Effects Of Vitamin A On Growth Performance And Nutrient Digestibility And Metabolism Of Calcium And Phosphorous In Broilers

The present study was conducted to investigate the effects of vitamin A(VA)on growth performance, nutrient digestibility and metabolism of calcium(Ca) and phosphorus(P) in broilers. A total of 450 1-day-old AA mixed-sex broilers with similar body weight were randomly allotted into 5 treatments with 6 replicates in each treatment, with 15 broilers in each replicate. The trial period was 42d. The basal diet was mainly composed of corn and soybean. Broilers were fed five levels of dietary VA (3000, 6000, 15000, 30000 and 60000 IU/kg) in a single factorial arrangement.Under the present experimental conditions, the results showed as follows:1. Excess VA would result in decreases in growth performance. The growth rates and feed conversion efficiency would tend to decrease(p<0.10) for broilers fed the diets containing VA 30000 and 60000 IU/kg individually.2. While the dietary VA was excess ,crude protein and calcium digestibility were decreased. The dietary crude protein digestibility tended to decrease in a linear dose-dependent manner(P<0.10) and the dietary Ca digestibility decreased in a linear dose-dependent manner(P<0.05)with the supplementation of VA in diet of broilers. The supplementation of 3000～6000IU/kg VA was higher in digestibility, while the supplementation of 30000～60000IU/kg VA was lower in digestibility.3. There was an obvious influence of excess VA on bone growth and strength. While the dietary VA levels were increased from 3000IU/kg to 60000IU/kg, serum Ca and P concentrations were decreased in a significant linear dose-dependent manner (P<0.05), and Ca concentrations in tibia and mineral density(BMD) and tibia ash were decreased in quadratic dose-dependent manner(P<0.05), and P concentration in tibia was increased in quadratic dose-dependent manner (P<0.01), and serum AKP activity had the tendency to be decreased.4. While dietary VA levels were 30000 and 60000 IU/kg, serum AKP activity was significantly decreased(P<0.05). While dietary VA level was 60000 IU/kg, BMD and Ca concentration in tibia were significantly decreased (P<0.05), and tibia ash had the tendency to be decreased (P<0.10). While dietary VA levels were increased from 15000 to 30000 IU/kg, the indexes above were also decreased slightly.5. The diets containing VA 30000 and 60000IU/kg individually would result in significant increases in VA concentrations in liver, kidney and serum(P<0.05).While dietary VA level was 15000 IU/kg, VA concentration in liver was significantly increased, and VA concentrations in serum and kidney also had a tendency to be increased.6. While dietary VA levels were increased from 15000 IU/kg to 60000IU/kg, VE concentrations in serum were significantly decreased(P<0.05), but VA concentrations in liver was increased(P<0.05), especially for the 30000 and 60000IU/kg VA levels.7. In conclusion, the addition of 3000 to 6000 IU/kg VA would be appropriate for broilers considering of the growth performance, and the addition of 15000 IU/kg VA would probably be excessive for broilers, and he addition of 30000 to 60000 IU/kg VA would be excessive for broilers.