted. When considered overall, the literature, with support from metabolic profile studies, appears to favour a reduced impact on energy metabolism in early lactation in circumstances when the DP is shortened or waived. Clear positive effects on parameters relevant to energy metabolism however only apply to multiparous animals, and other factors, such as milking frequency before and after calving, exert an influence. Positive effects of shortening the DP on the reproductive performance were shown in several studies. Time from calving to first ovulation as well as indicators for assessing the success of artificial insemination and reproductive performance showed better results in animals with no or shortened drying off periods. Again, this only applied to multiparous animals. Overall, there is no single clear answer to the question of an optimal length of the DP, but conversely it is abundantly clear that a dry period of 55-60 days is not necessary in all cases and does not make sense under certain circumstances. Based on the study findings from recent years, the determination of dry periods should be used as a farm-specific and needs-oriented applied management decision.