PSXIV-2 - Inclusion of a slow-release nitrogen ingredient associated or not with monensin on performance, metabolism, and carcass parameters of finishing beef cattle fed high starch diets

Abstract: This study aimed to assess the effects of a slow-released nitrogen (N) ingredient in association or not with monensin on the performance, metabolism, and carcass parameters of finishing young bulls. To investigate these outcomes, 112 Nellore young bulls (380 kg ± 16.2) were used in a 2 × 2 factorial arrangement. The young bulls were allocated to 28 feedlot pens (four animals per pen) and fed a finishing high starch (51% starch) corn grain and corn silage based diet. The following treatments were randomly assigned to the experimental units: (1) Control (CON, n = 7) - finishing diet without additives; (2) Monensin-enriched diet (MON, n = 7) - monensin (Rumensin®, Elanco Animal Health, Greenfield, IN) provided at a level of 30 mg per kg of dry matter (DM); (3) Gradual-N-release enriched diet (SRN, n = 7) - slow-N-release supplement (Timafeed Boost®, Roullier Group, Saint-Malo, France) provided at a dose of 250 g per animal per day; or (4) Monensin + SRN diet (MON + SRN, n = 7) - monensin (30 mg per kg of DM) associated with the SRN (250 g per animal per day). The experimental period comprised 102 days, with the first 15 days designated for diet adaptation. The average daily gain (ADG) over the experimental period was reduced for young bulls fed SRN + MON (P = 0.02) compared to those fed only SRN. Young bulls fed MON had greater DMI during the finishing phase than MON × SRN (P = 0.03). Overall, young bulls fed CON diet had greater day-by-day dry matter intake (DMI) variation than other treatments (P ≤ 0.05). The SRN inclusion in the diet improved feed efficiency by 5.7% (P = 0.04). Young bulls fed diets without SRN inclusion tended to have higher blood urea concentration (P = 0.06). Blood D-lactate and glucose levels were similar between treatments (P ≥ 0.21). The SRN use tended to increase (P = 0.09) DM digestibility (5.6% increase). The microbial crude protein was reduced by MON + SRN association (P = 0.02) compared to other treatments. The hot carcass weight was greater for the SRN group compared to MON × SRN (P = 0.02). The use of SRN in the diet increased (P ≤ 0.04) total and daily carcass gain, carcass yield, and biological efficiency. In summary, although additional studies are suggested, these data indicate that the association between SRN and monensin might require careful consideration when used in finishing diets. The SRN inclusion in finishing diets without monensin shows important potential for increasing animal performance and efficiency.