Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/9/2009
Publication Date: 3/1/2010
Citation: Krizsan, S.J., Ahvenjarvi, S., Volden, H., Broderick, G.A. 2010. Estimation of rumen outflow in dairy cows fed grass silage-based diets by use of reticular sampling as an alternative to sampling from the omasal canal. Journal of Dairy Science. 93:1138-1147. Interpretive Summary: The dairy cow obtains her needs for amino acids, the building blocks of proteins, mostly from protein formed by the microbes living in the rumen, the first compartment of the cow's stomach. The balance of the cow’s protein supply derives from feed protein that escapes breakdown in the rumen. Moreover, energy supply to the cow is also determined largely by digestion occurring in the rumen. However, a great many factors, such as dietary composition, level of intake, and the rate of digestion and passage in the rumen, influence both the amounts of microbial protein produced in the rumen and dietary protein escaping the rumen undegraded. That is why it is essential that experiments be conducted to measure the effects of many diet characteristics that can influence these processes in the rumens of typical dairy cows. In the last few years, these measurements have been made using cows with rumen cannulas (holes made into the rumen by veterinarians using surgery) to sample digesta (partially digested feed) as it flows through the omasum (the stomach compartment immediately after the rumen). This approach allows accurate measurement of protein outflow from the rumen, but it requires elaborate equipment to aspirate digesta samples from the omasal compartment of the stomach. We conducted an experiment using eight cows with rumen cannulas and collected digesta using both the elaborate omasal sampling equipment or using only a beaker to obtain digesta just before it left the rumen. There were small differences in characteristics of the digesta samples collected using the two different approaches. However, both techniques gave similar measurements of the flow of microbial protein and feed protein out of the rumen, and similar measurements of nutrient digestion in the rumen. This research indicates that protein and energy digestion in the rumen can be measured accurately in rumen cannulated dairy cows without the use of elaborate omasal sampling techniques. This research will allow many more dairy scientists to more easily determine how a multitude of dietary factors affect the nutrition and well-being of lactating cows. Dairy farmers will benefit as application of this new research approach leads to more answers about how different dietary characteristics alter the nutrition of their cows.
Technical Abstract: TA study was conducted to compare nutrient flows determined by a reticular sampling technique with those made by sampling of digesta from the omasal canal. Six lactating dairy cows fitted with ruminal cannulas were used in a design with a 3 x 2 factorial arrangement of treatments and 4 periods. Treatments were 3 grass silages mainly differing in neutral detergent fiber (NDF) concentrations: 412 (G1), 530 (G2), or 639 (G3) g/kg of dry matter (DM), each combined with 1 of 2 levels of concentrate feed. Digesta was collected from the reticulum and the omasal canal to represent a 24-h feeding cycle. Nutrient flow was calculated using the reconstitution system based on 3 markers (Co, Yb and indigestible NDF) and using 15N as microbial marker. Large and small particles and the fluid phase were recovered from digesta collected at both sampling sites. Bacterial samples from the reticulum and the omasum were separated into liquid and particle associated bacteria. Reticular samples were sieved through a 1-mm sieve before isolation of digesta phases and bacteria. Composition of the large particle phase differed mainly in fiber content between the digesta obtained from the two sampling sites. Sampling site did not affect marker concentration in any of the phases with which the markers were primarily associated. The 15N enrichment of bacterial samples did not differ between sampling sites. The reticular and omasal canal sampling techniques gave similar estimates of marker concentrations in reconstituted digesta, ruminal flow estimates, and ruminal digestibilities of DM, organic matter, starch and N. Sampling site x diet interactions also were not significant. Concentration of NDF was 2.2% higher in reconstituted omasal digesta than in reconstituted reticular digesta. Ruminal NDF digestibility was 2.7% higher when estimated by sampling the reticulum than the omasal canal. The higher estimate of ruminal NDF digestibility with the reticular sampling technique was due to differences in NDF concentration of reconstituted digesta. This study shows that nutrient and microbial protein outflow from the rumen can be measured using a reticular sampling technique. The reticular sampling technique provides a promising alternative to sampling from the omasal canal because there is less interference with the animal and does not require advanced sampling equipment.