When your newborn calves arrive this spring, remember this word: anestrus. Anestrus is that period of time right after a cow gives birth, when her reproductive abilities are put on hold until her body can build up enough energy reserves to allow her to become receptive to rebreeding.

If she's in poor condition, and her newborn calf is suckling, chances are it could take months for her to rebreed. And that's bad news if you're a cattle producer in these tough times, because more pregnant cows means more calves to market.

That's the message of Dr. Robert Short, a leading reproductive scientist for the Department of Agriculture's Ft. Keogh Livestock and Range Research Laboratory in Miles City, Mont. Short says that suckling and poor nutrition are the major causes of anestrus. "Producers who solve nutritional problems and use body condition scores (BCS) to monitor nutritional status can partially overcome anestrus, but other management decisions can also reduce the negative effects of suckling and nutritionally induced anestrus," he explains.

Short offers six suggestions to producers who want to improve the reproductive performance of their cow herd. These include:

Monitor nutrition: Cows that don't have their nutritional needs met experience more problems with reproduction than cows in good condition. Cows in good condition can rebreed in 30 to 40 days after calving, while the effects of anestrus can inhibit a poor-condition cow from rebreeding for up to 100 days.

"Suckling greatly exaggerates the effects of poor nutrition and can slow the return of estrus, so nutritional and body reserve deficiencies are usually the first place to look when problems with postpartum anestrus are encountered,"says Short.

Short suggests that producers consider BCS to monitor the condition of their cattle - particularly in the fall shortly after weaning and a few months before calving. Most commonly scores from 1 to 9 are assigned to cows with the thinnest possible score being 1 and the fattest possible being 9. A BCS of 5 is considered optimum breeding condition. "If you do not have these body reserves at a minimal level your cows cannot reproduce; they will be able to do a lot of other things but they will not be able to reproduce," Short says.

Evaluate time of weaning: An array of weaning systems exist for producers who wish to achieve higher conception rates in their cow herds, but generally, there are two approaches.

The first approach can result in immediate effects on your cow herd, bringing them back out of anestrus and into their reproductive cycle. This involves weaning your calves for a partial, temporary or complete basis during the breeding season.

Partial weaning, explains Short, involves separating calves from their dams for most of the day and then allowing one or two short periods during the day to suckle. Temporary weaning is a system in which calves are separated from their dams for 2 to 4 days. Complete weaning is when calves are removed from their dams at a earlier-than-normal period but still during the breed period. "These systems can increase the number of cows that return to estrus during the breeding season," he says. "However, the response to these treatments is variable and management of these options is somewhat difficult."

The second approach is nothing more than weaning when calves are 5 to 10 months of age. The trick is balancing available feed resources with desirable cow condition and weaning weights and then determining at what point in those five months your operation is best served to wean your calves.

"If you're going to wean later in the year, when your calves are eight to 10 months old, you may get heavier weaning weights but you have to recognize that there may be negative impacts on next spring's conception rates because your cows may be in l ower condition," explains Short. "Cows that calve in late winter or early spring are normally wintered in situations where quality of feed is low, and are often subjected to colder temperatures and environmental stresses. This limited quality feed and cold stress make it hard to recover from body condition scores that are too low going into winter."

Short advises producers to evaluate the quality and quantity of their forage. If quality is low but grass is available and cow condition is good, he suggests the use of protein supplementation-which can increase BCS, weaning weights and future conception rates. He also believes producers should consider weaning calves at later than five to six months of age and weigh the risks and/or benefits of doing so.

At the same time, "if cows are going into the fall are in poor condition and forage is limited in amount and quality, it would be not be wise to wean late even with protein supplementation," Short says. "If cows are thin enough to require an increase in BCS, then supplemental protein along with weaning at 5 to 6 months of age can help cows recover."

Shorten the length of breeding season: While no system works for everyone, Short suggests that producers shorten their breeding system to 45 days or less. That way, you identify the best reproductive performers in the cow herd and you also force many of your cows out of anestrus sooner.

"The longer you leave that bull out there the more difficult it will be to manage your cow herd for maximum fertility," he says. "Breeding seasons that are 45 days or less have several advantage that include weaning a larger, more uniform calf crop, but there is also an advantage in alleviating many of the problems due to anestrus.

"On a 365-day calving interval with a 283-day gestation length you have about 82 days to get that cow rebred," Short continues. "So if you go from the first cow that calves to the last cow that calves with a 45-day breeding season all cows are going to be at a point where they have some reasonable amount of fertility. When you start lengthening that breeding season to 60 days or especially 82 days there are going to be many cows that have no potential fertility at the beginning of the breeding season."

Use estrous synchronization: "Synchronization of estrus is a useful tool for shortening the breeding season, concentrating labor and making use of AI more feasible for beef cattle," says Short. Some synchronization treatments that include the use of progesterone or progestin often induce some anestrus cows to start cycling again.

Try a teaser bull: Research shows that the presence of a bull in a cow herd during postpartum period will decrease the interval to first estrus, says Short. "It may be advantageous to use a sterile teaser bull to run with postpartum cows before the breeding season starts to stimulate earlier resumption of estrous cycles," he explains. "Care should be used in selecting these teaser bulls to ensure that they are sound and free of disease.

Minimize calving difficulty: Cows that experience difficulty during calving have more difficulty overcoming effects of anestrus and take longer to rebreed. "Management systems that not only minimize calving difficulty will not only save more calves but will also have higher rebreeding rates the next breeding season," concludes Short.

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