Utilização de promotores de crescimento em ração para frangos de corte

Abstract

Two experiments were carried out to evaluate the effects of using distinct growth promoter over the energetic metabolism and performance of poultry farming. Two experimental diets (ND normal diet according to nutritional requirements and RD reduced diet, with 5% less of nutrients), supplemented or not with antibiotics and prebiotics from 1 to 10, 11 to 21, and 22 to 42 days of age. For performance, we used 1152 chickens, divided into 48 boxes following a completely casualized 2x3 factor design (two diets x three growth promoter) composed of six treatments and eight repetitions. At the end of each period, the animals and the food leftovers were weighed to calculate the performance variables. At 21 days of age, one chicken per experimental units (EU) was slaughtered and portions of the small intestine were collected for morphological analyses. After 33 days, two chickens per EU were selected and the cecum content was removed for microbiological analysis. After 35 days, blood samples were taken from brachial puncture to evaluate blood parameters. By the end of the experimental period, two chickens per EU were slaughtered for evaluating the dressing percentage. For metabolism analysis, we used 180 poultry chicks, divided into 36 cages, distributed according to the experimental design abovementioned in performance analysis by using the traditional method of excreta collection. The animals fed with RD presented the worst results (P<0.05) for mean weight, weight gain, food intake and feed conversion rate. There was no effect (P>0.05) over villi height in duodenum and ileum. However, interaction (P<0.05) was detected between the evaluated promoter and the villi height in jejunum, the crypt depth and the relationship villi:crypt in all segments, inasmuch as ND containing prebiotics yielded the best results. The growth promoter had no effects over cecum microflora although RD resulted in higher amounts of Lactobacilos and Bifidubacterium (P<0.05) when diets were compared. Food free of growth promoters yielded higher levels of triglycerides and calcium (P<0.05). The RD reduced the concentration of triglycerides (P<0.05) but increased the deposition of abdominal fat (P<0.05). Interaction between diet and growth promoters was observed (P<0.05) in relation to the coefficients of ileum digestibility (CID) of dry matter (DM), raw protein (RP) and ethereal extract (EE). The RD containing antibiotics presented lower CID in DM. The ND containing antibiotic presented higher CID in RP (P<0.05), while RD containing prebiotics resulted in higher CID of RP and EE (P<0.05). The coefficient values of total digestibility (CTD) in DM, RP and EE showed interaction (P<0.05) between diets and growth promoters, where the RD containing antibiotic yielded the lowest DTD of DM and EE. The ND resulted in higher values of apparent metabolizable energy (AME) and nitrogen-corrected apparent metabolizable energy (AMEn) (P<0.05). We conclude that prebiotics can be used as growth promoters in poultry, without hindering their performance while the reduction of nutritional demands in food decreases the digestibility of nutrients