Heat stress can compromise intestinal integrity and induce leaky gut in a variety of species. Therefore, the objectives of this study - published in Journal of Animal Science - were to determine if heat stress directly or indirectly (via reduced feed intake) increases intestinal permeability in growing pigs.

Authors S.C. Pearce of Iowa State University and colleagues there and Virginia Tech University hypothesised that an increased heat-load causes physiological alterations to the intestinal epithelium, resulting in compromised barrier integrity and altered intestinal function that contributes to the overall severity of heat stress-related illness.

Crossbred gilts (n=48, 43±4kg bodyweight) were housed in constant climate-controlled rooms in individual pens and exposed to:

1. thermal neutral (TN) conditions (20°C, 35–50 per cent humidity) with ad libitum intake,
2. heat stress conditions (35°C, 20–35 per cent humidity) with ad libitum feed intake, or
3. pair-fed in TN conditions (PFTN) to eliminate confounding effects of dissimilar feed intake.

Pigs were sacrificed at one, three or seven days of environmental exposure and jejunum samples were mounted into modified Ussing chambers for assessment of transepithelial electrical resistance (TER) and intestinal fluorescein isothiocyanate (FITC)-labelled lipopolysaccharide (LPS) permeability (expressed as apparent permeability coefficient, APP).

Further, gene and protein markers of intestinal integrity and stress were assessed.

Irrespective of day of heat stress exposure, plasma endotoxin levels increased 45 per cent (P<0.05) in heat stressed compared with TN pigs, while jejunum TER decreased 30 per cent (P<0.05) and LPS APP increased two-fold (P<0.01).

Pigs heat-stressed on day 7 tended (P=0.06) to have increased LPS APP (41 per cent) compared with PFTN controls.

Lysozyme and alkaline phosphatase activity decreased (46 and 59 per cent, respectively; P<0.05) over time in heat stress pigs, while the immune cell marker, myeloperoxidase activity, was increased (P<0.05) in the jejunum on days 3 and 7.

Pearce and co-authors conclude their results indicate that both heat stress and reduced feed intake decrease intestinal integrity and increase endotoxin permeability. They hypothesise that these events may lead to increased inflammation, which might contribute to reduced pig performance during warm summer months.

Reference

^{Pearce S.C., V. Mani, T.E. Weber, R.P. Rhoads, J.F. Patience, L.H. Baumgard and N.K. Gabler. 2013. Heat stress and reduced plane of nutrition decreases intestinal integrity and function in pigs. J. Anim. Sci. 91(11):5183-5193. doi: 10.2527/jas.2013-6759.}

November 2013