Comparative characterization of reticular and duodenal digesta and possibilities to estimate microbial outflow from the rumen based on reticular sampling in dairy cows

¹ Department of Animal and Veterinary Science, University of Idaho, Moscow, Idaho

^* To whom correspondence should be addressed. E-mail: ahristov{at}uidaho.edu.

	Abstract

The objective of this experiment was to investigate the possibility of estimating outflow of nutrients and microbial protein from the rumen based on sampling reticular contents as an alternative to duodenal sampling. Microbial protein flow estimates were also compared to a third method based on sampling of ruminal contents. Reticular and duodenal digesta and ruminal contents were recovered from 4 cows used in a 4 x 4 Latin square design experiment, in which the ruminal effects of 4 exogenous enzyme preparations were studied. Large and small particulate and fluid markers were used to estimate digesta flow in a triple-marker model; ¹⁵N was used as a microbial marker. Reticular and duodenal digesta was segregated into small and large particles (SP and LP) and fluid phase, and ruminal digesta into particulate and fluid phases. Compared with digesta recovered at the duodenum, reticular digesta had lower OM and higher NDF content. The proportion of microbial N was notably greater in the fluid phase of reticular digesta. Ruminal outflow of DM and OM were greater (by 17 and 28%) and that of NDF lower (by 14%) when estimated from duodenal than from reticular samples. There was no difference in the estimated flow of starch and non-ammonia and microbial N between the reticular and duodenal techniques. Microbial N flow estimated based on ruminal sampling was similar to those based on duodenal and reticular sampling. The ruminal method, however, grossly overestimated flow of DM, OM, and NDF. This study supports the concept that microbial protein outflow from the rumen can be measured based on sampling of ruminal or reticular digesta. The reticular sampling technique can also provide reliable estimates for ruminal digestibility of OM, N, and fiber fractions. These findings need to be confirmed in experiments with basal diets varying in structure and forage to concentrate ratios.

Key Words: dairy cow, duodenal digesta, microbial protein synthesis, reticular digesta

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