Evaluation of n-alkanes as digesta markers in dairy cows

Recovery of hentriacontane (C31 alkane) in feces as influenced by amount consumed and level of dietary fat was examined in a 2 x 2 factorial study in a 4 x 4 Latin square. Treatments were 1) alfalfa hay:concentrate (70:30; AH); 2) AH + calcium soap (500 g/d); 3) grass hay:concentrate (70:30, GH); and 4) GH + calcium soap. Fat did not influence C31 recovery in feces. Fecal recovery (grams/day) decreased quadratically with increasing C31 intake. Compared with AIA, which was 100% recovered in feces, DM digestibility was estimated more accurately (P less than .05) by AIA than by C31. In a second experiment, site of loss of alkane in the intestinal tract was examined by dosing C32 into the rumen or duodenum. Recovery was lower with ruminal dosing, suggesting ruminal loss of the marker. Alkanes are potentially useful markers of particulate matter in the digestive tract; however, documentation of their behavior in a wider range of diets is needed.