Effects of feeding hybrid rye grain as a replacement for barley grain on dry matter intake, ruminal fermentation, and the site and extent of nutrient digestion in finishing beef heifers.

ABSTRACT

The objective of this study was to evaluate effects of increasing the inclusion of dry-rolled hybrid rye (HR) as a replacement for dry-rolled barley grain (DRB) on feed intake, ruminal fermentation, and the site and extent of nutrient digestion for finishing cattle. Eight ruminally and duodenally cannulated Hereford-cross heifers were used in a replicated 4 × 4 Latin square design with 21-d periods including 15 d of dietary adaptation and 6 d of data and sample collection. Dietary treatments included a control diet with 10.00% grass hay, 85.21% DRB, 4.51% of a vitamin and mineral supplement, and 0.28% of urea on a dry matter (DM) basis. Hybrid rye grain replaced 33%, 67%, or 100% of the DRB. Feed ingredients, feed refusals, ruminal pH, ruminal fluid, duodenal digesta, and fecal samples were collected from days 18 to 21 in each period. Data were analyzed using the Proc Glimmix procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC) to evaluate the linear, quadratic, and cubic effects of increasing HR inclusion. Increasing HR inclusion as a substitute for DRB linearly decreased (P < 0.01) DM intake, linearly decreased mean ruminal pH (P < 0.01), and increased the duration (P < 0.01) and area (P = 0.02) that ruminal pH was < 5.5. There were no effects of HR inclusion on total short chain fatty acid and lactic acid concentrations in ruminal fluid. Likewise, the molar proportions of acetate and butyrate were not affected by HR inclusion. Propionate was cubically affected by HR inclusion (P = 0.02). Ruminal ash-free neutral detergent fiber (aNDFom) digestibility linearly increased (P = 0.03) with increasing HR, but there was no effect on ruminal starch digestibility averaging 71.1% (SEM = 3.611). Increasing HR inclusion linearly increased intestinal DM digestibility (% of flow to the duodenum; P = 0.03), tended to linearly increase intestinal digestibility of organic matter (P = 0.08), and tended to quadratically affect intestinal digestibility of aNDFom (P = 0.07). Increasing hybrid rye linearly increased apparent total tract DM, organic matter, crude protein, aNDFom, and starch digestibility (P ≤ 0.05). In addition, increasing HR inclusion linearly increased GE digestibility (P < 0.01) and the DE concentration (P < 0.01). Increasing the inclusion rate of HR grain as a substitute for DRB in finishing diets decreased DMI and increased risk for low ruminal pH, which may be influenced by greater digestible energy concentration arising from greater DM, OM, aNDFom, and starch digestibility.

Rye grain is not a common cereal grain used for finishing cattle due to risk for ergot contamination and concerns with palatability; however, the development of varieties with low ergot risk may increase its use. In this study, dry matter intake, ruminal fermentation, and the site and extent of nutrient digestion were evaluated when dry-rolled hybrid rye (HR) replaced dry-rolled barley (DRB) in diets for finishing beef cattle. Increasing the inclusion of HR as a substitute for DRB linearly decreased dry matter intake while linearly increasing the duration that ruminal pH was <5.5. Ruminal digestibility of ash-free neutral detergent fiber (aNDFom) linearly increased with increasing HR inclusion, while ruminal starch digestibility was not affected. Total tract digestibility of dry matter, organic matter, crude protein, aNDFom, and starch, along with the digestible energy concentration, linearly increased as HR inclusion increased as a substitute for DRB. These results suggest that incorporating HR as a replacement for DRB has the potential to improve the ruminal digestibility of aNDFom and total tract digestibility for most chemical constituents but may reduce dry matter intake while increasing risk for low ruminal pH.