Effects of ruminal SCFA concentration and pH on histology, hematology, and inflammation in cannulated Holstein dairy calves.

Optimizing rumen development is key to preparing calves for weaning; however, it is unclear what effect rumen development has on calf health via ruminal infusion. This study investigated the effects of ruminal SCFA concentrations and pH on hematology, gut morphology, and inflammation of liver and rumen tissues in dairy calves. Holstein calves (n = 32) had the rumen cannulated within the first week of life and at wk 2 were blocked by body weight and randomly assigned in a 2 × 2 factorial arrangement of treatments. The treatments included 2 different SCFA concentrations (10 vs. 285 mM) and pH levels (5.2 vs. 6.2), yielding 4 treatment groups: low pH, low SCFA (LS-LP), low pH, high SCFA (LS-HP), high pH, low SCFA (HS-LP), and high pH, high SCFA (HS-HP). On wks 3, 5, and 7, calves underwent a 4-h reticulorumen wash procedure with a physiological buffer containing the various treatments. Blood samples were collected weekly after feeding. Rumen biopsies were taken after each infusion and liver and rumen samples were harvested at necropsy at wk 7. Data were analyzed with repeated measures, using week, SCFA and pH as fixed effects. Low rumen pH increased respiration rate, but no other changes in clinical parameters were observed. No differences were detected in red blood cells or platelet numbers. Total white blood cell numbers decreased in the LS-LP group from wk 5 to 7 but increased in the HS-LP group along with hemoglobin and the hematocrit during the same period. Cortisol and β-hydroxybutyrate levels were unchanged by treatment or time, while haptoglobin decreased over time regardless of treatment. Calf liver morphology was unaffected by treatment; ruminal tissue changes associated with epithelial cell sloughing tended to increase with low SCFA, and mucosal eosinophil infiltration increased with high SCFA. Gene expression was unchanged by treatment in both rumen (barrier function and inflammation) and liver (inflammation). Overall, the data demonstrate that stress and inflammatory responses can be impacted by changing rumen environments. Notably, these changes are transient as values returned to pretreatment baseline levels after a period as short as a week.