Liver proteolytic activity in tannic acid-fed birds.

The influence of tannic acid in the rate of growth (BWG), feed intake, protein efficiency ratio, and liver proteolytic activities (cathepsin A and D) were measured in growing male chickens. These birds were fed ad libitum over a 15-d experiment on 20% protein standard diets containing heated soybean (control, C) as the main source of protein. Tannic acid (TA; 25 g/kg diet) was added to all diets, except the control. It has been found that in comparison to control-fed birds, TA-fed birds showed a significant reduction (P < 0.01) in BWG, protein efficiency ratio, and relative weight of liver, together with a significant increase (P < 0.01) in the activities of cathepsin A and D in liver. Addition of TA to the control diet had no significant effect on feed intake. The possible nature of these results is discussed.