Ruminant Nutrition: Beef: By-Products and Dietary Modifications

The objective of this research was to study the effect of fat concentration from corn coproducts, fed during the growing phase on DMI, gain, carcass traits, digestibility, and rumen metabolism of steers. Exp. 1: 40 steers (age = 140d; BW = 185 ± 11 kg) were randomly allotted to 1 of 5 dietary treatments: (1) corn-based control (CNT), (2) 0% corn distillers solubles (CDS), (3) 10% CDS, (4) 19% CDS, or (5) 27% CDS. Diets 2–5 included coproducts (corn gluten feed and soybean hulls) and were formulated to achieve fat concentrations of 3, 5, 7, and 9%, respectively. Diets were fed once daily for 106 d (growing phase, GP). All steers were fed a corn-based diet from d107 to 196 (finishing phase, FP). Contrasts were used to examine a) the difference between CNT and 10% CDS; b) linear and quadratic effects of CDS inclusion. During the GP, steers fed CNT had increased (P ≤ 0.03) BW, G:F and ADG compared with those fed 10% CDS. Increasing CDS inclusion increased (linear; P = 0.01) ADG and G:F. At the conclusion of the GP, back fat thickness (BF) determined via ultrasound increased (P = 0.05) in CNT-fed calves compared with 10% CDS. There were no treatment differences (P ≥ 0.14) in FP ADG, DMI, or G:F. Steers fed CNT had increased(P = 0.02) overall ADG compared with steers fed 10% CDS, and increasing CDS inclusion increased (linear; P = 0.05) overall ADG. Final BW, and overall DMI and G:F were not different (P ≥ 0.06). There were no effects (P ≥ 0.10) of treatment on carcass traits. Exp. 2: steers (n = 5; BW = 345 ± 22 kg) were fed Exp.1 diets for ad libitum intakes in a 5x5 Latin square design. Apparent dry matter digestibility (DMD) increased (linear; P = 0.02) with increasing dietary CDS inclusion. Steers fed CNT had increased (P = 0.01) DMD compared with those fed 10% CDS. Fat digestibility increased (linear; P < 0.01) as CDS inclusion increased, but NDF digestibility was unaffected (P ≥ 0.17). In conclusion, feeding a coproduct diet with 10% CDS during the GP decreased overall ADG compared with feeding corn; however, increasing CDS inclusion improved DM and fat digestibility as well as overall ADG.