Utilização de fontes de gorduras em rações de vacas leiteiras

FREITAS JUNIOR, J. E. Fat Sources in Dairy Cows Rations. [Utilização de fontes de gordura em rações de vacas leiteiras]. 2008. 93 f. Dissertação (Mestrado em Medicina Veterinária) – Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, Pirassununga, 2008. This study was carried out to evaluate the use of different fat sources in dairy cows rations on intake and nutrients digestibility, ruminal fermentation, milk yield and composition, milk protein fraction composition, and balance of energy and nitrogen. Twelve Holstein cows were allocated in three balanced latin square 4x4, and fed with the following rations: 1) Control; 2) Refined soybean oil; 3) Whole soybean; and 4), Calcium salts of fatty acids (Megalac-E). Was evaluated daily the dry matter intake and the milk yield during though the experimental period. The samples used for milk composition analysis were collected from two alternated days, and from the two daily milkings. The samples of blood were collected with vacuolized tubes per puncture of coccygeal vein and/or artery. The samples of ruminal fluid were collected with use of esophageal probe into two times, before (zero time) and three hours after morning fed (three time). The digestibility was determined by use of ADFi as internal indicator. There was observed an decrease in dry matter and nutrients intake from cows supplemented with the ration containing calcium salts of fatty acids regarding control. Not was observe difference in apparent total digestibility of nutrients between experimental rations. Also, not were observed effects of rations used in ruminal pH in the evaluated times. The ruminal ammonia nitrogen was greater for cows receiving whole soybeans in rations on the time zero. However, after three hours after morning fed, no difference were observed in the concentration of ruminal ammonia nitrogen between rations. Among the diets containing fat sources, the ration with whole soybeans resulted in decrease of milk yield and fat content, without changing, however, contend of total dry and fat-free extract. Fat sources added in the rations had no effects on milk crude protein, non protein and non casein nitrogen, true protein, casein, relationship casein/true protein and whey protein. The concentrations of total cholesterol and cholesterol-LDL were higher for cows that received rations with fat sources in relation to control ration. The concentrations of urea and urea nitrogen, in serum and in milk were similar between the rations, except for the diet containing calcium salts of fatty acids, that concentration decreased in relation of control ration. The ration containing calcium salts of fatty acids showed great energy efficiency between the experimental rations, especially on the ration with whole soybeans. There were not effects of the experimental rations on the nitrogen balance, but the ration containing calcium salts of fatty acids resulted in small intake and total nitrogen excretion. The utilization of fat sources in dairy cows rations influence the intake, productive performance, and metabolism, depending of the fat source used. Key Word: Dairy cows. Lipids. Milk yield and composition. Digestibility. Blood parameters.