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1006 PD: Cracking a dairy cow conundrum

Published on 02 October 2006

Call it the high-producer paradox – as dairy cows’ milk production rises, pregnancy rates fall and reproductive difficulties increase. The most profitable, highest producing cows in a dairy herd can become the least profitable because of reproductive problems.

Cows that have trouble conceiving cost producers through lost milk production and are more likely to be culled for reproductive failure. Having to repeat inseminations on balky breeders also raises semen costs. Today’s top-of-the-line Holsteins produce more than 25,000 pounds (about 8,000 gallons) of milk per year. Farmers aren’t anxious to cull high producers, but they have no choice if the cows have serious reproductive problems.

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Much of the increase in milk production per cow is due to improved genetics made possible by artificial insemination, which gives farmers access to the world’s best sires. But dairy scientist Milo Wiltbank doesn’t think the relationship between milk production and reproduction is due to the genetics of the animals. Conception rates in heifers are unchanged from 20 years ago, but once the animals start lactating, changes in reproduction become obvious, he points out.

Lactating cows give fewer indications they are coming into heat (ready to breed), are more likely to double-ovulate (produce twins) and have lower conception rates. Wiltbank and his colleagues are working to pinpoint the cause of these changes and to develop practical strategies to deal with them.

Increase feeding, decrease hormones
“Cows that produce so much milk eat an incredible amount of feed. That process has changed reproduction in an intriguing way that we really didn’t appreciate until we got into it,” Wiltbank says. “We need to understand the physiology and how things are working, then develop a program that matches that physiology.”

A high-producing Holstein will consume 53,000 calories per day, compared with 12,500 calories for a dry cow or about 2,500 for an average human. As a cow eats more, she sends more blood to her digestive tract to pick up nutrients. All this blood flow goes through the liver, which metabolizes estrogen and progesterone. The more blood that goes to the liver, the more these key reproductive hormones disappear from circulation. Wiltbank believes these hormonal changes are the culprits behind the high-producer paradox.

“This changes the profile of the steroid [hormones] in the cow’s bloodstream. Since the blood circulates to all tissues, this can change conception rates,” he says. “If we know how changes in the cow’s hormone profile reduces her conception rate, we may be able to devise ways to reduce the problem.”

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In a series of experiments, he found lactating cows metabolized estrogen and progesterone more than twice as fast as dry cows.

“In lactating cows, a continuous high plane of nutrition appears to chronically elevate liver blood flow and metabolism of these hormones to about double the amount observed in nonlactating cows of similar size and age,” Wiltbank says. “This may be the underlying physiological basis for reduced expression of estrus, increased double ovulation and possibly other reproductive changes in lactating cows.”

Ovulating on schedule
Estrogen makes cows show heat. When it’s broken down quickly, high producers may show heat for only a few hours, making it difficult for farmers to determine when to breed those cows.

Ovsynch, an ovulation synchronization technique, has solved or simplified the heat-detection problem for many dairy operations. The technique, developed by Wiltbank and veterinary scientist O.J. Ginther, is now widely used.

“Our original Ovsynch work was related to basic research on the ovary,” Wiltbank says. “We realized we could synchronize the follicle function and do timed inseminations without heat detection. Ovsynch synchronizes ovulation and allows dairy farmers to inseminate unbred cows all at once, so that solved part of the not-showing-heat problem.”

Since it eliminates the need for heat detection, Ovsynch also saves on farm labor. The technique is ideal for stanchion-barn farms, where heat detection is difficult because cows aren’t out milling around all day.

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Wiltbank and Ginther developed Ovsynch using two hormones already approved for dairy cattle. Three injections over nine days initiate ovulation, and all treated cows remain fertile for 24 hours. “Essentially what you are doing is breeding to an ovulation instead of to heat,” said Wiltbank. Since the insemination is based on the injection schedule, heat detection isn’t necessary. About 90 percent of cows will ovulate after Ovsynch treatment.

Back milking sooner
Ovsynch isn’t cheap, but it can increase profitability because it reduces the number of days open (not pregnant) by about one estrus cycle (about 21 days), getting the cow back into the milking string that much quicker. Fewer cows fail to become pregnant during lactation, so fewer have to be culled. In addition, cows that do not show heat or have cystic ovaries can be bred effectively after Ovsynch. Many dairy farmers have adopted Ovsynch as a breeding program for all their cows. Others use the technique only for problem cows, says Wiltbank.

The technique is also an excellent research tool.

“Ovsynch is helping us evaluate factors leading to low fertility in dairy cows that have high milk production,” Wiltbank said. “It has allowed researchers to look at many of the factors that may be causing the low conception rates. Researchers have been able to evaluate nutritional programs that could potentially improve or decrease reproductive efficiency.”

“Hormonal treatments before or after Ovsynch have also been evaluated to understand how hormonal factors limit reproductive efficiency. Because this protocol can eliminate the need for heat detection, it has allowed researchers to focus on what is causing low fertility in lactating cows.”

Ovsynch does not increase the pregnancy rate per A.I. service. While 90 percent of cows in the herd will have a synchronous ovulation after treatment, the rate of pregnancies from each A.I. is the same as when cows are bred after a detected heat (about 40 percent). Wiltbank and his colleagues are working on a variety of ways to improve that figure because farmers lose a lot of money by breeding too late. For example, when students in the college’s dairy science capstone course analyzed a 200-cow Wisconsin herd recently, they found late breeding was costing the farm about $200,000 per year in lost milk production, room and board for nonproductive cows, higher semen costs and other expenses.

Conception rates are affected by several management practices including insemination procedures, the bull’s fertility, the cow’s health, environmental factors on farms, nutrition and others. Dairy geneticist Kent Weigel is looking at factors related to reproductive success on commercial farms, with help from Wisconsin farmers and a major breeding and A.I. company. Weigel and Nigel Cook of the [University of Wisconsin –Madison’s] School of Veterinary Medicine are analyzing the records of 70 dairy herds enrolled in Alta Genetics’ Alta Advantage program.

On the nutritional front, Wiltbank is looking at how farmers might use forages and feed supplements to influence hormone metabolism. In ongoing trials, Wiltbank is testing different types of clovers and alfalfas that may contain nutriceuticals (naturally occurring, health-enhancing compounds) that block metabolism of estrogen and progesterone. He’s also testing whether various fatty acids added to the ration might reduce steroid transport to the liver. College dairy nutritionists Dave Combs, Randy Shaver and Lou Armentano are also looking at how various feed issues and strategies might influence reproduction.

Less down-time for cows
A milking cow pays for her room and board, but cows don’t produce milk 365 days a year. After each lactation, the cow undergoes a dry period to regenerate the cells in her milk secretory tissues so that when she calves, she’s ready to handle the upcoming milk production. Eight weeks has long been the standard dry period, but that may be changing.

Wiltbank and dairy nutritionist Ric Grummer compared reproduction in cows with standard diets and typical (eight-week) dry periods to that in cows with high-energy diets and shortened (four-week) or no dry periods. They found cows with shortened or no dry periods ovulated much earlier than cows in the typical group. The earlier ovulating cows were also more likely to conceive the first time they were inseminated and spend fewer days open. The upshot: These cows could calve sooner, milk sooner and spend less time as unproductive cows.

“In the future, improved reproductive performance may be an important consideration as dairy producers contemplate shortening or eliminating dry periods,” Wiltbank says.

Too many twins
High-producing cows often produce two eggs instead of one; if both are fertilized, the cow will carry twins. If you’re raising beef cattle, twinning is great. If you’re a dairy farmer, it’s not so great because dairy cows carrying twins have more metabolic problems, more uterine infections and more displaced abomasums than their herdmates. They’re also more likely to have problems during calving, and if they carry bull and heifer twins, the heifer is usually born a “freemartin,” with defective reproductive organs.

In a recent study, Wiltbank and Paul Fricke, an extension dairy reproduction specialist, found that low producers had double-ovulation rates of 7 percent, high producers had rates of 20 percent and top producers had rates above 50 percent. “This is an incredible difference in double-ovulation rate,” Wiltbank says. “From a practical standpoint, there may be little we can do to change this.”

“We must align our management procedures to deal with this increasing twinning rate,” he says. “First, we must set a program to diagnose twins. Second, we should set up procedures to manage cows likely to have twins. These cows will calve earlier and are more likely to have problems during calving. These twin-calving cows are usually the highest producing cows during their previous lactations. We must design calving and early lactation procedures with these cows in mind.”

Worldwide impact
As they continue the quest to improve reproduction rates of high-producing cows, dairy scientists don’t have to look far for motivation. Feedback from the industry is plentiful and positive. Extension specialist Paul Fricke heard some of that feedback during the 2006 Dairy Science Extension Road Show, which drew 550 producers to 13 locations [across Wisconsin].

“I asked those in attendance to raise their hand if they had ever used Ovsynch on a cow in their herd,” he recalls. “From the response, I estimate more than 90 percent of the attendees have used Ovsynch on at least one cow in their herd. I’ve been asking that question over the past 10 years, and it is clear Ovsynch use has increased dramatically and is used at some level by nearly all herds.

“The Ovsynch story is a great example of basic research leading to an applied management strategy. It has transformed reproductive management in dairy farms. This is true not just for Wisconsin; it’s a worldwide thing. It has changed the way dairy cattle are managed almost around the globe.” PD

References omitted due to space but are available upon request.

—From University of Wisconsin - Madison, 2006-2007 College of Agriculture and Life Sciences Science Report

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