Using a Stochastic Model to Evaluate Swine Production Management withPaylean II: Investigating Optimal Paylean Onset Time

Purdue University 2003 Swine Research Report. When to start feeding Paylean to late finishing pigs is an important decision for pig producers. Currently, producers seem to have different management strategies regarding the Paylean onset weight or age. Some producers follow the recommended strategies of feeding Paylean for four weeks before marketing, while others believe it is optimal to start RAC after the first batch of heaviest pigs is marketed. To find out the impact of Paylean onset ages on production returns, a stochastic model was employed to investigate the optimal return and management under alternative Paylean onset ages (model development is presented in Part I). In addition, swine producers face the problem of estimating the average weight of a group of pigs in order to start feeding Paylean at the right time point. The stochastic growth model implicitly assumed that producers know the exact weight of each animal, and thus make precise decisions based on this complete knowledge. This assumption can be approximately realized only with the recently invented automatic weighing/sorting system, where one or more electronic scales are equipped in a barn and animals are weighed and sorted automatically. However, in the traditional way of pig farming, producers have to rely on their experience to estimate the average weight for a group of pigs. Inevitably, the estimation made based on experience is not accurate, and the difference between the estimated weight and the true weight is referred to as the visual inspection error. It was reported that the standard deviation of visual inspection error ranged from 9 to 11 lb depending on experience (Korthals, 2000; 2001). It follows that if the Paylean onset decision is made based on the average weight of the herd, the existence of visual inspection error will lead to a deviation in Paylean starting time, which would be a few days from the desired time. To estimate the loss of non-optimal Paylean starting age induced by visual inspection error, sensitivity analysis of return with respect to non-optimal Paylean starting age was performed at days around the optimal values. Elasticities of return with respect to optimal Paylean onset age were calculated, where the elasticities portrayed a percentage change in optimal return when Paylean was administered one day off the optimal.