The goal on any dairy should be to get cows pregnant. The metric we need to evaluate to determine if we are reaching this goal is the 21-day pregnancy rate (PR). All too often, dairy producers concentrate on conception rate (CR) and fail to recognize the economic value of pregnancy rate.
So, what are the differences? CR can be mathematically expressed as the number of cows confirmed pregnant divided by the total number of cows inseminated. So, if we breed 100 cows and 35 are pregnant, our CR is 35 percent.
Pregnancy rate is expressed as the number of cows confirmed pregnant divided by the number of cows eligible to be inseminated in a 21-day period. It is the efficiency by which we get cows inseminated and confirmed pregnant. If we confirm 25 pregnancies and there were 100 cows eligible to be bred in a 21-day period (for this calculation we do not care how many we actually did breed), then our PR is 25 percent.
Of course, we want to optimize the conception rate. However, if our goal was to maximize conception rate, then we would only breed cows that were in an absolutely obvious standing heat and forget about any synchronization programs. We need to get cows inseminated. That is the bottom line.
The key concept we must concentrate on is decreasing the interval between inseminations. We need to identify open cows in a timely manner and get them rebred. Obviously, excellent heat detection is one very important aspect to attain this. Regular herd health pregnancy/open exams and a consistent resynchronization program are the others.
When utilizing synchronization programs, it is important to keep the cow’s natural estrus cycle in mind. I still find many programs that are not combining examination for pregnancy and resynchronization at the most biologically opportune time. We need to work with Mother Nature, not against her.
Through all of these decisions, we must remain conscious of the significant impact reproduction has on the economics of the dairy. By increasing pregnancy rate, we:
• Increase milk production (Increase the time a cow is in the higher production portion of her lactation curve.) This holds true even with the use of bST.
• Increase herd replacement opportunities. Every dairy has cows that should be replaced.
• Increase lactation number. Second-lactation cows produce more milk than first-lactation cows, as do thirds over seconds.
• Increase the number of calves born per year. Although the near-term economic impact of this is small, eventually these heifers can replace suboptimal cows or be sold as springers (assuming the dairy can raise heifers better or less expensive than they can purchase them).