THE EFFECTS OF PARTIAL REPLACEMENT OF BARLEY STARCH WITH SUGARS ON RUMINAL FUNCTION, OMASAL NUTRIENT FLOW, UREA-N RECYCLING, AND PRODUCTION PERFORMANCE IN DAIRY COWS.
De Seram, Eranga Lakshitha 1986-
A considerable number of studies have shown that the partial substitution of corn starch with sugars is beneficial in terms of improving dry matter (DM) intake, milk yield and efficiency of nitrogen utilization in dairy cows without putting them at risk of developing ruminal acidosis; however, research with dairy cows fed barley-based diets is limited. The objective of this study was to determine the effects of partial replacement of barley starch with dried whey permeate (DWP; contained 83% lactose) on ruminal acidosis, transport of short-chain fatty acids (SCFA) across the ruminal wall, urea-N recycling to the digestive tract, ruminal microbial protein production, omasal nutrient flow, and production performance in dairy cows. Eight Holstein cows (97 ± 10 days-in-milk; 733 ± 63 kg body weight) were used in a replicated 4 × 4 Latin square design with 28-d periods (18 d of adaptation and 10 d of measurements). Four cows in one Latin square were ruminally-cannulated to facilitate ruminal fluid and omasal digesta sampling. Cows were fed a barley-based diet (3.5% total sugar [TS]; control), or diets that contained 6.5, 9.5 or 12.5% TS (DM basis). Diets were isonitrogenous (17.3% crude protein) and contained 24.3, 22.2, 21.2, and 19.1% starch for the control, 6.5, 9.5 or 12.5% TS diets, respectively. Dietary inclusion of DWP did not affect DM intake (mean = 26.6 kg/d) and milk yield (mean = 34.9 kg/d); however, milk lactose content quadratically changed (4.40, 4.42, 4.46, and 4.40% for the control, 6.5, 9.5, and 12.5% TS diets, respectively) across diets. Ruminal concentration of acetate, propionate, and total SCFA were not affected by dietary treatment; however, ruminal concentration of butyrate was cubically increased (12.8, 13.0, 14.1, and 14.9 mM for the control, 6.5, 9.5, and 12.5% TS diets, respectively) as dietary content of DWP increased. When expressed as absolute (mmol/h) or fractional (%/h) rates of absorption, the rates of acetate, propionate, and total SCFA absorption across the ruminal wall were cubically decreased by the 9.5% TS diet compared to control and 6.5% TS diets, then increased by the 12.5% TS diet compared to the 9.5% TS diet. The rate of butyrate absorption across the ruminal epithelium tended to change cubically as level of dietary DWP increased. For individual and total SCFA, Cl--insensitive and Cl--competitive rates of absorption across the ruminal wall were largely unaffected by dietary treatment, except that the Cl--competitive absorption of propionate tended to be cubically altered as dietary content of DWP increased. Mean ruminal pH tended to change quadratically (6.32, 6.31, 6.34, and 6.22 for the control, 6.5, 9.5, and 12.5% TS diets, respectively) as dietary content of DWP increased. Dietary addition of DWP cubically changed the ruminal concentration of ammonia-N (NH3-N; 12.1, 12.3, 10.9, and 9.40 mg/dL for the control, 6.5, 9.5, and 12.5% TS diets, respectively). The omasal flow of bacterial N quadratically changed (513, 517, 539, and 468 g/d for the control, 6.5, 9.5, and 12.5% TS diets, respectively) as dietary content of DWP increased. The ruminal digestibility of DM linearly increased as dietary content of DWP increased, but total-tract DM digestibility was unchanged. The ruminal and total-tract digestibilities of water-soluble carbohydrates (WSC) cubically increased as dietary content of DWP increased. There were no dietary effects on ruminal and total-tract digestibility of neutral detergent fiber and acid detergent fiber. Total urinary N excretion quadratically changed (223, 255, 238, and 223 g/d for the control, 6.5, 9.5, and 12.5% TS diets, respectively), and fecal N excretion linearly increased as dietary content of DWP increased; however, productive N was unaffected by dietary TS content. Quadratic changes were observed in absolute amounts of endogenous production of urea-N (i.e., UER; 467, 531, 522, and 472 g/d for the control, 6.5, 9.5, and 12.5% TS diets, respectively). Although the absolute amount of urea-N transferred to the gastrointestinal tract (i.e., GER; 307, 354, 340, and 309 g/d for the control, 6.5, 9.5, and 12.5% TS diets, respectively) tended to change quadratically, there was no difference across diets when GER was expressed as a proportion of UER. Increasing dietary TS by adding DWP tended to change microbial utilization of recycled N in a cubic manner (15.8, 13.7, 15.8, and 15.9 % for the control, 6.5, 9.5, and 12.5% TS diets, respectively); however, recycled N that was utilized for anabolism (UUA) was unaffected by diets. These results suggest that the partial replacement of barley starch with DWP does not affect the production performance of dairy cows; however, dietary TS concentration of 9.5% potentially improve ruminal N efficiency by decreasing NH3-N concentration and increasing omasal microbial N flow.
DegreeMaster of Science (M.Sc.)
DepartmentAnimal and Poultry Science
CommitteePenner, Gregory; Van Kessel, Andrew; Buchanan, Fiona; Zello, Gordon
Copyright DateDecember 2016
Dried whey permeate