Anabolic Implants Research Articles

Effects of repetitive use of hormonal implants on beef carcass quality, tenderness, and consumer ratings of beef palatability.

Effects of repetitive use of anabolic implants on beef carcass quality, tenderness, and consumer ratings for palatability were investigated using crossbred steer calves (n = 550). Steers from five ranches were randomly allocated to one of 10 different lifetime implant strategies or to a nonimplanted control group. Cattle were implanted at some or all of five phases of production (branding, weaning, backgrounding, feedlot entry, or reimplant time). Carcasses from the control group had higher (P < 0.05) marbling scores than carcasses from steers in all other treatment groups. Implanting steers at branding, weaning, or backgrounding vs. not implanting steers at these production stages did not affect (P > 0.05) marbling scores. Steers implanted twice during their lifetime produced carcasses with higher (P < 0.05) marbling scores than did steers receiving a total of four or five implants. Steaks obtained from carcasses in the control group had lower (P < 0.05) shear force values and were rated by consumers as more desirable (P < 0.05) for tenderness like/dislike than steaks obtained from carcasses in all other treatment groups. Implanting steers at branding or weaning production stages did not affect (P > 0.05) steak shear force values, consumer ratings for like/dislike of steak tenderness, or percentage of consumers rating overall eating quality of steaks as satisfactory. Implanting steers at backgrounding vs. not implanting steers at this production stage increased (P < 0.05) steak shear force values, but did not influence (P > 0.05) consumer ratings for like/dislike of steak tenderness or percentage of consumers rating overall eating quality of steaks as satisfactory. Steaks from nonimplanted steers were rated as more desirable (P < 0.05) for overall eating quality than steaks from steers implanted two, three, four, or five times. Use of implants increased (P < 0.05) average daily gain by 11.8 to 20.5% from weaning to harvest compared with nonimplanted controls. Implant strategies increased (P < 0.05) hot carcass weight of steers by 8.9 to 13.8% compared with the control group. Use of implants also increased (P < 0.05) longissimus muscle area and decreased (P < 0.05) estimated percentages of kidney/pelvic/heart fat, but did not affect (P > 0.05) dressing percentage or adjusted fat thickness. Our findings suggest that beef quality, palatability, and production characteristics are influenced by lifetime implant protocols.

Review: Androgenic, Estrogenic, and Combination Implants: Production and Meat Quality in Beef

Literature was reviewed to determine the value of using growth implants in cattle with regard to production parameters and carcass merit. The beef industry's need to balance increased growth traits with acceptable carcass quality is of critical concern when evaluating implant strategies. Anabolic implants affect specific muscles by impacting the action of somatotropin and the rates of muscle accretion and turnover. Muscles showing the greatest response are extensor muscles associated with long bones; muscles showing little response to anabolic implants are believed to be at maximum capacity for growth. Implants may also affect the proliferation rate and (or) activation state of satellite cells. The benefits of implants to production of beef cattle have been well documented, with significant documentation of increased growth rates, ADG, and feed efficiency. Implants increase the vigor of feedlot steers by reducing the incidence of certain illnesses and, in combination with gonadotropin-releasing hormone (GnRH) immunization, replace castration for improving meat quality. Anabolic implants result in both beneficial and detrimental effects on meat quality. Implants increase ribeye area but reduce fat deposition and marbling scores. Skeletal maturity is increased by implants. The most severe quality problem from implant use is an increased incidence of dark cutters. Producers need to weigh the benefits and the disadvantages of anabolic implants for use in animal production strategies.

Effects of anabolic implants of oestradiol alone or in combination with trenbolone acetate on the ultrastructure of mammary glands in female lambs regarding their interference in prolactin secretion.

The side-effects of anabolic steroid implants on mammary gland ultrastructure were evaluated in female lambs treated with oestradiol (n = 10) and with oestradiol plus trenbolone acetate (n = 10). Ten non-implanted lambs were used as controls. Apart from the ultrastructural study of the mammary gland, an assessment of the prolactin pituitary cell population was carried out by immunological methods. Our results showed that oestrogenic implants exert stimulating effects on mammary gland development, both by activating the synthesis process at mammary gland cell levels and by increasing prolactin pituitary production. Nevertheless, there was no evidence of secretory products in the lumen of the gland. Implants containing trenbolone acetate counteracted the mammary stimulus of oestrogens showing ultrastructural images of cell autolysis and necrosis.

Residues from anabolic preparations after good veterinary practice.

The purpose of this study was to determine the endogenous concentrations of estrogens, particularly estradiol-17beta (E2beta, in edible tissues of beef cattle (females and intact and neutered males) and the concentrations of E2beta, and trenbolone beta and alpha (betaTb, alphaTb) after an E2beta and/or trenbolone acetate (TA) ear implant. Radioimmunoassays were validated for quantitation of E2beta (active isomer), E2alpha, estrone (E1), betaTb and alphaTb for bovine muscle, liver, kidney and fat tissues. The criteria of accuracy, precision, specificity and sensitivity were applied according to the standards of the U.S. Food & Drug Administration. In steer tissues, endogenous E2beta was <15 ppt, as was heifer muscle; but heifer liver and kidney were 3-fold greater. An E2beta implant in steers had no effect on muscle E2beta concentration, but increased E2beta in liver and fat 4- and 3-fold, respectively, but by 24 h post-implant removal, E2beta had fallen by half. Tissue E1 concentrations in cyclic females were similar to E2beta, but rose many fold greater than did E2beta during gestation; E2beta rose 3-fold during gestation. After E2beta/TA implant, steer tissues had E2beta concentrations equal to (for muscle and fat) and one-half (for liver) the E2beta measured in E2beta implant only steers; betaTb was in a low range (250-380 ppt) in muscle, liver and fat and alphaTb was even lower, except in liver (800-1500 ppt). An implant of TA only (no E2beta) resulted in betaTb and alphaTb concentrations 2-3-fold greater in liver, kidney and fat, but no greater in muscle than betaTb in tissues of E2beta/TA implant steers. In conclusion, anabolic implants in steers resulted in tissue E2beta concentrations less than the FDA allowable increment and betaTb in the lowest quartile (0.25) of a part per billion 30 days after implant.

Implant strategies in an integrated beef production system

Anabolic implants are used to reduce the cost of beef cattle production. Implant products are available for suckling calves, grazing cattle, and finish- ing cattle. Improvements of 6, 15, and 20% in average daily gain can be realized in calves, stockers, and feedlot cattle, respectively, with implanting. Producers have numerous choices available today when using implants to lower production costs. In the current segmented beef industry, implanting decisions are dictated by phase of production in which the cattle are marketed. General recommendations have been to use implants predomi- nately in the finishing phase, and some feedlots cur- rently offer premiums when purchasing unimplanted cattle. However, in totally integrated beef production systems, traditional implant schemes may not be opti- mal. The primary objective of an integrated system is

Optimizing carcass value and the use of anabolic implants in beef cattle

The historical use of implants in ruminants dates to 1947 with the first implanting of Hereford heifers with diethylstilbestrol. Since that time, several different implants have been developed with varying degrees of commercial success. It is recognized that the use of anabolic implants in beef cattle offers the greatest return on investment outside of ensuring adequate nutrition. Although this may be true with respect to increased weight gain and improved feed efficiency, the influence of anabolic implants on carcass characteristics has not all been positive. Since the early use of diethylstilbestrol, packers have been concerned about the influences of implants on meat tenderness and carcass value as indicated by quality grade. This concern has been renewed and amplified with the increased use of anabolic implants and the introduction of combination implants. Estrogenic, trenbolone acetate, and combination implants used today have been shown to increase live performance, rate of empty body protein

Effects of energy intake, implantation, and subcutaneous fat end point on feedlot steer performance and carcass composition.

The purpose of this experiment was to evaluate the effects of energy intake, implantation, and fat end point on feedlot performance and carcass composition of steers. Three hundred eighty-four yearling crossbred steers (368 +/- 23.1 kg) were allotted in a completely randomized design. Treatments were arranged in a 2 x 3 x 2 factorial experiment. Main effect factors were two levels of intake, three implant strategies, and two compositional fat end points at slaughter. The levels of intake were ad libitum (AL) and restricted (RS) intake (90% ad libitum). The three implant strategies were Revalor-S (REV) (120 mg trenbolone acetate, 24 mg estradiol), Synovex-Plus (SYN) (200 mg trenbolone acetate, 28 mg estradiol benzoate), and no implant (control). The compositional target end points were 1.0 and 1.4 cm s.c. fat cover over the 12th and 13th rib. Restricted-intake steers consumed 9.2% less (P < .01) DM than AL steers. Ad libitum-intake steers gained weight 15.5% more rapidly (P < .01) than RS-intake steers. Steers implanted with REV tended (P < .07) to gain faster than SYN steers, who in turn gained 15.2% more (P < .01) than control steers. Ad libitum-intake steers were 4.8% more (P < .01) efficient than RS steers. Steers fed to a targeted 1.4 cm s.c. backfat cover were 2.9% less (P < .05) efficient than steers fed to 1.0 cm, and steers implanted with either REV or SYN had similar (P = .47) feed efficiencies, whereas control steers had lower (P < .01) feed efficiencies. Steers fed to a targeted compositional fat end point of 1.4 cm had 1.3% higher (P < .01) dressing percentage (DP) than steers fed to 1.0 cm. Control and SYN steers had similar (P = .13) DP; however, REV steers had 6.1% greater (P < .01) DP than SYN steers. Steers fed to 1.4 cm s.c. fat end point had higher (P < .01) numerical yield grades than steers fed to 1.0 cm (3.34 vs 2.71). There was an interaction (P < .01) for intake level and implant for marbling score. Marbling scores were lower (P < .05) for RS x SYN and AL x REV than in other treatments. Steers on the RS x REV treatment were intermediate in marbling to all treatments except AL control, which was higher (P < .01) than RS x SYN, AL x REV, and RS x REV. No interaction for dry matter intake level and anabolic implants was observed for growth performance. The depression in carcass quality resulting from implanting is reduced as backfat increases from 1.0 to 1.4 cm at slaughter.

Effect of anabolic implants on beef intramuscular lipid content.

Sixty ribeye steaks were used to determine the effects of anabolic implants on i.m. lipid composition of beef steers. Steaks were obtained from carcasses (346 kg) of steers assigned to four treatment groups (C = nonimplanted control; ET = 28 mg of estradiol benzoate plus 200 mg of trenbolone acetate on d 0; ET/ET = ET on d 0 and d 61; and S/ET = 20 mg of estradiol benzoate plus 200 mg of progesterone on d 0 and ET on d 61) and fed a high-concentrate diet for 127 d. Total fatty acid content of the longissimus was less (P < .05) for implanted steers. Implanting increased (P < .05) stearic and linolenic acid percentages and reduced (P < .05) oleic acid percentage but did not alter (P > .05) percentages of other fatty acids. These changes translated into increased (P < .05) percentages of saturated fatty acids and reduced (P < .05) monounsaturated fatty acids in the longissimus of implanted steers. However, on a per-steak weight basis, implanting did not alter (P > .05) the amounts of any of the individual fatty acids, but it increased (P < .05) the total cholesterol amount. Implanting with an estrogenic compound first reduced (P < .05) the percentage and total amounts of linoleic and polyunsaturated fatty acids. On a percentage basis, implanting alters fatty acid amounts; however, when the increase in ribeye size with implanting is accounted for and fatty acids are evaluated on a per-steak basis, these differences are not significant.

Anabolic implant effects on visceral organ mass, chemical body composition, and estimated energetic efficiency in cloned (genetically identical) beef steers.

Six sets of four genetically identical Brangus steers (n = 24; X BW 409 kg) were used to determine the effect of different anabolic implants on visceral organ mass, chemical body composition, estimated tissue deposition, and energetic efficiency. Steers within a clone set were randomly assigned to one of the following implant treatments: C, no implant; E, estrogenic; A, androgenic, or AE, androgenic + estrogenic. Steers were slaughtered 112 d after implanting; visceral organs were weighed and final body composition determined by mechanical grinding and chemical analysis of the empty body. Mass of the empty gastrointestinal tract (GIT) was reduced approximately 9% (P < .10) in steers implanted with estrogen alone or in combination with an androgen. Liver mass was increased (P < .10) from 6 to 14% by implants. Steers implanted with the AE combination had greater (P < .10) daily protein accretion (163.4 g/d) than either E (128.8 g/d) or A (137.1 g/d), and, because the combination improved gain above C (101.1 g/d), this demonstrates the additive effects of a combination implant on protein deposition. Anabolic implants did not alter (P > .10) the efficiency of ME utilization. In general, estrogenic implants decreased GIT, androgenic implants increased liver, and all implants increased hide mass. Steers implanted with an AE combination had additive effects on protein deposition compared with either implant alone. The NEg requirements for body gain are estimated to be reduced 19% by estrogenic or combination implants.

Influence of steroid implants and concentrate feeding on performance and carcass composition of cull beef cows.

Sixty nonpregnant, mature beef cows were used to evaluate the influence of steroid implants on performance and carcass composition of beef cows fed a high-concentrate diet. Twelve nonfed cows were slaughtered at 0 d. Remaining cows were stratified by weight and randomly assigned to an implant treatment and feeding period (28 or 56 d). Treatments included 1) no implant (control), 2) a 200-mg trenbolone acetate (TBA) implant, 3) a 200-mg testosterone propionate +20 mg of estradiol benzoate (TEB) implant, or 4) both implants (TBA + TEB). As days on feed increased, hot carcass weight (HCW), carcass soft tissue (CST) weight, adjusted fat thickness (AFT), longissimus muscle area (LMA), percentage of CST, and percentage of CST lipid increased (P < .05) and percentage of CST crude protein and moisture decreased (P < .05). Cows fed for 56 d accumulated (P < .05) more kilograms of lean than cows fed for 28 d, and cows fed for 28 d tended (P = .08) to have more kilograms of lean than nonfed cows. Cows fed for 56 d had (P < .05) higher dressing percentages than nonfed cows or cows fed for 28 d, and nonfed cows had (P < .05) higher dressing percentages than cows fed for 28 d. Implanted cows compared with control cows had (P < .05) heavier final weights, increased gains, improved feed efficiency, heavier hot carcass weights, larger LMA, higher cutability yield grades, compositionally leaner CST (higher percentage of moisture and protein and lower percentage of lipid), and more kilograms of lean. In addition, double-implanted (TBA + TEB) cows had (P < .05) more kilograms of CST than control and TBA-implanted cows. Furthermore, cows implanted with TBA had (P < .05) lower dressing percentages than TEB-implanted cows, less AFT than controls, and fewer kilograms of lipid than cows on the other three treatments. Full feeding of thin beef cows for 28 or 56 d increased carcass weight through an increase in CST lean as well as fat (lipid). The live performance and accretion of lean during realimentation can be enhanced by using anabolic implants.

Sex-related susceptibility of bulls to gastrointestinal parasites

The effects of sex and anabolic implants on fecal egg counts and pasture contamination were examined in 77 naturally infected yearling bulls, steers, and heifers of mixed beef breeds grazing the same contaminated pasture in southern Ohio in the spring of 1990. Fecal egg counts were compared in seven groups of 10–14 animals each, twice before anabolic implants and twice after implants. Comparisons were made between untreated bulls, steers, and heifers, between steers with and without implants, and between heifers with and without implants. Bulls had significantly ( P<0.01) higher fecal egg counts than steers, and counts from steers were not significantly different to those from heifers. There were no significant differences between counts from implanted and control steers or heifers. The results have important practical implications both for parasite control and for bovine parasite research. There is a need to pay special attention to young bulls when designing parasite control programs, and to distribute the sexes equally between groups when doing research trials with cattle of mixed sexes. Some previous studies on worm population dynamics and anthelmintic evaluation may need to be re-examined in the light of sex differences.

Efficacy of vaginal spaying and anabolic implants on growth and carcass characteristics in beef heifers.

Ninety crossbred beef heifers averaging 260 kg were blocked by weight and allotted randomly to 15 pens of six heifers each, with three replicates per treatment. The treatments were spayed heifers (S); intact heifers (I); S + Synovex-H7 (SH); I + Synovex-H (IH); and S + Synovex-S7 (SS). The heifers were spayed vaginally with a Willis instrument; intact heifers were rectally palpated for reproductive soundness. Heifers were fed a growing diet (55 d), re-implanted and subsequently fed a finishing ration (73 or 101 d). All heifers were observed for estrus daily at approximately 0600 and 2000 until d 69. A jugular vein blood sample was obtained from each heifer on d 48, 55, 62 and 69 for blood progesterone analysis. Results of blood progesterone analysis and reproductive tract examination indicated that two spayed heifers were incompletely spayed, a 96% success rate. The SH and SS heifers continued to exhibit estrous behavior despite being successfully spayed. Heifers implanted with Synovex-H had greater (P less than .01) ADG and were more efficient (P less than .03) than nonimplanted heifers. The SS heifers had greater ADG (P less than .05) during the finishing phase than SH heifers, but no advantage of SS over SH was apparent during the growing phase. The overall ADG response to implantation was fourfold greater (P less than .07) in the spayed heifers than in the intact heifers (32 vs 8%). Heifers implanted with Synovex-H had greater adjusted hot carcass weight (P less than .02) and ribeye area (P less than .002) than nonimplanted heifers. For adjusted live weight and ribeye area, the response to implantation was approximately threefold greater in the spayed heifer than the intact heifer. These results demonstrate that spaying and implanting heifers can increase rates and efficiency of gain even though behavioral estrus is not eliminated.

Growth and hormonal response of intact and castrate male cattle to trenbolone acetate and estradiol.

Effects of castration and anabolic implants on weight gain, rib soft tissue composition and serum hormones were studied in cattle using a completely random design with a 2 x 2 factorial arrangement. Half of 16 bulls and 16 steers (Angus or Angus x Brahman) aged 9 mo and weighing 290 kg were treated with an implant (200 mg trenbolone acetate and 24 mg estradiol). Half of each group were not treated with an implant. A growing diet was fed for 95 d and half the animals in each group were slaughtered. Animals in the treated groups were reimplanted with trenbolone acetate and fed a finishing diet for 84 d and slaughtered. Percentage dry matter, fat and protein were determined on soft tissue from the 9-10-11th rib. Two blood samples were collected from each animal every 2 wk. Serum was assayed for five hormones. During the growing phase, untreated and treated bulls and treated steers gained more weight and had leaner rib sections that untreated steers (P less than .05); after the finishing phase, there were no differences among groups. Untreated steers had lower insulin-like growth factor (IGF-I) and higher cortisol concentrations during both phases of growth than untreated bulls did (P less than .05). Treatment with implants increased IGF-I concentrations in steers during both phases and reduced cortisol during the finishing phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of anabolic status and phase and rate of growth to priorities for protein and fat deposition in steers.

The effects of anabolic implants, growth phase (growing vs finishing) and rate of growth on the priorities for protein and fat deposition were determined in yearling cattle. Santa Gertrudis crossbred yearling steers weighing 290 kg were individually fed diets varying in forage and grain content and either not implanted (n = 16) or implanted (90-d intervals) with Ralgro (n = 13) or Synovex-S (n = 12) implants. The cattle were fed toward a similar expected final empty BW (455 kg). Initial and interim empty body composition was measured via deuterium oxide dilution; final composition was determined by carcass specific gravity. During a 100-d growing phase, rates of protein gain were increased (P less than .12) to 118 and 131 g/d from 98 g/d for Ralgro and Synovex vs nonimplanted cattle, respectively. Concurrently, the fraction of protein in empty body growth was increased (P less than .09) from 17.5% for controls to 23.8 and 19.7% for Ralgro- and Synovex-implanted steers, respectively. This change in protein growth occurred concomitant with mobilization of fat and a reduction (P less than .04) in fat gain with Ralgro and Synovex implants. During the 136-d finishing phase, protein accretion was 115 and 132 vs 93 g/d for Ralgro- and Synovex-implanted cattle vs nonimplanted cattle; this represented a 24 and 42% increase (P less than .03) with Ralgro and Synovex, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Anabolic implant and frame size effects on growth regulation, nutrient repartitioning and energetic efficiency of feedlot steers.

Rates of growth and partitioning of nutrients among tissues were measured in large (Simmental x [Hereford x Brahman]; n = 34) and very large (Chianina x Angus and Maine Anjou x Angus; n = 37) steers implanted with different anabolic growth regulators. All cattle were fed individually a whole shelled corn (13% crude protein) diet. Implant strategies were: none (n = 13), Ralgro 36 mg (n = 15), Ralgro 72 mg (n = 14), Synovex-S (n = 15) and Ralgro 36-Synovex-S (n = 14) administered at d 0 and 90. Empty body composition of all cattle was measured initially and at 90 d by D2O dilution procedures and at slaughter (average, 182 +/- 4.1 d) by carcass specific gravity. Empty body weight for large and very large cattle averaged 274 and 324 kg (P less than .05) initially and 497 and 603 kg (P less than .05) at slaughter. Empty body protein differed (P less than .05) for large and very large steers and averaged 51 and 61, 67 and 79, and 87 and 103 kg initially, at midpoint and at slaughter, respectively. Percentage empty body fat was lower for very large steers (13.5 vs 15.6%) initially (P less than .05) but was similar for very large and large steers at the midpoint (18.7 vs 18.1%) and at slaughter (23.2 vs 21.9%). Daily rates of empty body gain (DEBG) were greater (P less than .05) for very large vs large steers for both growing and finishing periods and averaged 1.53 vs 1.26 kg/d overall. Daily rates of protein gain (DPG) were similar for very large and large steers for the growing phase (204 vs 202 g/d) but greater (P less than .05) in very large steers for the finishing phase and overall (253 vs 204, and 229 vs 202 g/d). All implant strategies, except R36, increased DEBG and DPG and tended to decrease the percentage of fat in daily gain. In both large and very large cattle, implant growth regulators increased growth rate and partitioned nutrient use away from fat toward protein accretion, with the magnitude of partitioning toward protein increasing with greater rates of growth. These data indicate that anabolic growth regulators are viable strategies to enhance lean beef production in steers, regardless of animal size.

Growth and sexual characteristics of suckling beef calves as influenced by age at castration and growth implants.

A 2-yr study using crossbred male calves (n = 228) evaluated castrating at birth or at 4 mo of age and use of anabolic growth implants (none, zeranol or estradiol-17 beta). Angus, Hereford and Brahman crossbred calves produced in seven cow-calf units that varied by breed component, stocking rate and calving season were allotted to treatment at birth in a 2 x 3 factorial arrangement. Growth implants decreased (P less than .01) testicular weight and expression (P less than .05) of male secondary sex characteristics in suckling bull calves at 4 mo. Implanted calves were shorter (P less than .05) at the hips and had shorter front legs (P less than .01) at both 4 mo and at weaning. Cannon bone circumference at weaning was increased (P less than .05) by growth implants. Age at castration did not affect (P greater than .05) calf performance or body characteristics. Calves given growth implants had higher (P less than .05) rates of gain from birth to 4 mo than did nonimplanted calves (.75 vs .71 kg/d). Implanted calves were heavier (P less than .01) at weaning and had higher (P less than .01) ADG from 4 mo to weaning than did nonimplanted calves. These data indicate no benefit from delaying age at castration, but implanting increased weaning weight an average of 8.2 kg.

Influence of Sustained-Release Estradiol-17-Beta in Pellet Form on Performance of Growing-Finishing Steers

Three trials, utilizing a total of 490 growing-finishing steers, were conducted (202-260 d) in different geographical regions (Missouri, Indiana, Kansas) under different feeding and management regimens to evaluate the efficacy of a sustained-release estradiol-17-beta implant. The implant formulation consisted of a copolymer pellet (5mm long, 2.4mm in diameter, and 27mg in total weight) impregnated with 19mg estradiol and dusted with oxytetracycline-HCl. Treatments were 1) nonimplanted control, 2) positive implanted control, and 3) 19mg, 4) 38mg, or 5) 57mg of estradiol in the test formulation. Implanted steers grazing native range (Kansas) gained faster (P<.05) compared to nonimplanted control steers. However, non-significant improvements were observed for cattle pastured on endophyte-infested tall fescue-red clover (Missouri) or backgrounded on a relatively high energy (75% corn silage:25% high moisture corn) program (Indiana). A treatment X experiment interaction (P<.05) indicated that steers severely restricted in the growing phase (Missouri) had no daily gain response to anabolic implants during the finishing phase. Implanting with 57mg estradiol increased warm carcass weight by 15.4kg (P<.05). Implanted steers had less (P<.05) body cavity fat, and tended to have less backfat, lower yield grades and larger ribeye areas.Pooled data indicate that total experiment weight gains were greater (P<.05) for all implant groups compared to the nonimplanted controls. The experimental implant was efficacious for a period of at least 200 d, but the magnitude of response to any anabolic implant may be affected by feeding and management regimen.

EFFECT OF ANABOLIC IMPLANT AND IONOPHORE ON THE PERFORMANCE OF GRAZING STEERS

In a 110-d grazing study, 75 yearling steers were left unimplanted or implanted at Day 0 with 24 mg 17β-estradiol, 36 mg zearanol, 72 mg zearanol, or 36 mg zearanol at Day 0 and 84. Within each implant group, steers were also supplemented with barley (0.5 kg head−1 d−1) with or without lasalocid (0.75 mg kg body weight−1 d−1) or were given no supplement in a 5 × 3 factorial design. Average daily gain (ADG) for all implanted steers was 17.5% greater (0.94 vs. 0.80 kg d−1) than for unimplanted steers (P &lt; 0.01). Increasing the dosage of zearanol from 36 to 72 mg extended the time over which ADG was increased but total liveweight gain and ADG over the 110-d grazing season were similar for all implant types. A second implant of zearanol (2 × 36 mg) increased ADG during the final 26 d of the pasture phase and during the drylot period, compared with 72 mg zearanol given initially. Barley + lasalocid-supplemented steers had ADG 17.3% greater (1.02 vs. 0.87 kg d−1) than barley-supplemented steers (P &lt; 0.01). During the following drylot phase, when no lasalocid was fed, ADG was lower (P &lt; 0.10) for steers that had previously received lasalocid than for other groups. No interactions were observed between implant and supplement type. Thus, the anabolic implants and ionophores used in this study are additive in improving growth rate. Key words: Cattle, feedlot, grazing, lasalocid, zearanol, 17β-estradiol, growth

Effects of Anabolic Implants and Breed Group on Carcass Traits and Palatability Characteristics of Bullock Beef

Effects of Anabolic Implants and Breed Group on Carcass Traits and Palatability Characteristics of Bullock Beef