@conference {40125,
	title = {Optimal cow replacement on New Zealand seasonal supply dairy farms},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {48},
	year = {1988},
	month = {Jan},
	pages = {243-246},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {The use of computer models to predict the ratio of outputs to inputs can be considerable assistance in developing breeding objectives and assessing research priorities and evaluating the impact of changes in management on efficiency of production in the deer industry. Therefore we have developed a model (based on Parks (1982) which quantifies the inputs of feed and the output of carcass to calculate the biological efficiency of the hind/calf unit over the lifetime of the breeding hind. The model has been used to examine the effects of reproductive lifespan (age of culling), calving rate, twinning, changes in sex ratio and changes in calving date on efficiency. In all cases there was a peak in efficiency at 62-64 weeks of age. In terms of reproductive lifespan, the most efficient sustainable system involved slaughtering hinds after only 3 calvings, although the overall impact of this factor on efficiency was small. Changes in calving rate (proportion of hinds calving) had a marked effect with efficiency declining by 5 to 7\% for a 10\% decline in the calving rate. Twinning also had a major effect with about a 3\% change for a 10\% change in twinning rate although the higher pre-weaning mortality of twins compared with singles would markedly reduce real gains. Changes in the sex ratio also altered the efficiency of the system by 3 to 4\% per 10\% unit change in the proportion of males. In contrast, advancing the calving rate by 3 or 6 weeks did not change efficiency or live weight of progeny at the same age but did result in a 2.8\% increase in live weight at the same date for every 3 weeks advancement in calving.},
	issn = {1176-5283},
	author = {Harris BL}
}
