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Effect of supplementing increasing levels of RUP on growing performance in calves fed a silage-based diet
An 84-d growing study, utilizing 60 steers (initial BW = 290; SD = 18 kg), evaluated the effects of supplementing increasing levels of RUP on growing performance of calves fed a silage-based diet. All steers were individually fed using the Calan gate system. Five levels of supplementation were evaluated with 12 steers per level of supplement. Supplement levels consisted of 0, 3.25, 6.5, 9.75 and 13% RUP (as a % of diet DM). The RUP supplement consisted of 60% SoyPass and 40% Empyreal. The diet consisted of 85% corn silage with the remaining 15% of the diet being accounted for in the supplement (DM basis). Supplement included RUP, urea, minerals, and carrier replaced by RUP. Initial and ending BW were obtained by collecting BW across 3 consecutive days and averaging after cattle had been limit fed a 50% Sweet Bran and 50% alfalfa diet at 2% of BW for 5 d. Cattle were assigned to treatment based on d -1 and 0 BW. Interim BW were collected on d 36 and 37 and shrunk 4% to account for gut fill. There were no differences in DMI (P = 0.33) among treatments for period 1 (d 1-37). However, ADG (P < 0.01) and G:F (P < 0.01) both increased linearly as RUP inclusion increased during period 1. Using the NRC model, MP balance for period 1 increased from -200 to +65 g/d as RUP inclusion increased from 0 to 13%. At 9.75% RUP inclusion MP balance was reached at +2 g/d. There were no differences in DMI (P = 0.16), ADG (P = 0.11) or G:F (P = 0.32) for period 2 (d 38-84). For the overall growing period (d 1-84), as supplemental RUP inclusion increased from 0 to 13%, a linear increase was observed in ending BW (P < 0.01). With no difference in DMI (P = 0.19) between the five treatments, averaging 7.67 kg/d, and a linear increase in ADG (P < 0.01), G:F linearly increased (P< 0.01) from 0.148 to 0.174 as RUP inclusion increased. The MP balance increased from -186 to +98 g/d as RUP inclusion increased from 0 to 13%, at 9.75% RUP inclusion MP balance was reached at +26 g/d. Increasing the amount of RUP in silage growing diets increases ending BW, ADG and G:F by meeting MP requirements.
Keywords: Corn Silage, Growing Cattle, Rumen Undegradable Protein