Digestibility and nitrogen efficiency of growing beef cattle fed diets containing different proportions of Stylosanthes Campo Grande and corn silages
The objectives of this study were to evaluate total, ruminal and intestinal digestibility of nutrients, ruminal pH, ruminal ammonia concentration and nitrogen efficiency in growing beef cattle fed diets with varying proportions of <i>Stylosanthes</i> Campo Grande silage (SSt) replacing corn silage (CS). Treatments consisted of diets with ratios of 0:100, 25:75, 50:50, 75:25 and 100:0% SSt:CS. Diets consisted of 50% silage and 50% concentrate, formulated to be isonitrogenous (12.5% CP, DM basis). Ten crossbred Holstein-Zebu bulls with an average initial weight of 272 ± 86 kg, distributed in two 5x5 Latin squares were used. The bulls were non-castrated and rumen and abomasum-fistulated. This trial lasted 90 days divided in five experimental periods. Each period lasted 18 days and was divided into ten days for adaptation to the diets and eight days to collect samples. Chromium oxide (Cr2O3) was used to determine the fecal excretion and abomasum flow of nutrients. All data were analyzed using the MIXED procedure in SAS (version 9.1). Rumen apparent digestibility of CP and the intestinal apparent digestibility of NFC increased linearly (P < 0.05), with the addition of SSt to the diet. Intestinal digestibility of DM showed a quadratic effect (P < 0.05). Nitrogen balance, urea excretion in urine and urea nitrogen in the blood plasma showed no effect in response (P > 0.05) to the inclusion of SSt in the diet. Ruminal pH values were not affected (P > 0.05) by proportion of SSt in the diet (P > 0.05), but ruminal pH was affected (P < 0.05) by the time of collection, for which a cubic model was fit to the data. There was an interaction effect (P < 0.05) between treatment and collection time for rumen ammonia nitrogen concentration. Based on the results obtained in this study, it can be concluded that <i>Stylosanthes</i> Campo Grande silage can be used as a source of roughage in the diet of beef cattle during the growing phase at a proportion of 50% of dry matter in the total diet.
Sponsored by FAPEMIG, CNPq and INCT-CA
Keywords: ammonia nitrogen, legume silage, ruminal pH