J. P. Schoonmaker
F. L. Fluharty
T. B. Turner
D. M. Wulf
S. J. Moeller
S. C. Loerch1
The Ohio State University
Department of Animal Sciences
1 For more information contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 1680 Madison Ave., Wooster, OH 44691; 330-263-3903.
Sixty-seven Angus x Simmental crossbred steers (initial BW 341.3 ± 13.7 lbs.) were used in a 2 x 2 factorial experiment to determine the effects of weaning age and implant regimen on growth and carcass characteristics. Steers were either early-weaned at an average age of 113 days (EW) or normal-weaned at an average age of 204 days (NW), and allotted by weight to an aggressive (A) or nonaggressive (NA) implant regimen. EWA and NWA steers were implanted with SynovexC at an average age of 163 days, and RevalorS at an average age of 204 days, or 295 days if BW was < 1,050 lbs. EWNA and NWNA steers were implanted with SynovexS at an average age of 204 days, and 295 days if BW was < 1,050 lbs. Steers were penned individually and fed an 85% concentrate, 12.4% crude protein (CP) finishing diet. Steers were slaughtered when they reached 1,205 lbs. There were no differences (P > 0.37) in carcass characteristics or final empty body composition between EW and NW treatments. Yield grade (P < 0.08) tended to be lower for A vs. NA (3.5 vs. 3.8, respectively), but no difference (P > 0.81) existed for quality grade. Placing early-weaned calves on an aggressive implant regimen is a viable management option.
Previous research has shown that early-weaned calves experience slow growth late in the feedlot phase, and produce lightweight carcasses that are excessively fat at the time of slaughter (Williams et al., 1975; Fluharty et al., 1996). Excessively fat carcasses with poor yield grades are unacceptable in today's value-based marketing system.
Anabolic implants are used to improve the growth rate, performance, feed efficiency, and leanness of cattle, primarily through an increased rate of protein deposition. There are concerns that the use of implants, particularly those containing trenbolone acetate (TBA), may have detrimental effects on carcass quality grade and beef tenderness (Smith et al., 1992). Trenkle (1990) observed a 50% reduction in U.S. choice carcasses when steers were implanted with an estrogen + TBA implant twice during finishing. Bartle et al. (1992) noted a linear decrease in marbling score as implant dosage gradually increased from no implant to a 140 mg TBA, 28 mg estrogen implant. Herschler et al. (1995) noted a similar response.
An aggressive implant regimen could complement early weaning and allow for rapid and efficient growth while increasing lean tissue accretion such that young, early-weaned calves can achieve a lean, high quality carcass.
The objectives of this experiment were to determine the effects of weaning age and implant regimen on composition of growth and carcass characteristics.
Refer to page 48, "Effect of Weaning Age and Implant Regimen I. Steer Performance," for a description of treatments, procedures, diets, and animal care.
At 113 and 204 days of age, steers were scanned with an Aloka 500v ultrasound machine to measure backfat depth and loin eye area, and to determine composition of gain of steers prior to 204 days of age. Steers were removed from the trial on an individual basis when they reached a predetermined terminal body weight (1,205 lbs.). Steers were taken to a common terminal weight because carcass fat percentage has been shown to be directly related to carcass weight (Berg and Butterfield, 1967; Waldman et al., 1971; Ferrell et al., 1978). Hot carcass weight, backfat depth, percent kidney, pelvic and heart fat, L. dorsi area, and USDA quality and yield grades were determined at slaughter. The 9-10-11th rib section was removed from the right side of each carcass. Rib sections were deboned, ground three times, and subsampled for determination of moisture, nitrogen (N), and ether-extractable lipid (AOAC, 1984). A conversion factor of 5.72 (Sosulski and Imafidon, 1990) was used to convert N to protein, and regression equations of Hankins and Howe (1946) were used to determine the chemical composition of the edible carcass. Final empty body composition of steers was determined using the procedures of Hankins and Howe (1946) and equations of Garrett and Hinman (1969).
Data were analyzed using the GLM procedures of SAS (SAS, 1988) for a completely randomized 2 x 2 factorial experiment. The model included effects due to weaning status, implant regimen, and the weaning status by implant regimen interaction. Animal was the experimental unit.
Hot carcass weight, dressing percent, percent KPH, backfat depth, ribeye area, and yield grade were not different for early-weaned (EW) vs. normal-weaned (NW) steers, however, final backfat depth (P = 0.13) and yield grade (P < 0.08) tended to be lower for aggressive (A) vs. non-aggressive (NA) (0.54 and 3.5 vs. 0.61 in. and 3.8, respectively). Early-weaned, NW, A, NA treatments graded 90.6%, 89.9%, 91.0%, and 89.5% choice, respectively, suggesting that young, aggressively implanted cattle can grade choice. Early-weaned steers tended (P < 0.16) to have a higher percentage of carcasses grading low choice (41.1 vs. 24.0), and tended (P < 0.15) to have a lower percentage of carcasses grading average choice (16.1 vs. 31.7), but an equal percentage (P > 0.77) of steers grading high choice (30.6 vs. 34.1) compared with NW steers. A similar trend was noted for A vs. NA, however only the percentage of A steers grading average choice (15.3) tended (P < 0.11) to be lower than the percentage of NA steers grading average choice (32.6). Marbling was not different between EW and NW steers and A and NA steers (P > 0.70).
An interesting trend was noted for protein and fat accretion in EW steers. Initial (113 days) backfat (P > 0.84) and ribeye area (P > 0.14) were similar. However, at 204 days EW steers had 0.11 in. more backfat (P < 0.0001) than NW steers (0.25 vs. 0.14), and had a 1.4 in.2 larger ribeye area (P < 0.0001) than NW steers (8.8 vs. 7.4 in.2). Final backfat depth and ribeye area were not different between treatments, suggesting that the pattern of growth was changed but not to the extent of growth.
Meat samples from EW steers tended (P < 0.15) to have a lower shear force value than those from NW steers (11.05 vs. 11.88 lbs.), but no difference (P > 0.28) existed for tenderness when measured by a taste panel on a scale from 1 (tough) to 10 (tender). Juiciness, when measured by a taste panel on a scale from 1 (dry) to 10 (juicy), tended (P < 0.09) to be higher for samples from EW steers than samples from NW steers (5.17 vs. 4.69). Flavor was not different between treatments (P > 0.38). No difference existed for shear force between A and NA (P > 0.66), but tenderness, when measured by a taste panel on a scale from 1 (tough) to 10 (tender), was lower (P < 0.02) for A vs. NA (4.74 vs. 5.49). No difference existed for juiciness or flavor between A and NA (P > 0.34).
Carcass composition was not different for EW vs NW. Aggressive implant steers had a higher percentage (14.3% vs. 13.9%) of carcass protein (P < 0.02), a higher percentage (52.3% vs. 51.0%) of carcass moisture (P < 0.06), and had a lower percentage (31.9% vs. 33.7%) of carcass fat than NA steers. Carcass ash was not different for A vs. NA.
Nearly 90% of all treatments graded choice, suggesting that young, aggressively implanted cattle can grade choice. Early weaning can change the pattern of growth, but not the extent of growth as evidenced by different changes in ribeye area and backfat depth between EW and NW steers. Slight improvements in shear force and juiciness measurements of meat were seen when early weaning was compared with normal weaning, probably due to the fact that EW steers were younger at slaughter. An aggressive implant regimen for early-weaned steers fed a high-concentrate diet is a viable management option.
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