Calves and carryover effects of toxic fescue

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Cattle buyers often discount calves based on their perceptions of how well they will perform during subsequent production phases. “Fescue” calves are such a situation.

Buyers may be concerned that calves born and raised on fescue will have carryover effects from the tall fescue toxins resulting in reduced performance or increased health-related issues after they purchase these calves. Whether or not these discounts are justified has been the subject of debate for a number of years.

Numerous studies have looked at the carryover effects on subsequent feedlot performance of grazing yearling cattle on toxic fescue. However, few have looked at the effects that pre-weaning exposure to toxic fescue has on subsequent calf post-weaning performance and health.

We grazed both spring and fall-calving cow-calf pairs on toxic fescue throughout the year, or allowed some groups to move to non-toxic, novel-endophyte infected fescue (NE+) for four weeks prior to weaning. In addition to these treatments, we grazed groups of spring-calving cow-calf continuously on NE+. The study was run for three years resulting in 258 steers and 245 heifers. After weaning, fall-born calves were moved to common bermudagrass pastures and spring-born calves were grown on winter annuals.

Steer actual and adjusted weaning weights were improved by moving them to NE+ four weeks before weaning, but these differences were not maintained through subsequent production phases.

Spring-born steers weaned from all toxic fescue weighed 122 pounds less at weaning than their counterparts weaned from NE+ and weighed 100 pounds less at the end of a feedlot period. This means they compensated for 22 pounds of the 122 pounds of reduced weaning weights. Heifers, on the other hand, weighed 90 pounds less at weaning and only weighed 47 pounds less at breeding from toxic fescue vs. NE+. This means that heifers weaned from toxic fescue compensated for approximately half of the reduced weaning weight.

Post-weaning performance by spring-born steers and heifers was greater than the post-weaning performance by fall-born steers and heifers, reflecting the forage options available for those groups of calves. Therefore, “fescue” calves should not be discounted at the auction market, because they should perform at least equally to calves that were not exposed to fescue prior to weaning.

Source: Ken Coffey



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