Avaliação da parte aérea de cultivares de mandioca, desempenho e digestibilidade em dietas simplificadas e semi-simplificadas com ou sem suplementação enzimática para coelhos em crescimento

Abstract

Cassava consists of major source of food for many communities worldwide. The aerial part of this plant, however, is not employed for human feeding. Animals, in contrast, eat that part of cassava, although it is not largely used for animal feeding. The rabbit production is a strategic activity due the animal high prolificacy and its excellent meat quality. Besides, rabbit demand relatively small areas to be raised, accept diets with great content of fibrous ingredients, and cause low environmental impact, an important question for sustainable development of the modern society. The main objectives of this work were to select a variety of cassava adequate for feeding farmed rabbits, to evaluate the digestibility of the nutritional principles of simplified and half-simplified diets for rabbits, as well as the performance of the animals fed these diets, and to evaluate in vitro digestibility methods for rabbits. In the first trial, 12 cassava varieties developed by EMBRAPA Mandioca e Fruticultura research station, harvested 10 months after planting and made into cassava hay, had evaluated their chemical composition, cianidric acid (HCN) content and in vitro digestibility with gas production. In the second trial, it was investigated the potential of the fractions (1 to 5) of the aerial part cassava processing. In the third trial, the productivity of both parts, the cassava root and the upper third foliage hay (CUTFH), were studied. The CUTFH had studied its chemical composition, and its production cost was estimated. A fourth trial was set up to compare with a reference diet the in vitro digestibility of the simplified and half-simplified diets, with basis of the mixture of forage crops, with or without exogenous enzymes. The following types of food were tested: CUTFH, alfalfas hay (ALH), and cassava leaves flour (CLF), being utilized a completely randomized design, with 11 treatments and eight replications. Carbohydrase (xylanase, beta glucanase, alpha galactosidase and galactomanase) and phytase enzymes were also added. The productive performance and digestive parameters had been evaluated also from the diets previously cited, being the animals weighteds to each five days. In the last two assays, the in vitro digestibility methods with gas production and Tiley e Terry had been used for evaluation of the experimental diets being the second method modified on the time of incubation and the second stage (enzymatic digestion). KIRIRIS, GRAVETINHO and CIGANA cassava varieties showed better chemical composition, no presence of HCN, as well as a high degradability and gas production. Therefore, those varieties were selected for the productive performance trial (trial 4). Fraction 1 of the processing seemed favorable for use in the feeding of the rabbits, as it characteristics were very similar to the ALH. GRAVETINHO variety was chosen since it yielded greater productivity of root (19 t/ha) as well as a high productivity of CUTFH. Production cost for cassava upper third foliage hay was R$0.36/kg. While digestibility of the nutritional principles of the diets was negatively influenced by the type of food (p<0.05), the exogenous enzymes improved it. It was also observed that a large amount the crude protein (CP) of the CLF was conjugated, since it was undergone high temperatures during its processing. Fibrous ingredients had 1822.7 kcal DE/kg DM and 12.26% CP in the DM for the CUTFH, 2232.5 kcal DE/kgDM and 15.54% DP in the DM for ALH and 1888.9 kcal/kg DE/kg DM and 7.36% DP in the DM for the CLF. Feed consumption was affected by the type of food (p<0.05). Treatments with higher inclusion of CFL resulted in lower feed conversion and lower carcass yield. For daily weight gain (DWG) the best results were obtained in the treatment reference, the half-simplified CUTFH and half-simplified on the basis of the mixture of ALH and CLF (p<0,05). In contrast, no significant positive effect of exogenous enzymes was observed for DWG (p>0.05). The not linear models of Logistic, Gompertz and Von Bertalanffy adapted to the growth of the animals while Brody model did not. Diets with greater fiber content allowed greater development of the gastrointestinal tract. For the economic view, the simplified diet on the basis of the CUTFH seemed interesting, since it made possible a 4% reduction in the cost for production of 1 kg of rabbit. Regarding to the digestibility methods tested in this experiment, a excellent correlation was found between data obtained in vitro and data obtained in vivo.