Beef cows in New Zealand are traditionally calved in late winter so that calves will be as big as possible for the weaner sales. This can create spring pasture supply problems and may contribute to poor reproductive performance in many beef herds. Early (11 August) and late (25 September) calving have been compared in 2 trials run on steep hill country. Comparisons were made in self- contained farmlets between June and February under 2 grazing strategies (set-stocking and rotational grazing). Later calving reduced interval to first oestrus by 16 d in both trials and increased pregnancy rates by 4 to 6%. Late born calves grew at the same rate as early born calves in both trials (0.87 and 0.97 kg/d) and so were lighter at weaning at a fixed date. A rotational grazing strategy favoured cow performance, but set-stocking favoured calf weaning weight by 12 kg and 5 kg in the 2 trials. Later calving is likely to result in better reproductive performance in many hill country beef herds, but because calves will be lighter as weaners it would best suit systems where steers are currently retained and finished over 2 years or sold as store cattle at 18 months. The 18 month finishing policy will require earlier calving to maximise steer weight at sale time.

WJ, Parker, and RJ Townsley

Proceedings of the New Zealand Society of Animal Production, Volume 46, , 133-138, 1986
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