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Heat stress (HS) negatively influences animal welfare and profitable pork production during the warm summer months. Environmental hyperthermia compromises the intestinal barrier function resulting in increased permeability to luminal content. HS-induced economic losses are a result of poor sow performance, reduced and inconsistent growth, decreased carcass quality, and increased veterinary costs. Dietary zinc improves a variety of bowel diseases, which are characterized by increased intestinal permeability. The main objectives of this study were to evaluate the effects of supplemental a premix of zinc as zinc amino acid complex (ZnAA) on intestinal integrity in heat-stressed growing pigs. Crossbred gilts (43 ± 6 kg BW) were ad libitum fed one of three diets: (1) control (ZnC; 120 ppm Zn as ZnSO4; n=13), (2) control +100 ppm Zn as ZnAA (Zn220; containing a total of 220 ppm Zn; n=14), and (3) control +200 ppm Zn as ZnAA (Zn320; containing a total of 320 ppm Zn; n=16). After 25 days on their respective diets, all pigs were exposed to constant HS conditions (36°C, ≈50% humidity) for either 1 or 7 days. At the end of the experiment, pigs were euthanized and blood and intestinal tissues were harvested immediately after sacrifice.
As expected, HS increased rectal temperature (P<0.01) and respiratory rate (P<0.01). HS caused an immediate and similar markedly decrease in FI and caused BW loss in all dietary treatments. Small intestine integrity parameters (permeability and resistance) markedly deteriorated with progressive heat exposure. As the results showed, as HS progressed from days 1 to 7, both ileal and colonic transepithelial electrical resistance (TER) decreased (P<0.05; 34% and 22%, respectively). This was mirrored by an increase in ileal and colonic permeability to the macromolecule dextran (P<0.01; 13- and 56-fold, respectively), and increased colonic lipopolysaccharide permeability (P<0.05; threefold) with time. There was a quadratic response (P<0.05) to increasing ZnAA on ileal TER, as it was improved (P<0.05; 56%) in Zn220-fed pigs compared with ZnC. Reasons why intestinal barrier function was not further improved in the Zn320-fed pigs is not clear, but there appears to be a breakpoint where excess dietary Zn is not beneficial and it may in fact have negative consequences.
It is concluded that HS progressively compromises the intestinal barrier and supplementing ZnAA at the appropriate dose can improve aspects of small intestinal integrity during severe HS.
Sanz Fernandez, M V, Pearce,S C, Gabler, N K, Patience, J F, Wilson, M E, Socha, M T, Torrison, J L, Rhoads, R P and Baumgard, L H. (2014). Effects of supplemental zinc amino acid complex on gut integrity in heat-stressed growing pigs. Animal, 8:1, 43–50. doi:10.1017/S1751731113001961