MANAGING HERD COMPOSITION OF RANGE CATTLE: SALE WEIGHT AND SEASONAL FACTORS

We estimate the weight gain for range calves as a polynomial function of calf age accounting for weather, sex, lagged calf weights relative to the growth function, and compensatory gains. Birth weights plus single day weighings that occurred around 3, 8, 12, and 20 months of age are the data used to estimate our 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, we evaluate the profitability of feeding supplement by increasing the rate of gain associated with our growth function when forage and nutrients are limiting for the two grazing environments of Southeast and Central Arizona. Using prices from 1980 to 1998, results indicate that the most profitable herd mix, sale date, and feeding protocol is 450 lb. calf sales with no supplemental feeding and sales occurring in May for both regions. Although, feeding supplement was not associated with the most profitable outcome, supplement increased the average return by $45 to $70 per AUY for sale weights of 550, 650, and 750 lbs.