Effects of Feeding Hybrid Rye Grain as a Replacement for Barley Grain on Feed Intake, Ruminal Fermentation, and Site of Nutrient Digestion for Finishing Beef Cattle.

The objective of this study was to evaluate effects of increasing hybrid rye as a replacement for barley grain on feed intake, ruminal fermentation, and site of nutrient digestion in finishing cattle. Eight ruminally and duodenally cannulated Hereford-cross heifers (starting body weight = 514 ± 25.3 kg) were used in a replicated 4×4 Latin square design with 21-d periods including 15 d of dietary adaptation and 6 d of sample collection. Dietary treatments included a control diet with 10.0% hay, 85.2% barley grain, and 4.8% of a vitamin and mineral supplement on a dry matter (DM) basis. Hybrid rye grain replaced 33, 67, or 100% of the barley grain. Both cereal grains were dry rolled to 80% processing index. Feed, refusals, ruminal fluid, duodenal digesta, and fecal samples were collected. Data were analyzed using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC). Increasing hybrid rye inclusion tended (P = 0.052) to linearly decrease DM intake. Additionally, increasing hybrid rye grain linearly decreased mean and minimum ruminal pH (P < 0.01) and increased the duration (P < 0.01) and area (P = 0.01) that pH was less than 5.5. There was no effect of hybrid rye inclusion on total short chain fatty acid, lactic acid concentrations, or osmolality. Likewise, the molar proportion of acetate and butyrate were not affected by hybrid rye inclusion. Propionate tended to linearly increase with increasing hybrid rye inclusion (P = 0.08). Increasing hybrid rye linearly increased NH₃-N concentration (P = 0.03). Ruminal organic matter (OM) digestibility tended to linearly increase (P = 0.08) and ash-free neutral detergent fiber (aNDFom) digestibility linearly increased (P < 0.01) when increasing hybrid rye. There was no effect on ruminal starch digestibility (71.1 ± 5.12%). Intestinal digestibility of CP linearly decreased (P = 0.050), but there were no effects for other nutrients. Increasing hybrid rye linearly increased apparent total-tract DM, OM, and aNDFom digestibility (P < 0.05) but did not affect starch digestibility (97.4 ± 0.42%). Increasing the inclusion rate of hybrid rye grain at the expense of barley grain in finishing diets may decrease DMI and increase risk for ruminal acidosis; however, hybrid rye inclusion did not influence the site or extent of starch digestion and increased total tract digestibility of DM, OM, and aNDFom. [ABSTRACT FROM AUTHOR]