Body Condition Score Changes Affect Pregnancy Rates
Paul Fricke and Richard Pursley
Over the past two decades, a reproduction revolution has occurred in the dairy industry. The development of fertility programs and their adoption by the dairy industry over the past decade has largely driven this reproduction revolution.
Yet reproductive performance can vary dramatically among herds that use the exact same fertility programs. Although variation among herds in protocol compliance remains an issue, it cannot explain all of this variation. In 1992, Jack Britt classified cows based on weekly body condition scores (BCS) into two groups: cows with a higher BCS at calving that dramatically lost BCS over the first five weeks of lactation, and cows with a lower BCS at calving that maintained BCS over the same period. Cows that maintained BCS post calving had a strikingly greater conception rate at first service than cows that lost BCS post-calving (62% versus 25%). The results from three recent studies; two from the University of Wisconsin–Madison, and one from Michigan State University, support Britt’s observation and challenge the long-held assumption that all cows normally lose BCS after calving.
BCS AFFECTS CONCEPTION
In the first paper 1,887 Holstein cows from two commercial Wisconsin dairy farms were submitted to a Double-Ovsynch protocol for first timed AI, and BCS was evaluated at calving and 21 days after calving. Overall, 42% of cows lost BCS, 36% of cows maintained BCS, and 22% of cows gained BCS during the first three weeks of lactation. Surprisingly, Average milk production did not differ among these groups. Most impressively, conception rate 40 days after timed AI was 25% for cows that lost BCS, 38% for cows that maintained BCS, and 84% for cows that gained BCS.
A second experiment associated dramatic loss of body weight from calving to three weeks in lactation with negative effects on embryo quality, which likely explains these dramatic differences in fertility. Based on these results, the key question is: how do I make my cows gain BCS after calving? In the second study, BCS change was evaluated in 233 Holstein cows from three weeks before the expected date of calving until three weeks after calving. Similar to the first experiment, conception rate for cows submitted to first timed AI was 18% for cows that lost BCS (28% of cows), 27% for cows that maintained BCS (23% of cows), and 53% for cows that gained BCS (49% of cows). Again, average milk production during the first three weeks of lactation did not differ among these groups.
GAIN BCS AFTER CALVING
In this study, only 34% of cows with BCS less than 3 lost BCS during the transition period, whereas 51% of cows with BCS of 3 lost BCS and 92% of cows with BCS greater than 3 lost BCS. So, how can we make cows gain BCS after calving? Nearly all cows in this study that gained BCS during the transition period had a BCS of less than 3 three weeks before calving. Based on these results, the next question is: how do I prevent calving cows with a high BCS?
The last study evaluated BCS change within one week of calving until 30 days after calving. This study linked previous calving intervals of individual cows to BCS changes after calving. The calving interval is determined by the fixed interval of gestation length and the highly variable interval of calving to conception. Thus, cows with longer calving intervals during the previous lactation took longer to get pregnant. In this study, cows with longer previous calving intervals had greater BCS at calving and lost BCS during the first 30 days after calving.
Similar to the first two studies, cows that maintained or gained BCS after calving had greater conception rates, less pregnancy loss and were healthier than cows that lost BCS after calving.
Timely pregnancies in one lactation might lead to less BCS loss, fewer health issues, greater fertility and reduced early pregnancy losses in the next lactation. Based on results from these three studies we can define a relationship in which herds that manage to get their cows pregnant rapidly after the end of the voluntary waiting period have cows with less BCS at calving, which in turn leads to more cows maintaining or gaining BCS after calving. Cows that maintain or gain BCS after calving have greater fertility than cows that lose BCS.
The high fertility cycle coupled with the dramatic increases in reproductive performance due to the development and adoption of fertility programs is a new paradigm that we can now use to explain much of the variation in reproductive performance among herds. The goal of every farm should be to strive to get their cows into the high-fertility cycle and keep them there. We now have management tools to help get cows pregnant quickly after the end of the voluntary waiting period, and this is reflected by the unprecedented high 21-day pregnancy rates now achieved throughout the dairy industry today.