Influence of implanting grazing steers with Ralgro® or Synovex-S® followed by Synovex® PlusTM or a Ralgro®/Synovex® PlusTM reimplant program in the feedlot on pasture/finishing performance and carcass merit

In an 84-day pasture/132-day finishing study using 480 crossbred steers (675 lb), Ralgro® increased (P<.05) pasture gains 9.3% compared to nonimplanted controls. Gains of Synovex-S®-implanted steers were intermediate. Pasture treatments were split into two finishing-phase implant treatments: Synovex® PlusTM or initial Ralgro with a Synovex Plus reimplant on day 56. No interactions occurred between pasture and finishing implants with respect to finishing performance or carcass traits. Steers on the Synovex Plus treatment gained 11.7% faster and 7.9% more efficiently (P<.01) during the first 56 days of the finishing phase than the Ralgro-implanted steers. However , when those steers were reimplanted with Synovex Plus, they gained 22.2% faster and 21.1% more efficiently (P<.01) during the last 76 days. Over the entire 132-day finishing phase, the feedlot reimplant program improved rate (4.0%; P<.06) and efficiency (7.5%; P<.01) of gain compared to Synovex Plus alone. Overall , gains and intakes during the finishing phase were similar for all pasture implant treatments. However, control pasture steers were 4.5% more efficient (P<.08) than Ralgro and Synovex steers during the finishing phase. Neither pasture or finishing implant treatment influenced carcass traits. This study indicates that implanting during grazing may reduce feed efficiency during the finishing phase, especially when a feedlot reimplant program is not used. However, this finding disagrees with several previous research studies where pasture implantation had no effect on feedlot performance.


Introduction
Estrogeni c implants enhance performance and profitability of grazing cattle.However, many stocker producers still do not implant because of concerns about negative carryover effects on feedlot performance and/or carcass grade.These concerns have increased as a result of the recent, widespread use of androgenic implants containing trenbolone acetate (TBA) and estrogen.Although these androgenic products maximize feedlot performance, they hav e the potential to reduce USDA quality grades more than their estrogenic counterparts.This is especially evident in aggressive reimplant programs.
Synovex Plus (200 mg TBA and 28 mg estradiol benzoate) was approved recently by the FDA for fe edlot cattle.This TBA/ estrogen combination contains 67% more TBA than Revalor-S® (120 mg TBA and 24 mg estradiol) , suggesting a greater potential for reducing carcass quality, especially when used in a reimplant progra m.In theory, that problem could be minimized by using a mild estrogenic prod uct initially in the pasture and/or feedlot.Our objective was to test the effects of Ralgro vs. Synovex-S on stocker performance and effects of subsequent Synovex Plus or Ralgro with a Synovex Plus reimplant on finishing performance and carcass attributes.

Experimental Procedures
Approximatel y 750 head o f yearling steers (650 to 700 lb) were purc hased from Oklahoma livestoc k auctions during late April and early May.Upon arrival at t he KSU feedlot, all cattle were individually weighed, vaccinated against commo n viral and bacterial diseases, and treated for internal and external parasites.The ears of each steer were palpated and those with pre-existing implants were excluded from the study.The cattle were fed a nutritionallybalance d receiving ration containing Rumensin ® during the short pre-trial stage.From this group, 480 head of more uniform, predominantly British and Conti n ental crossbred steers with no more than one-fourth Brahman breeding were selected for the study.
At the beginning of the grazing trial (May 15), on-test weights were based on the average of two consecutive, early-morning, unshrunk weights .All 480 steers were stratified by weight and randomly allotted within strata to three grazing implant treatments: Control (no implant), Ralgro, and Synovex-S.In addition, cattle were pre-assign ed to one of two finishing implan t treatments: a single Synovex Plus (Syn+) or an initial Ralgro implant with a Syn+ reimplant , using the same stratification/randomizatio n technique based on pregrass weights.Cattle then were shipped to a single intensive-early stock ed native Flint Hills pasture in eastern Kansas.The cattle were monitored weekly on grass, and a medicated complete minera l supplement was provided.On August 5, the cattle were returned back to the KSU Beef Cattle Research Center.Upon arrival, steers were fed a standardized amount of a high-roughag e receiving diet for 3 days to equalize gut fill, then two consecutive morning unshrun k weights were used to determine final 84-day grazing-phase weights.
The finishing phase began immediately, using the average of the two final grazing body weight s as the starting point.All steers were dewo rmed and treated for lice and grubs and received a booster viral vaccination.Cattle from each of the three pasture implant treatments were placed into randomly preassigne d pens (eight pens of 1 5 head, and four pens of 10 head).Half of the pens from each grazing treatment were implanted with Syn+, and the remaining half were implanted initially with Ral, followed by Syn+ after 56 days on feed (Ral/Syn+).Cattl e were located in 36 pens (24 dirt pens and 12 concrete pens) with six replication s per treatment.Cattl e were moved up on feed over 15 days using four step-up rations, with the fina l ad-libitum finishing ration (dry basis) consisting of 83% dry-rolled corn, 9% ground alfalfa hay, 4% Car-mil Glo® (a molasses-fa t source), and 4% supplement.The final ration was formulated to contain 13.8% crude protein (1% urea), .75%calcium, .70%potassium, .35%phosphorus, .
25% magnesium, and .30%salt, plus 30 g Rumensin® and 10 g Tylan ® per ton on a dry matter basis.Trace minerals and vitamins A and E were supplemente d to exceed 1996 NRC requirements.
Interim body weights ( days 30, 56, 84, 112) and impla nt status (missing, abscess, etc.) were monitored during the finishing period.The 132-da y finishing period ended on December 16, and a n average of unshrunk weights on two consecutive mornings was determined.Eleven steers were removed because of health problems unrelated to t he study.The remaining 469 were slaughtered at a commercial packing plant on the same day that the last weight was obtained , and complete carcass data were obtained.

Results and Discussion
No significant pasture × finishing phase treatmen t interactions occurred.Pasture gains were 9.3% higher (P<.05) for steers implanted with Ral vs. controls, and gains of steers implanted with Syn were intermediate (Table 1).Overall stocker gains (1.35 lb/day) were below normal as a result of the dry, late spring.Control pasture steers gained faster (P<.06) than Ral steers during the first 56 days in the finishing period, while gains of Syn steers were intermediate .Overall, 132-day finishing gains were similar for all pasture implant treatments.Intakes during the finishin g phase were similar for all pasture implant treatments.However, control pasture steers tended to be more efficient (P<.08) than pasture implanted steers during the first 56 days and over the entire 132day finishing phase.
In the finishing period, steers implanted with Syn+ at the start of the finishing period gained 11.7 % faster (P<.01) than the Ral/ Syn+ steers during the first 56 days; however, followin g reimplantation of the Ra l steers with Syn+ at 56 days, the reimplanted group gained 22.2% faster (P<.01), resulting in 4.0% better (P<.06 ) gain over the entire 132-day finishing period (Table 2).Correspondingly, steers on the Syn+ treatment were 7.0% more efficient (P<.01) during the first 56 days, 21.1% less efficient (P<.01) during the last 76 days , and 7.5% less efficient (P<.01) over the enti re 132-day finishing period than the Ral/Syn+ treatment.These results indicat e that the payout from Syn+ may have declined after 56 days, resulting in reduced performance .Table 3 shows the finishing performanc e for each of the pasture/finishing implant combinations.
Table 4 shows the carcass chara c teristics for each of the pasture/finishing implant strategies.Treatmen t had no effects (P>.10) on dressing percentage, ribeye area, backfat, or yield grade.Additionally , carcass quality characteristics, such as marbli ng score, percentage Choice, and lean/bone maturity s cores, were the same for all pasture/feedlot implant combinations.

Table 3 . Effect of Pasture and Finishing Implant Combinations on Steer Feedlot Performance Table 4. Effect of Pasture/Feedlot Implant Strategy on Carcass Traits
ab Means in a row not bearing a common superscript differ (P<.01).cd b grader.