Implanting Young Bulls With Zeranol for Meat Production12

Implanting Young Bulls With Zeranol for Meat Production 1,2

higher incidences of dark and coarse-textured lean, reduced tenderness and juiciness, and inadequate "finish" at carcass weights desired by packers have often been cited as reasons for not feeding young bulls for meat production (21). Consumer preferences for leaner meat and the need for more efficient production, have stimulated investigations of production systems to optimize the growth traits of young bulls without compromiSing meat quality and palatability. Zeranol (Ralgro@ ; an anabolic agent which produces estrogen-like responses) is commonly used to improve daily gain and feed efficiency of steers and heifers. Recent research has revealed varied responses for performance and carcass traits of young bulls implanted with zeranol (9, 12, 14, 15, 23). Age at initial and subsequent implantings appears to influence the carcass and secondary sex characteristics of young bulls fed for slaughter (12). Implanting young bulls with zeranol postweaning (during the feedlot period only) has had minimal effects on behavior, secondary sex characteristics and carcass characteristics (9, 15, 16). In contrast, bulls sequentially implanted from near birth until slaughter had improved behavior, decreased masculinity and(or) improved carcass characteristics compared with non implanted bulls (12, 14, 19, 23 , 24, 25) . This manuscript will focus on two experiments and other related studies to discuss the effects of implanting young feedlot bulls with zeranol on growth, carcass and palatabilty traits.

J. A. Unruh Washington State University3 Pullman 99164-6310 Summary The benefits from implanting young bulls with zeranol (Ralgro@ ) for meat production appear to depend on the initial implanting age and the subsequent implanting schedule. Bulls implanted initially at weaning have shown few production advantages except for possible increases in average daily gain. In contrast, implanting bulls initially soon after birth and sequentially through slaughter enhances the feasibility of using bulls for meat production. Studies in which young bulls were implanted from near birth to slaughter reported reduced masculinity, scrotal development and behavioral interactions, and varied responses for average daily gain compared with non implanted bulls. These studies have also indicated decreased carcass masculinity, increased carcass fatness and marbling, improved tenderness, and reduced connective tissue (collagen) amount and maturation. By both a trained sensory panel and take-home consumer evaluation, bulls implanted from near birth to slaughter were similar to steers in flavor, tenderness and overall acceptability. Therefore, implanting young bulls with zeranol from near birth to slaughter may maintain performance traits similar to the nonimplanted bull, and improve palatability to a level comparable with the steer. For maximum benefit, implanting young bulls must be coupled with management techniques recommended for feeding young bulls for meat production.

Materials and Methods Experiment 1. Fifty-five fall-born Simmentalcrossbred male calves were used to investigate the influence of implanting schedule on performance, carcass and palatabilty characteristics. Calves were allotted at birth to one of five treatments: bulls castrated at 5 mo and implanted four times from birth to slaughter (ST); bulls implanted four times from birth to slaughter (BI-BS); bulls implanted twice from birth to weaning (BI-BW); bulls implanted twice from weaning to slaughter (BI-WS) and nonimplanted control bulls (NIB). Implanted calves received 36 mg of zeranol within 3 d of birth and(or) at weaning and were reimplanted approximately 100 d later. Calves were weaned at an average age of 7.5 mo and fed a high-concentrate diet from 8.1 mo of age to an average slaughter age of 17 mo. Detailed management, carcass and meat palatability evaluation procedures are presented by Gray et al. (12) and Unruh et al. (26). Experiment 2. Seventy-two fall-born Simmental bull calves were used to determine the effects of implanting bulls from birth to four slaughter ages on performance,

Introduction The future of the livestock industry depends on the efficient production of wholesome, palatable, nutritious meat products that are free of excess fat. Therefore, profits must be realized by optimizing weight gain and feed-conversion, while producing retail products of acceptable compOSition, quality and palatability. The option of feeding young bulls for meat has been utilized to a very limited extent in the United States despite many production advantages. Young bulls, compared with steers, gain more rapidly with less feed and produce leaner carcasses (8, 11, 21). However, management difficulties, lower USDA quality grades,

1Scientific Paper No. 7731, College of Agri. and Home Economics, Res. Center, Washington State Univ., Pullman. 2Reviewed by J. R. Romans and C. J. Brown . 3Dep t. of Anim . Sci.

25

26

UNRUH

behavior, carcass, meat palatability and muscle-collagen characteristics. In experiment 2, calves were assigned randomly at birth to either a zeranol-implanted bull (liB) or a nonimplanted control bull (NIB) treatment. Calves assigned to the liB treatment were implanted with 36 mg of zeranoi within 3 d of birth and reimpianted at average intervals of 84 d until slaughter. Bulls were placed on ad libitum 83% concentrate diet at 8.3 mo of age and randomly assigned within treatment to slaughter end points of 12, 14, 16 and 18 mo (actual average ages were 12.0, 13.8, 15.7 and 17.4 mo, respectively). Detailed management, behavior, carcass, meat palatability and muscle collagen procedures and treatment x slaughter interaction means are presented in Gray et al. (13) and Unruh et al. (24, 25).

masculine than all other bull treatments. Scrotal circumferences at slaughter were smaller (P ...... 06) for bulls implanted at birth (BI-BW and BI-BS) than for BIWS and NIB. However, scrotal circumference differences were greater among treatments at weaning . Experiment 2. Feedlot performance traits of initial weight, final weight, average daily gain and feed: gain were similar for liB and NIB (Table 2). However, scrotal circumferences for liB were smaller than NIB (P ..... 05) initially and at all ages except for the final measurement at 17.4 mo of age. Scrotal growth of liB was delayed before weaning, but faster than NIB during the feeding period. Gonadal hom ones (testosterone, Figure 1; and estradiol 17B) were lower than 8.3 and 13.3 mo of age for liB than for NIB. After 13 mo . serum testosterone and estradiol-17B were similar for the two treatment groups. Peak concentrations of testosterone were observed near 11 and 14 mo of age for liB and NIB, respectively . In addition, visual masculinity scores, based on a visual score relative to age, were lower (P ..... 05) at all ages for liB than NIB. Prior to 13.8 mo, liB had fewer (P ..... .05) encounters for bunting , mounting attempts, and lower (P .... .05) activity scores than NIB bulls. Thereafter, liB and NIB bulls were similar (P~.1 0) for all behavioral traits observed . Other Studies. Others have found that implanting bulls with zeranol initially after 6 mo of age has resulted in increased daily gains (15) and slaughter weights (3) or similar daily gains and slaughter weights (9, 20, 27, 28) . In these studies, testicle development measured by scrotal circumference or testis weight, was similar (9, 15,28) or slightly reduced (20,27). Behavior traits (2, 15, 20, 27) and secondary sex characteristics (9, 1 5) were unaffected by initial implanting after 6 mo of age.

Results. Growth Traits. Experiment 1. Weaning weights (table 1) were similar (P~.1 0) among treatments, but animals in the ST treatment tended to weigh less than animals in the bull treatments. Scrotal circumferences at weaning were smaller (P ..... .05) for bulls receiving implants at birth (BI-BS, 18.4 cm; BI-BW, 19 .8 cm) than for bulls not implanted at birth (BI-WS, 26.4 cm; NIB, 26.5 cm). Feedlot average daily gains were lower (P ..... 05) for ST than for all other treatments. Both BI-BS and BI-BW were intermediate and slower gaining (P ..... 08) than BIWS and NIB. However, final slaughter weights for all bull treatments were similar (P~.1 0) and heaver (P ...... 05) than the ST treatment. Masculinity scores at slaughter were lowest (P ...... 05) for ST; while BI-BS were less (P ..... 05)

TABLE i. liVE MEASUREMENTS AND CARCASS CHARACTERISTICS OF ZERANOL IMPLANTED BULLS AND STEERS (EXPERIMENT 1)a Treatment b Trait

ST

BI-BS

BI·BW

BI -WS

NIB

No. of cattle

11

11

11

11

11

211 1.13 e 502 e

238 1 .25 ,f 560' 35 .0 ef

230 1.35 g 577 1 37.6 fg

240 1 .33 fg 582 1 39 .3 g

4.4 e

235 1.25 f 556 f 34.5 e 3 .0 f

2.49

2.1 g

2.1 g

312 e .91e 79 .7 e 2 .5 e Sm-33 e 5.1 e

344f .86 ef 91 .8 f 2.0 fg SI-75 f 4.3 f

349 f .71 f 94.8 f 1.8 g SI-78 f 3.7 g

352f .86 ef 87.9 f 2.3 ef SI-63 f 4.1 g

365 f .66 f 94 .0f 1.9 fg SI-92 f 3.6 g

Live Weaning weight, kg Feedlot avg daily gain, kg Slaughter weight, kg Scrotal circumference, cm Live masculinityC Carcass Hot carcass weight, kg Adj . fat thickness (12th rib). cm Longissimus area, cm USDA Yield grooe Marbling score Masculinity scored

~ray et al. (12) . . bST =steers castrated at 5 mo and implanted from birth to slaughter; BI-BS = bulls implanted from birth to slaughter; BI -BW = bulls implanted from birth to wean ing; BI-WS = bulls implanted from weaning to slaughter; NIB = nonimplanted bulls. cScores of 1 to 5: 1 = very masculine and bully, 5 = steer. drccores based on evaluation of pizzle eye, jump muscle and crest; 1 = very prominent, 5 = barely evident. e gMeans in the same row that do not have a common superscript letter differ (P .... .05).

IMPLANTING BULLS WITH lERANOL Performance results comparing young bulls initially implanted prior to 3 mo of age and sequentially through slaughter are mixed. Increased (5, 14, 19), similar (4) or decreased (23) daily gains have been reported . However, all studies (4, 5, 14, 19, 23) have shown reduced scrotal circumferences, testicle weights and (or) secondary sex characteristics. Early initial implanting also reduced aggressive behavior measured by Ryder scores (a method of assessing riding activity, 19) and mounting activity (5). Carcass Traits_ Experiment 1. Fat thickness was greater (P ...... 05) for ST than for BI-BW and NIB, while BI-BS and BI-BW were intermediate and tended (P~.08) to be greater than NIB (table 1). Carcass weights and longissimus areas were similar (P~.1 0) among bull treatments, but ST had lighter (P ...... 05) carcass weights and smaller (P~.05) longissimus areas than any bull treatment. Implanted steers had higher (P ...... 05) yield grade numbers than any bull treatment except BI-WS. Marbling scores and USDA quality grades were similar (P~.1 0) among bull treatments, but ST had (P ...... 05) the most marbling and the highest quality grades. Overall carcass masculinity scores revealed that BI-BS were less masculine (P ...... 05) than the other bull treatments, and ST were the least masculine . Experiment 2. Hot carcass weights were similar (P~.1 0) for liB and NIB (table 2) . All measures of increased carcass fatness (marbling score, adjusted fat thickness and yield grade) were greater (P ..... .05) for liB than NIB. Indicators of carcass muscle and masculinity (ribeye area, jump muscle and crest) followed similar developmental patterns. For these traits, liB and NIB had similar (P~.1 0) means at 12.0 mo, NIB had greater (P~.05) means at 13.8 mo, and liB and NIB had similar (P~.1 0) means later in the feeding period at 15.7 and 17.4 mo of age. These data suggest that muscle growth and maturation of young bulls is delayed by implanting with zeranol from birth to slaughter, with NIB reaching a muscle and masculinity development plateau by 13.8 mo, and liB reaching their development plateau by 15.7 mo of age. Associated with masculinity development, forehead sample (400 cm 2 ) hide weights and dermis layer thicknesses were less (P ...... 05) for liB than NIB. As a result, implanting bulls from birth to slaughter may reduce the frequently cited carcass masculinity and hide curing and skinning problems of young bulls. Other Studies. Most studies with bulls initially implanted after weaning have shown minimal effects on carcass·traits(9, 15,17,18,20,27,28). Measures of carcass fatness were increased (28) or similar (9, 15, 17, 18, 20, 27) for bulls implanted after 6 months of age, compared with nonimplanted control bulls. Marbling scores were depressed (27) or similar (9, 15, 17, 28)

27

for bulls implanted later in life compared with non implanted bulls. Bulls implanted with zeranol continuously beginning early in life (near birth) had increased carcass fatness and(or) marbling scores (4, 5, 14, 23). Calkins et al. (4) found that implanting young bulls early and throughout life made them similar to steers in fatness. Palatability Experiment 1. Longissimus (ribeye) steaks were evaluated by both a trained sensory panel and a takehome consumer panel (table 3). Neither panel was able to detect differences in flavor due to treatment (P~ .05). The trained sensory panel found steaks from ST to be more juicy (P~.05) than steaks from all bull groups. The consumer panel found steaks from ST to be more juicy (P ..... .05) than steaks from BI-BW, BI-WS and NIB, but have similar (P ...... 10) juiciness scores to steaks from BIBS. Both panels found all measures of steak tenderness and acceptability to be similar (P~ .05) for ST and BI-BS. However, steaks from ST were superior (P~.05) to steaks from BI-BW, BI-WS and NIB for all indicators of tenderness and acceptability . The trained sensory panel found steaks from BI-BS to be more tender (P~.05) than steaks from BI-BW and BI-WS and tended (P~.07) to be more tender than steaks from NIB. The consumer panel found steaks from BI-BS to be (P~.05) more tender and acceptable than steaks from BI-WS and NIB. Experiment 2. Longissimus (ribeye) steaks were evaluated by a trained sensory panel and for muscle colTABLE 2. PERFORMANCE AND CARCASS TRAITS OF ZERANOLIMPLANTED AND NONIMPLANTED BULLS FED TO FOUR SLAUGHTER AGES (EXPERIMENT 2)a Treatment Trait No. of Bulls Feedlot Performance Initial weight, kg Initial scrotal circumference, cm Final weight, kg Final scrotal Circumference, cm Average daily gain, kg Feed: Gain ratio Carcass Hot carcass wI., kg Adj. fat th ickness, cm Ribeye area, cm Yield grade Marbling score

Implant

Nonimplant

36

36

215 17.7 b 540 33.4 d 1.56 5.55

220 25.7 c 545 38 .6 e 1.53 5.66

326 .50 b 86 .2 f 1.gb Slight-54 b

331 .35 c 90 .gg 1.5 c Slight-23 c

aGray et al. (13); Unruh et al. (24, 25); unpublished data. bCMeans in the same row that do not have a common superscript letter differ (P ..... 05) deTreatment x age interaction (P ..... 05), implanted bulls, compared with nonimplanted bulls, had smaller (p~.05) scrotal circumferences at 12.0, 13.8 and 15.7 mo of age, but similar (P".10) scrotal cir~umference at 17.4 mo of age . gTreatment x age interaction (P ..... 05) at 13.8 mo of age, zeranolimplanted bulls had (P ..... 05) smaller ribeye areas than nonimplanted bulls.

28

UNRUH

lagen (table 4). The trained sensory panel did not detect differences (P~.1 0) in flavor intensity and juiciness for liB and NIB steaks. Treatment x slaughter age interactions for myofibrillar and overall tenderness indicated that liB bulls at 12.0 and 13.8 mo were more tender (P ...... 05) than NIB bulls at 13.8 and 17.4 mo. The trained sensory panel also detected less (P ...... 05) connective tissue in steaks from ZIB than NIB. In agreement, steaks from liB had less (P ...... 05) insoluble (mature) and total collagen than NIB. Further investigation indicated than NIB synthesized more collagen early in the feeding period, and mature collagen accumulated at a faster rate than ZIB. These events appear to be linked to zeranol delaying the hormonal effects associated with puberty and maturation of the bull. Other Studies. Other sensory panels found no significant differences in palatability traits between bulls implanted after weaning and non implanted bulls (16, 17, 18, 28). However, bulls implanted initially near birth and continued through slaughter had improved palatability traits compared with nonimplanted bulls. Greathouse et al. (14) found steaks from bulls implanted from soon after birth to slaughter had greater flavor intensity, less detectable connective tissue and greater tenderness scores . Calkins et al. (4) reported that steaks from bulls implanted with zeranol beginning at 9 wk and continuing until slaughter were more juicy than non implanted bulls. However, their tenderness scores, total collagen and percentage collagen were similar for zeranol-implanted bulls, nonimplanted bulls and zeranol-implanted steers. They concluded that the accelerated production system used in their study and slaughter at a young age (13 to 14 mol was sufficient to ensure adequate palatability for both bulls and steers. Discussion Initial Implant Age. Implanting bulls with zeranol has been proposed to either supplement the bull's natural

compliment of sex steroids or delay pubertal maturation resulting in depressed steroid synthesis from the testis. A major factor which appears to influence the bull's steroid balance is the age of initial implanting and the subsequent implanting scheduling of zeranol. Data in experiment 1 (12, 26) indicated that implanting bulls from near birth and sequentially through slaughter was the only effective implanting program that maintained performance near that of the non implanted bull, yet improved palatability and consumer acceptance to a level near that of the steer. To investigate the influence of initial implanting age, Silcox et al. (22) began implanting young bulls at ages of 100, 1 50, 200 and 250 d. Each bull implant treatment group was implanted 4 times during a 235 d trial and compared to a non implanted group of similar age. leranol treatments beginning at 1 00 and 1 50 d of age decreased scrotal circumference, paired testis weight, epididymis growth, sperm production, seminiferous tubulediameter and serum testosterone levels. leranol treatment beginning at 200 d of age reduced only paired testis weight, seminiferous tubule diameter and serum testosternone levels. Implantation beginning at 250 d of age did not affect any reproductive trait measured. Results from this study, indicated that implantation beginning prior to 5 to 7 mo of age will suppress development of testes growth and function. This period of time (5 to 7 mo of age) also is considered critical in the pubertal maturation of the hypothalamic-hypophyseal-gonadal axis of bulls (1). Therefore, zeranol may provide its primary influence on the bull through the suppression of the episodic release of luteninizing hormone (7), delay testicular development and decrease gonadal hormone secretion (13). Both Gray et al. (Figure 1 ; 13) and Staigmiller et al. (23) reported decreased serum testosterone levels early in the feeding period for bulls implanted from near birth to slaughter compared with nonimplanted bulls. However,

TABLE 3. TRAINED SENSORY PANEL AND TAKE-HOME CONSUMER PANEL TRAITS OF LONGISSIMUS (RIBEYE) STEAKS FROM ZERANOLIMPLANTED BULLS AND STEERS (EXPERIMENT 1)a Treatment b ST

BI-BS

BI-BW

BI-WS

CB

Trained Sensory Panel Flavor c Juiciness c Connective-tissue amountC Myofilbriller tenderness c Overall tenderness c

6.2 6.3 e 7 .0 e 6.5 e 6.7 e

6.1 5 .91 6.8 el 6.3 el 6.5 el

6.0 5.9 1 6.6 1g 5.8 g 6 .0g

5.9 5.8 1 6.4g 5.7 g 5.9 g

5 .9 5.7 1 6.6 1g 5 .9 1g 6.01g

Take-Home Consumer Panel Flavord Juiciness d Tenderness d Overall acceptabilityd

6.9 6.g e 7.0 e 7.1e

6.6 6.6 el 6.8 el 6.7 el

6.6 6.2 1 6.2 1g 6.2 1g

6.2 6.1f 6.0 g 6.1 g

6.5 6.41 6.1 g 6 .31g

Trait

aUnruh et al. (26). bSee footnotes to table 1 lor explanation of treat groups. cScores 01 1 to 8: 5=slightly intense, slightly juicy, slight or tender; 6 = moderately intense, moderately juicy, traces or moderately tender; 7 = very intense, very juicy, practically none or very tender. drccores of 1 to 8 = 1 =Ieast prelerred; 8=most prelerred. e gMeans n the same that do not have a common superscript letter differ (P~.05).

IMPLANTING BULLS WITH ZERANOL '0

IMPLANT CONTROL

0

SE

------l

•

-.

.

~ 6

!

!

TABLE 4.

f f

~

a

~

~

4

2

,.....,..I

I

I '0

I I

i

f ,.,

12

Alii

1

If '6

( •• )

Figure 1. Serum Testosterone Levels at Different Ages of ZeranolImplanted and Nonimplanted (Control) Bulls (Experiment 2) . Gray et al. (13) .

differences in these studies were not observed past 13.0 and 12.3 mo of age, respectively . Decreases in scrotal circumference, testis weight and/or secondary sex characteristics (4, 5, 12, 13, 14, 19, 22) also indicate that zeranol delays the sexual development and maturation of young bulls. Potential Benefits. By delaying maturation of the young bulls, undesirable traits cited most often by producers and packers for excluding young bulls from production system may be reduced. Initial implanting of bulls with zeranol soon after birth through 3 mo of age and continued sequentially through life has resulted in improved behavioral (19, 24), carcass quality (4, 5, 22, 24) and palatability traits (14,25,26). With the superior rate of gain and leaner carcasses of bulls, compared with steers, thought to be dependent upon testicular testosterone (10, 11), bulls implanted from soon after birth sequentially until slaughter may have slight decreases in performance and fatter carcasses (12, 22) than non implanted bulls. However, the anabolic effect of zeranol, no castration setback, and small supplemental levels of testosterone, may result in performance superior to the steer (12) and comparable with the nonimplanted bull (13). Experiment 1 (26) indicated that palatability benefits from implanting bulls with zeranol are realized only when bulls are implanted from soon after birth and continued through to slaughter, and is the only effective zeranol implanting program that improves palatability traits to a level similar to steers. Coupled with other cited benefits of decreased masculinity (12, 24), decreased behavioral problems (19, 24), higher marbling scores and quality grades (4, 24) and slightly varied, but usually similar, performance (4, 12, 14, 24), to that of nonimplanted bulls, makes implanting young bulls with zeranol from birth to slaughter an attractive beef production alternative. Results from experiment 2 (24) indicated that largeframed bulls implanted with zeranol could be used in some consumer preferred lean-beef production systems by allowing feeding of young bulls to 14 mo (as opposed to 1 2 mo for nonimplanting bulls) before behavioral disad-

29

TRAINED SENSORY PANEL TRAITS AND MUSCLE COLLAGEN OF LONGISSIMUS (RIBEYE) STEAKS FROM ZERANOL-IMPLANTED AND NONIMPLANTED BULLS FED TO FOUR SLAUGHTER AGES (EXPERIMENT 2)a

Trait

Implant

Nonimplant

Flavorb Juiciness b Connective-tissue amo~ntb Myofibrillar tenderness Overall tenderness b Muscle collagen, mgig

6.2 6.4 6.6 c 6.2e 6.3 e 3.75 c

6.2 6.3 d 6.3 5.8 f 5.9 f 4.32 d

aUnruh et al. (25); unpublished data. bScores of 1 to 8: 5=slightly intense, slightly juicy, slight or slightly tender; 6=moderately intense, moderately juicy, traces or moderately tender; 7=very intense, very juicy, practically none or very tender. cd Means in the same row that do not have a common superscript letter differ (P ..... 05). efTreatment x age interaction (P .... .05), steaks from zeranol-implanted bulls at 12.0 and 13 .8 mo were more tender (P ..... 05) than non implanted bulls at 13.8 mo and 17.4 mo of age.

vantages and increased carcass masculinity become apparent, and by improving carcass desirability. However, with beef packers' current desire to slaughter cattle at optimum weights, lifelong implanting of small-framed bulls with zeranol may provide the greatest benefits by allowing for increased performance and heavier, more desirable carcass weights than their small-framed steer counterparts. In addition, implanting would retard masculinity and behavioral development and improve carcass quality and palatability compared with nonimplanted bulls. Management Practices. The production tool of implanting young bulls with zeranol must be incorporated with sound management practices. A North Central Regional Research Committee (6) has provided sound recommendations for feeding young bulls for meat production. Most of the studies reported in this manuscript incorporated many of these practices. They include the following: 1. Indentify markets before feeding young bulls for slaughter. 2. Select slaughter endpoints based on cattle type (or frame size) and market conditions. 3. Creep-feed bull calves when an early weaning program is followed or when economically feasible. 4. Under normal production conditions, wean bull calves at 6 to 7 mo of age and not later than 9 mo of age. 5. After weaning, condition calves for 3 to 4 weeks and then start them on a feeding program. 6. Minimize fighting and social order disruption by not mixing with other calves after the feeding phase has began. 7. Feed a high energy diet for maximum growth to capitalize on their growth and feed efficiency advantage. The high energy diet should contain 80 to 90% concentrate and be fed shortly after weaning until slaughter to achieve maximum weight gain. 8. Avoid co-mingling bulls with other cattle at any time, especially just before slaughter.

30

UNRUH

9.

Avoid unnecessary excitement of bulls when handling and transporting them. 10. Avoid transporting during fluctuating weather conditions. 11. Use transportation and handling facilities that minimize stress and provide protection. 12. Minimize transit time and deliver bulls within a few hours before slaughter. 13. Use appropriate postmortem techniques such as electrical stimulation, blade tenderization, steak restructuring, aging and vaccuum-packaging to improve consumer acceptability. 14. Cook meat from young bulls to a moderate endpoint temperature of 145 to 155 F, using a moderately slow-cooking rate . If zeranol is used as a production tool to increase product acceptability, producers also should: 1. Initially implant bulls from soon after birth (less than three mo of age) and reimplant at intervals (less than 1 00 days) to substantially delay masculinity and maturation . . Observe the lega! withdrawal period. qo not 2. reimplant within 65 d of slaughter. 3. Do not implant young bulls that will potentially be used as breeding stock. 4. Realize that manufacturers of zeranol have not petitioned the Food and Drug Administration for approval of its use in bulls because it causes delays in maturation, fertility and secondary sex characteristics.

9. 10. 11

12.

13. 14.

15. 16.

17 .

18. 19 20.

21.

Literature Cited 22. 1. 2. 3.

4. 5. 6.

7. 8.

Amann, R. P. and B. D. Schanbacher. 1983. J. Anim . Sci. 57:(Suppl. 2):380-403 . Baker, A. M. and H. W. Gonyou. 1986. J . Animal Sci. 62:1224-1232. Brethour, J. R. 1982. Proc. U.S. Beef Symp.: Beef from Young Intact Males. Kansas State Univ., Manhattan. pp 41-48. Calkins, C . R., D. C. Clanton, T. J . Berg and J. E. Kinder. 1986. J. Anim. Sci. 62:625-631 Corah, L. R., L. Fink, G. H. Kiracofe and M. McKee. 1979. J. Anim. Sci. 49(Suppl. 1 ):287. Dikeman, M. E., H. R. Cross, J. D. Crouse, M. P. Hoffman and F. K. McKeith. 1985. Kansas Agr. Exp. Sta. Bull. 648:1-12, Kansas State Univ., Manhattan. Fabry, J. and R. Renaville, 1984. J. Anim. Sci. 59(Suppl. 1):318. Field, R. A. 1971. J. Anim. Sci. 32:849-858.

23 .

24. 25. 26.

27.

28.

Ford, J. J. and K. E Gregory. 1983. J. Anim. Sci. 57:286-291. Galbraith, H., D. G. Dempster and T. B. Miller. 1978. Anim. Prod. 26:339-342. Gortsema. S. A.. J. A. Jacobs, R. G. Sasser, T. L. Gregory and A. C. Bull. 1974. J . Anim . Sci. 39:680-686. Gray, D. G., J . A. Unruh, M. E Dikeman and L. R. Corah. 1984. Kansas Agr. Exp. Sta. Rep . of Prog. 448:14-1 6. Gray, D. G., J. A. Unruh, M. E Dikeman and J. S. Stevenson. 1986. J. Anim. Sci. 63:747-756. Greathouse, J. R .• M. C. Hunt, M. E. Dikeman, L. A. Corah, C. L. Kastner and D. H. Kropf. 1983. J. Anim_ ScL 57:355-363. Gregory, K. E. and J. J. Ford. 1983. J. Anim. Sci. 56 :771-780. Gregory. K. E, S. C. Seideman and J. J. Ford. 1983. J. Anim. Sci. 56:781-786 . Johnson, D. D., J. W. Savell, G. C. Smith, D. R. Gill, D. E. Williams, L. E. Walters and J. J. Martin. 1984. J. Anim. Sci. 58 :920-925 . Johnson. A. C., D. H. Gee, W. J. Costello and C. W. Carlson. 1986. J. Anim . Sci. 62 :399-406 . McKenzie, J. A. 1983. New Zealand J. Exp. Agr. 11 :225-230. Price, M. A., M. Makarechian, T. Tennessen and G. W. Mathison. 1983. Can. J. Anim. Sci. 63:803-809 . Seideman, S. C., H. R. Cross, A. A. Oltjen and B. D. Schanbacher. 1982 . J. Anim. Sci. 55:826-840. Silcox, R. W., J. T. Keeton and B. H. Johnson. 1986. J . Anim. Sci. 63:358-368. Staigmiller, R. B., R. M. Brownson, R. J. Kartchner and J. H. Williams. 1985. J. Anim. Sci. 60:342-351. Unruh, J. A., D. G. Gray and M. E. Dikeman. 1986. J. Amim. Sci. 62:279-289. Unruh. J. A., D. G. Gray and M. E. Dikeman. 1986. J. Anim. Sci. 62:388-398. Unruh, J. A., C. D. Pelton, D. G. Gray. M. E. Dikeman, D. M. Allen and L. R. Corah. 1987 . J. Anim. Sci. 64:(ln Press). Vanderwert, W., L. L. Berger, F. K. McKeith, A. M. Baker, H. W. Gonyou and P. J. Bechtel. 1985. J. Anim. Sci. 61 :31 0-319. Vanderwert, W., L. L. Berger, F. K. McKeith, R. D. Shanks and P. J. Bechtel. 1985. J. Anim. Sci. 61 :537-545.