Evaluation of a duodenal cannula for dairy cattle.

Two dairy cows fitted with rumen cannulas and closed T-shaped duodenal cannulas were utilized to examine duodenal cannula function and indigestible marker performance. Cows were fed one of two mixed diets and hay separately twice daily. Diets contained sources of supplemental protein that differed in expected rate of ruminal degradation. Duodenal DM flow was estimated with the indigestible markers, Cr-mordanted cell wall, Yb-soaked whole crop oat silage, and Co-EDTA. Duodenal DM flow using Co-EDTA was 49% higher than that estimated by reference to Cr-mordanted cell wall; Yb estimated an intermediate flow. Results are interpreted to suggest that the system developed to estimate duodenal digesta flow was not completely successful. However, qualitative assessment indicates that results are substantially better than those previously observed with simple gutter-type T-piece duodenal cannulas. Application of biological tests to the results suggests the failure of the system was not a result of cannula failure per se but due to the method of indigestible marker administration. Cows fed rumen-degraded proteins (slow versus rapid) had higher rumen nonammonia N pools, a trend for higher forestomach fiber fermentation, and a trend for lower forestomach digestion of N. These results are consistent with current knowledge of the influence of slowly degraded proteins on rumen fermentation.