A comparison of markers for estimating magnitude of rumen digestion

Effects of starch and protein sources on starch disappearance in the gastrointestinal tract of Hanwoo (Korean native) steers

Hanwoo (Korean native) steers (274.8 +/- 4.6 kg) with ruminal and duodenal cannulae were used in a 4 x 4 Latin square design experiment to examine the effects of dietary treatments on starch disappearance in the gastrointestinal tract. Dietary treatments consisted of concentrate that were based on ground corn with soybean meal (C-SBM), ground corn with corn gluten meal (C-CGM), ground barley with soybean meal (B-SBM) and ground barley with corn gluten meal (B-CGM). Although the intakes of starch and protein for steers fed experimental diets were different, it did not change ruminal pH and total volatile fatty acid concentrations. Average duodenal CP flow and quantity of CP apparently digested post-ruminally was higher (P = 0.001) for CGM-based diets than SBM-based diets. There were increases in quantity (P < 0.001) and percentage (P < 0.001) of corn starch digested post-ruminally compared to barley starch. Synchronized diets showed higher percentages (P = 0.03) of starch apparently digested post-ruminally than asynchronization. Hanwoo steers fed a corn-based diet with a large quantity of starch reaching the duodenum and fed C-CGM supplying great amounts of protein to the small intestine may have contributed to increased post-ruminal starch digestion.

Modeling ruminal digestibility of carbohydrates and microbial protein flow to the duodenum

Carbohydrates are the major source of energy for dairy cows and for microbial protein synthesis in the rumen. The prediction of ruminal carbohydrate digestibility and of the flow of microbial protein to the small intestine is difficult because of the variability among various feeds in the kinetics of digestion and passage of neutral detergent fiber and starch. Disappearance of fiber and starch in vitro or in situ and gas production in vitro have been extensively evaluated, improved, and reviewed. Similarly, markers and models to measure ruminal passage rate have been extensively researched and improved. Sources of variation and decreased accuracy for these techniques are discussed. Variation and potential errors also remain for the prediction of microbial protein flow to the duodenum using in vivo procedures. However, when in vivo results were accumulated into a database, microbial N flow to the duodenum over a wide range of conditions could be predicted accurately by intake of net energy for lactation or by dry matter intake and percentage of neutral detergent fiber in the diet. Although evaluation of feeding interactions and specific dietary limitations for microbial protein production in the rumen are possible with some models but not with this regression approach, mechanistic models need further validation and more accurate rate constants for improved accuracy over a wide range of conditions.

External and internal markers for appraising site and extent of digestion in ruminants

Digesta markers are used routinely to calculate fecal output and to estimate kinetics within the digestive tract. A marker suitable for estimating fecal output may not be a suitable kinetic marker because of problems with marker migration, phase separation, inhibition of digestion, osmotic effects within the gut, and quantitation. Marker validity should be checked when possible based on alternative methods (e.g., fecal output and ruminal evacuation). Certain parameters, such as pool size and passage rate, that can be estimated with markers cannot be measured by other noninvasive procedures. Nevertheless, only when marker results are verified by other methods can one evaluate the magnitude of error associated with assumptions inherent in marker mathematics (steady state, instantaneous mixing, and first-order kinetics). When marker results do not meet expectations, marker failure, rather than inadequate knowledge of gastrointestinal function or analytical difficulties, is blamed. No marker is ideal, but research to compare markers is useless if results are not related to direct flow or output measurements. Marker results often are adjusted for marker recovery based on the premise that analysis is precise and that losses are constant. Such adjustment is appropriate only if the error is analytical and proportional. Despite imprecision in marker procedures, inherent variation may be small relative to other sources of variation (e.g., gut physiology, diet, environment, and feed intake). Even though absolute values may be imprecise and inaccurate, marker-based estimates usually provide reliable information about the direction and extent of kinetic changes induced by treatments.

Effect of replacement therapy with cholylsarcosine on fat malabsorption associated with severe bile acid malabsorption. Studies in dogs with ileal resection

The efficacy of cholylsarcosine, a synthetic deconjugation-resistant and nonsecretory conjugated bile acid analog for the treatment of fat malabsorption caused by severe bile acid malabsorption, was assessed in an animal model. In two dogs, the ileum and ileocecal valve were resected, causing severe diarrhea, steatorrhea, bile acid malabsorption, and progressive weight loss. Cholylsarcosine was administered as the water-soluble sodium salt by mixing with the dog food. Various doses were explored as well as varying intakes of dog food. Fat absorption was assessed by gravimetric measurement of fecal fat; a nonabsorbable recovery marker (polyethylene glycol mol wt 4000) was used to correct for incomplete fecal collections. Cholylsarcosine caused a 5- to 30-fold increase in fat absorption but had no significant effect on weight loss or fecal weight. Duodenal content was collected during digestion of a meal via a surgically placed Thomas cannula; the aspirates were dilute, acidic, and had a low bile acid concentration. The bile acid concentration increased modestly when cholylsarcosine was administered, but remained below the critical micellization concentration. The results indicate that oral administration of cholylsarcosine improved dietary fat absorption in a canine model of severe bile acid malabsorption with associated steatorrhea and bile acid deficiency in the proximal small intestine. Studies with this compound in patients with nutritional problems because of steatorrhea and severe bile acid malabsorption appear warranted.

Measurement of the rate of flow of dry matter in digesta passing through the duodenum of sheep

1. A total of seven sheep fitted with re-entrant cannulas in the proximal duodenum were used in three experiments to measure the passage of dry matter (DM) in duodenal digesta. 2. Fifty-three 24 h measurements and ten 48 h measurements of DM flow were made in Expt 1. Coefficient of variation (CV) of these measurements was 22-1% which was similar to variability reported for chromic oxide 'corrected' flows and for an estimate of day-to-day variation. DM flow on day 1 was 103-2% (SE = 8-94) of flow on day 2 in 48 h measurements. 3. In two 3 X 3 Latin-square design experiments, duodenal DM flow was measured continuously over 72 h and on days 1, 2 and 3 DM flow was 100-4, 102-6 and 96-9% (SE = 5-82) of mean flow (Expt 2) and 95-8, 101-2 and 103-0% (SE = 6-70) of mean flow (Expt 3) respectively. 4. It was concluded that no depression in duodenal DM flow occurred during the first 24 h of collection in these experiments and that the variability of repeated 24 h measurements of flow was within day-to-day variation.

Dynamics of fermentation of a purified diet and microbial growth in the rumen

Ruminal fermentation and disappearance of glucose, starch, and cellulose, and incorporation of glucose and starch into microbial cells were estimated in a fistulated Jersey cow fed twice daily a purified diet containing urea as the sole nitrogen source. Estimated rumen volume was 59.8 liters. Turnover time and rate of passage of rumen contents were 33.4 h and 1.8 liters per h. Turnover times of glucose, starch, and cellulose were .17, 4.7, and 14.2 h. Fermentation times of glucose, starch, and cellulose were .17, 5.5, and 25.1 h. Percentages of glucose, starch, and cellulose utilized in the rumen were 99.4, 85.4, and 60.6. Thus, 18.5% of the carbohydrate fed bypassed rumen fermentation, and 81.5% was utilized in the rumen. All glucose disappeared from the rumen within an hour. An average of 32.1, 43.0, and 14%, respectively, of glucose utilized was incorporated into microbial cells, volatile fatty acids, and carbon dioxide. Percentage of starch incorporated into cells varied, with time being highest 2 h after feeding at 40% and lowest at 20%, 10 h after feeding. Respective percentages of starch incorporated into microbial cells, volatile fatty acids, and carbon dioxide were 32.4, 45.9; and 13.3. Total microbial protein and cell yields per kilogram carbohydrate utilized in the rumen were 77.1 and 117.5 g. Microbial cell yield per mole (estimated) of adenosine triphosphate was 16.2 g.

Digestion of dry and high-moisture maize diets in the stomach of the pig

1. Pigs were fitted with re-entrant duodenal cannulas anterior to the pancreatic duct, and total collections of digesta were made for 12 h periods.

2. Maize–soya-bean diets were made from maize which had been harvested with a dry-matter content of 770 g/kg and either dried, preserved with acetic or propionic acid or ensiled naturally. The pigs received two meals of these diets/d at 12 h intervals, and the amount of digesta flowing through their cannulas was measured.

3. Between 4.5 and 5.25 l of digesta flowed through the cannulas in the 12 h collection period, 0.9 of the total 12 h flow passed through the cannulas in the first 9 h with the dry-maize diet and 0.8 with the acid-treated-maize diets.

4. The mean total dry matter intake was 358 g/meal, and 304 g dry matter passed through the duodenal cannulas in the 12 h collection period. The corresponding intake and flow of nitrogen (g/12 h) was 11.1 and 9.6, and for chromic oxide 1.13 and 0.94.

5. The pigs consumed 205 g starch (total α-linked glucose polymers)/meal, and 1.5 g free glucose/meal. Only 110 g starch and 4.1 g free glucose reached the duodenal cannulas, suggesting that digestion and absorption of up to 92 g glucose had taken place anterior to the pancreatic ducts.