Is 60 the Magic Number?
Posted: February 28, 2017
We see the number 60 a lot in dairy management, especially in reference to 60-day dry periods before calving and 60-day voluntary waiting periods (VWP) after calving. What is so special about 60?
A Penn State Extension publication from 1996 explains that the dry period for a dairy cow is an important event for mammary gland involution and secretory cell proliferation into early lactation. The publication summarizes research showing the impact of dry period length on subsequent lactation performance, concluding that a length of 60 days is an ideal target for maximizing milk production. Since 1996, various research and industry recommendations continue to favor a 60-day dry period.
After calving, the reproductive tract of the cow typically needs 30 to 40 days to involute (heal and shrink back to a normal size) after a trouble-free calving, and fertility will typically continue to increase until about 100 days in milk as negative energy balance is worked out, postpartum health issues are resolved, and the reproductive system establishes regular cyclicity. A short VWP (less than 60 days) allows more time for estrous detection and multiple services before excessive days in milk become a concern. Though waiting too long can be problematic, a VWP of 70 to 80 days may work well when some of the more successful timed AI protocols are effectively implemented, since first service can be accomplished within a narrow timeframe and conception rates are relatively high.
So what are we seeing about the length of the dry period or VWP in current research?
In an economic study reported by Inchaisri et al. (2011) it was found that, in the average Dutch dairy cow, any VWP longer than 45 days resulted in economic loss. However, a long VWP was beneficial for some first lactation cows or in situations such as low milk production, high milk persistency, postpartum disorders, or while costs of milk production are low.
Reviewing research on how short dry periods compare to a traditional 60-day dry period, van Knegsel et al. (2013) confirmed that a shorter dry period of approximately 30 days results in a drop of three pounds of milk per day across the subsequent lactation. With no dry period, production drops by thirteen pounds per day. Though a drop in production is generally undesirable, there are some things to consider. Short or non-existent dry periods typically involve fewer dramatic changes in diet and production. As a result, a remarkable improvement has been demonstrated in energy balance, postpartum health, and reproductive performance. Also, the extra days of production before calving, during the time the cow would have been dry if following a 60-day dry period, shouldn’t be discounted.
Chen et al. (2016) reported findings from monitoring cows over their first two dry periods and the following lactations. Cows were assigned to dry periods of 0, 30, or 60 days. Young cows assigned to dry periods of 0 or 30 days had lower peak yields, a later time of peak yield, and lower overall production in their following lactation. However, after going through another dry period of similar length, leading into their third lactation, the effects of dry period length were less pronounced. Peak yield was impacted, but not time to peak yield or 305-day production. Persistency of lactation, typically better in first lactation cows than multiparous cows, was not affected by dry period length. Kok et al. (2017) found the length of a previous dry period did not significantly affect milk yield in relation to a subsequent dry period.
Across the literature, first lactation cows seem to get more benefit from a full 60-day dry period than multiparous cows, presumably due to continued udder development in the young cow. If dry periods have tended to be short, one might consider giving first lactation cows more time than the older cows.
With the development of new research findings and the advance of technology available to dairy operations, we can probably expect that there will soon be tools available to evaluate cow performance and select an ideal VWP (affecting length of lactation) and dry period length.
Meanwhile, there are still many factors to consider before suggesting a significant shift in VWP or dry period length.
- For VWP, consider postpartum health, efficiency of heat detection, first service conception rates, and anticipated late lactation milk production. In a high-producing herd with an aggressive timed AI program, it might pay to have the VWP set somewhere closer to 70 or 80 days.
- For dry period length, consider mammary gland health, feed costs, and labor.
Though it can be adjusted with valid reasoning in some situations, 60 is still a pretty good number to go by in many cases.
- Chen, J., A. Kok, G. J. Remmelink, J. J. Gross, R. M. Bruckmaier, B. Kemp, and A. T. M. van Knegsel. 2016. Effects of dry period length and dietary energy source on lactation curve characteristics over 2 subsequent lactations. J. Dairy Sci. 99:9287-9299.
- Heinrichs, A. J., V. A. Ishler, and R. S. Adams. 1996. Feeding and managing dry cows. Penn State Extension Circular 372.
- Inchaisri, C., R. Jorritsma, P. L. A. M. Vos, G. C. van der Weijden, and H. Hogeveen. 2011. Analysis of the economically optimal voluntary waiting period for first insemination. J. Dairy Sci. 94:3811-3823.
- Kok, A., A. T. M. van Knegsel, C. E. van Middelaar, B. Engel, H. Hogeveen, B. Kemp, and I. J. M. de Boer. 2017. Effect of dry period length on milk yield over multiple lactations. J. Dairy Sci. 100:739-749.
- Kuhn, M. T., J. L. Hutchison, and H. D. Norman. 2007. Dry period length in US Jerseys: Characterization and effects on performance. J. Dairy Sci. 90:2069-2081.
- Stevenson, J. 2012. What is the ideal waiting period? Hoard’s Dairyman.
- van Knegsel, A. T. M., S. G. A. van der Drift, J. Cermakova, and B. Kemp. 2013. Effects of shortening the dry period of dairy cows on milk production, energy balance, health, and fertility: A systematic review. Vet. J. 198:707-713.