The relevant point to consider is the reduction in revenue per pound. The key performance variables that would translate into a financial effect would be ADG, mortality, FCR, treatment costs, and percent cull pigs. It may be valuable to necropsy pigs that die and record a reason for death on a mortality form for the vaccinated and placebo groups. After the last group is closed out, the data should be analyzed using valid statistical methods. Other statistical analysis techniques may be preferred, depending on the nature of the study, the particular variable being examined, and the number of treatment groups in the study.
Bad information leads to bad decisions.
The purpose of an on-farm trial is to yield objective information about the potential for improved profitability as the result of using a particular product. Neither do you want to not use a product that does. The goal of a properly conducted trial is to help you tell the difference.