Combinação de óleos vegetais e fontes de carboidratos em dietas para cabras leiteiras

Abstract

The aim of this study was to evaluate the combination of vegetable oils (castor oil and sunflower oil) and two carbohydrate sources (ground corn or dehydrated citrus pulp) in diets for dairy goats on the nutritional variables, microbial protein synthesis, milk production and composition, including its fatty acid profile and information about ricinoleic acid derivatives. Eight crossbreed goats, multiparous, at early lactation (40.78 ± 5.14 kg body weight and 1.02 ± 0.34 kg milk/day) were distributed in double 4 × 4 latin square design in a factorial scheme 2 × 2 with two sources carbohydrate: starch - ground corn or pectin - dehydrated citrus pulp, with or without the inclusion of castor oil and sunflower oil mixture (20 g/kg dry matter). It was used the roughage: concentrate ratio 50:50 for the diets, using Tifton-85 grass hay as roughage. The experimental period lasted 76 days and was divided into four periods of 19 days, being 14 days of adaptation and five days of collection. Experimental treatments did not influence (P> 0.05) the dry matter (DM) intake of the animals, obtaining means of 1,567 g/day, 3,72 g/kg body weight (BW) and 94,60 g / kg BW0,75. The animals fed the diet containing ground grain corn had higher digestible energy and metabolizable energy consumption. There was an interaction effect between carbohydrate sources and the inclusion or not of the oil mixture on the digestibility coefficient of dry matter, organic matter, crude protein, neutral detergent fiber, total carbohydrates and non-fibrous carbohydrates. Experimental treatments did not influence urinary, milk and basal endogenous nitrogen, getting averages 1.31 g / day, 6.92 g / day and 6.04 g / day, respectively. Excretion of purine derivatives, absorbed purines, microbial protein production, and microbial protein synthesis efficiency was not influenced either. Milk yield (kg/day) and milk yield corrected for 4% fat were not influenced by experimental treatments, with mean values of 1.02 ± 0.35 and 1.09 ± 0.32 kg of milk/day, respectively. The physicochemical composition of milk was not influenced by treatments either, except for the pH variable. Diet containing dehydrated citrus pulp promoted higher milk pH. Experimental diets did not influence the concentration of 11 fatty acids (7:0, 9:0, iso-13:0, iso-14:0, c13-18:1, 18:3n-6, 20:2n-6, 20:3n-9, 20:3n-6, 24:1, 22:5n-3) in the milk. The concentrations of eight fatty acids were influenced by the dietary carbohydrate source, of which, 18:2n-6 (linoleic acid) presented higher concentration in the milk of goats fed the diet containing ground corn, while the other seven fatty acids (iso- 15:0, iso-17:0, iso-18:0, c11-18:1, c15-18:1, t11c15-18:1) were higher in the milk of goats fed a diet containing dehydrated citrus pulp. The inclusion of oil in the diets influenced the concentration of nine fatty acids (11:0+10:1, c9-12:1, 13:0, c9-14:1, c7-16:1, c12-18:1, 20:4n-6, 20:5n-3 e 22:6n3) in the milk. There was significant interaction between carbohydrate sources and the addition of oil to the concentration of nine fatty acids (8:0, 16:0, c9-16:1, c9-17:1, 18:0, t10-18:1, 18:3n-3, 19:1 and 3,7,11,15Me-16:0) present in milk. With the addition of oil to the diets, the fatty acid concentration 8: 0, c9-16: 1, 3,7,11,15Me-16: 0 and 19: 1 was similar. The diet containing dehydrated citrus pulp without oil increased the concentration of acids 16: 0, 3,7,11,15Me-16: 0, c9-17: 1 and 18: 3n-3, however the concentration of acids 18: 0 and t10-18: 1 reduced. Carbohydrate sources did not influence the concentration of fatty acids derived from ricinoleic acid (12OH, c9-18:1) present in goat milk. Carbohydrate sources or the addition of oil influenced the partial sums of short and medium chain fatty acids (AGCCM), odd and branched chain fatty acids (AGCIR), saturated fatty acids (AGS), monounsaturated fatty acids- cis (AGMI-cis), trans-monounsaturated fatty acids (AGMI-trans), polyunsaturated cis-fatty acids (AGPI-cis) and biohydrogenation intermediates (IB). The addition of castor oil and sunflower oil mixture reduced the concentration of partial sums of SMCFA, BCFA and SFA present in goat milk. The partial sum of the ricinoleic acid derived fatty acids (AGDAR) was not influenced by the type of carbohydrate present in the diets. There was a significant interaction between the carbohydrate source and the addition of the oil mixture for the t10/t11-18:1 ratio. The diet containing ground grain corn promoted the reduction of t10/t11-18:1 ratio in goat milk. The association of dehydrated citrus pulp with the mixture of castor oil and sunflower oil in diets for dairy goats promoted the reduction of nutrient digestibility. Castor oil can be used in goat diets in order to favor the increase of conjugated linoleic acid - CLA, besides providing the accumulation of oxygenated and hydroxylated fatty acids in goat milk.