title: Impact of hard vs. soft wheat and monensin level on rumen acidosis in feedlot heifers.
abstract: Many feedlot finishing diets include wheat when the relative wheat prices are low. This study was conducted to examine the responses in ruminal pH and fermentation as well as site and extent of digestion from substituting soft or hard wheat for barley grain and to determine whether an elevated monensin concentration might decrease indicators of ruminal acidosis in feedlot heifers. Five ruminally cannulated beef heifers were used in a 5 × 5 Latin square with 2 × 2 + 1 factorial arrangement. Treatments included barley (10% barley silage, 86% barley, 4% supplement, with 28 mg monensin/kg DM) and diets where barley was substituted by either soft or hard wheat with either 28 or 44 mg monensin/kg diet DM. Intake of DM was not affected by grain source, whereas increasing monensin with wheat diets reduced (P < 0.02) DMI. Mean ruminal pH was lower (P < 0.04) and durations of pH < 5.8 and pH < 5.5 greater (P < 0.03) for wheat than for barley diets. However, ruminal pH was not affected by wheat type or monensin level. Total VFA concentrations were greater (P < 0.03) for wheat than barley diets with no effect of wheat type. The molar proportion of propionate was greater (P < 0.04), whereas butyrate (P < 0.01) and ratio of acetate to propionate tended to be lower (P < 0.09), with the high as compared to low level of monensin. Replacing barley with wheat in finishing diets did not affect the duodenal flow or the digestibility of OM, likely as a result of greater (P < 0.01) NDF digestion from barley offsetting the increased (P < 0.03) supply of digested starch from wheat. Feeding soft vs. hard wheat delivered a greater (P < 0.03) duodenal supply of OM and nonammonia N with no differences in total tract nutrient digestion. The increased monensin concentration decreased the flow of OM (P < 0.01), total N (P < 0.05), and microbial protein (P < 0.05) to the small intestine due to decreased DMI. These results indicated that hard and soft wheat exhibited digestive characteristics similar to barley, but ruminal pH measurements indicate that compared with barley, wheat increased the risk of ruminal acidosis. Although an increased level of monensin had limited impact on ruminal indicators of acidosis, an increase in propionate would be expected to improve efficiency of feed use by heifers fed wheat-based finishing diets.
authors.affiliation: Research Centre, Agriculture and Agri-Food Canada, Box 3000, Lethbridge, AB, T1J 4B1, Canada wenzhu.yang@agr.gc.ca.
authors.forename: W Z
authors.initials: WZ
authors.lastname: Yang
authors.affiliation: Research Centre, Agriculture and Agri-Food Canada, Box 3000, Lethbridge, AB, T1J 4B1, Canada Bao Tou Light Industry Vocational Technical College, Jianhua Road, P.O. Box 19, Baotou, Inner Mongolia, China 014035.
authors.forename: L
authors.initials: L
authors.lastname: Xu
authors.affiliation: Research Centre, Agriculture and Agri-Food Canada, Box 3000, Lethbridge, AB, T1J 4B1, Canada College of Animal Science, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, China.
authors.forename: Y L
authors.initials: YL
authors.lastname: Zhao
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Canada T6G 2P5.
authors.forename: L Y
authors.initials: LY
authors.lastname: Chen
authors.affiliation: Research Centre, Agriculture and Agri-Food Canada, Box 3000, Lethbridge, AB, T1J 4B1, Canada.
authors.forename: T A
authors.initials: TA
authors.lastname: McAllister
mesh_terms: D000138:Acidosis / Q000139:chemically induced / Q000662:veterinary*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000139:chemically induced*; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D004063:Digestion / Q000502:physiology; D004386:Duodenum / Q000502:physiology; D002523:Edible Grain; D005260:Female; D005285:Fermentation; D001467:Hordeum; D008985:Monensin / Q000494:pharmacology*; D012417:Rumen / Q000737:chemistry*; D012820:Silage; D014908:Triticum / Q000737:chemistry / Q000145:classification*
chemical_list: D008985:Monensin
keywords: barley; beef heifers; digestibility; monensin; ruminal pH and fermentation; soft and hard wheat