Metabolic evaluation of grazing suckling beef calves supplemented with different energy sources

The objective of this study was to evaluate the metabolic characteristics of grazing suckling beef calves supplemented with different energy sources. Thirty four Nellore calves (12 males and 22 females) were subjected to creep-feeding, with an average weight 108?3.9 kg and age of four months in the period from March to June 2013. The animals were housed in a 20 ha area with grass Urochloa decumbens, accompanied by their mothers. The concentrate supplements have 20% crude protein consisting of soybean meal, mineral mixture, molasses and the following energy sources: corn (C); corn + sorghum (C+S); corn + sorghum + wheat bran (C+S+WB), supplied in an amount of 0.5% of body weight. In the control treatment (MM) was supplied mineral mixture ad libitum. Urine and blood samples were taken approximately four hours after the intake supplement. For quantification of urea in blood and urine was used an automated device for biochemistry (Mindray mark, model BS200E), fixed-time kinetic method. Nitrogen balance (NB) was calculated as the nitrogen intake under which was excreted in feces and urine. Data were submitted to an analysis of variance according to a randomized block design with four treatments and two blocks (gender of animals). Means were compared by the Fisher's least significant difference test at 5%. The concentrate supplementation did not affect (P>0.05) serum urea nitrogen (SUN) levels. The levels of SUN, mg/dl, were 11.56, 11.96, 11.78 and 11.02 for the treatments MM, C, C+S and C+S+WB, respectively. The urea urine nitrogen levels (UUN, g/day) were not affected (P>0.05) by supplementation. The values found for the treatments MM, C, C+S and C+S+WB were 18.60, 23.57, 23.17 and 18.82, respectively. The NB was higher (P<0.05) in animals fed C (13.86a), C+S (35.29a) and C+S+WB (24.48a) compared to animals MM treatment (4. 61b). Animals supplemented were more efficient in the use of nitrogen when compared with animals of the control treatment, once the animals supplemented had higher nitrogen balance.