Reproduction Research Challenges Conventional Wisdom
Published in Dairy Star February 15, 2008
Getting cows pregnant is one of the most challenging tasks on dairy farms. New research is emerging that is challenging some of the conventional wisdom about how to best get cows pregnant in a timely manner. Conventional wisdom is that decreasing the voluntary waiting would help us get more cows pregnant. Another thought is that the early pregnancy diagnosis will be beneficial to our reproductive program.
Let's first look at the length of the voluntary waiting period for producers implementing heat synchronization programs. Conventional wisdom is that since heat detection efficiency is typically less than 50% on most farms, dairy producers should begin breeding cows whenever they are able to catch them in heat. Some producers have moved their voluntary waiting period as early as 40 days postpartum. Because synchronization protocols increases the heat detection rate on first breeding (now more appropriately called AI submission rate) from less than 50% to 100%, it is not as important to begin breeding cows extremely early. Because of the high production we have achieved in many of our herds, a high percentage of cows begin cycling later. Research shows that cows that have multiple estrus cycles before insemination have higher conception rates. Figure 1 shows that conception rates increase substantially from 40 to 70 days in milk. Lengthening the voluntary waiting period may increase the conception rate enough to actually increase the overall pregnancy rate, even though cows are inseminated later.
Caution: Do not lengthen the voluntary waiting period without being on a synchronization program and examining your records to determine if it is the right decision for you.
If DHIA records show that conception rate is considerably higher on 2nd service breedings than on first service breedings, you might benefit from increasing days in milk at first breeding. Another option is to implement a longer voluntary waiting period for cows in their first lactation only. First lactation cows are more persistent and are still growing. Some producers have delayed first breeding of first lactation cows to 70 days in milk while breeding other cows at 60 days post partum. Work with your veterinarian and reproductive specialist to determine if this is the correct decision for you. But you must have an excellent reproductive record keeping system to implement this idea.
The second consideration is to delay pregnancy diagnosis until after 30 days after insemination. With ultrasound technology, many competent technicians are able to determine pregnancies starting at 26 days after insemination. Conventional wisdom has been that earlier is better because we are able to identify and re-inseminate an open cow sooner. One problem with early pregnancy diagnosis is the high amount of early embryonic loss that subsequently follows. Wisconsin research (Figure 2) shows that most of the pregnancy losses occur early and losses decrease rapidly after about 40 days post insemination. Pregnancy losses are about 11% from 28 to 42 days after breeding and only 6% from 42 to 56 days after breeding. Therefore, when early pregnancy diagnosis is done, a higher percentage of cows will show up 'open' at a later date. These cows will have to be re-inseminated and have a greatly extended calving interval. Even moving the pregnancy diagnosis from 26 days after breeding to mid-30 days after insemination will greatly increase the percentage of non pregnant cows that are identified and can be re-inseminated quickly.
In a large field trial by Dr. Paul Fricke, University of Wisconsin Extension Specialist in Dairy Reproduction, there were 11% more open cows identified when pregnancy checking cows at 33 days after insemination compared to 26 days after insemination. The concept that delayed pregnancy testing may improve pregnancy rates seems counterintuitive. But if you are currently using ultrasound to identify open cows from 26 to 28 days post insemination, delaying pregnancy diagnosis may actually improve reproductive efficiency. This is due to the high rate of pregnancy loss occurring from 26 days to the mid- to late-30 days in milk. Once again, this is not something you should pursue on your own and a protocol must be developed to rapidly inseminate the non-pregnant cows.
The concepts of delaying the voluntary waiting period and delayed pregnancy testing is only for dairy producers that currently have excellent reproductive performance. They may help to fine-tune an already good reproductive program. Work with your herd veterinarian and reproductive specialists to examine your records to determine if these concepts may be right for you. Developing protocols and examining records will allow you a better opportunity to have consistently good reproductive performance.