Growth and muscle development of steers implanted with hexoestrol

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Abstract
A muscle biopsy technique was employed in an experiment designed to assess the effects of hexoestrol implantation on 2-year-old and 6-year-old Aberdeen Angus steers under New Zealand grazing conditions. This paper reports the results concerning live-weight gains, carcass weights and detailed analyses of samples of m. semitendinosus and associated subcutaneous fat.There was some evidence of an adverse effect of the biopsy operation on the older, less tractable, animals, despite the observation of no apparent effect of repeated muscle biopsies in a preliminary trial with sheep.Hexoestrol implantation, of four 15 mg. pellets for the 2-year-old steers and six 15 mg. pellets for the 6-year-olds, led to significant increases in live weight gains during the later part of the trial only, and reduced the dressing-out percentage of the younger animals. Although there were indications of a positive response in carcass weight to hexoestrol implantation, it was concluded that, under the conditions of this experiment, implantation of relatively large dosages was not economically justified in terms of increased meat production.Absorption of the implanted pellets varied from 42 to 85% of the total dosage, but evidenced little association with live weight changes.Deposition of subcutaneous fat appeared to be reduced under the hormone treatment, but the responses in this respect of the 6-year-old steers were highly variable.