Evaluation of dietary nucleotides for broilers
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Nucleotides are the basic units that make up nucleic acids, such as deoxyribonucleic acd (DNA) and ribonucleic acid (RNA). Nucleotides are involved in many biological processes. They are important in nucleic acids (e.g. DNAs and RNAs) synthesis and as a source of cellular energy. They affect the immune system and are involved in physiological and morphological changes in small intestinal development. Nucleotides are not considered an essential nutrient because they can be synthesized by a de novo pathway from amino acid precursors and recycled through a salvage pathway. However, these mechanisms may not always be adequate to supply nucleotides for an organism during times of stress. Stressors which may impact nucleotide requirements include high stocking density, unsanitary conditions, disease challenges, and recovery from injuries. A series of experiments were conducted to determine the effect of the dietary nucleotides on the performance and development of the gastrointestinal tract (GIT) of broilers under certain stress conditions. In the first experiment, Torula yeast RNA (as a source of dietary nucleotide supplementation) and a commercial nucleotide product (Nupro®) were fed to broilers raised under normal conditions and environmental stressed conditions; previously used litter. Body weight gain, feed intake, feed conversion ratios, mortality, and physical and morphological development of the gastrointestinal tract were measured. Supplementing the diet with dietary nucleotides had no effect on performance of broilers under normal conditions; however, dietary nucleotide supplementation improved performance of birds reared in previously used litter. In the second experiment, the effect of Torula yeast RNA supplementation on performance, intestinal tract development and morphology of broilers challenged with a high-dose Coccivac-B® vaccine and reared in an increased stocking density were determined. Supplementing the diets with Torula yeast RNA had improved performance of birds challenged with a high-dose Coccivac-B® vaccine and reared in the increased stocking density conditions. In the third experiment, two dietary nucleotides (Torula yeast RNA and Nupro®) and a nucleotide precursor (glutamine) were fed to broilers challenged with Coccivac-B® vaccine. Broiler performance and nutrient utilization (nitrogen corrected apparent metabolizable energy; AMEN) were measured. Dietary nucleotide (0.25% Torula yeast RNA and 2% Nupro®) supplementation was effective at alleviating the negative effects of Coccidiosis vaccine challenge. The increased AMEN value of diets with supplemental levels of Torula yeast RNA and Nupro® resulted in increased growth performance. However, the supplementation of a nucleotide precursor, glutamine, did not replace nucleotides in broilers. In the fourth experiment, Torula yeast RNA was added to semi-purified diets containg high levels of casein or crystalline amino acids mixture of broilers challenged with Coccivac-B® vaccine. Performance and relative weight, morphology, and gross lesion score in small intestine of birds were measured. Birds fed semi-purified diets containing high levels of casein or crystalline amino acids mixture had very low feed intake and slow growth rate. The 25 × dose Coccivac-B® challenge did not affect performance and the supplementation of 0.25% Torula yeast RNA to the semi-purified diets had no an effect on the performance of birds. Thus, nucleotides do not appear to be an essential nutrient without sufficient stress conditions. Overall, nucleotides are not an essential nutrient under normal conditions. However, the dietary nucleotide supplementation may be important to maintain maximum growth and performance when birds are exposed to stress conditions.