Note: This information was presented during a Dairy Cattle Reproduction Council webinar earlier this year. Anovular cows – those that are not cycling – are a significant concern and management challenge for U.S. dairy producers, as the incidence rate is quite significant.

These animals impede a dairy’s reproductive performance, which has a costly effect on an operation’s profitability.

The actual number of anovular cows is quite variable between farms, but overall, nearly one-quarter of the national herd is anovular. Data from more than 16,000 cows across multiple studies across the country show that about 23 percent of cows are anovular at 60 to 65 days in milk.

Dairy producers are concerned about anovular cows for a number of reasons. The first reason is that cows do not receive A.I. because they do not show estrus. In addition, many anovular cows incorrectly receive A.I. Since these cows are not ovulating, they have essentially no fertility to the A.I. This results in a loss of time and increased expense.

The Ovsynch protocol offers one potential solution. It does increase service rates for these cows, but fertility remains low.

In addition, pregnancy losses are high for these cows if they do, indeed, become pregnant due to the Ovsynch protocol. Normal early pregnancy loss for a herd may be about 15 percent, but early pregnancy losses for anovular cows are about 25 percent.

Anovulation influencers

Researchers have spent much effort to explore the issues that impact the anovulatory condition and have determined that several risk factors are at play.

1. Body condition score (BCS) impacts anovulation. Cows with a lower BCS have a higher rate of anovulation than those with a higher BCS. But the group of cows that range from 2.5 to 3.5 BCS has a substantial amount of anovulation. Even in this “pretty good” or normal BCS group, there’s still a 20 percent incidence of anovulation.

2. Parity also influences anovulation. Data from several studies demonstrates that first-lactation cows have a lower level of cyclicity than older cows.

Although cyclicity is also influenced by BCS, and as BCS improves more cows are cycling, first-lactation cows never quite reach the level of cycling achieved by their older herdmates.

Anovulation isn’t just a first-A.I. problem. Two recent studies show that about 29 percent of cows that received the Ovysnch protocol did not have a corpus luteum (CL) at the time of pregnancy diagnosis.

These cows didn’t meet the classic definition of anovular – although some may truly have been anovular – but this is the same kind of problem dairies are dealing with on a regular basis.

Origins of anovulation

The question then becomes: What else causes anovulation? Research published in 2009 shows that the heritability of anovulation is 0.171. By comparison, the heritability of most reproductive traits is 0.03 to 0.07.

Reproductive traits, in general, have a much lower heritability than what was found for anovulation, meaning that the incidence of anovulation has some genetic basis.

The impact of milk production on cyclicity is often confusing because there doesn’t seem to be a clear tie between milk production and anovulation. This is unlike the more linear effect of milk production on estrous behavior or fertility when breeding to estrus.

Milk production’s influence on cyclicity is more complicated and is not a big effect. In fact, milk production has a surprisingly low effect on anovulation.

In truth, parity, milk production and BCS really only explain a small amount of anovulation.

Bigger influences

Cow health makes a substantial difference on cow cyclicity. As you would expect, healthy cows have the highest levels of cyclicity. Cows with subclinical disease incidence or combined clinical and subclinical disease incidence generally exhibit the lowest levels of cyclicity.

In addition, there seems to be a significant “farm” effect for anovulation. Some dairies have much higher cyclicity than others. This can’t be explained very well by BCS, nutrition or other factors.

The root cause has yet to be determined, but there is a clear impact on cyclicity that varies from herd to herd and more work needs to be done to better understand this factor.

Lastly, there are physiological causes for anovulation that require additional exploration.

For example, it’s known that cause for large anovular follicles (the major type of anovulation) seems to be a blockade of specific hormone-responsiveness in the cow’s brain (at the hypothalamus). But what leads to this blockade in cows on a commercial dairy is currently unknown.

Optimizing outcomes

All this being said, anovulation doesn’t have to be a big problem in your dairy herd if you use the tools and methods available to treat and manage it.

In recent years, producers have used Ovsynch to treat anovular cows, but better methods have been developed, including:

• Ovsynch and a second dose of prostaglandin (24 hours after the first dose)
• Ovsynch with supplemental progesterone
• Double Ovsynch
• GnRH – Ovsynch

Therefore, implement nutritional, management or hormonal strategies that will reduce the number of anovular cows in your herd.

For first A.I., expect anovular cows and treat early. Implement a protocol that will induce ovulation and synchronize a high percentage of anovular cows.

For second and later A.I., check for a CL at the time of pregnancy diagnosis and determine subsequent treatment of the cow. Do not proceed with Ovsynch if the cow does not have a CL. Instead, begin a new Ovsynch protocol with progesterone supplementation. Use two doses of a prostaglandin to ensure regression of the CL.

Reproductive goals

Lastly, in addition to treating anovular cows on your dairy, develop and implement a strong set of reproductive goals to increase your operation’s productivity. Use the following recommendations to get you started:

1. Cows must receive first A.I. by 100 days in milk.

2. High fertility at first A.I. Strive for pregnancy per A.I. (conception rate) greater than 40 percent. If you do not achieve this level, think about changing your program.

3. For second and later A.I., there should be a short time between inseminations (no more than 42 days).

4. High fertility at second A.I.

• Conception rate greater than 35 percent.

In conclusion, many herds consistently achieve a 21-day pregnancy rate of 25 percent or higher with the use of these strategies.

The dairy industry has the tools in place to be able to attain this level of reproductive performance and overcome a significant portion of anovulation. What might have been “mission impossible” 10 years ago is now really a very achievable goal.  PD

To access the webinar on managing anovular cows from the Dairy Cattle Reproduction Council, visit the website. Registration is required.

Milo Wiltbank is a professor of dairy reproductive physiology at University of Wisconsin.