Supplementation with different protein profiles for grazing beef cattle supplemented in tropical grass during the rainy-dry transition season

The objective of this study was to evaluate increasing levels of inclusion of dry distillery grains (DDGs) in substitution of corn and urea in multiple supplements for beef cattle of Urochloa brizantha cv. Marandu on the consumption, digestibility, and efficiency of microbial synthesis and use of nitrogen. We used four Nellore bulls cannulated in the rumen with an average age of 24 months and 445.12 ± 34.4 kg of body weight (BW), in a 4 × 4 Latin square design. Supplements differed by the inclusion level of DDG (0%, 31.5%, 63.0%, and 94.5%). Increasing levels of DDG inclusion decreased dry matter intake (DMI) (P = 0.002), forage (P = 0.002), organic matter (OM) (P = 0.001), crude protein (CP) (P = 0.037), and total digestible nutrients (TDN) (P < 0.001) and had a quadratic effect on the intake of non-fibrous carbohydrates (NFC) (P = 0.002). It was observed an increase in the digestibility of ether extract (EE) (P = 0.005), however a decrease in the digestibility of NFC (P = 0.001). Inclusion of DDG did not influence ruminal pH. There was a quadratic effect at collection times for ruminal ammoniacal nitrogen (P < 0.05), except for the supplement with 94.5% DDG where the effect was linear (P = 0.002). Nitrogen intake was 10.9% higher when there was no DDG in the supplement, compared with the supplement with 94.5% DDG (P = 0.039). The excretion of N by feces was greater when there was a greater amount of DDG in the supplement (P = 0.027), the opposite occurred with urine excretion of N, being higher when there was less amount of DDG in the supplement (P = 0.027). Increasing levels of DDG did not affect ruminal microbial protein yield (P > 0.05). Replacing corn and urea with up to 94.5% DDGs in multiple supplements resulted in no adverse effect efficiency of microbial synthesis, although nutrient intake, total digestible nutrients, and use of nitrogen were reduced at 94.5% DDG inclusion.