Physiological effects of starter-induced ruminal acidosis in calves before, during, and after weaning

摘要

The objectives were to nutritionally induce or bluntruminal acidosis in young calves and to compare indicatorsof rumen and systemic health. Ten bull calves (n =5/diet) were ruminally cannulated at 3 wk of age andreceived milk replacer and 1 of 2 calf starter diets thatwere designed to cause (AC; pelleted, 42.7% starch,15.1% neutral detergent fiber, 57.8% nonfiber carbohydrates)or blunt (BL; texturized, 35.3% starch, 25.3%neutral detergent fiber, 48.1% nonfiber carbohydrates)ruminal acidosis. Mean birth weight was 38.7 ± 1.3kg. Body weight and calf starter intake were measuredweekly. Rumen contents were sampled at −8, −4, 0, 2,4, 8, 12, and 24 h relative to starter feeding during wk6, 8, 10, 12, 14, and 16 of age. Blood was collected fromthe jugular vein during the same weeks for completeblood cell count, blood pH, and partial pressures ofoxygen and carbon dioxide. Rate of starter consumptionwas assessed during wk 16. Marker systems wereused to estimate liquid passage and volatile fatty acidabsorption rates. Calves were slaughtered at 17 wk, andrumen tissue was collected and assessed for papillaelength, width, and degree of tissue degradation. Meanruminal pH ± standard error was 5.37 ± 0.24 and 5.63± 0.24 for AC and BL calves, respectively. Lowest pHvalues were observed the week after weaning. Total ruminalvolatile fatty acid concentrations were 131.5 and124.8 ± 2.4 mM in AC and BL calves, respectively, andincreased with age and time after feeding. Dry matterintake was lower in AC calves at wk 4 and remainedlower through wk 16. Rate of starter consumption wasalso lower in AC calves at wk 16. Body weight also wasalso lower for AC calves from wk 5 through 16. Bloodhemoglobin and hematocrit were lower in AC calves, butother blood characteristics were not different. Rumenvolume increased with age and tended to be greater inBL calves. Passage rate and papillae length and widthwere not different between diets, but AC calves experienceda greater degree of tissue degradation. Ruminalacidosis symptoms in calves appear similar to those inadult cattle, and the etiology of the disease seems tofollow similar mechanisms. It is clear from this studythat symptoms can be moderated by diet, but furtherresearch is needed to determine whether symptomscan be nutritionally prevented or whether calves thatexperience ruminal acidosis are more susceptible to thedisease as adults.