Effect of repeated administration of combination trenbolone acetate and estradiol implants on growth, carcass traits, and beef quality of long-fed Holstein steers

Our objective was to determine the effect of repeated use of implants on feedlot performance and carcass characteristics of Holstein cattle. Holstein steers (n = 128) weighing an average of 211 kg were blocked by weight and randomly assigned to 16 pens. At the start of the trial (d 0), pens were assigned to one of four treatments: 1) nonimplanted control (C); 2) implant on d 0, 112, and 224 (T3); 3) implant on d 112 and 224 (T2); and 4) implant on d 224 (T1). Component TE-S implants (120 mg of trenbolone acetate and 24 mg of estradiol per implant) were used for all treatments during the 291-d feeding period. Over the course of the study, T2 and T3 cattle had greater ADG and final weights than C and T1 cattle (P < 0.05). Steers were harvested at a commercial abattoir on d 291. Hot carcass weights of T3 steers were greater than those of C and T1 steers (P < 0.05). Dressing percentage, adjusted 12th-rib fat, percentage of kidney, pelvic, and heart fat, yield grade, and longissimus color were not different among treatments (P > or = 0.26). Longissimus muscle areas (LMA) of T2 and T3 carcasses were larger than LMA of C (P < 0.01). No USDA Select carcasses were produced from C cattle, whereas the percentage of Select carcasses from implanted cattle ranged from 10 to 18%. Skeletal maturity advanced (P < 0.05) progressively with each additional implant. Steaks from T3 carcasses had a higher percentage of protein than controls (P < 0.05) and were less tender than all other treatments (P < 0.05). Repeated administration of combination trenbolone acetate and estradiol implants increased ADG and resulted in heavier carcasses with larger LMA. Administration of three successive implants decreased tenderness of Holstein beef, and resulted in more advanced skeletal maturity scores.     

Effects of zeranol and trenbolone acetate on testis function, live weight gain and carcass traits of bulls

The ability of zeranol and trenbolone acetate (trenbolone) to alter testis function, weight gain and carcass traits of young bulls was studied. In Exp. 1, the effects of age at initial zeranol implantation was determined. After a 235-d experimental period, sequential implantation (56-d intervals) beginning at 100 or 150 d of age had reduced testis growth (P less than .01), sperm production (P less than .01) and serum testosterone concentration in response to gonadotropin releasing hormone (GnRH; P less than .01). The 200-d age group was partially suppressed, while the 250-d age group was not affected. Body weights were similar to controls in all groups. In Exp. 2, bulls previously implanted with zeranol at 175 and 231 d of age received single implants of zeranol, trenbolone or trenbolone plus zeranol at approximately 300 d of age. At slaughter (135 d later), body weight and carcass characteristics in all treatments were similar to controls. However, trenbolone reduced sperm production (P less than .05), zeranol reduced sperm production and testes weight (P less than .05), but trenbolone plus zeranol was similar to controls. Mean testosterone response to GnRH was suppressed in all implant groups on d 65 (P less than .01), but only in trenbolone or trenbolone plus zeranol groups on d 112 (P less than .05). Results indicate that zeranol suppresses spermatogenesis and testosterone production if implanted before approximately 200 d of age. Reduction of endogenous testosterone without alteration of weight gain or carcass characteristics may be of benefit if behavioral or masculinity traits of bulls are altered. Also, it appears that no benefit is derived from implanting bulls with both trenbolone and zeranol.     

Effect of an implant of trenbolone acetate and estradiol on growth, feed efficiency, and carcass composition of Holstein and beef steers.

The effects of an implant of 140 mg of trenbolone acetate and 28 mg of estradiol (TBA + E2) on performance and carcass composition were evaluated with 72 individually fed steers. Holstein (n = 24), Angus (n = 24), and Angus x Simmental (n = 24) steer calves were allocated by breed and implant treatment to either an individual feeding pen (n = 36) or an electronic feeding door in a group pen (three pens with 12 animals per pen). Intake and refusal of the 85% concentrate diet were recorded daily. Animals were slaughtered when ultrasonic attenuation values of the longissimus muscle at the 12th rib reached .55, which is correlated with low Choice marbling. At slaughter, complete carcass measurements were taken and the right side of each carcass was separated into boneless wholesale cuts. Implanting with TBA + E2 improved (P less than .01) daily gain and feed efficiency. Daily gain was increased 17, 26, and 21% in Holstein, Angus, and crossbred steers, respectively. The implant increased overall daily protein and fat accretion 23%. Carcass conformation and dressing percentage were not affected (P greater than .05) by TBA + E2 treatment. Implantation with TBA + E2 had little effect on yield of wholesale boneless cuts when expressed as a percentage of carcass weight but increased absolute weight as a small degree of marbling by 6 to 40 kg.     

Time of zeranol implantation on growth, reproduction and calving of beef heifers

Zeranol implants were administered to 250 crossbred heifer calves at 1, 6 or 9 mo of age to evaluate growth, reproduction and calving performance. Heifers were assigned to eight treatment groups with 25 animals per group. Two additional groups of 25 heifers each were used to study the effects of multiple implants at two levels of nutrition on heifer performance. Implants at 1 mo of age (branding) increased heifer weights at 6 mo of age (weaning) by 5 kg (P = .08). Heifers receiving a combination of two implants gained faster (P less than .05) from weaning to breeding (6 to 13 mo) than controls or heifers implanted three times. Implants at either 6 or 9 mo increased (P less than .05) precalving pelvic areas (247 vs 241 cm2 and 248 vs 240 cm2 over controls, respectively). Implants did not affect the percent of heifers reaching puberty prior to breeding season. Conception rates in 62 d of breeding were comparable for implanted and control heifers (93 vs 96%), with the exception of heifers receiving implants at both 1 and 6 mo of age (56%). Calf birth weight, dystocia score, cow rebreeding rate and calf weaning weight were not affected by implant treatments. Heifers that received three implants and were fed at a high nutritional level (gained .62 vs .49 kg/d for regular level after weaning) tended (P greater than .10) to reach puberty at a higher rate prior to breeding and to have a higher total conception rate than implanted heifers on the regular nutrition level.     

Growth, carcass and palatability traits of intact males and steers implanted with zeranol or estradiol early and throughout life

This study was conducted to assess the impact of implanting intact beef males with protein anabolic agents at varying intervals throughout life. Ninety-six intact males were assigned to three implant treatments: 1) not implanted, 2) implanted at 9 wk of age, weaning and at 56-d intervals thereafter with a 36-mg zeranol implant or 3) estradiol implant at 9 wk of age and 68 d post-weaning. During the 118-d, post-weaning growing period, eight animals per treatment (one replication) were castrated. After a 114-d finishing period, cattle were slaughtered (average age of 13 to 14 mo). Feedlot performance, carcass and palatability data were obtained. Average daily gains and feed efficiency did not differ (P greater than .05) between zeranol and estradiol-implanted intact males. Regardless of implant treatment, steers had lighter carcass weights (P less than .05) and higher (P less than .01) quality grades than intact males. Implanting either intact males or steers with zeranol or estradiol resulted in higher (P less than .05) numerical yield grades. Quality grades were higher in zeranol-implanted cattle than the non-implanted or estradiol-implanted cattle. Intact males implanted with zeranol were similar in carcass fatness to zeranol-implanted steers. No differences (P greater than .05) in tenderness or connective tissue were detected. Implanting intact males early and throughout life with zeranol made them similar to steers in fatness, while estradiol implantation had few effects on carcass and palatability traits of intact males or steers.     

Effects of restricted feeding, low-energy diet, and implantation of trenbolone acetate plus estradiol on growth, carcass traits, and circulating concentrations of insulin-like growth factor (IGF)-I and IGF-binding protein-3 in finishing barrows

Effects of restricted feeding (80% ad libitum), feeding a low-energy diet containing 84% DE (2.95 Mcal/kg) of the control diet, and implantation of Revalor H (140 mg trenbolone acetate plus 14 mg estradiol-17beta) on growth, carcass traits, and serum concentrations of insulin-like growth factor (IGF)-I and IGFbinding protein-3 (IGFBP-3) were studied in crossbred finishing barrows beginning from 59 +/- 0.9 kg of body weight. Blood samples were taken every 3 wk and the animals were slaughtered at approximately 105 kg body weight. Restricted feeding caused a decrease (P < 0.01) in ADG; feeding the low-energy diet was effective in reducing backfat thickness but decreased gain:feed; the implantation caused a decrease in ADG, feed intake, and backfat thickness and increased gain:feed. Overall pork quality based on pH, drip loss, and the lightness in color of longissimus muscle was not affected by any of the treatments. Serum IGF-I concentration increased following the implantation but did not change (P > 0.05) due to other treatments. Immunoreactive IGFBP-3 concentration was not changed by any of the treatments. Overall ADG was positively correlated with early-stage (d 21) IGF-I and IGFBP-3 concentrations only in unimplanted barrows, whereas backfat thickness was negatively correlated with d-42 IGF-I concentration in all but unimplanted barrows with ad libitum intake. A strong positive correlation (P < 0.01) between IGF-I and IGFBP-3 concentrations was apparent with increasing age of the animals. Results suggest that growth rate and backfat thickness are decreased by a moderate restriction of feed or energy intake with no accompanying changes in circulating IGF-I and IGFBP-3 concentrations and that the beneficial effect of Revalor H implantation on feed efficiency may be mediated, in part, by IGF-I. Moreover, both IGF-I and IGFBP-3 concentrations may be useful as growth indices in pigs.     

Use of trenbolone acetate and estradiol in intact and castrate male cattle: effects on growth, serum hormones, and carcass characteristics

The effects of anabolic implant on growth, carcass characteristics, and serum hormones were examined in 30 young bulls and steers fed a growing diet then a finishing diet. In a 2 X 3 factorial arrangement, steers and bulls received an implant of trenbolone acetate (TBA), TBA and estradiol-17 beta (E2), or no implant. Blood samples were taken serially (every 20 min for 6 h) at intervals during the growing and finishing phases. Percentage of DM, fat, protein, and ash and Warner-Bratzler shear test were measured and taste panel evaluations of the 9-10-11 rib section were obtained. Treatment with TBA and E2 increased weight gain in steers but not in bulls. There were no differences in feed efficiency, serum growth hormone (GH), and cortisol concentrations between bulls and steers or between treated groups and controls in bulls or steers, although during the finishing phase mean GH concentrations in treated steers were twofold higher than in controls and were similar to those in the bull groups. Serum insulin-like growth factor-I (IGF-I) increased twofold during the growing phase, then remained at that level. Steers implanted with TBA and E2, which had the highest gains among the steer groups, had the highest serum GH and IGF-I. Longissimus steaks from bulls treated with TBA alone or TBA and E2 were comparable to steaks from steers in the shear test. Taste panelists found steaks from TBA- and E2-treated bulls to be similar in tenderness and connective tissue to steaks from steers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Administration of estradiol, trenbolone acetate, and trenbolone acetate/estradiol implants alters adipogenic and myogenic gene expression in bovine skeletal muscle

Twenty crossbred yearling steers (421 kg) were used to evaluate the effects of implanting with trenbolone acetate (TBA; 120 mg), estradiol-17β (E(2); 25.7 mg), and a combination (120 mg of TBA and 24 mg of E(2)) on adipogenic and myogenic mRNA concentrations. Animals were blocked by BW and within each block were assigned to 1 of 4 treatments. Animals were housed and fed in individual pens with 5 animals per treatment. All animals were weighed weekly, and muscle biopsy samples were taken from the LM of each steer on d 0 (before implantation), 7, 14, and 28. Total RNA was isolated from each sample and real-time quantitative PCR was used to measure the quantity of C/EBPβ, PPARγ, stearoyl CoA desaturase (SCD), myogenin, and 3 isoforms of bovine myosin heavy chain (MHC) mRNA. Total BW gain from the 28-d period was adjusted to d 0 by use of covariant analysis, and steers in the implant groups tended (P = 0.09) to have increased BW gain compared with nonimplanted control steers. Analysis of the gene expression of MHC showed that neither implant nor day (P > 0.20) had a significant effect on the expression of type I or IIX MHC mRNA There was also no treatment effect (P > 0.20) on MHC-IIA and myogenin, but increasing days on feed increased (P = 0.05) the expression of MHC-IIA mRNA. Relative mRNA abundance of C/EBPβ, PPARγ, and SCD increased (P < 0.05) during days of feed but PPARγ decreased (P < 0.05) with the treatment of combined TBA/E(2) implant. Results of this study indicate that implanting with TBA, E(2), or both increased BW gain and decreased adipogenic gene expression of finishing steers without significantly affecting the concentration of type I, IIA, or IIX MHC mRNA. Increasing days on feed increased both MHC-IIA and adipogenic gene expression in bovine skeletal muscle biopsy samples. We conclude that administration of steroidal implants had no effect on the proportion of the 3 MHC mRNA isoforms but decreased C/EBPβ, PPARγ, and SCD mRNA in bovine skeletal muscle.     

Lipogenesis in adipose tissue from ovariectomized and intact heifers immunized against estradiol and (or) implanted with trenbolone acetate

Forty-two heifers were allotted randomly to six treatment groups: intact controls, intact heifers implanted with trenbolone acetate, ovariectomized heifers, ovariectomized heifers implanted with trenbolone acetate, intact heifers immunized against estradiol and intact heifers immunized against estradiol and implanted with trenbolone acetate. Blood titers of estradiol-17 beta were increased over 100-fold in heifers immunized against estradiol in Freund's complete adjuvant or saline:squalene/arlacel containing Mycobacterium. Lipogenic enzyme activities and acetate incorporation into fatty acids were increased in subcutaneous adipose tissue obtained at slaughter from heifers receiving immunization or the combination of immunization and trenbolone acetate. The increased lipogenic capacity was not reflected in either cell diameter or cells per gram adipose tissue. Ovariectomy in combination with trenbolone acetate caused the lowest activities for all enzymes measured. This treatments also caused the greatest decrease in cell diameter, which resulted in the largest number of cells per gram of adipose tissue. Trenbolone acetate alone had no detectable effect on lipogenesis in the intact heifer, but the combination of ovariectomy and trenbolone acetate caused substantial decreases in enzyme activities, in most cases a significant decrease as compared with ovariectomized heifers. The data suggest that trenbolone acetate is able to depress lipogenesis only when not competing with the effects of circulating estradiol.     

Effects of short- or long-term infusions of acetate or propionate on luteinizing hormone, insulin, and metabolite concentrations in beef heifers

Two trials were conducted to evaluate the effects of short- (Trial 1) or long-term (Trial 2) intraruminal isocaloric infusions of acetate or propionate on secretion of LH, insulin, and selected metabolites in short- or long-term energy-restricted beef heifers. In Trial 1, 16 Angus heifers were assigned on d 6 to 12 of a synchronized estrous cycle (estrus = d 0) to a body weight-maintenance (BWM; n = 4) or an energy-restricted, body weight-loss (BWL; n = 12) treatment. On d 12 of a synchronized estrous cycle, heifers received PGF2alpha to synchronize estrus, and 12 h later BWL heifers received intraruminal, isocaloric infusions of acetate, propionate, or vehicle for 6 h and BWM heifers received vehicle concurrently. Mean plasma LH and LH pulse frequencies and amplitudes were not affected by treatment (P > .05). In contrast, infusion of propionate increased plasma insulin (P < .05) and reduced plasma concentration of NEFA (P < .05). In Trial 2, six ovariectomized Angus heifers were energy-restricted for 30 d. On d 14 and 26 of restriction, heifers began receiving intraruminal isocaloric infusions of acetate or propionate for 96 h in a switchback approach. Intraruminal infusions of vehicle for 6 h preceded infusions of acetate or propionate. Jugular blood was collected at 12-min intervals during infusions of vehicle and during the last 6 h of infusion of acetate or propionate. Mean concentration of LH and amplitude of pulses of LH were lower during acetate vs propionate or vehicle infusion (P < .05). Infusion of propionate increased insulin relative to acetate or vehicle infusion (P < .05). Plasma NEFA were reduced by infusion of propionate (P < .05) and increased by infusion of acetate (P < .05).     

Growth, carcass composition and plasma melatonin in postpubertal beef heifers fed melatonin

Two experiments were conducted to determine if feeding melatonin alters plasma concentrations of melatonin, growth and carcass composition of postpubertal beef heifers exposed to 16 h light (L):8 h dark (D). In Exp. 1, 16 heifers were blocked by initial body weight (318 +/- 5.6 kg). Four heifers were killed before starting the melatonin treatment to obtain initial carcass composition. Six heifers received vehicle (95% ethanol) and six were fed melatonin (4 mg/100 kg body weight) daily for 58 d at 1330 to coincide with the middle of the 16-h light period. On d 59 heifers were slaughtered. Melatonin feeding increased the percentage of fat in rib (P less than .05) and longissimus muscle (LD; P less than .10) and carcass fat accretion 28% (P less than .09) but reduced the percentage of protein 8% in rib (P less than .05) and carcass protein accretion 30% (P less than .09). Other measures in the carcass and body weight gain were not affected (P greater than .10) by feeding melatonin. Plasma concentrations of melatonin increased (P less than .01) from 10 to 140 pg/ml within 30 min of feeding melatonin. In Exp. 2, 24 heifers were blocked by initial body weight (348 +/- 13.7 kg). Eight heifers were killed initially, eight received vehicle and eight were fed melatonin for 63 d as described in Exp. 1. Melatonin did not influence (P greater than .10) body weight gain or any measure in the carcass; however, these heifers were fatter (40.1%) than those in Exp. 1 (30.9%) at the beginning of the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Skeletal muscle protein metabolism and serum growth hormone, insulin, and cortisol concentrations in growing steers implanted with estradiol-17 beta, trenbolone acetate, or estradiol-17 beta plus trenbolone acetate.

Skeletal muscle protein degradation, measured by urinary N tau-methylhistidine excretion, and circulating concentrations of growth hormone (GH), insulin (INS), and cortisol (CT) were monitored in steers before and after implantation with estradiol-17 beta (E2; 24 mg) and trenbolone acetate (TBA; 300 mg). Yearling crossbred steers (n = 43) were randomly assigned to four treatment groups in a 2 x 2 factorial arrangement: nonimplanted controls (C); TBA; E2; and TBA plus E2 (TBA+E2). A subgroup (Block 1) of 16 steers was bled on d -12, 31, and 72 after implanting. Deposition of skeletal muscle protein was markedly increased (P less than .001) by E2 and TBA+E2 treatment. This response occurred mainly within the first 40 d after implantation and declined (P less than .001) in concert with decreasing (P less than .01) concentration of serum E2. Anabolic steroid treatment did not affect the rate of skeletal muscle protein breakdown. There was no apparent relationship between reduced serum CT concentration (linear effect; P less than .01) in TBA-treated steers and skeletal muscle protein degradation rate. Blood concentration and pulse activity of INS were not affected by anabolic steroid administration. Both TBA- and TBA+E2-implanted steers displayed a linear decrease (P less than .05) in serum GH concentration over time, which was similar to C. Lowered mean GH concentration resulted from a reduction (TBA main effect; P less than .05) in pulse amplitude of GH. Unlike TBA, TBA+E2, and C, only E2 maintained serum GH concentrations over time. Although increased muscle protein deposition was evident in TBA+E2-treated steers, an obvious causal relationship between this response and circulating GH, INS, and CT was not revealed. These results do not support the concept that combined androgenic agent and estrogen administration effectively reduce bovine muscle protein degradation by static modulation of circulating endogenous anabolic and antianabolic hormones.     

Influence of zeranol implants on growth, behavior and carcass traits in Angus and Limousin bulls and steers

A 2(3) factorial arrangement of treatments was utilized to determine effects of postweaning zeranol implantation, breed (Angus vs Limousin) and castration (bull vs steer) on growth, behavior and carcass traits. An initial slaughter group was used to account for breed differences in composition and to determine fat and lean growth in the 9-10-11th rib section (NTE). The remaining cattle were fed a finishing diet to a fat end point of .76 cm, as determined by a backfat probe. Control bulls outgained (P less than .01) control steers both to the first kill date and over the entire test and did not require significantly more time to reach the fat end point. The implant did not influence gain in bulls but did increase gain in steers. Angus and Limousins were similar in growth rate for the first 126 d before the first slaughter date. Limousins required more (P less than .01) time to reach the fat end point. Bulls and Limousins produced heavier (P less than .01) carcasses and larger rib eyes (P less than .05; bulls; P less than .01; Limousins). Steers and Angus had higher (P less than .01) marbling scores and lower bone maturity. Implanting decreased (P less than .05) marbling and increased carcass maturity. Small but significant shifts in carcass wholesale cut weight distribution were found between breed and sex condition groups. Bulls and Limousins had greater lean growth in the NTE. Bulls and steers were similar in fat growth, but Angus exceeded Limousin in this trait. Zeranol reduced scrotal circumference (P less than .01) and testicle weight at slaughter (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The use of a progesterone-releasing device (CIDR-B) or melengestrol acetate with GnRH,LH, or estradiol benzoate for fixed-time AI in beef heifers

The objective of this experiment was to compare two progestins and three treatments for synchronizing follicular wave emergence and ovulation in protocols for fixed-time AI in beef heifers. On d 0 (beginning of the experiment), Angus and Angus-Simmental cross beef heifers at random stages of the estrous cycle either received a CIDR-B device (n = 257) or were started on 0.5 mg x anima(-1) x d(-1) melengestrol acetate (MGA; n = 246) and were randomly assigned to receive i.m. injections of 100 microg GnRH, 12.5 mg porcine LH (pLH), or 2 mg estradiol benzoate (EB) and 50 mg progesterone (P4). The last feeding of MGA was given on d 6 and on d 7, CIDR-B devices were removed and all heifers received 500 microg cloprostenol (PG). Consistent with their treatment groups on d 0, heifers were given either 100 microg GnRH or 12.5 mg pLH 48 h after PG (and were concurrently inseminated) or 1 mg EB 24 h after PG and were inseminated 28 h later (52 h after PGF). Estrus rate (combined for both progestins) in heifers receiving EB (92.0%) was greater (P < 0.05) than that in heifers receiving GnRH and pLH (combined) and a CIDR-B device (62.9%) or MGA (34.3%). Although the mean interval from PG treatment to estrus did not differ among groups (overall, 47.8 h; P = 0.85), it was less variable (P < 0.01) in MGA-fed heifers (SD = 2.5 h) than in CIDR-B-treated heifers (SD = 8.1 h). Pregnancy rates (determined by ultrasonography approximately 30 d after AI) did not differ (P = 0.30) among the six treatment groups (average, 58.0%; range, 52.5 to 65.0%). Although fixed-time AI was done, pregnancy rates were greater in heifers detected in estrus than in those not detected in estrus (62.6 vs 51.9%; P < 0.05). In conclusion, GnRH, pLH, or EB treatment in combination with a CIDR-B device or MGA effectively synchronized ovulation-for fixed-time AI, resulting in acceptable pregnancy rates in beef heifers.     

Effect of prenatal trenbolone acetate treatment on lamb performance and carcass characteristics

Forty-three pregnant Dorset and Dorset crossbred ewes were assigned randomly to a control group or implanted with either 300 mg trenbolone acetate (Low TBA) or 1,200 mg trenbolone acetate (High TBA) between d 40 and 60 of gestation. Adjusted weaning weights for ewe lambs were 23.3% less (P less than .10) with vs without TBA treatments. Postweaning ADG of ewe lambs was lower (P less than .05) but ADG of ram lambs was greater (P less than .05) for high TBA vs low TBA. Ewe lambs receiving high TBA had 19% less (P less than .05) gain per unit of feed than those receiving low TBA. Days on test for ewe lambs was greater (P less than .05) due to TBA treatment and for high TBA vs low TBA. Days on test for ram lambs was decreased (P less than .05) due to high TBA compared to low TBA. Subcutaneous fat over the ribeye and lower rib were greater (P less than .05) for high-TBA ewe lambs vs low-TBA ewe lambs. Percentage kidney and pelvic fat of ewe lambs was lower (P less than .05) due to TBA treatments. Ribeye area per unit of carcass weight was lower (P less than .05) in high-TBA ewe lambs vs low-TBA ewe lambs. Yield grade of ewe lambs was lower (P less than .05) for low TBA vs high TBA. Prenatal trenbolone acetate treatment of ewe lambs did not improve their subsequent postnatal growth performance and carcass traits. In addition, TBA implantation of the pregnant ewe produced dystocia and less milk production, as evidenced by the need for more lambs to be grafted.     

Evaluation of growth, carcass traits and reproductive organs of young boars in response to zeranol implantation

Two experiments were conducted to evaluate the effect of implants containing zeranol on growth rate, carcass composition, palatability and reproductive organ development of intact male pigs. In Exp. 1, three treatment groups were evaluated: control barrows, intact control boars and implanted boars (implanted at either 28, 56 or 112 d of age with one 12-mg dose of zeranol). In Exp. 2, four treatment groups were evaluated: control barrows, intact control boars, boars implanted at 28 d with 24 mg of zeranol (single implant) and boars implanted at 28 d and re-implanted at 56 and 112 d of age with 24 mg of zeranol (triple implant). Differences for average daily gain and carcass traits were not consistent between treatment groups with the exception of 10th rib fat, where barrows were fatter than boars. There were no differences among treatments due to zeranol for the reproductive organ characteristics, with the exception that bulbourethal gland and teat weights were heavier for boars in Exp. 2. Penis weights and lengths were lower for barrows in both experiments. Juiciness, tenderness, Warner-Bratzler shear force, pork flavor intensity and sensory scores were not consistently affected by male condition or zeranol treatment. In two of the three comparisons, implanted boars had higher off-flavor intensity scores in Exp. 1, but no treatment difference was observed in Exp. 2. Zeranol implantation did not result in significant changes in growth rate, development of reproductive organs or carcass characteristics of young boars.     

Influence of zeranol and breed on growth, composition of gain, and plasma hormone concentrations

Seven Angus and six Brangus steers averaging 225 and 245 kg, respectively, were assigned randomly to zeranol (36 mg) implant (I) and no implant (NI) treatments. Steers had ad libitum access to a corn silage diet plus .68 kg of a soybean meal-based supplement fed daily. Steers were bled via jugular catheters on d 0, 28, 56, and 84 at 15-min intervals for 4 h before and 4 h after feeding. Concentrations of growth hormone (GH), insulin (INS), triiodothyronine (T3), thyroxine (T4), and glucose were determined. Whole-body protein and fat contents were monitored. A breed x I interaction (for d 56 to 84 and d 0 to 84) was observed for ADG (P less than .05 and P less than .07, respectively), feed conversion (P less than .05 and P less than .07, respectively), and protein deposition (for d 0 to 29 and d 0 to 84; P less than .07 and P less than .05, respectively). These interactions were attributed to a greater response to I by Angus than by Brangus steers. A feeding x period interaction (P less than .10) was observed for mean GH concentration, and INS, T4, and T3 concentrations were higher (P less than .05) during the 4-h postfeeding period than during the 4-h prefeeding period. The implant increased (P less than .08) mean GH concentration but did not alter the frequency, duration, or amplitude of plasma GH peaks. Steers that were implanted had lower (P less than .05) plasma T3. Brangus steers had lower (P less than .05) plasma glucose, T3, and T4 concentrations than Angus steers. Results indicate that growth factors beyond those measured are responsible for the anabolic response to zeranol.