With todays talk about stock efficency this article was worth a read. Most farmers are driven by increasing production but there are many ways to achieve it. Dr Alastair Nicol, a senior lecturer in animal science at Lincoln University, says in all species there is a point above which there is no benefit to reproduction in increasing bodyweight. In rising two-year-old Red hinds, for example, there is no increase in the pregnancy rate once their bodyweight hits 80kg, while in sheep there has been shown to be little increase in ovulation rate beyond 67kg. In beef cows there is no increase in the pregnancy rate beyond a bodyweight of 410kg reports Country-Wide. Nicol says the pregnancy rate in Red hinds flattens off at between 80 and 90kg bodyweight, so there is no advantage to trying to lift the bodyweight of these hinds beyond this point. Above these weights something else is limiting production, he says. The proportion of Elk genes also impacts on pregnancy rates and as soon as the proportion of elk genetics in a herd increases the probability of pregnancy drops off dramatically. "So the effect of any increase in hind liveweight on the reproductive rate must be measured to prevent any detrimental effects." Speaking about size and efficiency in breeding females at a recent deer industry focus day on North Canterbury's Mendip Hills, Nicol defined efficiency as the output divided by inputs on a per head or per hectare basis. Output is the number of offspring multiplied by the average weight in spring multiplied by the average value/kg. The biggest cost in feed is in just maintaining the breeding animal and maintenance accounts for 65% of annual feed requirements. Pregnancy only takes 6% of annual feed requirements, while lactation takes 30%. Nicol says farmers need to know the relationship between maternal liveweight and outputs, reproductive rate, offspring survival and weaning weight if they are to have a handle on the efficiency of their animals. Offspring survival is a function of the ratio of birthweight to maternal weight and not just about straight birthweight. However, this is variable between species. In ewes and breeding cows there is quite a small optimum range, but Nicol suspects there is possibly a wider acceptable birthweight range in deer, of about 7-14% of hind bodyweight.
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