Utilização de ureia associada a fontes de carboidratos na alimentação de caprinos

Abstract

The objective of this study was to evaluate different carbohydrates sources associated with urea on intake, apparent digestibility of nutrients, productive and physiological response in goats. Thirty-one castrated males without a defined race and initial average weight of 19.8 ± 3.1 kg were randomly assigned to one of four treatments in a complete randomized design with the initial weight as a covariate. The treatments were: 1. corn + soybean meal, 2. corn + urea, 3. cassava meal (Manihot esculenta crantz) + urea and 4. cactus (Nopalea cochenillifera) + urea. All treatments had Tifton 85 (Cynodon spp) hay as roughage source (581.3 g kg -1 of DM), mineral salt mixture and ad libitum water access. The experiment lasted 120 days (30 days of adaptation and 90 days of measurements). The animals fed with cactus + urea presented lower ingestion of dry matter (497.5 g DM d-1, P < 0.05), which promoted lower intake of nutrients and metabolizable energy in comparison to diets with corn and cassava meal (743.6 g DM d-1). Crude protein intake was similar for treatments with corn (+ soybean or + urea (127.7 g d-1) and differed from cassava meal + urea and cactus+ urea (84.6 g d-1, P < 0.05). Apparent neutral detergent fiber corrected for ash and protein (NDFap) intake was lower with cactus + urea (292.8 g d-1, P < 0.05), however, when it was expressed in relation to live weigh was similar among different sources of carbohydrates (12.4 g d-1, P > 0.05). Apparent digestibility of DM (656.8 g kg-1), organic matter (675.9 g kg-1), NDFap (530.9 g kg-1), and non-fibrous carbohydrates (831.7 g kg-1), were similar among the sources of carbohydrates associated with urea (P < 0.05). The time spent for feeding (265.5 min dia-1), rumination (447.4 min dia-1) and idle (727.4 min dia-1) were similar among carbohydrates sources. Blood glucose concentration was lower for animals fed with cactus + urea, and lower concentrations of triglycerides and cholesterol were observed in animals fed with cassava meal. Retention of nitrogen (5.27 g d-1) and microbial protein synthesis (22 g d-1) was similar for all treatments. Corn + soybean meal had higher final body weight (29.3 kg FBW), daily average gain (104.0 g d-1 AG), empty body weight (22.9 kg EBW) compared with cassava diet or cactus + urea (25.2 kg and 20.7 kg FBW, 18.9 e 15.2 Kg EBW, 73.1 and 21.4 g d-1 AG, respectively P > 0.05). Animals fed with cassava + urea showed similarity in variables response to corn + urea and differ from cactus + urea. Cactus + urea reduced commercial yield compared with corn (+ soybean meal or + urea) (39.2% vs43.5% , P <0.05). The carcass compactness and leg muscle indexes, muscle: fat and muscle: bone ratio were similar in animals fed with cassava and corn diets (+ soybean meal + urea) and superior compared with cactus + urea (P <0.05). The pH of the carcass at 0h (6.85) and 24h (5.5) after slaughter, the proportion of commercial cuts in the carcass, the chemical composition in Semimembranosus muscle, physical-chemical characteristics except shear force were similar among carbohydrate sources associated with urea (P > 0.05). The results suggested that despite the lower weight of the carcass, meat characteristics and quality for animals fed with cassava meal + urea were similar to those fed corn + soybean meal, indicating that cassava meal + urea could substitute corn and soybean meal in tropical regions due to availability and cost. The replacement of corn by cactus associated with high levels of urea (30 g kg MS-1) decreased nutrient consumption and, therefore performance, yield and carcass characteristics.