In vitro digestibility of expanded pork skin and rawhide chews, and digestion and metabolic characteristics of expanded pork skin chews in healthy adult dogs1

Abstract

Chews are an important part of the pet product industry, with many having potential to decrease plaque or calculus formation. However, their digestion characteristics and gut transit time are virtually unknown. Two experiments were conducted to determine in vitro DM digestibility of expanded pork skin chews and rawhide chews, and apparent total tract digestibility (ATTD), gastrointestinal transit time, and blood metabolite measurements in healthy adult dogs fed a weight-control commercial diet and expanded pork skin chews. In Exp.1, an in vitro method that simulated gastric and small intestinal digestion was used to determine DM digestibility of expanded pork skin chews and rawhide chews. In Exp. 2, after a 22-d baseline phase, 10 purpose-bred, intact female dogs (5 to 5.5 yr of age; 18.9 to 23.1 kg BW) were fed the diet plus an expanded pork skin chew (~45 g) each day for 22 d. In vitro gastric digestibility of expanded pork skin chews increased with time, with chews being 54.7%, 58.6%, 76.4%, and 86.4% digestible after 6, 12, 18, and 24 h of gastric digestion, respectively. By contrast, gastric digestibility of rawhide chews was 7.6% at 6 h, slowly increased over time, and reached a maximum of 41.6% at 18 h. In vitro gastric plus small intestinal digestibility results indicated near complete digestibility of expanded pork skin chews at all times, whereas rawhide chews were 50 to 85% digestible. In vivo ATTD of DM, OM, and N were greater (P < 0.05) when dogs were fed expanded pork skin chews along with the basal diet, compared with the basal diet alone. However, chew intake did not change transit time measured with a wireless motility device. By contrast, motility index and contraction pattern of the colon were altered (P < 0.05) during chew feeding relative to control. Blood urea N concentrations were greater (P < 0.05) in dogs fed expanded pork skin chews, compared with baseline; this was not surprising, given the increased N intake and absorption from the chews. Intake of expanded pork skin chews resulted in reduced blood cholesterol concentrations (P < 0.05) and tended to decrease blood triglyceride concentrations (P < 0.10). Expanded pork skin had a greater DM digestibility than rawhide chews. In addition, expanded pork skin decreased blood cholesterol and triglyceride concentrations, which may justify further research in this area.