Comparison Of Six Implant Strategies...

...In Feedlot Steers And Their Effect On Live Animal Peformance And Carcass Characteristics

Our understanding of implant management and its influences on production and carcass traits has increased dramatically in recent years.

Pritchard, 1998 reported that the use of Ralgro^{® implants} as an initial implant followed by Revalor^®-S in 140-day steers was an "optimum" strategy. Pritchard speculated that this was due to a more appropriate management of implant potency with stage of production than offered by using a single estradiol-trenbolone acetate (E₂+TBA) when steers were placed on feed. Following that principle, the previously successful Ralgro/Revalor-S strategy is indicated for future research. In the study reported here, several related issues are discussed.

Approach

The feedlot production aspect of this trial was conducted at the Agri Research Center, Inc, Canyon, Texas, under the supervision of D. Bechtol, DVM, and A. Waite. Statistical analysis and data summary were prepared by R. H. Pritchard, Ph.D.

Seven implant strategies were evaluated for their influence on production rates and efficiencies in steer calves and subsequent carcass traits. These strategies included:

Treatments were assigned to 350 steer calves (556 lb.), moderate frame size, housed in 35 pens of 10 steers each, 5 pens per treatment. Individual body weights were determined initially and after 70, 100, and 155 days for all steers. A final body weight was determined on day 194 for the two heavyweight blocks. Lightweight blocks were weighed at day 200, and a final body weight was determined at 222 days on feed.

Harvest processing was done by a major commercial packer while maintaining individual steer identity. Hot carcass weight and USDA Quality and Yield Grades were obtained from the plant records. Measurements of ribeye area, ribfat depth, KPH, and assessment of marbling and maturity were conducted by Cattleman's Carcass Data Service under the supervision of T. Montgomery, Ph.D.

Discussion

The results and trends occurring in this data set are consistent with expectations based upon previous research using these growth promotants.

During the initial 70 days, steers implanted with Ralgro Magnum implants tended (P<.10) to grow faster and more efficiently than steers implanted with Ralgro implants. From day 70 to day 100, steers that were re-implanted grew faster and more efficiently than steers experiencing latter days of a Ralgro Magnum implant.

Steers re-implanted at day 100 outperformed (P<.01) steers re-implanted at day 70 during the period 101 to 155 days on feed. This is a classic example of the sudden and dramatic increase in ADG associated with implanting. The day 100 re-implant also caused higher ADG (P = .0877) and higher DMI (P= .0092) during the final period on feed.

Implanting increased (P < .01) ADG and DMI. There was only a trend (P= .1380) for implanting to improve feed:gain. This was due in part to the pens that received Ralgro Magnum implants 152 days prior to harvest. This time window is substantially longer than the expected effective payout of this implant.

Among treatments 5, 6, and 7, using an E₂+TBA re-implant increased cumulative ADG by 4% and lowered F/G 2.7% compared with a Ralgro Magnum re-implant.

Marbling responses to treatments corroborate previous research. Using Ralgro implants as the initial implant allowed marbling to develop similar to non-implanted steers and had no detrimental effect on Quality Grade distributions.

This trial outcome is also consistent with other studies that have observed that Synovex Plus reduces the proportion of higher Quality Grades and increases the proportion of Select grade carcasses more than other implants currently available.

Conclusions

The most appropriate implant treatment in this study, considering production and carcass variables were Ralgro implants on day 1 followed by Revalor-S on day 70. This treatment increased ADG 20% over controls and reduced F/G 8.4% from controls without adversely affecting carcass quality grades. Ralgro Magnum implants on day 1 followed by Revalor-S on day 100 provided similar ADG and carcass responses, but these steers were 5.5% less efficient than steers treated with Ralgro implants on day 1 and Revalor-S on day 70. This difference is probably due to the heavier average body weight while on feed brought about by Ralgro Magnum implants' ability to increase ADG during the initial 70 days.

Zeranol-exclusive implant strategies did not increase production advantages as well as when E₂+TBA was used at re-implanting. While there was a trend for zeranol-based strategies to increase carcass value ($/cwt), further studies are needed to determine if this would offset the higher production costs for these treatments when steers are not so advanced in their fatness.