Effects of the inclusion of dried molassed sugar beet pulp in a low-forage diet on the digestive process and blood biochemical parameters of Holstein steers.

摘要

We evaluated the effects of substituting various concentrations of dried molassed sugar beet pulp (SBP) for barley grain in low-forage diets on chewing behavior, ruminal fermentation, nutrient digestibilities and blood biochemical parameters using four ruminally cannulated Holstein steers in a 4x4 Latin square design over 28-day periods. Steers (368+or-8 kg initial body weight) were fed 9.5 kg of dietary dry matter (DM) as a total mixed ration (TMR) (containing 350 g forage and 650 g concentrate per kg DM) twice daily at 0800 and 1600 h. The diets were formulated to supply approximately 2.3 times the maintenance requirements of the animals so that there was no refusal. Barley grain in the basal experimental diet (330 g/kg DM) was replaced with 0, 110, 220 and 330 g SBP on a DM basis to create the experimental diets SBP0, SBP110, SBP220 and SBP330, respectively. Ruminal fluid was collected by suction through the rumen cannula from before the morning feeding (0.0 h) to 8 h after feeding at 30-min intervals. Eating, ruminating and total chewing time linearly (P<0.01) increased with the proportion of SBP in the diet. Moreover, mean ruminal pH showed linear and quadratic increases (P<0.05) with the inclusion of SBP. In contrast, the substitution of SBP for barley grain resulted in a linear and quadratic decrease (P<0.01) in the mean ruminal ammonia concentration, which was highest in steers fed SBP0. In addition inclusion of SBP gave significantly (P<0.05) higher acetate and butyrate molar proportions and lower propionate and total volatile fatty acids (VFA) concentrations in the rumen fluid. Total tract apparent digestibility of DM and neutral detergent fiber (NDF) increased quadratically with the proportion of SBP in the diet, but crude protein (CP) and acid detergent fiber (ADF) digestibilities were similar among treatments. Plasma urea nitrogen (PUN) before the morning feeding decreased linearly (P<0.01) with SBP inclusion and was highest and lowest for SBP0 and SBP330, respectively (21 vs. 16.26 mg/dl). Other blood biochemical parameters and venous blood gasses (including plasma glucose, blood pH, CO₂ pressure, O₂ pressure, oxygen saturation, base excess of extracellular fluid, base excess of blood and bicarbonate) were not affected by the treatments (P >0.05). These results suggest that partial replacement of barley grain with SBP at low and moderate inclusion rates might improve the chewing behavior, ruminal environment and nutrient digestibility of Holstein steers fed low-forage diets.