Marginal Value of Improved Pregnancy Rate
Posted: August 30, 2007
It is defined as the percentage of cows eligible to become pregnant that do become pregnant within 21-day periods. In the simplest terms, PR is determined by heat detection rate (submission rate for insemination) multiplied by conception rate. Dairy management software programs utilize more detailed and accurate methods to calculate PR. On a herd basis, PR can be used to assess how rapidly cows become pregnant. The benchmark for 21–day PR is 20 percent.
During the 2007 joint annual meeting of the American Dairy Science Association and American Society of Animal Science, Dr. De Vries from the University of Florida used a computer stimulation of dairy herd performance to calculate the economic value of a marginal (1 percentage point) increase in 21-day PR. The following inputs were used in this analysis: lactation curves, submission rate for insemination, conception rate, feed intake, involuntary culling, body weights, and various costs and prices. Using the average US herd, $1600 heifer price and milk price of $14.09 /cwt. the economic values of 1 percent increase in PR at 7 percent, 14 percent, 18 percent, 23 percent and 34 percent PR were $32.04, $14.49, $9.92, $6.76 and $3.31 per cow/yr, respectively. The major contributing factors were reductions in herd turnover costs from lower cull rates. Altering heifer price, milk price, milk yield and involuntary culling independently by 20 percent showed that heifer price had the most effect on marginal value of PR. For example, when the heifer price was $1920 the economic values of PR were increased to $41.93, $17.89, $11.84, $7.98 and $3.73/cow/yr. Greater milk price and higher milk yield increased the marginal value only when PR was greater than 14 percent.
This analysis clearly demonstrates that the economic value of marginal improvement in 21-day pregnancy rate is much greater at lower pregnancy rates. The average PR in the northeastern US has been estimated to be 15 percent. There is a significant cost associated with poor reproductive performance. Increases in cull rate, heifer price, milk price, milk yield and other inputs above the averages used in this analysis would further increase the net income.
Michael L. O'Connor
Dairy and Animal Science Extension