20 May 2013

3 minute read

North America

The biggest concern with these pastures is their high endophyte levels. High endophyte levels can cause a multitude of problems in cattle, including reduced reproduction performance.

“Getting a high percentage of cows bred in May, June and July to calve in March, April and May can be a challenge,” said Roy Burris, beef extension specialist for the University of Kentucky College of Agriculture Research and Extension Center in Princeton. “I personally prefer fall calving for that reason, but I also believe that we can have successful breeding performance in the spring.”

Burris believes there are some keys to getting a high percentage of cows pregnant for a spring-calving season.

“The most general problem, in my opinion, is that the winter feeding program isn’t adequate to support required body condition for early rebreeding,” he said.

Cows should enter the breeding season in good body condition, Body Condition Score 5, which doesn’t always result from many producers’ winter feeding programs.

“It seems that we sometimes try to ‘rough ‘em’ through the winter and hope that spring grass will straighten them out,” he said. “That is a sure formula for delayed breeding or open cows.”

Burris said spring-calving cows really need to conceive early in the breeding season, preferably before late June, for best results. The UKREC conducted a trial several years ago where they separated similar cows into three breeding periods of 45 days each on high-endophyte fescue.

Cows exposed to bulls from June 19 to Aug. 4 had a pregnancy rate of only 59 percent. The average maximum daily temperature reaches 90 degrees Fahrenheit by June 20 at the UKREC. The elevated temperature, coupled with the endophyte present in most fescue pastures, likely contributed to that decreased performance.

“We have also measured the alkaloid levels in high-endophyte fescue at this location,” Burris said. “The primary culprit in toxicity of high-endophyte pastures seems to be ergovaline. After our July 10 measurement, the ergovaline levels dramatically increased. So this toxicity, coupled with high temperatures, appears to mean that breeding will not occur at acceptable rates in July, August and September. Therefore, we believe cows need to be pregnant by the end of June for best results.”

He explained that ergovaline levels differed greatly by pasture and that could make it possible to avoid the “hot” pastures, those with higher endophyte levels, during the summer months, especially during breeding and heat stress.

There are several other keys to a successful breeding season. Obviously, fertile bulls are extremely important and breeding soundness evaluations are essential. Producers should supply a complete mineral supplement on a year-round basis. If producers use artificial insemination, they will need to manage the details of artificial insemination and estrous synchronization protocols.

“In the short run, don’t let cows lose body condition as the breeding season nears,” Burris emphasized. “Lush, watery grass might not support regaining condition after calving, peak milk production and rapid rebreeding. Do whatever it takes to get ‘em bred and bred early.”

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