Implants contain three types of growth-promoting agents: progesterone, estradiol benzoate/estradiol and testosterone/trenbolone acetate.
These agents are known as repartitioning agents directing more nutrients to muscle growth and less to fat deposition. The effect of the implant on repartitioning nutrients toward muscle growth depends on the type and dosage of the growth-promoting agent.
Implants can be classified as low, moderate and high potency, with high-potency implants having the greatest effect on increasing muscle growth.
A dent on quality?
Since growth-promoting implants repartition nutrients away from fat deposition toward muscle growth, implants reduce marbling score and carcass quality grade, especially during the finishing phase even when cattle are fed to similar fat endpoints.
In a summary of published studies, researchers at Kansas State University reported that finishing-phase implants reduce marbling score by 28 points and percentage of carcasses grading USDA choice or higher by 10 percent.
Additionally, more potent implants containing 200 mg of trenbolone acetate (TBA; the maximum dosage of the most potent growth-promoting agent) reduce marbling score and percentage of carcasses grading USDA choice or higher more than less-potent implants.
There has been much debate about the impact of implants administered prior to the finishing phase on marbling score, and research results have been mixed. A study by researchers raised several concerns with regard to lifetime implant strategy.
In this study, steers implanted during the stocker and feedlot phase tended to have lower marbling scores than those steers only implanted during the feedlot phase.
Several research studies have been conducted over the last 20 years evaluating the use of growth-promoting implants during the stocker phase (Table 1).
In all of these studies, all cattle received growth-promoting implants during the feedlot phase. Compilation of the data from these studies indicates an interaction between stocker phase implant strategy and genetic potential for marbling in cattle.
In cattle with low genetic potential for marbling, that is studies where non-implanted cattle had less than 70 percent of carcasses grading USDA choice or higher, using a growth-promoting implant in the stocker phase had no negative effect on carcass quality grade.
But in cattle with high genetic potential for marbling, which had greater than 70 percent of carcasses grading USDA choice or higher when not implanted, using a growth-promoting implant in the stocker phase negatively affected carcass quality grade.
Economic trade-offs
Currently, there is not enough available research data to determine the effect of implant potency during the stocker phase on carcass quality grade in cattle with low or high genetic potential for marbling.
It would make sense that a less-potent implant during the stocker phase would reduce the negative effects on carcass quality grade in cattle with high genetic potential for marbling, but the extent to which the negative effects would be reduced is unknown.
Additionally, the economic trade-off between decreased weight gain and maintained carcass quality grade that may be achieved with less- potent implants is unknown. The choice-select spread will impact the economics of this trade-off, making the decision of implanting stocker cattle and the potency of the implant dependent upon market conditions.
Fewer studies have evaluated the effect of growth-promoting implants administered to nursing calves on quality grade. The two studies comparing implants administered to nursing calves reported similar results, but both studies were conducted using cattle with low genetic potential for marbling.
A study by Nebraska researchers found similar marbling score and percentage of carcasses grading USDA choice and prime in calves given a growth-promoting implant pre-weaning as calves not implanted pre-weaning.
All calves were implanted during the stocker and feedlot phases. In the Nebraska study, calves not implanted pre-weaning had 69 percent of carcasses grading USDA choice and prime.
In a Colorado study, implanting nursing calves at branding did not negatively impact marbling score or the percentage of carcasses grading USDA choice and prime. All calves were implanted during the stocker and feedlot phases; the calves not implanted at branding had 65 percent of carcasses grading USDA choice and prime.
Impact based on segment
Based on the available research, implant strategy may need to be tailored according to the genetic potential for marbling of cattle. During the feedlot phase, implanting cattle decreases carcass quality grade regardless of genetic potential for marbling, but using less-potent implants may moderate this effect.
To date, no one has studied the interaction with genetic potential for marbling during the feedlot phase.
In contrast, there is an interaction between implant strategy during the stocker phase and genetic potential for marbling, with implants decreasing carcass quality grade in cattle having high genetic potential for marbling.
In the cow-calf phase, the available data indicate that implant strategy will not decrease carcass quality grade in cattle with low genetic potential for marbling, but currently no data are available evaluating pre-weaning implants in cattle with high genetic potential for marbling.
Thus, knowing the genetic potential for marbling of the cattle will allow better management decisions to optimize growth and carcass quality grade. 
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Phillip Lancaster
- Assistant Professor – Beef Cattle Production
- Missouri State University
- Email Phillip Lancaster
