Ammonia production, ammonia absorption,
and urea recycling in ruminants. A review

Tan, Zhi Liang; Murphy, Michael R.

doi:10.22358/jafs/67425/2004

Cited by 26 publications

(15 citation statements)

References 34 publications

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“…Dietary supplements of folic acid also had very limited effects on the net flux of nutrients across the rumen wall; only the net uptake of urea-N by the rumen wall tended to increase when cows were fed supplementary folic acid. Urea transfer to the rumen is inversely related to the concentration of ammonia in rumen and positively related to plasma concentrations of urea (Tan and Murphy, 2004) but neither of these 2 variables was modified by folic acid supplementation in the present experiment. Nevertheless, urea flux across the rumen wall was positively correlated (r = 0.52, P = 0.001) with the arterial concentrations of urea but not correlated with ammonia concentrations in rumen fluid (r = 0.09, P = 0.49).…”

Section: Discussioncontrasting

confidence: 65%

Net flux of nutrients across the rumen wall of lactating dairy cows as influenced by dietary supplements of folic acid

Girard

Benchaar

Chiquette

et al. 2009

Journal of Dairy Science

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The objective of the present study was to determine whether a dietary supplementation of folic acid, at levels used in our previous studies, would affect ruminal fermentation and the net flux of nutrients across the rumen wall of lactating dairy cows. Approximately 4 wk after calving, 5 lactating multiparous cows were surgically equipped with a ruminal cannula, an ultrasonic flow probe around the right ruminal artery, and indwelling catheters in the right ruminal vein and the ileocolic artery. Cows were fed a total mixed ration served in 7 equal meals per d (i.e., every 3.4 h). The experimental design was an unbalanced crossover arrangement with 3 periods of 4 wk each. The vitamin supplement, incorporated in equal amounts into each meal, was supplied at 0, 3, or 6 mg of folic acid per kg of BW per d. During the last week of each experimental period, blood samples were taken simultaneously from the 2 catheters every 30 min and rumen fluid was collected every 60 min during 2 consecutive meal intervals. Dietary supplementation with folic acid had no effect on milk production (27.2 +/- 1.3 kg/d) or DMI (19.9 +/- 0.7 kg/d), but milk concentrations and yields of total solids, fat, and protein increased linearly with increasing doses of folic acid ingested. Concentrations of folates in rumen fluid and arterial plasma, averaged over time, increased linearly with the dose of folic acid ingested but the net flux of folates across the rumen wall was not different from zero. Concentrations of butyrate in ruminal fluid decreased quadratically with the daily supply in folic acid. Dietary supplements of folic acid had no effect on pH and osmolality of ruminal fluid, nor on ruminal concentrations of lactate, ammonia, acetate, or propionate, total VFA, or microbial counts. The uptake of urea-N by the rumen wall tended to increase quadratically with the dose ingested but net fluxes of other nutrients were not affected by treatments. These results suggest that the effects of folic acid supplements on lactational performance cannot be explained by effects on rumen metabolism.

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Section: Discussioncontrasting

confidence: 65%

Net flux of nutrients across the rumen wall of lactating dairy cows as influenced by dietary supplements of folic acid

Girard

Benchaar

Chiquette

et al. 2009

Journal of Dairy Science

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“…Protozoa-free lambs fed a mixed diet showed an ammonia concentration below the threshold level (5 mg/100 mL) required to maxi-mize microbial growth in vitro (Criswold et al, 2003). However, no significant changes either in rumen fermentation or microbial protein synthesis were detected, suggesting the existence of alternative metabolic pathways to scavenge NH3 under critical ammonia concentrations (Firkins et al, 1992;Tan and Murphy;. 1 …”

Section: Digestion and Rumen Variablesmentioning

confidence: 96%

Study of the effect of presence or absence of protozoa on rumen fermentation and microbial protein contribution to the chyme1

Belanche

Abecia²,

Holtrop

et al. 2011

Journal of Animal Science

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The aim of this study was to investigate the effect of presence or absence of protozoa on rumen fermentation and efficiency of microbial protein synthesis under different diets. Of 20 twin paired lambs, 1 lamb of each pair was isolated from the ewe within 24 h after birth and reared in a protozoa-free environment (n = 10), whereas their respective twin-siblings remained with the ewe (faunated, n = 10). When lambs reached 6 mo of age, 5 animals of each group were randomly allocated to 1 of 2 experimental diets consisting of either alfalfa hay as the sole diet, or 50:50 mixed with ground barley grain according to a 2 × 2 factorial arrangement of treatments. After 15 d of adaptation to the diet, the animals were euthanized and total rumen and abomasal contents were sampled to estimate rumen microbial synthesis using C(31) alkane as flow marker. Different ((15)N and purine bases) and a novel (recombinant DNA sequences) microbial markers, combined with several microbial reference extracts (rumen protozoa, liquid and solid associated bacteria) were evaluated. Absence of rumen protozoa modified the rumen fermentation pattern and decreased total tract OM and NDF digestibility in 2.0 and 5.1 percentage points, respectively. The effect of defaunation on microbial N flow was weak, however, and was dependent on the microbial marker and microbial reference extract considered. Faunated lambs fed with mixed diet showed the greatest rumen protozoal concentration and the least efficient microbial protein synthesis (29% less than the other treatments), whereas protozoa-free lambs fed with mixed diet presented the smallest ammonia concentration and 34% greater efficiency of N utilization than the other treatments. Although (15)N gave the most precise estimates of microbial synthesis, the use of recombinant DNA sequences represents an alternative that allows separate quantification of the bacteria and protozoa contributions. This marker showed that presence of protozoa decrease the bacterial-N flow through the abomasum by 33%, whereas the protozoa-N contribution to the microbial N flow increased from 1.9 to 14.1% when barley grain was added to the alfalfa hay. Absolute data related to intestinal flow must be treated with caution because the limitations of the sampling and maker system employed.

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“…Differences in the proportion of net PDV NH 3 absorption attributable to MDV tissues among these studies could be attributable to both technical considerations (e.g., site of mesenteric vein sampling) and diet composition effects, but it is notable that within specific studies, effects of diet composition on the ratio of MDV to PDV NH 3 absorption have been small (e.g., Huntington, 1989). Dietary factors that are known to influence relative amounts of NH 3 absorption from the rumen have been reviewed previously (e.g., Parker et al, 1995;Tan and Murphy, 2004) and include amounts and degradability of dietary and endogenous sources of N in the gastrointestinal tract, as well as dietary carbohydrate sources. The use of NH 3 for microbial protein synthesis is energy-dependent; therefore, the amount and degradability of dietary carbohydrate can influence NH 3 absorption.…”

Section: Ammonia N Absorptionmentioning

confidence: 99%

Nitrogen recycling through the gut and the nitrogen economy of ruminants: An asynchronous symbiosis1

Reynolds

Kristensen

2008

Journal of Animal Science

338

226

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The extensive development of the ruminant forestomach sets apart their N economy from that of nonruminants in a number of respects. Extensive pregastric fermentation alters the profile of protein reaching the small intestine, largely through the transformation of nitrogenous compounds into microbial protein. This process is fueled primarily by carbohydrate fermentation and includes extensive recycling of N between the body and gut lumen pools. Nitrogen recycling occurs via blood and gut lumen exchanges of urea and NH(3), as well as endogenous gut and secretory N entry into the gut lumen, and the subsequent digestion and absorption of microbial and endogenous protein. Factors controlling urea transfer to the gut from blood, including the contributions of urea transporters, remain equivocal. Ammonia produced by microbial degradation of urea and dietary and endogenous AA is utilized by microbial fermentation or absorbed and primarily converted to urea. Therefore, microbial growth and carbohydrate fermentation affect the extent of NH(3) absorption and urea N recycling and excretion. The extensive recycling of N to the rumen represents an evolutionary advantage of the ruminant in terms of absorbable protein supply during periods of dietary protein deficiency, or asynchronous carbohydrate and protein supply, but incurs a cost of greater N intakes, especially in terms of excess N excretion. Efforts to improve the efficiency of N utilization in ruminants by synchronizing fermentable energy and N availability have generally met with limited success with regards to production responses. In contrast, imposing asynchrony through oscillating dietary protein concentration, or infrequent supplementation, surprisingly has not negatively affected production responses unless the frequency of supplementation is less than once every 3 d. In some cases, oscillation of dietary protein concentration has improved N retention compared with animals fed an equal amount of dietary protein on a daily basis. This may reflect benefits of Orn cycle adaptations and sustained recycling of urea to the gut. The microbial symbiosis of the ruminant is inherently adaptable to asynchronous N and energy supply. Recycling of urea to the gut buffers the effect of irregular dietary N supply such that intuitive benefits of rumen synchrony in terms of the efficiency of N utilization are typically not observed in practice.

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Ammonia production, ammonia absorption, and urea recycling in ruminants. A review

Cited by 26 publications

References 34 publications

Net flux of nutrients across the rumen wall of lactating dairy cows as influenced by dietary supplements of folic acid

Net flux of nutrients across the rumen wall of lactating dairy cows as influenced by dietary supplements of folic acid

Study of the effect of presence or absence of protozoa on rumen fermentation and microbial protein contribution to the chyme1

Nitrogen recycling through the gut and the nitrogen economy of ruminants: An asynchronous symbiosis1

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