Livestock: May 2000

Extensive research has repeatedly proven the benefits of implanting cattle. Generally, a low-potency implant administered to suckling calves at first working (about four months of age) will increase weaning weights by 7.5-10 percent. Assuming a calf has the genetic and nutritional potential to weigh 500 pounds at six to eight months old, that's 35 to 50 pounds more per weaned calf. During the stocker phase, again assuming adequate genetic potential for growth and diet quality, implanting can increase average daily gain 0.25-0.33 pounds and efficiency by 10-20 percent. Heifer calves to be used or marketed as replacements may be implanted once with a low-potency product during the suckling phase but should not be implanted again. An implanted feeder calf will gain faster (0.25-0.50 pounds per day) and more efficiently (10-12 percent) than a nonimplanted calf. These increases in gain and efficiency are realized only when diet quality supports average daily gains over a pound.

The release period of properly administered implants is stated on the product package: 60-120 days, 80-120 days, 150-200 days, and the like. Questions arise when the period of cattle ownership doesn't exactly fit the release periods of initial or subsequent implants. For instance, assume you are going to own stocker calves for 150 days and plan to use a moderate-potency product with an 80- to 120-day release period. If you implant initially and again in 80-120 days, will the added gain from a second implant outweigh the costs associated with reimplantation? What are you giving up if you forgo the second implant? What would happen if you implanted once, later in the feeding period, so the release period ends at shipping? These are good questions we don't have solid answers for.

Our project involves 260 stocker heifers purchased this spring to graze out small grain pasture through mid-May; they will be moved onto warm-season forages for the duration of the summer. Average initial weight was 440 pounds. Treatments consist of no implant, one at the beginning of the trial, one at the beginning with a second one after 90 days, and one 90 days before shipping. The heifers will be weighed the day the trial begins, every 30 days, and at shipping. The same implant product will be used for all treatments. We will be looking for differences in total gain and distribution of gain, as well as cost-return relationships, for each treatment.

We hope this project and similar work will enable us to arrive at implant strategies for specific production situations. The results will be summarized and reported in a later issue of this publication.