Effect of different dietary inclusion levels of whole raw soyabean on ruminal fermentation and nutrient utilization in Nelore steers

The aim of this study was to evaluate the effects of increasing level of whole raw soyabean (WRS) in the diet of Nelore steers on nutrient intake and digestibility, ruminal fermentation, nitrogen utilization and blood profile. Twelve steers (2-year-old; 400 ± 28.5 kg body weight) were used in a triple 4 × 4 Latin square design. The animals were randomly assigned to the following treatments: control (WRS0; without WRS), and diets containing 80 (WRS8), 160 (WRS16) and 240 (WRS24) g · kg−1 DM of WRS in the diet. The steers were fed diet with 40:60 forage:concentrate ratio. Ingredients, refusals and faeces were sampled to determine total tract apparent digestibility. Samples of ruminal fluid were collected on day 19 before the morning feeding and 2, 4, 6, 10 and 12 h after the morning feeding for pH, ammonia and short-chain fatty acid analyses. Spot urine samples were obtained on day 20 for nitrogen balance analysis. Blood samples were collected on day 21 for protein and energy metabolism analyses. Inclusion of WRS decreased DM and non-fibre carbohydrate intake, increased ether extract intake, affected ruminal pH, ammonia and acetate concentrations, and linearly increased serum high density lipoprotein and total cholesterol contents. Nitrogen excretion in urine increased linearly with WRS inclusion. Addition of WRS exerted a quadratic effect on nitrogen balance. In conclusion, WRS inclusion into the diet of Nelore steers did not change nutrient digestibility, promoted few changes in rumen metabolism and blood parameters, and was not detrimental to digestive function