Differences in monocarboxylic acid transporter type 1 expression in rumen epithelium of newborn calves due to age and milk or milk replacer feeding.

The aim of the present study was to investigate whether besides age and solid feed intake, monocarboxylic acid transporter type 1 (MCT1) expression in the rumen epithelium of calves is affected by liquid feed type [whole milk (WM) or milk replacer (MR)]. Thirty bull calves at the mean age of 5 days were randomly allocated to five experimental groups (six calves/group). Six calves were slaughtered immediately after allocation to the trial (5 days of life), eighteen calves were fed MR and slaughtered at week intervals (on 12, 19, 26 days of life respectively), and six calves were fed WM and slaughtered at the 26 days of life. MCT1 protein abundance and the MCT1 mRNA level were investigated in the dorsal and ventral sack of the rumen. Solid feed intake and short-chain fatty acids (SCFA) concentration in the rumen fluid increased linearly with calves' age. The amount of the MCT1 protein and mRNA in the dorsal sac of rumen as well as the amount of MCT1 protein in the cranial ventral sac of rumen also increased linearly with calves' age. Calves fed WM had greater solid feed intake in the last week of the study as compared to calves fed MR, but SCFA concentration in the rumen fluid was not different. MCT1 mRNA expression in the cranial dorsal sac of rumen and protein MCT1 expression in both dorsal and ventral cranial sack of the rumen were higher in calves fed WM as compared to calves fed MR. This study confirmed age-dependent changes of MCT1 expression in the rumen epithelium of newborn calves and showed that its expression might be affected by liquid feed type. Journal of Animal Physiology and Animal Nutrition