Ureia em dietas para vacas F1 Holandês x Zebu em lactação

Abstract

The objective of this work was to evaluate the effects of replacing of soybean meal by urea in the diet of F1 Holstein x Zebu cows on intake, digestibility of nutrients, production, milk composition and ingestive behavior. Four experimental diets were used consisting of increasing levels of urea (0, 33, 66 and 100 % replacement of soybean meal) corresponding to 0, 0.36, 0.73 and 1.1 % urea in DM and 0, 0.92, 1.84 and 2.77 % of CP as NPN, formulated according to NRC (2001) to be isoproteic and an average production of 10 liters of milk a day-1. The experimental design was two 4 x 4 Latin squares, composed of 4 animals, 4 treatments and 4 experimental periods each. The experiment lasted 72 days, which were divided into four periods of 18 days. We used 8 F1 cows (1/2 Holstein x 1/2 Zebu), primiparous, with lactation period of approximately 150 days. A complete ration was provided twice daily, at 8 a.m and at 4 p.m. and adjusted every day, so that the remains represent 10 % of the total offered. Milk yield was recorded in the last 3 days of each experimental period. Samples of feed, orts and feces were collected for bromatological analyses and rumen incubation. Cows were subjected to visual observation to assess ingestive behavior after the adjustment period of each experimental period for two consecutive days. Intake of DM (kg and % PV), CP, NDF, NFC and TDN were not affected (P> 0.05) by increasing levels of urea in replacement of soybean meal. However, consumption of EE and NDF in kg / day and % PV showed a quadratic effect, being observed minimum consumption in the levels 2.31 and 2.24 % of NPN in the diets, respectively. Apparent digestibility of DM, EE, NFC and NDF were not affected (P> 0.05) by urea in diets. However, there was linear increase (P <0.05) on the digestibility of CP. Milk production with or without correction for fat were similar (P> 0.05) in all of the experimental diets. Weight gain and body condition score of the cows were not affected (P> 0.05) by urea. The feed conversion (FC) and feed efficiency (FE) did not differ (P> 0.05) either. There were differences (P <0.05) for feeding and idle times, with quadratic effect for the two variables, in which the feeding time decreased with the level of 1.78 % dietary NPN and idle time increased with level of 1.96 % dietary NPN. There was no difference (P> 0.05) for rumination. There were differences (P <0.05) for the total chewing time with quadratic effect, whose level which decreased it was 1.95 % dietary NPN. The time of consumption, chewing and rumination of DM and NDF in min. / kg did not differ (P> 0.05) between treatments. The efficiencies of feeding and rumination of DM and NDF in g / h did not differ (P> .05). Total replacement of soybean meal by urea in the diet of F1 Holstein x Zebu cows did not affect intake and digestibility of DM and nor yield and composition of milk, caused changes in feeding and idle times, and total chewing time, but did not alter other variables from ingestive behavior.