Short communication: Relationships between physical form of oats in starter, rumen pH, and volatile fatty acids on hepatic expression of genes involved in metabolism and inflammation in dairy calves

In early-weaning programs, dietary effects on calf rumen development have been studied extensively, but very little information is available about the effects of a solid diet on hepatic metabolism in preweaned dairy calves. The objective of this experiment was to determine the effect of physical form of oats in calf starter on the expression of key hepatic gluconeogenic, β-oxidation, and acute phase protein genes in preweaned dairy calves. Samples were analyzed from 3 experiments that fed either ground or whole oats in calf starters. Briefly, 7 calves were slaughtered at 5 wk of age in experiment 1, 6 were slaughtered at 6 wk in experiment 2, and 7 were slaughtered at 7 wk in experiment 3, and liver tissue was collected for gene expression analysis. Calves from experiments 1 and 2 were cannulated, and their rumen pH and volatile fatty acids were measured during treatment periods. The mRNA expression of gluconeogenic enzymes pyruvate carboxylase (PC), cytosolic and mitochondrial phosphoenolpyruvate carboxykinase (PCK1 and PCK2), fatty acid oxidation enzyme carnitine palmitoyltransferase I (CPT1), and positive acute phase protein haptoglobin (HPT) was measured by real-time quantitative reverse-transcriptase PCR. Expression of HPT was greater in calves fed whole oats than in calves fed ground oats; however, PC, PCK1, PCK2, and CPT1 were not affected by the physical form of oats. All enzymes (PCK1, PCK2, HPT, and CPT1) except PC were affected by experiment; PCK1 and CPT1 had greater expression in experiment 2 than in experiments 1 and 3. Expression of PCK2 was similar in experiments 2 and 3 but greater than experiment 1. Expression of HPT was similar in experiments 1 and 2 but greater than experiment 3. The mRNA expression of enzymes PCK1, PCK2, and CPT1 differed between experiments 1 and 2 and was negatively correlated with rumen propionate and butyrate but had a positive relationship with rumen acetate. Similarly, rumen pH was different in experiments 1 and 2, averaging 5.69 in experiment 1 and 4.81 in experiment 2, and there was a negative correlation between mRNA expression of rate-limiting gluconeogenic PCK1, PCK2, and β-oxidation CPT1 enzymes and rumen pH of calves in experiments 1 and 2. We concluded that the physical form of oats in calf starter did not affect gene expression of gluconeogenic and β-oxidation enzymes in preweaned dairy calves. However, lower rumen pH may be related to the upregulation of these enzymes.