Winter Rate of Gain & Implant Strategy Influences Hot Carcass Weight

Winter backgrounding systems can vary greatly from backgrounding in a drylot to grazing cornstalks or native range. Calves winter-backgrounded at a low rate of gain typically experience compensatory gain during the summer grazing period. While this compensatory gain can be more cost-effective through reduced winter feed costs, it does not typically result in the heaviest body weight at the end of the summer grazing season. Some common questions that producers often have during this winter growing phase include:

• What is the optimum rate of gain?
• What implant strategy should be used (and is on label with new reimplanting regulations) during the winter backgrounding and/or summer grazing phases?
• How does winter rate of gain and implant strategy during the stocker/yearling phase influence finishing performance and carcass characteristics?

In an effort to evaluate the potential compensatory effects of winter rate of gain and implant strategy across the entire production system, a recent two-year study by the University of Nebraska addressed these questions.

Winter Rate of Gain

Steer calves were backgrounded in a drylot for 148 days with a target rate of gain of either 1 lb/d (low rate of gain) or 2 lb/d (high rate of gain). The diet consisted of smooth bromegrass hay, modified distillers grains, and a supplement, which provided 200 mg/head daily of monensin. During the summer grazing period, steers rotationally grazed smooth bromegrass pasture for 56 days.

As expected, steers wintered at a low rate of gain had greater gains on grass due to compensatory gain. However, steers wintered at a high rate of gain maintained heavier body weights through the summer grazing period.

Implant Strategy

Calves received one of three implant strategies, which are on-label reimplantation procedures: none, Revalor-G^® during the summer grazing period, or Ralgro^® during winter backgrounding and Revalor-G^® during summer grazing. All cattle were implanted with Revalor-XS^® during the finishing phase.

For steers backgrounded at a low rate of gain, those that were not implanted compensated by 21 to 23% during summer grazing while those implanted with Ralgro^® only compensated 9%. However, Ralgro^® increased gains by 11.4% and resulted in an additional 26 lb of body weight at the end of the winter backgrounding phase. During the summer grazing period, the use of Revalor-G^® increased gains by 17% regardless of winter rate of gain.

Finishing Performance

Both winter rate of gain and implant strategy greatly influenced hot carcass weight (HCW). All cattle were targeted to be harvested at a common fat endpoint of 0.6 inches of backfat. During the finishing phase, there were no differences in gains, feed efficiency, or marbling scores, but steers wintered at a high rate of gain maintained heavier body weights and had greater HCW. For steers backgrounded at a low rate of gain, an additional 28 lb of HCW was attributed to Revalor-G^® administered during summer grazing. For steers wintered at a high rate of gain, an additional 32 lb of HCW was attributed to Ralgro^® administered during the backgrounding phase. The combination of a high winter rate of gain and implant during each production phase increased HCW by 75 lb.

Summary

The use of implants improved cattle performance within each phase of production. Wintering calves at 2 lb daily gain increased final body weight and hot carcass weight. For cattle in a three-phase yearling system that are wintered at 1 lb daily gain, implanting at least during the summer grazing period can be beneficial. Cattle wintered at a high rate of gain can benefit from administering an implant during each phase of production. Winter rate of gain and implant strategy can have additive effects on improving performance throughout the entire production system. Cost of gain, value of additional weight gain, and timing of marketing should all be taken into consideration when determining target daily gains and implant strategies for growing cattle in wintering and summer grazing programs.