Dry Off Dilemma
Posted: December 2, 2007
According researchers at the USDA Animal Improvements Program Laboratory in Beltsville, MD, the last time that we took a really hard look at determining the optimal dry period for maximizing production across two adjacent lactations Ronald Regan was President; the Camaro Z28 was Motor Trend’s car of the year; and “Mountain Music”, by Alabama, was a number one hit. Yes, you trivia buffs, that was 1982. In a recently published study in the Journal of Dairy Science (Kuhn et al., JDS 2006, 89:1713-1722), research from Dr. Norman’s lab at the AIPL revisited this important question with the realization that Holstein cows have changed a lot since then. Most importantly cows are producing roughly 8,000 lbs more milk and are most certainly producing more at dry off than in 1982. Previous work had suggested that at least 60 days dry maximized yield in two adjacent lactations, except for very low producers or cows with extended calving intervals. However, the dry period that maximizes production across two lactations might not be optimal if it results in higher rates of culling at the end of the second lactation. Therefore, this research also addressed the important question of impact of days dry on lifetime production. The researchers used actual lactation yields (not 305 day) collected from DHIA on Holstein cows first calving after January 1997. Records from 458,370 adjacent lactations from 4,173 herds in 44 states were used. In addition, the actual and reported calving dates were required to be within 10 day of each other so that the farmer was managing the cow for the correct calving date.
Now let’s look at the facts (data), because, as President Regan famously said “facts are stubborn things”. It is well documented that first-parity cows have a more persistent lactation. This was illustrated by the fact that first-lactation cows showed the least negative impact of a dry period less than 60 days in length compared to higher-parity cows. The loss, however, was modest for first-lactation cows and yield across first and second lactations was maximized when cows were dry approximately 40-45 days. For higher-parity cows, a minimum of 55 days dry was required to maximize yield across two adjacent lactations. However, dry periods greater than 60 days resulted in yield losses across adjacent lactations which were primarily due to the lower persistency of these subsequent lactations.
Now, what about the effects of days dry on lifetime production? The story was a bit different here but makes sense in light of what we know about the physiology of lactation. First of all, cows with fewer than 30 days dry showed a substantial loss in lifetime production. In addition, very long dry periods reduced lifetime production. For example dry periods of 90 days or more resulted in over 8,000 lbs less lifetime milk production than cows with 40-60 day dry periods. Even cows with dry periods of 70-90 days showed losses (~5000 lbs less). The potential impact of this research is clear in light of the fact that roughly 11% of all U.S. Holstein cows experience dry periods that exceed 70 days. One important conclusion from this research is that, regardless of lactation number, dry periods less than 30 days or longer than 90 days should be avoided. Shorter dry periods are better tolerated between the first and second lactations due the greater persistency of first lactation cows. For lifetime production aim for ~45 days dry after the first lactation and ~35 days dry for subsequent lactations. The good news is that there does not appear to be a negative impact on lifetime productivity by extending the dry period to 60 days if a cow is still milking well. Remember: Cows with shorter days dry have longer lifetime days in milk. The results presented in this paper highlight the important impact that fertility has on lifetime production, because days dry are primarily affected by days open.
Troy L. Ott, Associate Professor of Reproductive Biology Dairy and Animal Science, Center for Reproductive Biology and Health