For years, 50 to 60 days has been branded as the ideal length of time between calving and first service, but a recent study is looking at how giving dairy cows closer to 90 days before breeding could impact reproductive performance, and the results may surprise you.
Dr. Julio Giordano at Cornell University is conducting an ongoing trial that includes several thousand cows on three well-managed New York dairy farms to better understand how duration of voluntary waiting period (VWP) impacts reproductive performance along with uterine health, cyclicity, metabolic status and cow profitability.
His trials compared breeding cows at 60 days in milk (DIM) versus 88 DIM using a protocol for timed A.I. (double Ovsynch). Thereafter, all cows were managed equally with heat detection and timed A.I. after resynchronization of ovulation with Ovsynch.
“Traditionally, U.S. dairies have been breeding cows within 60 days of calving because suboptimal estrus detection and fertility required cows to receive multiple services to conceive,” Giordano explains.
However, advances in cow health and reproductive management programs have, in turn, improved reproductive and productive performance. “Better estrus detection and overall fertility has reduced the number of inseminations and the variation in the timing required for cows to become pregnant,” Giordano adds.
“Thus, farms have the opportunity to have more control of the timing of pregnancy, which may help cows achieve pregnancy at a stage of lactation that maximizes profitability.”
Below are key findings from the study and Giordano’s comments on what those outcomes mean for dairy producers:
Key finding #1: Extending the duration of the VWP from 60 to 88 DIM increased fertility of first A.I. service in first-lactation cows by improving conception rate (CR) by 8.7 percentage points.
GIORDANO: “This is a dramatic improvement in CR considering the fact that no additional treatments and interventions are required other than providing cows with extra time to recover after calving.”
Key finding #2: There was no statistically significant difference in CR observed among second-lactation and older cows when VWP was extended to 88 days. Only a numerical difference of 3.5 percentage points in CR was observed.
GIORDANO: “The lack of difference in CR for the multiparous group was surprising and rejected our original hypothesis that extending the duration of the VWP would improve first-service CR and overall reproductive performance in all cows.”
Key finding #3: Cows in the 60-day VWP group which failed to conceive after first service had more chances of being re-inseminated because first service occurred earlier. By the time cows in the long VWP group received their first service, cows in the short VWP group detected in estrus received their second service, creating enough pregnancies to compensate for the lower CR to first service.
GIORDANO: “Though the time during lactation that the cows became pregnant differed, about the same number of cows were open at 350 DIM. However, the delay in VWP to 88 days shifted the time of pregnancy toward later lactation.
Shifting time to pregnancy may have some important economic implications that we will determine in the second phase of our study.”
Key finding #4: Fewer cows had endometritis at the time of synchronization and 10 days before the first breeding. Also, extending the duration of the VWP allowed more cows to resume cyclicity before the beginning of the synchronization protocol.
GIORDANO: “This is beneficial because a healthier uterus and more estrus cycles before breeding are associated with better fertility to first service.”
Key finding #5: Once cows received the synchronization protocols, there were no differences in cyclicity status.
GIORDANO: “This is because the protocol we used has been designed to induce cyclicity in cows. This observation, which was not related to our main objectives, is useful for demonstrating to dairy producers that there are alternatives to reduce the detrimental impact of lack of cyclicity in their herds.”
Key finding #6: Cows in the long VWP group had better body condition scores before breeding. First-lactation cows had better body condition scores than older cows at all time points evaluated.
GIORDANO: “Better body condition score is associated with better fertility.”
Conclusions
Giordano notes that determining the ideal duration of VWP should not be based on observed or expected first-service CR alone. The time and method used to submit cows for first and subsequent services should be accounted for as well. “Our results clearly show that lower CR to first service can be compensated by additional opportunities for breeding,” he states.
The next step in Giordano’s research is to determine the economics of VWP length through a detailed evaluation of the impact of timing of pregnancy at different stages of lactation on herd profitability. 
The project is funded by the New York Farm Viability Institute and conducted in collaboration with Dairy Health and Management Services.
-
Peggy Coffeen
- Editor
- Progressive Dairyman
- Email Peggy Coffeen
