Potential contribution of absorbed volatile fatty acids to whole-animal energy requirement in conscious swine

Chronic cannulas were placed in the hepatic portal vein, ileal vein, and carotid artery in seven crossbred growing gilts trained to consume once daily 1.2 kg of a 16% CP corn-soybean meal diet. Eleven days after surgery, each pig (37.4 kg BW) was placed in an open-circuit calorimeter and its cannulas were connected to a system for determining portal absorption of nutrients. The whole-animal heat production and net portal absorption of gut VFA were measured simultaneously for 12 h after the pig was fed 1.2 kg of feed. Plasma concentrations of VFA, including acetic, propionic, isobutyric, butyric, isovaleric, and valeric acids, in portal and arterial samples were determined by gas chromatography after a cleanup by ion-exchange chromatography. The net portal absorption of VFA was calculated by multiplying the porto-arterial plasma concentration difference of the VFA by portal vein plasma flow. Plasma flow was estimated by the indicator-dilution technique using p-aminohippuric acid as the indicator. The energy value of absorbed VFA was the sum of products of each individual VFA multiplied by its corresponding value of the heat of combustion. The mean hourly energy value of absorbed VFA during the 12-h postprandial period was .65 +/- .03 kcal.h-1.kg BW-1. The mean hourly whole-animal heat production was 2.70 +/- .04 kcal.h-1.kg BW-1. Thus, in our 37.4-kg pigs, which were trained to consume 1.2 kg of a 16% CP corn-soybean meal diet once daily, the gut VFA absorbed into the portal vein could contribute 23.8 +/- 1.1% to whole-animal heat production if all of the absorbed VFA were combusted to CO2.