Implanting Young Bulls with Zeranol from Birth to Four Slaughter Ages: III. Growth Performance and Endocrine Aspects2

Abstract

Seventy-two Simmental bull calves were assigned randomly either to a zeranol implanted (I) or nonimplanted (NI) control group. Within 3 d after birth, bulls assigned to the I treatment were implanted with 36 mg zeranol and reimplanted every 84 d until slaughter. Calves were weaned at 7.2 mo, preconditioned for 2 wk, and assigned within treatment to slaughter ages 12.0, 13.8, 15.7 and 17.4 mo. Blood samples were taken bimonthly from 8.3 to 16.6 mo of age. Weight gains, feed:gain ratios and slaughter and carcass weights were similar (P greater than .10) for I and NI bulls for the total feeding period. Weight gains for NI bulls were larger (P less than .05) from 7.7 to 9.5 mo and from 11.3 to 12.2 mo of age, whereas gains for I bulls were greater from 12.2 to 14.1 mo. Serum estradiol-17 beta (E2) and testosterone (T) concentrations were higher (P less than .05) for NI bulls at 8.3, 9.2, 10.2, 11.1, 12.1 and 13.0 mo. However, at 13.9 and 14.8 mo, E2 concentrations were higher (P less than .10) for I bulls. A similar, but nonsignificant (P greater than .10), trend was noted for T concentrations of I bulls at 13.9 and 14.8 mo. Rapid increases in E2 concentrations were observed from 8.3 to 9.2 mo in NI bulls, but from 12.1 to 13.9 mo in I bulls. Similarly, T concentrations increased rapidly from 8.3 to 10.2 mo in NI bulls, but from 12.1 to 14.8 mo in I bulls. Peak concentrations of T and E2 for NI bulls were observed near 11 and 13 mo, respectively, whereas peak T and E2 levels were delayed in I bulls until near 14 mo. Periods of greater weight gains for both NI and I bulls corresponded to rapidly increasing E2 and T concentrations. Serum thyroxine concentrations were lower (P less than .05) for I bulls at 13.9 mo but similar to NI bulls at all other ages. Serum insulin concentrations were higher (P less than .05) for I bulls than for NI bulls at 8.3, 10.2, 11.1 and 12.1 mo. Regardless of treatment, insulin concentrations increased with increasing age. Carcasses from I bulls were fatter (P less than .05) and tended (P = .09) to have smaller ribeye areas/100 kg carcass. Fat thicknesses for both treatments increased (P less than .05) from 13.8 to 15.7 mo. Skeletal maturity scores, 9-10-11th rib bone percentages and femur measurements indicated an increased skeletal maturation in I bulls.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of incremental zeranol implant doses on the chemical and physical characteristics of third metacarpal bone and chemical composition of liver and soft tissue from feedlot steers.

“…Hot carcass weight was 318.5, 320.2, 318.9, 323.8, 319.5, and 320.3 kg for the 36, 48, 60, 72, 84, and 96 mg zeranol doses, compared with 308.0 kg for ZEFUNOL EFFECTS ON STEER BONE AND SOFT TISSUE 3 controls. Gray et al (1986) found that bulls implanted with zeranol (36 mg) had a reduced percentage of bone in the 9-10-11 rib section, whereas Fumagalli et al (1989) found no effect of zeranol on the weight or percentage of bone in the carcasses of steers.…”

“…This is in contrast to the current study in which steers implanted with 24 mg or more of zeranol had 12% smaller ( P < ,051 external AP diameters than unimplanted controls. Gray et al (1986) found that bulls implanted with zeranol had reduced femur lengths and circumference. Increasing zeranol levels in the current study reduced ( P < .08) internal (marrow cavity) AP diameter linearly.…”

Veterinary pharmacovigilance. Part 2. Veterinary pharmacovigilance in practice – the operation of a spontaneous reporting scheme in a European Union country – the UK, and schemes in other countries

“…Some of these substances, for example testosterone, zeranol, trenbolone acetate and allyl trenbolone had previously been used, some quite legally, as growth promoters or production enhancers, particularly in cattle (Patterson et al. , 1985; Baker & Gonyou, 1986; Gray et al. , 1986; Hunt et al.…”

The effect of oestrogenic agents on live-weight gain, carcass composition, reproductive function and tissue residues in intensively reared beef bulls given cereal-based diets

“…There Unruh, Dikeman and Stevenson, 1986;Silcox, , 1987b E f f e c t s o f z e r a n o 1 o n reproduction in beef bulls: , , , . The highest zeranol concentration in reduced testis weight while mean epididymis any sample from the present study was weight was the same as for controls.…”