Patterns of carbohydrate and protein digestion in the chicken as derived from sampling the hepatic portal system

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Abstract
A technique for chronic catheterization of the hepatic portal system of the chicken via the duodenal vein is described. The system has been used to evaluate digestive processes in fasted, adult White Leghorn males by repeatedly measuring differences in glucose and amino-N between portal and wing vein blood (i. e., portal increments) following a test meal. The system was found to be sufficiently sensitive to follow carbohydrate and protein digestion, using as little as 13 g. of a practical poultry ration as a test meal. Digestion and absorption began rapidly, with near peak portal increments of both glucose and amino-N occurring approximately 15 minutes after a test meal. A consistent, positive portal increment of amino-N was observed after 16-18 hours of fasting, presumably from endogenous sources. Amino-N absorption appears to be completed sooner than glucose (by 2 hours) whereas signs of glucose absorption were seen for as long as 6 hours. Systemic levels of amino-N were elevated only during the first half hour, then they fell below starting levels, although absorption of both amino-N and glucose were still preceeding, and systemic glucose remained elevated. Force-feeding per se apparently had little effect on the absorption patterns of glucose and amino-N presented by the portal increments, but tended to be associated with lower peripheral levels than ad lib. feeding, particularly in glucose. Size of a force-fed test meal, dry weight equal to 1 or 0.5 % of body weight, and in a suspension with 1 ½% times its weight in water, was negligible on the absorption pattern, but the 1 % level is considered a maximum because of a tendency for regurgitation.