The aim of this study is to evaluate the replacement of monensin by functional oils(Cashew + Copaiba) on digestibility, ruminal fermentation and efficiency of N for dairy cows. In the experiment, four dry cows cannulated in the rumen will be used in randomized 4x4 Latin square. Each period will last for 20 days with 14 days for adaptation and 6 days of collection. The treatments are: a) T1 : Control (without additive ) ; b ) T2 : Addition of monensin (300 PPM / day) ; c ) T3 : Adding dose 1.5 g / day of functional oil ( Prophytus , São José dos Campos - SP ) ; d ) T4 : Adding dose 2.5 g / day of functional oil ( Prophytus , São José dos Campos - SP ) . The experimental diets are composed of corn silage ( 60 %) and concentrate ( 40 % ) from corn ( 40 % ) , citrus pulp ( 40 % ) , soybean meal (15 %), urea ( 1 % ) and premix vitamin and mineral (4%). Fecal output required for the calculation of digestibility is estimated with the use of external markers chromic oxide and titanium dioxide for 15 days (10 for adaptation and 5 fecal collection). Samples of concentrate, silage and faeces will be analyzed for DM, ash , CP, NDF, EE , ADF and lignin being determined only for samples of silage and concentrate. On the 15th day of the experimental period , ruminal fluid samples will be collected for determination of VFA and NH3 N . Cows will be weighed and have their body condition assessed. The body condition score will range from 1 (extremely lean) to 5 (extremely obese cows) , as proposed by Wildman et al . , (1982 ) . In the 19th and 20th days of the experiment blood samples will be collected after 4 hours of morning delivery of TMR , by punching in the coccygeal vein for determination of plasma levels of non - esterified ( NEFA ) fatty acids , insulin, glucose and urea. The analyzes will be performed with kits comerciais. A microbial protein production is also estimated based on the concentration of purine derivatives in urine from each animal. The spot urine collection will be held on the 16th and 17th day of the collection period, four hours after the diets. Statistical analyzes will be performed with the PROC MIXED of SAS.
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