Effects of hay supplementation in corn-based and dried distillers grains with solubles-based diets on performance and ruminal metabolism in feedlot cattle1

Sulfuric acid in dried distillers grains with solubles (DDGS) decreases ruminal pH, potentially inhibits fiber digestion, and may increase the risk of polioencephalomalacia. At high dietary inclusions of DDGS, increased forage may be needed to attenuate negative effects of low ruminal pH. The objectives of this research were to determine the effects of hay inclusion (7 or 14% of dietary DM), energy source (corn or DDGS), and their interactions on performance and ruminal metabolism in feedlot cattle. In Exp. 1, Angus-cross steers (n = 47) and heifers (n = 24; BW = 253 ± 3 kg) were evenly allotted to treatments by sex, blocked by BW, and allotted in a 2 × 2 factorial arrangement of treatments to 12 pens. Dietary treatments were 1) 7% hay and cracked corn, 2) 14% hay and cracked corn, 3) 7% hay and DDGS, and 4) 14% hay and DDGS. Increasing hay did not affect (P > 0.12) DMI, ADG, G:F, or final BW. Cattle fed DDGS had 5.8% lower DMI (P = 0.01), 2.7% decreased final BW (P = 0.05), and tended to have decreased (P = 0.06) ADG compared with those fed corn. In Exp. 2, ruminally fistulated heifers (n = 8; BW = 645 ± 14 kg) were used in a replicated 4 × 4 Latin square design and fed the diets used in Exp. 1. Increasing dietary hay concentration tended to increase (P ≤ 0.08) ruminal pH from 0 to 3 h postfeeding but did not affect (P ≥ 0.15) pH thereafter. In situ DM disappearance of soy hulls was 35% greater (P = 0.01) for heifers fed DDGS than for those fed corn and tended (P = 0.09) to be greater with 14% hay. Heifers fed DDGS had less (P = 0.01) total VFA and greater (P = 0.01) ratio of acetate to propionate than those fed corn. Increasing hay from 7 to 14% of the diet did not increase performance of cattle fed corn or DDGS-based diets. However, increasing dietary percentage of hay tended to increase ruminal pH and in situ DM digestion.