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Abstract
A 2 × 2 factorial design experiment investigated effects of differential planes of grazing nutrition and of implantation of 30 mg hexoestrol in 3-year-old Aberdeen Angus steers.
Hexocstrol-implanted and control animals were provided with abundant grazing for 87 days in the spring, followed by 68 days of sub-maintenance summer grazing ; ample feed was resumed in the autumn (HP-LP-HP). In contrast, other implanted and control steers had liberal grazing at all times (HP).
Attainment of a constant Final Liveweight determined the time of slaughter of each animal.
Control animals took significantly longer than implanted steers to attain the prescribed slaughter liveweight. HP steers were killed significantly earlier than HP-LP-HP animals, No interaction was evident.
Increased growth rate under hormone treatment was most apparent immediately after implantation. Growth of cattle in the summer and autumn, under either HP or HP-LP-HP management, was not affected by hormone treatment.
Dressing-out percentage, and thus carcass weight, was reduced under hexoestrol treatment and HP-LP-HP management.
Estimated carcass weight gain per day was increased by hormone implantation and reduced by HP-LP-HP management, with no interaction.