Cow Tales: Preweaning implants |

Cow Tales: Preweaning implants

Growth promoting implants have been around for over 60 years. They include natural and artificial compounds with anabolic properties. Some implants contain a small amount of antibiotic designed to decrease bacterial infections associated with placing the implant under the skin of the ear. Different types of implants have been used in all classes of cattle from baby calves to cull cows. More recently, implant technology has been adapted as a route to administer some solid vaccines.

Typically there are two anabolic implants used in suckling calves: Ralgro and Synovex C. Ralgro contains zeranol, an estrogenic compound derived from mold. It is approved for use in calves greater than one month of age. The package insert includes cautionary statements to avoid use in bull calves and post-weaning heifers. Synovex C contains progesterone and estradiol benzoate. Similarly, Synovex C should not be used in bull calves and the manufacturer recommends calves be at least 45 days of age.

The effect of implants is variable and highly dependent on environmental factors and nutritional plane. Implants are designed to increase average daily gain and therefore body weight. In fact, published data suggest producers should be able to expect a 10- to 30-pound increase in weaning weight in both steers and heifers when implanted. They also increase the animal’s nutritional demands to support the added growth.

As a result, the effects of implants are dependent on the nutrient content and nutrient density in available forage as well as milking potential of the dam. It can be difficult to predict nutrient availability at the beginning of the growing season due to environmental variables. But, differences in forage quality can explain different results observed from year to year.

Implants have a few more effects on heifers. Implanting suckling heifers has been shown to increase pelvic area and may negatively affect fertility. Implants fairly consistently increase the pelvic area of heifers for the first two years of their life. The effect diminishes by the time the female reaches three years of age when compared to non-implanted heifers. The increased pelvic size can be expected to decrease the incidence of difficult births as first calf heifers. On the other hand, some studies would suggest preweaning implants reduce fertility in heifers during the beginning of the breeding season. Additionally, like data have shown a diminished pregnancy rate at the end of the breeding season by as much as 10 percent. The authors indicated less than optimal yearling weights as a possible cause for the reduce fertility. Again, implants are dependent on nutritional plane, which can be hard to predict from year to year.

The use of implants in suckling calves is worth considering for your operation. Implants placed at branding my increase weaning weights by 10 to 30 pounds. That could potentially increase the calf’s value by $50 or $60 given current market conditions. However, the nutritional demands of the calves will also increase, which can be difficult to ensure nutrient supply throughout the grazing season. Additionally, implants may decrease heifer fertility by as much as 10 percent. These effects are short lived and should not affect subsequent breeding. Implanted heifers will have an increased pelvic area and therefore are less likely to experience difficulty calving. Using implants is just one tool producers can use to help achieve production goals. Talk to your veterinarian if you have any questions.

A synthetic androgen with growth promotion properties similar to testosterone.

Kenny Barrett Jr. is a veterinarian at the Belle Fourche Veterinary Clinic in Belle Fourche, SD and pens “Cow Tales” monthly. Learn more about the clinic at, or drop them an e-mail at: to suggest a topic for the next installment of “Cow Tales.”

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