Effects of nitrogen source and level on the performance of chicks and rats fed low and high tannin sorghum

Two experiments were conducted with chicks and one with rats to investigate the effects of feeding high tannin (HTS) and low tannin sorghum (LTS) in diets supplemented with either isolated soybean protein (ISP) or crystalline amino acids (CAA) at two levels of nitrogen. CAA were added in the same amounts provided by ISP. Within an experiment, the amount of sorghum protein was held constant for all diets, while the amount of non-sorghum nitrogen added to the higher nitrogen diet was double that of the lower nitrogen diet. At the lower level of nitrogen, HTS depressed growth rate in all experiments regardless of the nitrogen source. Increasing the dietary nitrogen as ISP overcame essentially all of the adverse effects of HTS on growth rate. In contrast, increasing nitrogen as CAA, although improving growth with both LTS and HTS diets, did not correct the growth depression caused by HTS; the differences between LTS and HTS were essentially the same at both levels of CAA supplementation. These results suggest that reduced protein digestibility is not the primary reason for the reduced growth rate observed by feeding HTS.