Zeranol and fattening bulls

Authors: McKenzie JR
Publication: New Zealand Veterinary Journal, Volume 31, Issue 6, pp 104-105, Jun 1983
Publisher: Taylor and Francis

Animal type: Cattle, Livestock, Production animal, Ruminant
Subject Terms: Animal remedies/veterinary medicines, Behaviour, Growth/development, Treatment/therapy, Reproduction, Reproduction - male
Article class: Correspondence

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Abstract: It is well documented in the literature that bulls grow 10-20% faster and have a higher efficiency of feed conversion than steers. New Zealand`s beef production could well be increased markedly if more dairy and traditional beef calves are fattened as bulls. The secondary sex characteristics (behaviour problems) of bulls fattened is one of the main reasons why bull beef production is not practised extensively. Under feedlot conditions, zeranol (marketed under trademark RALGRO) was shown to reduce riding when bulls were implanted every 100 days, from birth. Since November 1980, we have been exploring the use of zeranol in fattening bulls for improved behavioural control and increased weight gain. Ministry of Agriculture and Fisheries animal husbandry specialists have been closely involved throughout the trials. The first major trial involved 206 Friesian bull calves. At weaning (12 weeks) they were randomised into two mobs, each containing treated and untreated animals. The treated animals in one mob were to be implanted six times at 70-day intervals, while four implants were to be given 105 days apart in the other mob. Steers were also included in the latter group for comparative behavioural assessment…

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