2010 Volume 56 Issue S Pages S22-S28
Fertility of dairy cows has decreased for the past several decades. Measures of energy balance (EB; e.g. change in EB, EB nadir, cumulative negative EB, or duration of negative EB) are related to reproductive performance. Our research group has concluded that modification of diets fed during the dry or transition period are unlikely to have significant effects on postpartum EB and fertility. Rather, more radical alterations in dairy management are needed if energy status of postpartum cows is to be improved. We have examined the potential to alter EB by shortening or eliminating the dry period. In an initial study, the effects of a 56, 28, and 0 d dry period on ovarian dynamics and reproductive performance of dairy cows were examined. Postpartum EB was improved by reducing the dry period; however, only significantly for the 0 d dry period. Cows on the 0 d dry period did not experience negative EB. Improvements in EB were a reflection of lower milk production and greater feed intake. Consistent with the improvements in EB, time to first ovulation and first service, first service conception rate, services per conception, and days open were all improved by reduction of dry period length. Because small animal numbers were used in the study, a second study was conducted on a commercial dairy with many more animals to determine if results from the initial trial could be duplicated. A comparison was made between a 55 and 34 d dry period. Shortening the dry period resulted in fewer days to first ovulation, fewer days open, and a greater percentage of cows pregnant at 150 days in milk, although the improvements in the latter two variables were only significant for cows in their third or greater lactation. A current study is being performed in a large commercial dairy to examine the effects of eliminating the dry period on reproduction utilizing a large commercial dairy.