Economics of sale weight, herd size, supplementation, and seasonal factors.

A growth function for range calves is estimated using a polynomial function of calf age that accounts for weather variation, sex, prior calf weights relative to a norm, and a compensatory gain factor. Data on rainfall plus calf weights at birth and when calves were roughly 3, 8, 12, and 20 months of age are used to estimate the growth function. This function is then used to determine the economic trade-off between herd size and calf sale weights, for both spring and fall sale dates. In addition, the profitability of feeding supplement is evaluated by increasing the rate of gain beyond that projected by the the polynomial age growth function for southeast and central Arizona grazing environments when forage and nutrients are limited. Using prices from 1980 to 1998, results indicate that the most profitable herd mix, sale date, and feeding protocol for the southeast Arizona region is 204 kg calves with no supplemental feeding and sales occurring in May. Supplemental feeding and sales occurring at 250 kg head-1 in May is the most profitable herd mix for the central Arizona region. More favorable average daily gain rates for May sales from the central versus southeast is why supplemental feeding is marginally better for the central region than feeding no supplement. DOI:10.2458/azu_jrm_v56i5_tronstad