The effect of tannic acid supplementation to the broiler diets containing inorganic or organic zinc on performance and digestibility

This study was conducted to investigate the effect of dietary tannic acid supplementation to broiler diets containing inorganic or organic zinc on performance (body weight, weight gain, feed intake and feed conversion ratio, vitality), carcass characteristics (hot carcass yield, relative liver weight and breast meat colour), zinc digestibility, zinc levels in serum, tibia, liver, and feather, viscosity of small intestinal contents and feather score. A total of 480 Ross 308 commercial hybrid male broiler chicks were used. The research was conducted with four experimental groups designed by 2x2 factorial arrangement (Group 1, supplementation of inorganic zinc without tannic acid; Group 2, supplementation of organic zinc without tannic acid; Group 3, supplementation of inorganic zinc with tannic acid; Group 4, supplementation of organic zinc with tannic acid). Chicks were randomly distributed into each treatment (120 to per group) with each containing 15 chicks per pen. Starter diet with 3010 Mcal/kg ME and 24% CP for 10 days, grower diet with 3175 Mcal/kg ME and 22% CP at days 11-28, and finisher diet with 3225 Mcal/kg ME and %20 CP at days 29-42 and digestion trial after day 42 were offered. Experimental diets were given ad libitum. To determine the zinc digestibility of the ration, randomly selected eight birds from each repetation of the first experimental group were weighed and were placed in individual cages thus, four treatment groups containing 16 animals were re-formed on the 42nd day of trial. Digestion trial was carried out as to include successive 12 hours pre-fasting period, 3 days feeding, and 12 hours last-fasting. Mean values of body weight, body weight gain and feed consumption at the end of the research were significantly (P<0,001) decreased by dietary addition of tannic acid but feed conversion ratio was not affected. Also, source of zinc did not show any significant effect on performance parameters. It was demonstrated that dietary tannic acid supplementation has negative impact on zinc digestibility (5.87% decrease, P<0,05) and different sources of zinc have similar digestibility levels (39.07% inorganic zinc; 37.59% organic zinc). Serum and feather zinc levels were not affected by addition of tannic acid to diets but a significant increase in tibia zinc level (P<0,001) and a significant decrease in liver zinc level (P<0.001) were observed. Dietary supplementation of organic zinc decreased serum zinc (P<0,001) and increased liver zinc (P<0,001). Zinc in tibia and feather was not affected by source of the zinc. Dietary addition of tannic acid showed negative effect on carcass yield (P<0,001) but did not affect relative liver weight and breast meat colour. Zinc source had no significant effect on carcass characteristics. It was demonstrated that the factors investigated in the present study (addition of tannic acid and different zinc source) had no significant effect on intestinal content viscosity and feather score. In respect to present data; in addition to provide nutritional requirements of birds with diet, an additional attention must be given to concentration of tannic acid in diets considering its depressive effect on broiler performance. The cost of zinc addition should be taken into consideration when will be selected according to its source, because supplementation of inorganic either organic zinc sources at the requirement level have similar digestibility values.