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Published online by Cambridge University Press: 22 November 2017
Recent reports have suggested that growth in entire male cattle (bulls) may be increased by implantation with the growth promoter zeranol. It is well known that given similar nutrition bulls grow faster than castrate male cattle (steers). This effect may be attributed to the presence of testicular steroids in bulls which stimulate lean tissue deposition and hence greater live-weight gain. A major objective of this study was to provide further information on the effects of zeranol implantation on growth and blood concentrations of endogenous hormones and metabolites. Effects on concentrations of the endogenous steroids, testosterone and oestradiol-17β were of particular interest.