Avaliação de dietas com diferentes volumosos para vacas mestiças em lactação

Abstract

This study aimed to evaluate the production, processing and quality of milk of crossbred cows fed different forages (sugarcane, sunflower silage, sorghum silage and Tanzania pasture). Four experimental diets were used, one for each one of the roughage, formulated according to NRC (2001) to be isoproteic and for yield potential of 20 liters of milk per day. The experimental design was two Latin Squares 4 x 4, consisting of four animals, four treatments and four experimental periods each one. The experiment lasted 72 days, which were divided into four periods of 18 days. The used animals were eight crossbred cows 1/2 (Holstein / Gyr), with the lactation period of 200 days. The production of Tanzania grass was estimated by collecting the material by means of a square of known area and estimated consumption was obtained by the difference between the available mass and residual one under rotational grazing. The whole diet was provided twice daily at 8 a.m. and 4 p.m, and adjusted daily, so that the remains represented 10% of the total offered. Milk production was recorded in the last three days of each experimental period. Milk samples were collected from each animal in the morning and in the evening, mixed and analyzed for fat, protein, lactose, crioscopy, density, pH, acidity, total dry extract and non-fatty one, and total solids. On the first day of collecting, the milk produced in each treatment was cooled for the production of Minas frescal cheese that after processing were weighed to determine yield, physicochemical characteristics (fat, protein, acidity and pH) and subjected to microbiological analysis and to of sensory analysis test. Blood samples were collected from the coccygeal vein for determination of glucose and plasma urea nitrogen levels. Samples of fodder, remains and feces were collected for chemical analysis and apparent digestibility. The ingestive behavior of the animals and the economic analysis of the experimental diets were evaluated. The dry matter intake and digestibility of the sunflower silage diet were lower than the other diets. Diets with sorghum silage and Tanzania-grass presented lower dry matter digestibility but high dry matter intake. The sugarcane diet showed low neutral detergent fiber intake, and low protein digestibility; however, did not affect dry matter intake. Sugarcane diets and the Tanzania grass pasture showed higher intakes of total digestible nutrients. Diets with sunflower silage and Tanzania grass pasture decreased weight loss and body condition score of the cows. Milk production was equal in all of the diets despite the difference in intake and digestibility of nutrients. Amongst the evaluated diets, the sugarcane one had the highest cost, and the diet with Tanzania grass grazing had the least cost. Net income from milk was lower for the sugarcane diet and greater, in increasing order, for diets with sunflower silage, sorghum silage and Tanzania grass pasture. In the evaluation of ingestive behavior, the cows fed with a diet of grass-Tanzania pasture had higher feeding time and lower efficiency of dry matter intake. Less rumination time and larger leisure time were observed in cows fed with sunflower silage. Greater feed efficiency of NDF in cows fed with sorghum silage and Tanzania grass pasture. The physico-chemical composition of milk was better with the sugarcane diet. The physicochemical composition of the cheese differed to fat content which was higher in diets with sugarcane and sunflower silage, but the cheese yield was the same for the different roughage. The nutritional quality of cheese was better for the diet with sunflower silage, since having presented a better profile of unsaturated fatty acids and lower proportion of satured ones. In the sensory analysis, the cheese from the diet with sunflower silage was the most preferred by the tasters.