Feed evaluation by measurements of sites of digestion in cannulated ruminants

Effects of an abrupt increase of starch-rich concentrates in the diet of dairy cows on concentrations of volatile fatty acids in the rumen and large intestine and on myoelectric activity of the spiral colon

OBJECTIVES

To describe the effects of an abrupt increase of concentrates in the diet of dairy cows on myoelectric activity of the spiral colon and on fermentation patterns in the rumen and large intestine.

ANIMALS

6 healthy lactating Simmental x Red-Holstein cows.

PROCEDURES

The diet of 6 cows implanted with bipolar electrodes in the spiral colon was changed from hay only to a ration of 50% hay:50% starch-rich concentrates during a period of 60 hours. Myoelectric activity of the spiral colon, concentrations of absolute and undissociated volatile fatty acids (VFA), and pH of ruminal and large intestinal contents were monitored before, during, and after the dietary change.

RESULTS

Significant changes in patterns of myoelectric activity of the spiral colon were restricted to phases III and IV of the bovine migrating myoelectric complex and to propagation velocity. Significant alterations were not observed in pH or VFA concentrations in ruminal fluid, but pH decreased and VFA concentrations increased significantly in fecal specimens after the change of diet.

CONCLUSIONS AND CLINICAL RELEVANCE

Although rumen fluid is of limited value for measurement of certain indicators of fermentation, fecal samples can be used for measurement of pH and VFA concentrations, which serve as indicators of fermentation patterns in the large intestine. Increased concentrations of VFA and low pH in large intestinal digesta have a minimal influence on myoelectric activity of the spiral colon. Increased luminal VFA concentrations are unlikely to play an important role in the etiopathogenesis of motility disorders of the large intestine in cattle.

Absorption and delivery of nutrients for milk protein synthesis by portal-drained viscera

The predictability of diet effects on milk composition is limited by the lack of understanding of the metabolic transformations that absorbed nutrients undergo within the portal-drained viscera and liver of high yielding dairy cows. The mass of splanchnic tissues increases dramatically in early lactation, but little is known about the regulation of gut growth and adaptation in early lactation, and further research may provide strategies for optimizing gut adaptation. Glucose is critical for milk synthesis, but portal-drained visceral tissues normally use rather than absorb glucose on a net basis. Dietary starch of low ruminal digestibility increases postruminal starch digestion and decreases net use of glucose by portal-drained viscera slightly, but increases in glucose absorption by portal-drained viscera never account fully for increases in starch disappearance from the small intestine and occur at the expense of VFA absorption. For cows in positive energy balance, greater glucose availability increases tissue energy balance and glucose oxidation, but has little effect on milk or milk protein yield. Similarly, chronic increases in propionate absorption have little effect on milk or milk protein yield. In contrast, casein infusion into the small intestine consistently increases milk and milk protein yield, but the mechanisms responsible remain unclear. There are few data describing the absorption and metabolism of AA by splanchnic tissues of lactating dairy cows, but, as for glucose and VFA, utilization of many AA by portal-drained viscera is substantial. In addition, the contribution of peptides to AA absorption and transport is uncertain and must be clarified. Therefore, measurements of nutrient disappearance from the lumen of the gut cannot be equated with nutrient appearance in the portal vein. Data describing metabolism of nutrients by portal-drained viscera and liver of high yielding dairy cows are needed to improve feeding standards.

Prediction of responses to required nutrients in dairy cows

Nutritional science is developing from the calculation of requirements toward prediction of responses to nutrients. Responses are defined as the consequences of the animal's interaction with its feed and other aspects of its environment. For dairy cows the important responses to predict are yields of major milk constituents (fat, protein, and lactose), rates of changes of body fat and protein, and voluntary feed consumption. In order to make predictions of cow responses, equal weight needs to be given to quantitative descriptions of cow characteristics, feed characteristics, and relevant aspects of the environment. This paper presents a framework that allows quantitative descriptions of these various attributes to be combined for the purposes of response prediction. The nutrients of importance are those major end products of digestion, which act as substrates for the generation of animal products. Quantitative aspects of genotype include description of potential milk constituent yield, mature body size and composition, and rate of maturing, including a description of "labile" protein mass and animal capacities for ingestion of potentially constraining feed attributes. A variety of approaches is available to simulate nutrient supply and use for purposes of response prediction. The synthesis of such models adds both intellectual richness to the process of developing nutritional science and improved frameworks for testing theories through experiment.

Effects of feed intake and protein degradability on ruminal characteristics and site of digestion in steers

Four multiple-fistulated Hereford steers were used in a 4 X 4 Latin square design with a 2 X 2 factorial arrangement of treatments [two intakes (9.1 and 6.1 kg dry matter/d) and two protein sources differing in ruminal degradability (dry distillers grains and dry corn gluten feed)]. Steers fed at the high intake had faster fluid dilution rates (7.63 versus 6.52%/h), higher ruminal fluid outflows (120.2 versus 91.7 L/d), lower apparent ruminal digestibilities of organic matter (41.3 versus 44.3%) and neutral detergent fiber (56.0 versus 60.2%), and lower total tract digestibilities of neutral detergent fiber (64.3 versus 68.7%) than when they were fed at the low intake. Steers fed dry corn gluten feed had higher apparent ruminal digestibilities of organic matter (45.5 versus 40.1%) and neutral detergent fiber (60.2 versus 56.0%) and lower duodenal flows of nonammonia-nonbacterial N (40.1 versus 52.2% of N intake) than when they were fed dry distillers grains. Efficiency of ruminal bacterial growth was higher when steers were fed at the high versus low intakes. Efficiency of ruminal bacterial growth and site and extent of fiber digestion, especially hemicellulose, but not ruminal escape of protein, can be readily altered by manipulation of feed intake of moderately high forage diets.

[Protein and amino acid metabolism in the digestive tract growing young bulls. 1. Flow of bacterial raw protein in the duodenum determined by 2,6-diaminopimelic acid as a marker]

The influence of the composition of the rations on the content of diamino pimelic acid (DAP) and N in the bacteria dry matter and on the flow of bacteria crude protein into the duodenum, determined with DAP as marker, was determined on the basis of experimental investigations with young bulls provided with duodenal cannulae and with 28 different rations whose details are described. At a production level corresponding to dry matter intake and a variation range of the crude fibre content of between 11.3 and 29.1% in the DM, a content of N-free extractives between 50.9 and 77.4% in the DM, a content of soluble carbohydrates ibetween 5.3 and 6.4% in the DM, a crude protein content of between 6.4 and 17.1% in the DM and a pure protein content of between 4.9 and 15.5% in the DM, the DAP content of the bacteria DM amounts the 0.350 g 100 g DM +/- 0.090 the N-content of the bacteria DM amounts to 7.37 +/- 1.08 g/100 g DM, there are no relations between DAP- and N-content in the bacteria DM and the content of the individual carbohydrate fractions of the ration, there are positive relations between DAP- and N-content of the bacteria DM, the flow of bacterial crude protein into the duodenum amounts to 133 +/- 14 g/kg truly fermentable organic matter or 130 +/- 14 g/kg apparently digestible organic matter, there is a negative relation between bacteria crude protein at the duodenum (BCPD)/kg truly fermentable organic matter and the crude fibre content of the ration, there is a positive relation between BCPD/kg truly fermentable organic matter and N-free extractives and soluble carbohydrate content as well as the digestibility of the organic matter of the ration, there is no specific influence of the flow rate (kg digesta/kg intake of org. matter) or the dilution rate (g bacteriafree org. matter D/kg LW075/b) on BCPD/kg truly fermentable org. matter, there is a dependence of BCPD/kg truly fermentable org. matter on crude protein concentration in the ration in the concentration range of 6.4-9.0% crude protein in the ration (provided endogenous CP equivalents are used).

Protein-energy interrelationships in dairy cows

In dairy cows two distinct and important aspects of the interrelationship between protein and energy-yielding nutrients can be identified. First, a change of protein input can influence performance by changing overall plane of nutrition. To a large extent this results from changes of digestibility and associated intake of ration ingredients. Within this context it appears that at high levels of feeding rumen microbial demand for nitrogen per unit fermentable organic matter is high; initial failure to meet this need for nitrogen probably accounts for many responses to protein supplementation in practice through stimulation of ruminal digestion. Second is that changing "protein" supply to tissues can alter the pattern and efficiency of absorbed nutrient use. In early lactation protein supplementation favors partition of available nutrients toward mammary secretion. There are effects on glucose and fatty acid metabolism, all interacting with the endocrine system within a metabolic framework that tends to conserve those nutrients (amino acids, glucose) that are in shortest supply relative to demand. Response to increased input of amino acids depends both on physiological state of the cow and balance of all nutrients absorbed from the gastrointestinal tract.