Three hundred crossbred steers that previously received either no implant (Control), or were implanted with Synovex-C^®, Synovex-S^® or Revalor-G^® during the dry-winter grazing phase were used to determine the effects of dry-winter implants on carcass characteristics. Following winter grazing, all steers were reimplanted with Ralgro^® and grazed a common tallgrass prairie summer pasture from March 29 to July 17 (110 d). Steers were then implanted with Revalor-S^®, placed in the feedlot, and harvested November 17, 1997 after a 123-d finishing period with individual carcass data collected. Steers implanted during the dry-wintering phase had more advanced skeletal and overall maturity scores compared with Control steers. Control steers tended to have higher yielding carcasses. There were no differences in marbling between implanted and non-implanted steers. The results of this trial indicate that an additional implant during the dry-wintering phase increased carcass weights, despite similar management during the interim summer grazing and feedlot phases; however, the benefits of increased weight gain may be offset by decreased quality grade due to advanced carcass maturity.

(Key Words: Growing Steers, Implants, Carcass Traits.)

We previously reported that daily gains of steers in a dry-winter grazing program implanted with Synovex-C^®, Synovex-S^® and Revalor-G^® were increased compared with non-implanted steers, despite having gains below 1.0 lb/d (Paisley et al., 1997). The increased weight gain of implanted steers resulted in increased gross returns ranging from $11.74 to $20.97/steer over Control steers. While implanting steers during the dry-wintering phase may improve weight gain, the effects of implanting on carcass characteristics may be important to producers interested in retaining ownership and selling on a carcass basis. The objective of this study was to determine the effects of an additional estrogenic and combination implant during the dry-winter grazing phase on carcass characteristics, including hot carcass weight, yield grade, marbling score, and overall carcass maturity.

Carcass Data. Steers were slaughtered at National Beef on November 19, 1997 with university personnel collecting individual carcass data. On the slaughter floor, individual steers were identified by ear tag prior to removal of hide and each steer was subsequently labeled with sequential tags placed in the brisket area using shroud pins. Corresponding plant identification numbers for each carcass were also recorded prior to its leaving the slaughter floor. Carcasses were chilled for approximately 31 h and railed off separately in the cooler immediately following USDA grading. University personnel estimated percent KPH fat, marbling scores, skeletal and lean maturity (USDA, 1997), recorded carcass weight, and measured external fat thickness and ribeye area for all carcasses. Recorded measurements were then used to calculate yield grade and overall maturity score, as well as determine quality grade.

Data Analysis. Carcass characteristics were analyzed using least squares analysis as a randomized complete block design (SAS, 1990) with feedlot pen used as a blocking factor to adjust for pen differences in feedlot performance and their effect on carcass characteristics. Treatment sums of squares were separated using non-orthogonal contrasts that compared Control vs implanted, Revalor-G^® vs Synovex-C^® (i.e., similar amounts of estrogenic activity) and Revalor-G^® vs Synovex-S^® to make direct comparisons of implant effects on carcass characteristics.

Carcass Value Analysis. The Oklahoma State University Boxed Beef Calculator (Gardner et al., 1996) was used to calculate individual boxed beef yield and carcass value estimates. Boxed beef yield represents the percentage of carcass weight as predominantly boneless, closely trimmed (.25 in or less) subprimals and lean trim. Carcass value is calculated using carcass weight, quality grade, and yield grade to generate boxed beef values in $/cwt based on January 6, 1998 prices for the 19 closely-trimmed boxed beef items which included a $3.70/cwt U.S. Choice to U.S. Select price spread. Calculated values also include a drop credit value of $7.30/cwt, cattle freight cost of $.35/cwt, and killing and fabrication costs of $86, $98, $102, and $120/steer, respectively, for yield grade 1, 2, 3 and 4 carcasses.

Quality Grade Traits. Steers implanted during the dry-winter grazing period produced carcasses that had more advanced skeletal and overall maturity scores (P<.01) than non-implanted control steers (Table 2). Implanting with Synovex-S^® accelerated skeletal maturity at a faster rate than Revalor-G^® (P=.05); Synovex-C^® implanted steers yielded carcasses that tended (P=.09) to have more advanced skeletal maturity indicies than Revalor-G^®. Physiological age, listed from youngest to oldest, was Control, Revalor-G^®, Synovex-C^® and Synovex-S^®, respectively. Results from this trial suggest that estrogenic compounds have a greater effect on increasing skeletal maturity, as physiological age determined by skeletal indicies increased as estrogen levels of implants increased. In a combined trial evaluating the same set of steers that were: 1) not implanted (control), 2) implanted once with Syonvex-Plus^®, 3) Syonvex-Plus^® reimplanted after 61 d with Syonvex-Plus^®, and 4) Synovex-S^® reimplanted with Synovex-Plus^®, Al-Maamari et al. (1995) and Johnson et al. (1995) found that when steers were fed to a time-constant endpoint, implanted steers had more advanced skeletal and overall maturities. Overall maturities, ranked by increasing physiological age, were Control, Syonvex-Plus^®, Syonvex-Plus^®/Syonvex-Plus^®, and Synovex-S^®/Syonvex-Plus^® treatments. The increased percentages of carcasses with "B" maturity or greater may best describe the effects of implant treatment on skeletal maturity. Dry winter implant treatments resulted in 23.8, 17.3 and 11.4% more "B" and "C" maturity carcasses, respectively, for Synovex-C^®, Synovex-S^®, and Revalor-G^®-implanted steers compared with non-implanted controls. This would have a definite impact if steers were marketed on a carcass basis.

Marbling scores were similar for Control and implanted steers (P=.99). Marbling score was numerically highest for steers implanted with Synovex-C^®; however, marbling scores did not appear to be consistently affected by implant protocol. Steers implanted with Synovex-C^® tended (P=.06) to have higher marbling scores compared with steers implanted with Revalor-G^®, with similar (P=.79) marbling scores between Revalor-G^® and Synovex-S^® implanted steers. In a review of 37 trials involving the use of implants, Duckett et al. (1997) found that marbling scores did not differ between implanted and non-implanted steers, although implanted steers had numerically lower marbling scores.

Steers were also assigned a quality grade based on degree of marbling and maturity score. Increased skeletal maturity also influenced quality grades, with implanted steers having higher percentages of steers with quality grades of U.S. Standard or lower. The decreased quality grades are partially due to the increased number of steers with maturity scores of "B" or higher, and their inability to grade U.S. Choice or U.S. Prime based on the new USDA grading system (USDA, 1997).

Carcass Value. Boxed beef yield, expressed as a percentage of carcass weight, was higher (P=.05) for Control steers compared with implanted steers. Contrasts did not detect any differences in boxed beef yield between Revalor-G^® and Synovex-C^® or Synovex-S^®. The increased closely-trimmed boxed beef yield may be attributed to numerically lower yield grades, including higher percentages of yield grade 2’s and(or) lower percentages of yield grade 4’s for Control steers. Carcass value, $/cwt of hot carcass weight, was higher for Control steers as compared to all implant treatments (P<.01; Table 3). There were no differences detected between Revalor-G^® and Synovex-C^® or Synovex-S^® (P>.21). The increased value for Control steers may be partially attributed to: 1) yield grades tended (P=.06) to be more desirable for Control steers, which would improve their closely-trimmed boxed beef yield, or percentage of the carcass that is included in boxed beef cuts, and 2) the effect of more advanced maturity on quality grades. Because implanted steers had increased numbers of carcasses with "B" or greater maturity, more carcasses associated with the implant treatments were discounted to U.S. Standard or lower quality grades. This resulted in a $4/cwt average decrease in closely-trimmed carcass value associated with steers implanted during the dry-winter grazing phase.

Total carcass value/steer attempts to factor in the benefits of implanting, as shown by the increased carcass weights. Although implanted steers had significantly lower carcass values when expressed as $/cwt, there were no differences (P=.30) in total carcass value/steer. The decrease in carcass value was partially offset by the increase in carcass weight. Overall, it appears that implanting steers during the winter grazing period increases weight gain, but the benefits of increased weight gain may be partially offset by the effects of implants on carcass quality.

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Johnson, E. S. et al. 1995. Okla. Agri. Exp. Sta. Res. Rep. P-943:35.

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SAS. 1990. SAS Procedures Guide (Version 6, 3^rd Ed.). SAS Inst. Inc., Cary, NC.

USDA. 1997. Official U.S. Standards for Grades of Carcass Beef. AMS, USDA, Washington, DC.

Appreciation is expressed to Sooner Cattle Company and Brett King, Hoechst-Roussel Agri-Vet Co., Farmland Industries, Inc. and National Beef Packing Company, L.P. for their cooperation and support of this study.