by Katie Navarra
Minimizing the time to achieve pregnancy in dairy cows is the most important factor to producers when it comes to breeding. Longer inter-breeding intervals are costly and detrimental to reproductive performance and productivity. Methods for shortening time to pregnancy through management strategies for second and greater A.I. services was the focus of a Cornell PRODAIRY webinar led by Julio Giordano, DVM, PhD, MS, a faculty member in Cornell University’s Department of Animal Science.
“The 21-day pregnancy rate is the standard metric all farms may want to optimize,” Dr. Giordano said. “Both the service rate and the conception rate should be maximized to achieve high 21-day pregnancy rate. To increase the service rate is critical to reduce the interval between breedings, to increase the conception rate is fundamental to have accurate estrus detection and use effective timed A.I. protocols.”
Giordano acknowledges that multiple strategies are available and can be used to achieve reproductive success. The method chosen should be based on the farm’s available resources for implementation.
“Effective options for second and greater artificial insemination (A.I.) services most likely consist of a combination of Artificial Insemination after detection of estrus and timed A.I. (TAI),” he said “Insemination of cows in estrus reduces the interbreeding interval and cost by avoiding TAI. On the other hand, TAI helps reduce the interbreeding interval for cows that are not detected in estrus. In some cases some TAI protocols can even be used to increase fertility.”
The choice of program Giordano suggested depends on the resources available to the farm. In particular, having available well-trained and committed personnel capable of conducting the reproductive management program of choice. Using software and technology for tracking protocols, breedings, and estrus is a must for some dairies and a good option to consider for others,” he said.
Despite the availability of effective programs, Giordano’s group continues conducting research for improving reproductive performance and simplifying management by reducing the interbreeding interval and optimizing fertility — in this case, through a project funded by the New Farm Viability Institute.
Giordano described an experiment in which two programs were compared. In one program the Short-Resynch protocol (PGF-24 h-PGF-32 h-GnRH-18 h-TAI), which did not include GnRH 7 days before pregnancy checking conducted on Day 32 after A.I., was used to reduce the interbreeding interval of open cows with a corpus luteum (CL). CL is the gland that is present on the ovary after ovulation and is responsible for producing the hormone progesterone). For open cows with No CL, a CIDR-Synch protocol with two prostaglandin treatments was used to increase the fertility of these cows expected to have low breeding success. The other program (Day 25 Resynch) differed only on the use a GnRH treatment 7 days before pregnancy checking.
The most important results presented indicated that when the Short-Resynch protocol was used, more cows were bred in estrus before the pregnancy check because no GnRH was given a week before. GnRH prevents some cows form showing estrus. This may be beneficial for farms that catch a lot of cows in heat and have good conception rate with estrus breedings. The fertility of CL cows was not the highest, and in fact was less than that of cows that received GnRH 7 days before pregnancy testing. However, the success of the estrus breedings fully compensated for the lower fertility.
Both management strategies had the same time to pregnancy (or days open) and percentage of cows pregnant at the end of lactation.
“The choice of program should be based mostly on the known or expected success of estrus detection and estrus breedings,” Giordano said. “Farms with good success breeding cows in estrus may benefit by the use of Short-Resynch. Farms that struggle with estrus breedings or prefer to rely more on TAI may benefit by giving the GnRH before pregnancy testing (i.e., use the Day 25-Resynch protocol for CL cows)”.
Another important aspect highlighted by Giordano was that the program not including GnRH before pregnancy testing reduces the number of hormonal treatments given to cows and the use of TAI. This may reduce labor needs and overall reproductive costs.
In all cases, the choice of the CIDR-Synch protocol for cows with no CL at pregnancy testing may be a good strategy as the fertility of these cows improves significantly as compared with the use of typical Ovsynch protocols.
The full webinar is available at https://www.youtube.com/watch?v=wPIsP07bATE&feature=youtu.be.