Effect of Dietary Fiber on Endogenous Nitrogen Flows in Lactating Dairy Cows

Abstract

The effect of dietary fiber on endogenous N secretion was studied using a 15N isotope dilution technique in four fistulated Holstein cows. Two isonitrogenous diets differing only in fiber (NDF and ADF) content were used in a crossover design. One diet (HF) contained 37.4% NDF, while the other (LF) contained 23.3%. A new model was developed to estimate endogenous N secretions and losses for the preintestinal, intestinal, and the total sections of the gastrointestinal tract. Three precursor pools: TCA-soluble fraction of plasma, intestinal mucosa, and milk were compared. Although endogenous losses estimated with the model were numerically different for each precursor pool selected (TCA-soluble fraction > mucosa > milk), treatment effects were similar. As intestinal mucosa is probably closest to the precursor pool, these data are discussed. Non-urea N endogenous secretions contributed 13% of the duodenal N flow but were not affected by the fiber content of the diet. The nonurea N endogenous flow at the duodenum was comprised of approximately equal inputs from endogenous N direct, and that incorporated into the microbial biomass. Total endogenous N flows at the duodenum exceeded, by nearly twofold, estimated inputs of urea-N to microbial biomass. Metabolic fecal output averaged 17% of fecal N and was not affected by level of dietary fiber, but net losses from secretions occurring in the small intestine were higher with the low fiber diet. Overall, endogenous N secretions represented 30% of total digestive tract protein synthesis.

Effect of rumen-degradable protein balance deficit on voluntary intake, microbial protein synthesis, and nitrogen metabolism in growing double-muscled Belgian Blue bulls fed corn silage-based diet1,2,3

“…Level of OEB in the diet had no significant effect on nonammonia-N (NAN) flows at the duodenum (Table 5) Calculated assuming 2.3 g of N/kg of DMI (Ouellet et al, 2002). ance across the forestomach, which increased linearly with the OEB deficit of the diets (Table 5).…”

“…The OM truly digested in the rumen was obtained by the subtracting of duodenal microbial OM flow from the total OM flow. Endogenous N was assumed to be 2.3 g/ kg of DMI for the calculation of endogenous N flowing to the duodenum (Ouellet et al, 2002). It was assumed that the treatments did not affect this value.…”

“…The endogenous N flow was subtracted from the duodenal nonmicrobial N to estimate the undegraded dietary N flowing to the duodenum. Nitrogen balance across the forestomach was estimated by the difference between N flowing at the duodenum and N ingested, whereas the net N balance across the forestomach was calculated by subtracting the duodenal endogenous N flow estimated according to Ouellet et al (2002) from N balance.…”

Responses of the bovine mammary glands to absorptive supply of single amino acids

“…1. Leucine, Lys and Phe flux from small intestinal disappearance to milk protein, presented as a proportion of available flux (mesenteric appearance minus endogenous loss) and as a proportion (mol 100 mol -1 ) of the sum of essential AA fluxes [adapted from MacRae et al (1997), Berthiaume et al (2001) and unpublished data, Blouin et al (2002), and Ouellet et al (2002)]. …”

Modelling endogenous leucine flows at the jejunum and ileum in lambs exposed to the intestinal parasite <i>Trichostrongylus colubriformis</i>

“…Endogenous protein secretions, plus associated losses, are an important feature of digestive tract metabolism in both ruminants (e.g., van Bruchem et al, 1997;Ouellet et al, 2002) and non-ruminants (e.g., de Lange et al, 1990;Hess et al, 1998). Various methodological and conceptual approaches have been used to quantify such secretions but the majority have considered the digestive tract as a single unit (e.g., de Lange et al, 1990), rather than a series of linked and interacting units (e.g., van Bruchem et al, 1997;Ouellet et al, 2002).…”