Digestion in the Rumen and Total Tract of Forage-Based Diets with Starch or Dextrose Supplements Fed to Holstein Heifers

Abstract

Three diets were fed to six cannulated heifers in a replicated 3 x 3 Latin square design. Diets were a high forage control, a high forage diet with dextrose (5.6% of DM), and a medium concentrate (39.7% of DM) diet. Diets contained 13.3% CP and 1% NaHCO3 and were fed as a TMR twice daily. Mean ruminal pH (6.47), glucose concentration (.55 mM), and reducing sugar concentration (.64 mM) in heifers were similar across diets. Rate of orchardgrass NDF digestion in situ was faster for heifers fed the dextrose than for those fed the medium concentrate diet, but both were similar to that for heifers fed the control diet. Heifers fed the medium concentrate and dextrose diets had faster ruminal particulate fractional passage rates than those fed the control diet. True ruminal and apparent total tract digestion of OM and NDF were similar among diets, but ruminal NDF digestion tended to be higher with the control than with the medium concentrate diet. Total NAN and bacterial N flow to the duodenum and efficiency of bacterial protein synthesis in the rumen were greater with the medium concentrate diet than with the control and dextrose diets. The results were consistent with others that demonstrated that factors related to nonstructural carbohydrates in the diet other than just low ruminal pH affect ruminal fiber digestion; however, these results were not as strong as those of our previous in vitro work.

Microbial Cellulose Utilization: Fundamentals and Biotechnology

“…Although environmental concentrations have not been determined directly, measurements in the rumen indicate that concentrations of glucose (0.06 to 0.8 mM) (114,320,378,537) are far higher than those of cellobiose (Ͻ0.02 mM) (321). Because the concentration of glucose is almost the same as the total concentration of reducing sugars, it is likely that cellodextrin concentrations are very low.…”

“…Consistent with hydrolysis being rate limiting, concentrations of soluble sugars resulting from cellulose hydrolysis are usually vanishingly small (Յ0.5 mM or undetectable) in cellulose-fed systems that approach or achieve steady state. Such systems include chemostats involving both pure cultures (409,516,727) and mixed cultures (111) as well as the rumen (114,320,537). Soluble sugars are commonly observed to accumulate in batch cultures of cellulolytic bacteria, but this is in most cases probably due to continuing activity of cellulase enzymes after growth ceases (156).…”

Fermentação ruminal e eficiência microbiana em bezerros holandeses alimentados com dietas contendo diferentes níveis de concentrado

“…KRYSL et al (1991) e JAAKKOLA e HUHTANEN (1993) relataram elevação do NA abo . O mesmo foi mencionado por outros autores, que obtiveram respostas lineares crescentes para NNA abo e NM abo (RODE et al, 1985;PIWONKA, et al, 1994).…”

“…Estes resultados são coerentes com a elevação dos valores de NM abo e MSB abo . PIWONKA et al (1994), que trabalharam com novilhas holandesas alimentadas com rações contendo 25% de concentrado à base de farelo de soja e cevada moída e volumoso, obtiveram valor médio de 37,5 g NM abo /kg MODR, interposto às médias correspondentes aos níveis de 30 e 45% de concentrado, apresentadas na Tabela 1.…”

Quantifying the Responses of Mixed Rumen Microbes to Excess Carbohydrate

“…5 mM glucose can be reached after feeding unadapted animals large quantities of grain (42,43). The highest concentration of glucose reported was 18 mM (after feeding glucose) (44). The highest concentration of soluble sugars was 69 mM glucose equivalents (after feeding beet pulp) (45).…”