If you’re having trouble getting cows pregnant, don’t throw your breeding program out the window just yet. It could be that some cows simply aren’t cycling. Producers today are becoming increasingly aware of the occurrence of truly anovular cows. But it takes good diagnostics, and some extra attention, to get the cows cycling.
Anovular vs. anestrus
Fred Moreira, DVM, PhD, Pfizer Animal Health, is quick to point out that an anestrous cow is not the same thing as an anovular cow. “Anestrus means that a cow is not showing standing heat,” he explained. “Anovular cows, on the other hand, are not ovulating.”
Moreira adds there are at least three different types of anovular cows:
- Cows with small ovaries that have almost no follicles
- Cows with active follicular development, but do not ovulate, which may be associated with low blood levels of key reproductive hormones
- Cows with ovarian cysts
“In any case, normal reproductive cycles are not occurring, and these animals have very little chance of becoming pregnant,” he says. Moreira adds that this is true even when anovular cows are bred using systematic breeding programs that do not require visual heat detection, like Ovsynch.
Anestrous cows that are ovulating, on the other hand, should be expected to respond well to synchronized ovulation programs. Many times lack of observed estrus could be due to a number of factors, including inadequate heat detection, poor footing or high milk production.
Possible causes of anovulation
“All cows undergo an initial period of anestrus and anovulation after calving. Anestrus may persist from 3 weeks to 60 days following parturition,” said Gavin Staley, DVM, Dipl. ACT, Pfizer Animal Health. Cows tend to return to regular ovulation before they show return to regular estrus. Anovulation and anestrus become an issue when they extend beyond that normal recovery period and past the voluntary waiting period (VWP).”
While it is not fully understood why some cows rapidly return to normal ovulatory function after calving and some don’t, Staley cites the following factors that can affect ovulation.
Negative energy balance—Cows that are mobilizing more energy than they are consuming have a greater likelihood to be anovular and anestrus. These cows tend to lose body conditioning score (BCS) rapidly after calving and take longer to regain it. Meeting the high demands for milk production and reproduction comes down to feed and adequate dry matter intake,” Staley says. “Poor cow comfort and overcrowding can prohibit cows from getting enough feed and force them to burn needed energy by standing unnecessarily long.”
Disease—Disease impacts a cow’s ability to eat well. Early identification and rapid treatment of disease is important in encouraging the rapid return to cyclicity.
Parity—Review of data from several reproductive studies indicates that, in general, first-lactation heifers have a higher incidence of anovulation than second- or greater-lactation cows.1
Days in milk—The interval between parturition and the voluntary waiting period has also been reported to be a significant factor.
Sorting out solutions
There are practical ways that producers and their veterinarians can assist anovular cows in becoming pregnant. In fact, Moreira recommends dairies have a system in place for addressing anovulation, such as progesterone supplementation, which has been shown to work well in remedying this situation. Moreira advises two possible approaches:
For those herds committed to detecting heats at first service, consider a modified Presynch breeding program. Presynch consists of two set-up shots of prostaglandin (PGF2α) injected 14 days apart. After the second PGF2α injection, cows may be bred after heat detection. Cows not detected in heat should be considered at high risk for being anovular. As such, during the Ovsynch portion of the Presynch program, those cows may benefit from progesterone supplementation. A large study conducted in
Moreira also suggests working with the herd veterinarian to screen herds for anovular cows by checking for a corpus luteum (CL) on the ovaries of open cows at pregnancy diagnosis. That can be done by using on-farm ultrasound or milk progesterone screening. “Cycling cows should have a CL. If they do not have a CL, they should be considered anovular,” says Moreira. Those cows may be targeted to receive progesterone supplementation for 7 days at initiation of the Ovsynch protocol at that time.
Above all, Moreira stresses the importance of the herd veterinarians’ involvement in diagnosing and assisting anovular cows. “The incidence of anovulation is an issue to be seriously considered on
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