Effect of Different Levels of Vitamin Premix Reduction or Removal During Finisher Period on Immunocompetence of Broiler Chickens
Three experiments were conducted to compare the effect of a decreasing vitamin premix amount in diets from 29 to 42 days of age on performance and immunocompetence of broiler chickens in floor (experiments 1 and 2) and battery cage (experiment 3) systems. The diets were based on corn/soybean meal (experiment 1) and wheat/barley (experiments 2 and 3). On day 34, two birds from each replicate were selected and antibody responses to inoculated sheep red blood cells were determined. The results of experiments 1 and 2 showed that vitamin premix reduction/withdrawal at 29 days of age did not impair performance during the final rearing period. However, the results of experiment 3 showed that from 29 to 42 days of age, performance of birds fed the diet without vitamin premix (T1) was significantly lower than other treatments. The results of three experiments demonstrated that immunocompetence response was not affected by treatments in the finisher period. In conclusion, the results of the present study indicated that in the battery cage system it is possible to reduce dietary vitamin premix during the finisher period but withdrawal can negatively affect performance of broilers. While in the floor system it is possible to withdraw vitamin supplements from finisher diets.