Effects of dietary hydroxides on intake, digestion, rumen fermentation and acid-base balance in sheep fed a high-barley diet

Eight mature wethers fitted with rumen cannulae were used in a double 4 X 4 Latin square feeding trial to study the effect of dietary alkalis on digestive physiology of sheep fed a high-barley diet. The treatments were: C = control diet composed of 17% alfalfa meal and 83% concentrate, on as-fed basis; CA = control plus 1% Ca(OH)2; MG = control plus 0.79% Mg(OH)2; CAMG = control plus 0.5% Ca(OH)2 and 0.39% Mg(OH)2. Dry matter intake averaged 1.91, 2.54, 2.79, and 2.72% of BW for diets C, CA, MG and CAMG, respectively (P < 0.01). Digestible DM intake was also affected by the treatments and averaged 0.97, 1.26, 1.35 and 1.37 kg d-1 for C, CA, MG, and CAMG diets, respectively (P < 0.01). Apparent DM digestibility was higher in sheep fed the C diet than in those fed the other diets (P < 0.03) and it was inversely related to intake (P < 0.01). Total VFA concentration was lower in sheep fed C than in those fed the hydroxides (P < 0.01). Proportions of individual VFA were not altered by the diet except for isobutyrate which was higher in sheep fed the C diet (P < 0.01). Rumen NH3-N concentration was lower in sheep fed the hydroxide-containing diets than in animals fed the control diet (P < 0.01). Plasma urea nitrogen was lower for the C diet (P < 0.01). Plasma glucose tended to be lower for the C diet than for the other diets (P < 0.06). The control diet induced a mild form of systemic acidosis as indicated by the decrease in blood pH, HCO3- and base excess (P < 0.01). Addition of Ca(OH)2 and Mg(OH)2 to the diet, alone or in combination, improved the systemic acid-base status of sheep and was associated with increased DM intake.