Evaluation of the effects of reducing crude protein content and supplementing with crystalline amino acids on growth performance and litter quality in turkey

Dietary factors contribute to ammonia emission and amount of nitrogen in the excreta. The excretion of nitrogen originating from dietary protein is largely responsible for some of the environmental issues associated with poultry production. Protein is essential as the very building block of the animal itself and hence protein nutrition takes a centre stage in poultry feeding. The use of dietary crude protein with crystalline amino acids as a means to decrease the impact on the environment of intensive poultry production is consequently of importance. Two experiments were carried out to investigate the effect of dietary manipulation using four different concentration of protein with and without amino acid supplementation on turkey performance, litter quality and nutrient utilization. The birds were raised in an environmentally controlled house and lighting procedure followed was the recommendation for the turkey breed. In the first study, the aim was to investigate the effect of dietary manipulation using four different concentrations of crude protein. One-hundred and twenty 7-day old BUT 10 turkeys were allocated to 4 treatments in a randomised complete block design. Each treatment had 6 replicate pens with 5 birds per replicate pen. The treatments were a diet adequate in protein and amino acids (diet 1) according to the breed specification and three other diets (diets 2, 3 and 4) formulated to have stepwise reduction of at least 1.4% protein from the previous diet such that the last diet had approximately 4% lower protein level than the first diet. The diets were fed in four phases of four weeks each (except the first phase that lasted 3 weeks). The highest protein levels were 28.8, 25.9, 21.7, and 18.5% and the lowest protein levels were 24.5, 21.0, 18.2 and 15.0%, respectively for phases 1, 2, 3 and 4. The diets were supplemented with appropriate crystalline amino acids that were present in the diet at lower than the requirement for the specific phase in each of the diets. The diets were formulated on digestible amino acid basis. Growth performance data were collected at the end of each phase. Overall there were no significant effects of diet on daily weight gain, feed intake or gain: feed. The final body weight was not influenced by the dietary treatments. The data from this experiment showed that supplementing a low-protein diet with crystalline amino acid produced weight gain similar to that of birds receiving adequate intact protein in their diets and support a superior efficiency of protein utilisation for weight gain. The second study was designed to investigate the nutrient utilisation response of turkey to reducing the dietary protein supply by soybean meal and supplementing with amino acids. A total of 96 seven-day old male turkeys (B.U.T.10) were used for the study. On day 7, the birds were allocated to four dietary treatments in a randomized complete block design using initial body weight as the blocking criterion to ensure equal body weight in all the treatments at the start of the experiment. Each treatment had 6 replicate cages with 4 birds per replicate cage. Body weight and feed intake data were collected at the end of week 3 to compute growth performance responses. Ileal digesta were collected on day 21 and excreta were collected the last three days of the study. There were no effects of dietary treatments on ileal nutrient digestibility of any of the treatments. Although, N excretion was lower (P < 0.05) in the lower-CP diets, the excretion as a proportion of intake was not. However, the dietary CP manipulation influenced (P < 0.05) energy metabolizability. It can be concluded from both experiments that it is possible to use reduced protein levels in diets formulated to have similar digestible amino acid content without affecting growth performance. The reduction in dietary protein can reduce the moisture content in excreta and consequently improve litter quality