Feed costs are approximately 70% of total production cost for poultry producers. Poultry diets in the United States generally consist of 2 grains: corn and soybean meal. In recent years, the cost of these grains has dramatically increased. Due to these price increases, producers seek alternative feeds that provide adequate nutrition, and are also more affordable than "traditional" grains. Cottonseed meal is one alternative that is both affordable and an excellent source of crude protein. However, cottonseed meal contains gossypol, a pigment toxic to chickens.

This study had two main objectives. The first objective was to determine if silymarin, an extract from milk thistle, could offset or prevent gossypol toxicosis. The second objective was to determine if divergent selection for humoral immune response would have an impact on the ability of the chicken to cope with gossypol toxicosis. Two preliminary studies were conducted. One determined basal activities of liver detoxification enzymes at various ages. The other determined concentrations of gossypol and silymarin that should be added to the diet to elicit a response. The information gathered from the second preliminary study was used to conduct the final experiment.

In the final experiment, chickens from each of 2 lines selected for humoral immunity were exposed to diets containing gossypol, silymarin, gossypol and silymarin, and a control. Humoral immunity had no impact on the ability of the chicken to cope with gossypol toxicosis. Silymarin did not alleviate gossypol toxicosis. Future studies will focus on using a lower gossypol concentration in the diet.