Breeding spring calving cows early in the breeding season offers farmers a chance to have higher production performance from their animals that graze fescue pastures.

Spring calving cattle grazing high endophyte fescue fields are likely to see reproduction rates lower as temperatures rise, said Roy Burris, University of Kentucky Extension beef specialist.

Studies at the UK Research and Education Center in Princeton were conducted to determine the optimum period of time for breeding spring- calving cows grazing high endophyte fescue pasture. Studies in Illinois have also shown that breeding early in the spring improves conception rates.

Based on the UK research, pregnancy rates were lowest for cows exposed to bulls beginning on June 19 when maximum ambient temperatures were frequently above 90 degrees. The data indicates that pregnancy rates decrease when temperature stress occurs after late June in Kentucky, Burris said.

Research has shown that as temperatures increase, the chance of embryonic survival or conception rates may decrease. And cattle grazing endophyte-infected fescue have elevated body temperatures of 1 to 1.5 degrees.

Higher body temperatures combined with outdoor temperatures, add to the stress on a cow and the resulting reduced pregnancy rate.

Calves born to cows bred earlier in the spring also performed better with the calves being heavier at weaning.

Where the primary pasture is high endophyte fescue an earlier breeding program will contribute to improved reproductive performance and improved profitability from commercial cow herds.

The practical applications of the research is the cows grazing high endophyte fescue and being exposed to bulls beginning May 20 should be in adequate body condition to be cycling at that time so that conception occurs prior to late June, Burris said.

Also head start calving is a good practice for two-year-old cows so that they have extra time to recover from calving and re-breeding prior to late June.