Barrier Function of the Gastrointestinal Tract of Holstein Steers When Exposed to Ruminal Acidosis and Low Feed Intake

Abstract

Ruminal acidosis and low feed intake are two nutritional challenges present on beef and dairy operations that result in reduced health and performance. The objective of this study was to determine the regional susceptibility of the gastrointestinal tract (GIT) to ruminal acidosis (RA) or low feed intake (LFI). Twenty-one Holstein steers, aged 6 to 8 mo, were blocked by body weight (BW) and within block randomly assigned to 1 of 3 treatments: 1) control (CON), 2) RA, and 3) LFI. All steers were fed a diet containing a 50:50 forage to concentrate ratio (F:C) and were exposed to a 5-d measurement period. The CON steers were provided the basal diet for ad libitum intake, the LFI steers were fed at 25% of ad libitum intake for 5 d before humane killing while the RA steers were restricted to 25% intake for 1 d and then were fed 30% of dry matter intake (DMI) in pelleted barley followed by their regular total mixed ration (TMR) allocation. The RA steers were killed 1 d after the RA challenge. After killing, tissues from the rumen, omasum, duodenum, jejunum, ileum, cecum, proximal, and distal colon were collected. Digesta from those regions were assessed and tissues were mounted in Ussing chambers in order to assess permeability using the mucosal-to-serosal flux of inulin (JMS-inulin) and mannitol (JMS-mannitol) and tissue conductance (Gt). Digesta pH were less for RA than CON in the rumen, cecum, and proximal colon while LFI had greater pH in the rumen and proximal colon compared to CON. Ruminal short-chain fatty acid (SCFA) concentrations in the rumen were less for the LFI (P = 0.010) and RA (P = 0.007) compared to CON steers. In the proximal colon, there was a greater proportion of butyrate (P = 0.025 and P = 0.022) and isobutyrate (P = 0.019 and P = 0.019), and a lower proportion of acetate (P = 0.028 and P = 0.028) for LFI and RA, respectively, when compared to CON steers. The JMS-mannitol differed between the CON and LFI steers in the proximal colon (P = 0.041) and in the distal colon (P = 0.015) with the LFI steers having a lower flux rate in both regions. Increases in gene expression for genes related to barrier function (in the rumen, jejunum, and distal colon), mucosal immunology (rumen and jejunum), and adaptive immunity (jejunum) were observed indicating compensatory mechanisms may have been stimulated. It was concluded from this study that an acute RA challenge had no effect on tissue permeability throughout the GIT within 1 d of the challenge, while steers that were on LFI for 5 d had reduced tissue permeability in the proximal and distal colon while other regions of the GIT were unaffected. Further research is needed to analyze different management strategies proposed to mitigate the negative impact of LFI shown in production animal agriculture.