Redução da proteína bruta em dietas suplementadas ou não com nitrogênio não essencial e relações nitrogênio essencial:nitrogênio não essencial para galinhas poedeiras leves

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Two trials were performed in order to evaluate laying hen responses to reduction on dietary crude protein supply and non-essential nitrogen supplementation (Experiment I) and to determine the essential to non-essential nitrogen ratio, which warrants optimum performance, and egg quality of laying hens (Experiment II). Both trials lasted 112 days, being divided in four 28-day intervals. In experiment I, a total of 240 Hy-Line W-36 laying hens were randomly assigned to 5 treatments, eight replicates with six hens each. The treatments consisted diets containing 170g (control diet), 150 and 130g crude protein/kg, which corresponded to the essential nitrogen to non-essential nitrogen ratios of 37/63, 42/58 and 47/53, respectively. The other two treatments consisted of the same diets containing 150 and 130g crude protein/kg, but supplemented with 37.60 and 79.15g glutamic acid/kg respectively in replacement to cornstarch to equal the essential nitrogen to non-essential nitrogen ratio in control diet (37/63). Reduction on dietary crude protein by 20g/kg elicited a decrease in egg weight and egg mass, whereas the reduction on dietary crude protein by 40g/kg decreased feed intake, egg weight, egg mass and albumen weight, beyond worsening feed conversion ratio per kilogram of eggs. Layers fed diets with 150 and 130g crude protein/kg had similar performance and egg quality. Glutamic acid-added diets with 150g crude protein/kg maintained similar layer performance and egg quality to that observed in layers fed control diet. However, when added to diets with 130g crude protein/kg, glutamic acid impaired layer performance and egg quality, leading to the lowest means for variables assessed herein when compared with all treatments. Based on results, the lack of non-essential nitrogen compromises layer productivity and glutamic acid may be considered as a potential source of non-essential nitrogen when added in low concentration to low-protein diets. In experiment II, 360 Hy-Line W-36 laying hens were randomly assigned to 5 treatments, eight replicates with six hens each. Experimental diets were obtained through the graded supplementation of a mixture of L- alanine, L-glycine and glutamic acid, at the proportion of 60%,20% and 20% respectively, in a low protein diet with the essential nitrogen to non-essential nitrogen ratio of 55/45. Four more diets with the ratios of 52/48, 48/52, 44/46 and 41/59 were produced from the aforementioned low-protein diet. Additionally, a diet with a higher crude protein content was formulated to contain the essential nitrogen to non-essential nitrogen ratio of 41/59. Layers given dietary essential to non-essential nitrogen ratios of 55/45 and 52/48 had lower egg weight and worsen feed conversion ratio per kilogram of eggs compared with layers fed control diet. Egg mass was impaired only when essential to non-essential nitrogen ratios reached the 55/45. Egg quality was unaffected by dietary treatments. Based on results, the dietary essential to non-essential nitrogen ratio for laying hens must not reach 48/52

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.