It's one thing to cheat on your diet. After all, a few potato chips or some chocolate can help perk up even the most dismal day.
However, it's quite another thing to try to improve reproductive efficiency by cheating cows on their voluntary waiting period — the time between calving and eligibility for first breeding. It seems like an easy fix. Breed cows sooner, and they'll get pregnant faster, right? It's certainly less problematic than addressing deeper issues like conception rates, nutrition and heat detection. It's also one of the few areas of reproduction over which you have complete control.
But, breeding cows much earlier than the standard 60-day VWP is not a wise decision. While the standard time for a VWP has been 60 days, some top-notch managers have been able to achieve success with a 45-day VWP. However, researchers agree, it's not just the length of time you wait that leads to reproductive success, it's setting a VWP based on the reproductive program you have in place and then never breeding cows before that time has passed. Here's why.
Recovery time needed
Shortening VWPs does enable some cows to become pregnant earlier after calving. But this offers a false sense of reproductive improvement because these pregnancies are the exception rather than the rule.
After calving, cows basically have zero fertility. This changes quickly in the following weeks, as the uterus involutes and returns to normal size, and normal estrus activities resume. But this natural progression to peak fertility post-calving takes about two months.
Keep in mind that this process varies from dairy to dairy, depending on management, nutrition and physical environment.
Any cows that have had some type of reproductive or metabolic incident at calving need more time to recover. They typically return to normal estrus about one cycle later than herdmates that calved without difficulties. For example, the first ovulation in normally calving cows occurs approximately 15 days postpartum. For cows that were challenged in the transition period, this occurs about 30 to 35 days postpartum, explains Roy Ax, University of Arizona extension dairy specialist.
Furthermore, multi-state university research indicates that as many as 20 percent to 30 percent of cows are "anovulatory" at 60 days in milk, which means they are not expressing estrus at the end of a typical VWP.
This doesn't mean you shouldn't breed a cow or two that come into heat a few days before your VWP expires. The caution is to not induce large numbers of cows for breeding prior to your VWP. "I tell producers that it's a good thing to see a cow in heat at 40 days in milk, because it means she's cycling normally and will respond very well to a breeding protocol like Ovsynch," says Paul Fricke, extension dairy reproductive specialist at the University of Wisconsin. But it doesn't mean that she should be bred at 40 days.
Still, according to a recent Dairy Records Management Systems DairyMetrics benchmarking report, 18 percent of cows in 4,105 herds with 100 cows or more were bred before the VWP (as defined by each farm) expired. Clearly, many farms try to rush cows through the postpartum reproductive process.
Avoid quick fixes
Early breeding, in and of itself, will not fix anyone's reproductive problems, says Mel DeJarnette, reproductive specialist for Select Sires. "In fact, it's usually mathematically impossible for a herd with poor reproductive performance to achieve its desired calving interval simply by shortening the VWP, because the VWP is not the root of the problem." Areas like nutrition and body condition score at all stages of production have much more impact on reproductive performance. And they usually require detailed analysis and solutions.
Instead of trying to find quick fixes, like shortening your VWP, experts say you need to commit to a breeding program that works with your VWP and then make everyone adhere to it.
"You don't want to arbitrarily chip away at your voluntary waiting period, trying to fix your reproductive problems," says Fricke. "Instead, select a breeding program that you want to use on your dairy, and then set a VWP that coincides with your protocol."
Research shows problems
European research reported in the 2003 Journal of Theriogenology found that cows bred after short VWPs had significantly lower conception rates for first services than those bred later. This held true for cows with above-average and below-average milk production.
For example, when first breeding was moved up to 53 to 59 days in milk, compared to 73 to 81 days in milk, the conception rate among cows in the low-production group dropped from 35 percent to 14 percent. (See chart below.)
A lower conception rate not only robs you of productivity down the line, there is the additional expense of monitoring those cows the next time they return to estrus, along with the cost of breeding shots and labor if those cows are enrolled in a synchronized-breeding program. Current estimated cost per cow per estrous cycle is $11 for Ovsynch and $17 for Presynch. (Labor and semen cost are not included in these figures.)
Furthermore, consider that cows that conceive at 40 days in milk create an additional complication. You must dry them off when they may still be producing 80 to 90 pounds of milk per day. That may not be a big deal to some, but it does create a management challenge that you otherwise could avoid.
Preliminary results from ongoing University of Arizona research indicate that following a synchronized-breeding program calling for cows to be bred at 70 to 80 days in milk, rather than 60 days in milk, actually increases reproductive performance.
"We're just giving cows a little more rest," says Ax.
So far, cows in the study have maintained a better-than-average pregnancy rate with the later breeding. The goal is to attain a 34-percent first-breeding pregnancy rate, which, if achieved, would be at least double the current industry average.
This preliminary research does not indicate that you should extend your VWP — it merely indicates that you should never breed a cow before the VWP expires.
Commit to a plan
Every single herd is different, says David Prentice, veterinarian and technical services specialist for ABS Global. You need to monitor performance on your operation to make the best possible decision for your dairy. From what ABS has seen in the field, it's not the length of the waiting period that is most important, but selecting a breeding program that's tailored to your dairy, monitoring results, and then sticking with the plan.
Prentice contends that management points like body condition scores, lameness scores, cleanliness and maintaining proper nutrition are more critical than VWP length in maintaining peak cow performance and reproductive efficiency.