TRANSCRIPTOMIC CHANGES IN RUMINAL TISSUE INDUCED BY THE PERIPARTURIENT TRANSITION IN DAIRY COWS

Abstract

To understand how the capacity for fat metabolism (uptake, synthesis, modification) changes in rumen epithelia immediately before and after onset of lactation in dairy cows, rumen fluid Short Chain Fatty Acid (SCFA) concentrations and mRNA expression profiles of rumen epithelia was determined in twelve Holstein dairy cows at three weeks prior to calving (wk -3, n = 12), one week post calving (week +1, n = 12) and six weeks (week +6, n = 12) after calving. The diet was modified from a dry cow formulation to a lactating cow formulation immediately following parturition and raised the non-fiber carbohydrate level from 34 to 43%. All data was analyzed using the mixed procedure of SAS, with cows blocked by anticipated calving date and week of sampling as the repeated measure. Propionate, butyrate, isovalerate and valerate levels rose significantly following the diet change (p≤0.001), although acetate and isobutyrate levels were unchanged (p>0.05). Mean rumen pH also changed during the transition period (6.38 Vs 5.81 and 5.85±0.08; -3 Vs +1 and +6; p<0.001) as did mean BW (716.00 Vs 635.82 kg and 615.45 kg ±16.20; -3 Vs +1 and +6; p≤0.002). Microarray analysis of total RNA from rumen epithelial biopsies revealed 1476 differentially expressed genes at a false discovery rate of 10%. These results were filtered for genes that were directly related to both the immune system and fat metabolism/homeostasis. Consequently, the expression of the resulting 28 genes was analyzed by quantitative PCR (qRT-PCR) to compare their expression at period -3 versus +6 periods. qRT-PCR analysis revealed that 13 genes were upregulated (p≤0.01), 2 were downregulated (p≤0.01) and 13 were unchanged during the transition period. Pathway and context analysis yielded a unique interactome pathway map which revealed a set of genomic interactions that indicate a link between selected genes from the immune system and those involved in the preparation for lactation.