Abstract

A computer simulation model was developed to explore how new reproductive technologies could improve beef productivity through embryo transfer (ET), sex ratio control and use of small cow breeds pregnant to `high growth rate` calf genetics. Assumptions were made about conception rates, embryo losses, sex ratios, cow and calf survival, animal weights, and the feed requirements of small and large cows rearing large calves. A range of pregnancy rates from ET (40 to 67%) were assumed compared to natural mating (67%) and it was also assumed that a small cow breed, such as a Jersey, could rear calves to similar weights of those from Hereford x Friesian (H x F) cows. Cow efficiency values were derived as the estimated intake of metabolisable energy by the cow plus calf unit per year per kg of calf weaning weight. The model was based on averages with variance information from fieldwork used for @Risk analyses. In the model, H x F cows subjected to the new technologies such as ET (involving synchronised calving) and sex ratio control were up to 9% more efficient than the `status quo` mating system. Using a small cow, however, gave gains in efficiency of up to 20%. These benefits were highly dependent on the assumptions used, in particular ET pregnancy rate and cow and calf losses at calving, all of which, singly or together, above threshold values, could destroy the gains or even create losses in efficiency.

DC, Smeaton

Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 112-115, 2001