Effect of Subcutaneous Implants of Zeranol on Weight Gains of Castrated Cattle at Pasture†

Abstract

Eight experiments involving a total of 480 castrated cattle grazing Australian pastures were conducted to assess the effect of subcutaneous implants of 36 mg zeranol on weight gain. A wide range of cattle ages, bodyweights and environmental and nutritional conditions was involved. Growth rates of untreated cattle ranged from minus 0.15 kg/day over 90 days to 1.23 kg/day over 52 days. In the other, cattle in both implanted and control groups lost weight over the duration of the experiment. Whilst the bodyweight of implanted cattle was less than that of untreated cattle the carcase weight of implanted cattle was 2.4 kg greater than for control cattle. Neither of these differences was significant (P > 0.10). No side effects were noted in any of the treated cattle.

Weight gain in steer and heifer calves treated with zeranol or oestradiol 17β

“…These results show that in suckling steers or heifers gaining weight at a rate of a least 1.0 kg/head/day, significant extra gains of 0.092 kg/day (8%) and 0.124 kg/day (11%) may be made from the use of zeranol or oestradiol 17{3 implants. The responses compare favourably with those found for zeranol by Sammons (1980), Geldard and Wellington (1981), Sully (1982) and Greathead (1984) in temperate southern Australia. In another comparative experiment Nicol et of (1984) recorded extra weight gains of 0.076 kg/day and 0.087 kg/day for zeranol and oestradiol treated calves respectively, by 92 days after implantation during drought affected conditions in south eastern Queensland.…”

“…In the present work the response did not persist beyond 35 days in either steer or heifer calves. Sammons (1980) also pointed out that the duration of response to zeranol was not clearly defined and that the main response could occur soon after implantation. Many other reports of growth promotant trials do not include details of weighings at intervals of less than 70 to 90 days and from these the period of response was not definable.…”

“…The rapid total response soon after zeranol implantation observed in this experiment and that of Greathead (1984), suggests that a further response might be obtained from additional zeranol implanted in calves growing rapidly on spring pasture prior to weaning. However, extra liveweight gain after repeat implantation in older cattle does not always occur (Sammons 1980;Roche 1980b;Sully 1982;Moran 1972). Further work is needed to determine if economic responses to re-implantation may be achieved in suckling calves prior to weaning.…”

“…Increased growth rates due to zeranol* implantation have been.~eported for most cattle breeds under a wide range of conditions by Perry et al (1970), Sharp and Dyer (1971) Moran (1972), Pryor (1973), Borger et al (1973), Bennett et ai (1974) Ralston et al (1975), Gartner and O'Rourke (1977), Shorrock et al (1978), Roche (I980a), Wood and Bonner (1982) and many .ot~ers.~eranol has.been favoured especially for use in st~ers m mtensive production systems, where, typically, weight gaIn~have been increased 10 to 15OJ~in 70 to ]00 days. Less consistent responses were observed In steers grazing pasture in Western Australia, Victoria and New South Wales where cattle were losing weight or gaining only at a low rat; (Sammons 1980). It was concluded by Wellington and Geldard (]~80) t~at providing sufficient feed.was available for average daily gains above 0.6 kg/head then Implantation with zeranol would increase the rate of gain by ]2 to 32010.…”

Isolation of Fusobacterium necrophorum from a case of bovine mastitis

“…Melb., Melbourne. In recent years reports on the influence of zeranol on the bodyweight gain of cattle and sheep have been published (Pryor 1973;Sammons 1980;Geldard and Wellington 1981). Knowledge of the effects of this anabolic agent on the bodyweight gain of Angora goats is limited.…”