Effect of resistant starch on the intestinal health of old dogs: fermentation products and histological features of the intestinal mucosa†

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Ageing can be defined as the progressive changes that occur after the maturity of several organs resulting in reductions in their functional ability (Fahey Junior, Barry, & Swanson, 2008). Intestinal morphology can be altered by ageing, and elderly animals have a lower surface area of duodenal villi, a reduced height of jejunal villi, and deeper crypts in the colon (Larsen & Farcas, 2014). Generally, small intestine motility and its absorption ability appear to remain intact in healthy old dogs as some studies have shown no age effect on nutrient digestibility and absorption (Gomes et al., 2011; Sheffy, Williams, Zimmer, & Ryan, 1985). However, the gut microbiota and the faecal concentrations of fermentation products differ among elderly and adult subjects (Kuzmuk, Swanson, Tappenden, Schook, & Fahey, 2005). Faecal concentrations of butyrate, histamine, agmatine, and spermine were shown to be lower and faecal pH higher in Beagle dogs of 10 years old compared with adults of 4 years old, suggesting alterations in bacterial metabolic activity or in the rate of intestinal absorption of these compounds (Gomes et al., 2011). Recently, scientific interest has been emerged on the modifications of gut microbiome with ageing in human beings, and the dietary interventions to programme the microbiota composition and activities that promote healthier ageing (O'Connor, O'Herlihy, & O'Toole, 2014).
Resistant starch (RS) is the sum of the starch and its degradation products that resist digestion in the small intestine and reach the colon (Nugent, 2005). In the colon, RS is readily fermented, altering the colon's environment through effects on bacterial populations and fermentation activity, reducing faecal pH, and increasing butyrate concentration (Birkett, Muir, Phillips, Jones, & O`Dea, 1996; Simpson, 1998). Short‐chain fatty acids (SCFA) derived from the bacterial fermentation of RS are the major substrates for the energy metabolism of colonocytes, and specifically, butyrate acts as a growth factor for a healthy epithelium in the colon (Ashwar, Gani, Shah, Wani, & Masoodi, 2016; Bird, Vuaran, Brown, & Topping, 2007; Birt et al., 2013; Zaman & Sarbini, 2016). Butyrate stimulates the regeneration of injured intestinal tissue after inflammation and may have a role in the prevention of several types of colitis in animals and humans (Brouns, Kettlitz, & Arrigoni, 2002; Moreau et al., 2003; Scheppach, 1994).
Based on this, it is possible that the intake of RS by old dogs promotes the production of SCFA and specifically of butyrate, favouring nutrient supply to the intestinal mucosa and possibly attenuating some effects of the age‐related alterations in their histological structure. Therefore, the objectives of this study were to evaluate the effects of two concentrations of RS in extruded diets on nutrient and energy digestibility, faecal concentration of fermentation products and IgA, and the histological features of the gastrointestinal mucosa of old dogs.
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