Measurement of volatile fatty acid disappearance and fluid flux across the abomasum of cattle, using an improved omasal cannulation technique.

Six steer calves, surgically fitted with a permanent cannula in the rumen, omasoabomasal orifice, abomasum, and duodenum were used to determine total digesta flow and volatile fatty acid (VFA) concentration at various points in the digestive tract. The omasoabomasal cannula had a flexible nylon sleeve that could be exteriorized through the abomasal cannula to collect omasal effluent. Three experiments were conducted: 95% concentrate fed at maintenance (2,670 g of organic matter intake/d); 95% concentrate fed ad libitum (3,484 g of organic matter intake/d); and brome hay fed ad libitum (2,927 g of organic matter intake/d). Calves were offered the diet in 12 portions daily. Each experiment included a 14-day adaptation period and a 2-day sample collection period during which chromic oxide was used as a digesta flow marker. In all 3 experiments, VFA concentration was greatest in the rumen sample (84 to 109 mM), intermediate in the omasal sample (32 to 40 mM), and lowest in the duodenal sample (7 to 14 mM, P < 0.01). Total fluid flow at the duodenum was 13 to 18 L/d greater than flow at the omasum (P < 0.10). Omasal VFA flow was twofold greater than duodenal VFA flow (P < 0.05). There was a net fluid increase and net disappearance of VFA across the abomasum. The cannulation technique was useful for repeated collection of omasal effluent for at least 3 months.