The Effect of Supplementation with Betaine and Zinc on In Vitro Large Intestinal Fermentation in Iberian Pigs under Heat Stress

SIMPLE SUMMARY: Heat stress has negative consequences in animal husbandry and pigs are highly susceptible because of their scattered sweat glands and elevated metabolic rate. Above 25 °C, pigs trigger mechanisms such as diverting blood from their internal organs to skin or decreasing the feed intake, which can affect the intestinal microbiota and capacity of fermentation. Betaine and zinc have been used as nutritional mitigation strategies to alleviate the effects of heat stress in pigs, but their effects on hindgut fermentation are unknown. By using an in vitro fermentation system and employing as the inoculum the rectal content from heat-stressed Iberian pigs supplemented or not with betaine or zinc, we showed that both supplements modified the pattern of hindgut fermentation in heat stressed pigs, having beneficial effects on acetate and butyrate production. The abundance of some bacterial groups was also modified, indicating an effect on the microbial structure. Because of the intricate interactions between the host and gut microbiota, additional studies are necessary to confirm these results under in vivo conditions. ABSTRACT: We investigated the effects of betaine and zinc on the in vitro fermentation of pigs under heat stress (HS). Twenty-four Iberian pigs (43.4 ± 1.2 kg) under HS (30 °C) were assigned to treatments for 4 weeks: control (unsupplemented), betaine (5 g/kg), and zinc (0.120 g/kg) supplemented diet. Rectal content was used as the inoculum in 24-hincubations with pure substrates (starch, pectin, inulin, cellulose). Total gas, short-chain fatty acid (SCFA), and methane production and ammonia concentration were measured. The abundance of total bacteria and several bacterial groups was assessed. Betaine increased the acetate production with pectin and inulin, butyrate production with starch and inulin, and ammonia concentration, and decreased propionate production with pectin and inulin. The abundance of Bifidobacterium and two groups of Clostridium decreased with betaine supplementation. Zinc decreased the production of SCFA and gas with starch and inulin, associated with diminished bacterial activity. Propionate production decreased with starch, pectin, and inulin while butyrate production increased with inulin, and isoacid production increased with cellulose and inulin in pigs supplemented with zinc. The ammonia concentration increased for all substrates. The Clostridium cluster XIV abundance decreased in pigs fed zinc supplemented diets. The results reported were dependent on the substrate fermented, but the augmented butyrate production with both betaine and zinc could be of benefit for the host.