Desempenho bioeconômico e controle parasitário em ovinos terminados intensivamente a pasto utilizando a torta de mamona como insumo alternativo

Abstract

The objective of this study was to evaluate castor bean cake as an alternative input for the control of gastrointestinal parasitism in sheep finished on irrigated Tamani grass pasture under continuous stocking in a 2 x 2 factorial randomized block design (RBD), with two sources of nitrogen fertilization, mineral (urea, UR) and organic (fresh castor bean cake, CC), and two dietary supplements (with and without detoxified castor bean cake, CCd), with four replications (paddocks) for the structural characteristics of the pasture and 16 replications (sheep) for intake, digestibility, blood parameters and animal performance, respectively, and eight replications (sheep) for behavioral and physiological blood parameters. In the case of behavior, repeated measures were added in time (periods of the day). A RBD was adopted with 16 replications (sheep), with repeated measures in time for the variables: infective larvae L3 in the pasture (L3.g DM- 1), eggs per gram of feces (EPG), and for counting adult gastrointestinal parasites, RBC was used, with six replications (sheep). The minimum unit of three hectares was considered for economic evaluation and the average slaughter weight of 28 kg was determined. A minimum selling price was established, in which the least profitable rearing system would become profitable at US$ 2.38/kg body weight and US$ 4.45/kg carcass. The profitability of production systems was evaluated by adopting a minimum rate of attractiveness of 3.5% per year, based on the Selic rate. Pastures fertilized with urea had higher leaf blade biomass production of 1,807 kg DM.ha.cycle-1 and tiller population density of 1,592 tillers.m-2, but with no effect (P>0.05) on the total forage accumulation. Animals supplemented with feed containing CCd and pasture fertilized with urea reduced grazing time by 65 minutes.day-1. The use of the by-product did not change physiological parameters of sheep in any of the systems evaluated. Average daily gain of 103.75 and 86.76 g.day-1 was found for sheep supplemented with feed containing soybean meal (SM) and CCd, respectively. There was no effect (P>0.05) on nutrient intake, growth curve, liver and kidney parameters of the animals. The ideal body weight for sheep slaughter occurred at 230 days of age, and a finishing period of less than 122 days is recommended for grazing. The mean number of L3.g DM-1 and EPG were 126 and 841, with no effect (P>0.05) from the systems tested. Split fertilization of fresh CC does not reduce pasture contamination with nematodes. The combination of supplementation and fertilization using CC reduces parasites in sheep abomasum. The sale of live animals was not attractive in any of the systems evaluated, the opposite was observed for the commercialization of carcasses and non-carcass components of sheep. The SMUR production system proved to be more profitable, with a gain of US$ 0.53 per kg carcass. Further studies are required to validate the use of CC as a supplement or organic fertilizer in commercial production systems.