Ergot alkaloids from endophyte-infected tall fescue decrease reticuloruminal epithelial blood flow and volatile fatty acid absorption from the washed reticulorumen.

An experiment was conducted to determine if ergot alkaloids affect blood flow to the absorptive surface of the rumen. Steers (n=8) were pair-fed alfalfa cubes and received ground endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum; E+) seed (0.015 mg ergovaline·kg BW(-1)·d(-1)) or endophyte-free tall fescue (E-) seed via the rumen cannula 2x daily for 7 d at thermoneutral (TN; 22°C) and heat stress (HS; 32°C) conditions. On d 8, the rumen was emptied and rinsed. A buffer containing VFA was incubated in the following sequence: control (CON), 15 µg ergovaline·kg BW(-1) (1×EXT) from a tall fescue seed extract, and 45 µg ergovaline·kg BW(-1) (3×EXT). For each buffer treatment there were two 30-min incubations: a 30-min incubation of a treatment buffer with no sampling followed by an incubation of an identical sampling buffer with the addition of Cr-EDTA and deuterium oxide (D2O). Epithelial blood flow was calculated as ruminal clearance of D2O corrected for influx of physiological water and liquid outflow. Feed intake decreased with dosing E+ seed at HS but not at thermoneutral conditions (TN; P<0.02). Dosing E+ seed decreased serum prolactin (P<0.005) at TN. At HS, prolactin decreased in both groups over the 8-d experiment (P<0.0001), but there was no difference in E+ and E- steers (P=0.33). There was a seed treatment×buffer treatment interaction at TN (P=0.038), indicating that E+ seed treatment decreased reticuloruminal epithelial blood flow at TN during the CON incubation, but the two groups of steers were not different during 1×EXT and 3×EXT (P>0.05). Inclusion of the extract in the buffer caused at least a 50% reduction in epithelial blood flow at TN (P=0.004), but there was no difference between 1×EXT and 3×EXT. There was a seed × buffer treatment interaction at HS (P=0.005), indicating that the reduction of blood flow induced by incubating the extract was larger for steers receiving E- seed than E+ seed. Volatile fatty acid flux was reduced during the 1×EXT and 3×EXT treatments (P<0.01). An additional experiment was conducted to determine the effect of time on blood flow and VFA flux because buffer sequence could not be randomized. Time either increased (P=0.05) or did not affect blood flow (P=0.18) or VFA flux (P>0.80), indicating that observed differences are due to the presence of ergot alkaloids in the rumen. A decrease in VFA absorption could contribute to the signs of fescue toxicosis including depressed growth and performance.

Spasmolytic effect of curcumin on goat ruminal artery is endothelium independent and by activation of sGC.

The aim of the present work was to study the mechanism of action of curcumin in vasomotion of a physiologically important artery of ruminant i.e. ruminal artery. ACh and SNP were used to study the role of endothelium in relaxation of this artery. Vasorelaxatation by curcumin was studied in a dose dependent manner, on rings precontracted with 5-hydroxy tryptamine and noradrenalin, in presence and absence of L-NAME, 4AP, ODQ and 4AP+ODQ combination. SNP (1 ηM-100 µM) produced a significant relaxation compared to ACh (0.1-100 µM) on 5-HT (10 µM) and NA (10 µM) induced contraction in endothelium intact rings. Curcumin (10 ηM-100 µM) relaxed the vascular rings in dose dependent manner with maximal relaxation up to 20.94% and 13.81% in 5-HT and NA induced contraction, respectively which was potently blocked by ODQ (10 µM) and combination of 4AP and ODQ (10 µM) but 4AP (10 µM) and L-NAME (100 µM) alone could not block the relaxation and interestingly we observed a slight increase in the tension at higher dose of the agonist (>10 µM). Therefore in goat ruminal artery, curcumin at least in part, act via direct activation of sGC mediated cGMP pathway followed by opening of K(+) ion channel. However other mechanisms may not be ruled out.

A model of ruminal volatile fatty acid absorption kinetics and rumen epithelial blood flow in lactating Holstein cows.

Ruminal absorption of volatile fatty acids (VFA) is quantitatively the most important nutrient flux in cattle. Historically, VFA absorption models have been derived primarily from ruminal variables such as chemical composition of the fluid, volume, and pH. Recently, a mechanistic model incorporated the control of VFA absorption from epithelial surface area of the reticulorumen. In the present study, we hypothesized that ruminal absorption of VFA was controlled through epithelial permeability to VFA and rumen epithelial capillary blood flow. The objective of the study was to construct a model of VFA exchange across the rumen wall that incorporates epithelial blood flow as a driving force for ruminal VFA removal. The bidirectional fluxes between the ruminal and epithelial pool of VFA were assumed mass action driven, given that passive diffusion of nonionized VFA is the dominant transmembrane VFA flux. Parameter estimates were derived by fitting the model to observed data. The model provided reliable unbiased estimates of ruminal VFA absorption and rumen epithelial blood flow. Blood flow was modeled using an equation that considered the effect of butyrate and dietary crude protein intake per kilogram of body weight. The rate constants related to the flux from ruminal fluid to epithelium were in the order isobutyrate < acetate < propionate < butyrate (0.32 ± 0.02, 0.72 ± 0.2, 0.91 ± 0.06, and 0.97 ± 0.02 /h, respectively). The rate constants for fluxes of isobutyrate, acetate, propionate, and butyrate from the rumen epithelium to the ruminal fluid, relative to the pool size of the epithelium, were 4.78, 10.6, 13.4, and 14.3 /h, respectively. Ruminal concentrations of acetate, propionate, butyrate, and isobutyrate were predicted with root mean square prediction errors as percentage of the observed means (RMSPE) of 5.86, 5.75, 11.3, and 4.12, respectively. The epithelial blood flow was predicted with 26.3% RMSPE. Sensitivity analyses indicated that when ruminal butyrate concentration increased from 4.0 to 37.4 mmol/L, blood flow of the epithelium increased 47% and the ruminal disappearance rate of propionate increased 11%. The concentration gradient of propionate between ruminal fluid and epithelium was no more than 3:1 and increased with increasing blood flow. In conclusion, a dynamic model based on rumen epithelial blood flow and bidirectional fluxes of VFA between ruminal fluid and epithelium gave unbiased predictions with low residual error of ruminal VFA absorption under washed rumen conditions. The model indicates that the effect of varying epithelial blood flow on the control of ruminal VFA absorption is related to the concentration gradient of individual VFA between ruminal fluid and epithelial blood. Epithelial blood flow may be an important determinant of ruminal absorption of VFA, a result that has not been evaluated on independent data.

Constriction of bovine vasculature caused by endophyte-infected tall fescue seed extract is similar to pure ergovaline.

Ergovaline has been extensively used to study vasoactive effects of endophyte- (Neotyphodium coenophialum) infected tall fescue (Lolium arundinaceum). However, initial results indicated that an extract of toxic tall fescue seed (E+EXT) is more potent than ergovaline alone in a right ruminal artery and vein bioassay. The E+EXT induced a greater contractile response than an equal concentration of ergovaline alone in the ruminal artery of heifers (P = 0.018). This led to a hypothesis that other compounds in the seed extract contribute to vasoconstriction. Thus, experiments were conducted to determine if vasoactivity of an E+EXT is different from a mixture of ergot alkaloids (ALK; ergovaline, ergotamine, ergocristine, ergocryptine, ergocornine, ergonovine, and lysergic acid) of similar concentrations and to determine if the vasoactivity of an E+EXT differs from an endophyte-free tall fescue seed extract (E-EXT). Segments of lateral saphenous vein and right ruminal artery and vein were collected from Holstein steers (n = 6) shortly after slaughter. Vessels were cleaned of excess connective tissue and fat and sliced into segments that were suspended in a multimyograph chamber with 5 mL of continually oxygenated Krebs-Henseleit buffer, equilibrated for 90 min, and exposed to a reference compound (120 mM KCl for ruminal vessels and 0.1 mM norepinephrine for saphenous vein). Increasing concentrations of each treatment (E+EXT, E-EXT, ALK, and ergovaline) were added to the respective chamber every 15 min after buffer replacement. Data were normalized as a percentage of maximal contractile response of the reference compound and fit to a sigmoidal concentration response curve. Ergovaline, ALK, and E+EXT induced similar responses in the saphenous vein, ruminal artery, and ruminal vein. The E+EXT displayed a smaller EC(50) (half maximal effective concentration) than ergovaline or ALK in the saphenous vein and ruminal vein (P < 0.008), but not the ruminal artery (P = 0.31). Extrapolated maximum response was greatest in the saphenous vein for ergovaline, least for E+EXT, and intermediate for ALK (P < 0.0001). The E-EXT did not induce a contractile response in any vessel tested (P > 0.1). Data from this study indicate that ergovaline is largely responsible for the locally induced vasoconstriction of bovine vasculature observed with endophyte-infected tall fescue.

Effects of ruminal ammonia and butyrate concentrations on reticuloruminal epithelial blood flow and volatile fatty acid absorption kinetics under washed reticulorumen conditions in lactating dairy cows.

The effect of reticuloruminal epithelial blood flow on the absorption of propionate as a volatile fatty acid (VFA) marker in 8 lactating Holstein cows was studied under washed rumen conditions. The cows were surgically prepared with ruminal cannulas and permanent catheters in an artery and mesenteric, right ruminal, and hepatic portal veins. The experiment was designed with 2 groups of cows: 4 cows adapted to high crude protein (CP) and 4 to low CP. All cows were subjected to 3 buffers: butyric, ammonia, and control in a randomized replicated 3 × 3 incomplete Latin square design. The buffers (30 kg) were maintained in a temporarily emptied and washed rumen for 40 min. The initial concentration of VFA was 84.2 mmol/L. Butyrate was increased from 4 to 36 mmol/L in butyric buffer by replacement of acetate, and ammonia (NH(3)) was increased from 2.5 to 22.5 mmol/L in ammonia buffer by replacement of NaCl. Increasing amounts of deuterium oxide (D(2)O) were added to the buffers as the order of buffer sequence increased (6, 12, and 18 g of D(2)O). Ruminal clearance of D(2)O was used to estimate epithelial blood flow. To increase accuracy of the epithelial blood flow estimates, data of ruminal liquid marker (Cr-EDTA), and initial and final buffer volumes were fitted to a dynamic simulation model. The model was used to estimate ruminal liquid passages, residual liquid, and water influx (saliva and epithelia water) for each combination of cow and buffer (n=24). Epithelial blood flow increased 49±11% for butyric buffer compared with control. The ruminal disappearance of propionate (marker VFA) was affected by buffer and followed the same pattern as for epithelial blood flow. The correlation between ruminal disappearance of propionate and epithelial blood flow (r=0.56) indicates that the removal of propionate can be limited by epithelial blood flow. The ruminal disappearance of propionate increased 30±12% for the butyric compared with ammonia buffer and 12.5±8% when compared with control. The net portal flux of propionate increased 32±6% in butyric compared with control. In conclusion, rumen epithelial blood flow is positively correlated with ruminal disappearance of propionate and affects the kinetics of ruminal VFA absorption.

Effects of nitrogen supply on inter-organ fluxes of urea-N and renal urea-N kinetics in lactating Holstein cows.

The effects of decreasing ruminal urea infusion in lactating dairy cows fed a basal diet deficient in rumen degradable protein on inter-organ urea-N fluxes, epithelial urea-N extraction, and renal urea-N kinetics were investigated. Eight Danish Holstein cows fitted with a ruminal cannula and permanent indwelling catheters in the major splanchnic blood vessels and the gastrosplenic vein were used. The cows were randomly allocated to a triplicate incomplete 3 × 3 Latin square design with 14-d periods. Treatments were continuous ventral ruminal infusion of water, 4.1g of feed urea/kg of dry matter intake, and 8.5 g of feed urea/kg of dry matter intake. Dry matter intake and milk yield decreased linearly with decreasing urea infusion. Arterial blood urea-N and ruminal ammonia concentrations decreased linearly with decreasing urea infusion. In absolute amounts, the urea-N recycling did not increase when urea infusion was decreased. Arterial urea-N extraction across the portal-drained viscera and rumen wall increased linearly with decreasing urea infusion (2.46, 3.65, and 4.32 ± 0.31% and 7.5, 11.5, and 16.9 ± 0.9%, respectively), indicating that cows responded to the changes in N supply. The relative urea-N extraction across the ruminal wall increased compared with the total portal-drained viscera extraction. We observed a postprandial decrease in ruminal extraction of arterial urea-N that might reflect that the activity of the protein, presumably facilitating urea-N transport, is regulated by ruminal ammonia. The urea-N clearance by the kidneys decreased (35, 30, and 25 ± 2L/h) and the urea-N reabsorbed by the kidney increased (42, 51 and 56 ± 3%) with decreasing urea infusion, indicating that the kidneys salvaged urea-N with low-N supply. The urea transporter B mRNA abundance in rumen papillae (papillae harvested at sampling days) was not affected by dietary N supply. The study showed, that rumen wall extraction of arterial urea-N is subjected to both long- and short-term regulation. Extraction increases with decreasing N supply long-term; however, a short-term postprandial decrease in extraction was observed. No association between long-term adaptation of urea-N extraction across the rumen wall and urea transporter B mRNA abundance could be demonstrated.

Effect of ergot alkaloids on contractility of bovine right ruminal artery and vein.

Ergot alkaloids produced by the endophyte (Neotyphodium coenophialum) associated with tall fescue (Lolium arundinaceum) are implicated in the clinical signs of fescue toxicosis. These compounds were hypothesized to correspondingly affect foregut vasculature. The objective of this study was to determine vasoconstrictive potentials of ergovaline, ergotamine, ergocryptine, ergocristine, ergonovine, ergocornine, and lysergic acid on right ruminal artery and vein. Segments of right ruminal artery and vein were collected from the ventral coronary groove of predominantly Angus heifers (n = 10) shortly after slaughter and placed in a modified Krebs-Henseleit buffer on ice. Vessels were cleaned of excess connective tissue and fat, sliced into 2- to 3-mm segments, and suspended in a multi-myograph chamber with 5 mL of continuously oxygenated Krebs-Henseleit buffer (95%O(2)/5% CO(2); pH 7.4; 37°C). Arteries and veins were equilibrated to 1.0 and 0.5 g, respectively, for 90 min followed by the reference addition of 120 mM KCl. Increasing concentrations of each alkaloid were added to the respective chamber every 15 min after buffer replacement. Data were normalized as a percentage of the contractile response induced by KCl. Alkaloid (P < 0.0001), concentration (P < 0.0001), and vessel type (artery or vein; P = 0.004) affected contractility. No arterial response was observed until 10(-6) M for ergovaline and ergotamine; 10(-5) M for ergocryptine, ergocornine, and ergonovine; and 10(-4) M for ergocristine. Lysergic acid did not induce a contractile response in the ruminal artery. No venous contractile response was observed until concentrations of 10(-6) M for ergovaline, 10(-5) M for ergotamine, and 10(-4) M for ergocryptine and ergocristine were achieved. Lysergic acid, ergonovine, and ergocornine did not induce a contractile response in the ruminal vein. A greater arterial maximal response was observed for ergovaline (P < 0.0001), whereas the arterial and venous responses were not different for ergotamine (P = 0.16), ergocryptine (P = 0.218), and ergocristine (P = 0.425). These results indicate that ergot alkaloids associated with toxic endophyte-infected tall fescue are vasoactive and can potentially alter arterial blood supply and venous drainage from the bovine foregut.

A vascular contractility bioassay using bovine right ruminal artery and vein.

Endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) produces ergot alkaloids that are associated with peripheral vasoconstriction in grazing animals, and ingestion of these alkaloids may affect splanchnic vasculature. Peripheral effects of ergot alkaloids have been well documented previously in cattle using a lateral saphenous vein bioassay. Because of significant differences in morphological and functional characteristics between vasculature supporting digestive and peripheral tissues, the bovine foregut vascular model required validation. Experiments were conducted, using dose-responses to norepinephrine and serotonin that were normalized to either 0.12 M KCl, or 0.1 mM norepinephrine or serotonin, to compare responses of vessels equilibrated at different tensions on the day of collection or the day after collection. Segments of a branch of right ruminal artery and vein were collected from the ventral coronary groove of healthy cattle of mixed breed, age, and sex (n = 20) at local abattoirs. Cross-sections of the artery and vein were suspended on luminal supports in a chamber of a multimyograph containing continuously oxygenated Krebs-Henseleit buffer (95% O(2)/5% CO(2), pH 7.4; 37°C). Vessels were allowed to equilibrate at either 0.5 or 1.0 g of tension for 1.5 h before exposure to a reference compound. Increasing concentrations of each biogenic amine were administered in 15-min intervals after buffer replacement. Data were normalized as a percentage of the contractile response induced by the reference compound for each tension and day of analysis. The ruminal artery and vein were both more responsive to KCl as a reference compound (P < 0.05) than to norepinephrine or serotonin and did not differ between days when normalized with KCl. Ruminal arteries had greater contractile responses (P < 0.05) when tension was set to 1.0 g, compared with 0.5 g, during equilibration. The ruminal vein response had a more stable maintenance of baseline tension in vessels equilibrated at 0.5 g of resting tension. Development of this bioassay allows separation of the effects tall fescue alkaloids exert on both the right ruminal artery and vein as representative vessels that service tissues functioning in nutrient absorption.

Effect of dietary nitrogen content and intravenous urea infusion on ruminal and portal-drained visceral extraction of arterial urea in lactating Holstein cows.

Urea extraction across ruminal and portal-drained visceral (PDV) tissues were investigated using 9 rumen-cannulated and multi-catheterized lactating dairy cows adapted to low-N (12.9% crude protein) and high-N (17.1% crude protein) diets in a crossover design. The interaction between adaptation to dietary treatments and blood plasma concentrations of urea was studied by dividing samplings into a 2.5-h period without urea infusion followed by a 2.5-h period with primed continuous intravenous infusion of urea (0.493+/-0.012 mmol/kg of BW per h). Cows were sampled at 66+/-14 and 68+/-12 d in milk and produced 42+/-1 and 36+/-1 kg of milk/d with the high-N and low-N diets, respectively. The arterial blood urea concentration before urea infusion was 1.37 and 4.09+/-0.18 mmol/L with low-N and high-N, respectively. Dietary treatment did not affect the urea infusion-induced increase in arterial urea concentration (1.91+/-0.13 mmol/L). Arterial urea extraction across the PDV and rumen increased from 2.7 to 5.4+/-0.5% and from 7.1 to 23.8+/-2.1% when cows were changed from high-N to low-N, respectively. Urea infusion did not decrease urea extractions, implying that urea transport rates were proportional to arterial urea concentrations. Urea extraction increased more across the rumen wall than across the total PDV for low-N compared with high-N, which implies that a larger proportion of total PDV uptake of arterial urea is directed toward the rumen with decreasing N intake. The ruminal vein - arterial (RA) concentration difference for ammonia increased instantly (first sampling 15 min after initiation of infusion) to the primed intravenous infusion when cows were adapted to the low-N diet. The RA difference for ammonia correlated poorly to the ventral ruminal concentration of ammonia (r=0.55). Relating the RA difference for ammonia to a function of both ruminal ammonia concentration and the RA difference for urea markedly improved the fit (r=0.85), indicating that a large fraction of ammonia released to the ruminal vein is absorbed from an epithelial ammonia pool not in equilibrium with the ventral ruminal ammonia pool. Changing cows from high-N to low-N affected the relative blood urea clearance by kidneys and PDV. The clearance by the kidneys decreased from 41 to 27+/-2 L/h and the clearance by the PDV increased from 52 to 105+/-12 L/h when the diet was changed from high-N to low-N. In conclusion, urea transport across gut epithelia in cattle is adapting to N status and driven by mass action. Data are commensurable with a model for urea transport across gut epithelia based on regulated expression or activity of facilitative urea transporters.

Net flux of nutrients across splanchnic tissues of lactating dairy cows as influenced by dietary supplements of biotin and vitamin B12.

Biotin and vitamin B(12) are coenzymes in reactions that are essential to propionate metabolism in dairy cows. The objective of the present studies was to determine whether an increased dietary supply of these vitamins would change the net flux of nutrients through the rumen, the portal-drained viscera (PDV), the total splanchnic tissues (TSP), and the liver. Four lactating cows equipped with ultrasonic flow probes around the right ruminal artery and the portal vein and catheters in the right ruminal vein, the portal vein, one hepatic vein, and one mesenteric artery were fed 12 times per day a mixed ration at 95% of ad libitum dry matter intake. Daily supplements of 500 mg of vitamin B(12)+20mg of biotin or no vitamin supplement (study 1) or 500 mg of vitamin B(12) alone or with 20mg of biotin (study 2) were fed according to a crossover design with two 4-wk periods in each study. On the last day of each period, blood flow was recorded and blood samples were collected every 30 min for 4h. In study 1, biotin and vitamin B(12) given together increased milk production and milk protein yields compared with the control diet. The supplement increased appearance of the 2 vitamins across the PDV and TSP. It also reduced the net portal appearance of ammonia and total volatile fatty acids across the PDV. In study 2, compared with the 2 vitamins together, vitamin B(12) alone increased glucose flux across PDV and TSP as well as its arterial concentration and PDV flux of ammonia. With the diet used in the present experiment, the major effects of the vitamin supplements seem to be mediated through changes in ruminal fermentation and gastrointestinal tract metabolism rather than by effects on hepatic metabolism.

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

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.

Portal-drained visceral metabolism of 3-hydroxybutyrate in sheep.

The present experiment was conducted to study the impact of portal-drained visceral (PDV) metabolism of arterial 3-OH-butyrate on estimates of the portal recovery of intraruminally infused butyrate. Three multicatheterized and rumen-fistulated Leicester ewes were subjected to three intraruminal infusion protocols in a Latin square design: control (C; water), butyrate (B; 20 mmol x h(-1)), and butyrate (20 mmol x h(-1)) + propionate (40 mmol x h(-1)) (BP). During the experiments, the sheep were infused with 1,2,3,4-13C4-D-3-OH-butyrate in a mesenteric vein. Portal recoveries of intraruminally infused butyrate and propionate were obtained by comparing Treatments B and BP, respectively, with Treatment C. The portal net appearance of butyrate and the portal net appearance of butyrate + 3-OH-butyrate accounted for 20 +/- 2% and 48 +/- 14% of intraruminally infused butyrate, respectively. Metabolism by the PDV tissues accounted for 32 to 44% of the whole-body irreversible loss rate of 3-OH-butyrate (12.0 to 24.7 +/- 0.5 mmol x h(-1)). The portal net appearance of butyrate plus the unidirectional PDV output of 3-OH-butyrate accounted for 62 +/- 5% of the intraruminally infused butyrate, and this estimate was comparable to the portal recovery of intraruminally infused propionate (62 +/- 7%). The results from the present study show that the extent of epithelial butyrate oxidation is overestimated and the portal recovery of butyrate carbon underestimated if only portal net appearance rates of butyrate and 3-OH-butyrate are considered.

Influence of lasalocid, cationomycin and feeding frequency on the postprandial kinetics of some plasma parameters in the rumen vein, portal vein and mesenteric artery of sheep.

Two adult sheep, A and B, received successively during three experimental periods a forage-based pelleted feed, then the same diet supplemented with 33 mg/kg of lasalocid (L) or cationomycin (C). The feed was given in either eight (sheep A) or two (sheep B) daily meals. After four weeks of adaptation, 11 blood samples were taken through catheters in the rumen vein (RVA) and the mesenteric artery (MAA) in sheep A and in the rumen vein (RVB) and portal vein (PVB) in sheep B over a 5-hour period after the morning meal. Because of a blockage in the catheter it was not possible to measure the effect of C in MAA. Food intake had no immediate effect on the plasma levels measured: the distribution of eight daily meals stabilized plasma levels and made it easier to determine the effect of the ionophores. This effect varied according to the sampling site, the animal and the antibiotic, sometimes contradictorily. All the plasma parameters monitored in RVA were significantly modified by either one of the ionophores. A decrease in plasma albumin concentration (P < 0.05) was observed with L in MAA and with C in RVA and MAA. Aceto-acetate concentration decreased (P < 0.05) with L in MAA but increased with L and C in RVB. A decrease in glycaemia and uraemia (P < 0.05) was observed with L in MAA, RVA and RVB and with C in RVA. Total amino acid concentration decreased (P < 0.05) with C in RVA or increased (P < 0.05) with L in PVB and RVB. These variations in results may be due to different mechanisms of action of L and C on digestion, particularly in the rumen. While the changes undergone by the ketone bodies in the blood suggested a decrease in hepatic ketogenesis with L, there was no evidence that the ionophores had a direct postprandial effect.

[Methods of analysis relating to blood flow measurement of the viscera and aorta in sheep]. / Méthodes d'exploitation de données concernant les débits sanguins mesurés au niveau des viscères et du train-arrière chez la brebis.

Two methods of analysis of blood flow data are presented. They are aimed at reducing: 1) the methodological variability associated with splanchnic blood flows measured by dilution (PAH) and 2) the variability of aortic blood flows measured ultrasonically associated with physical activity. Six multicatheterized ewes were used; they were first fed at maintenance and then at half-maintenance. Observed splanchnic blood flows were very variable when PAH was infused in mesenteric vein only (average CV = 17%). Variability was first reduced by a PAH infusion via both a mesenteric and a ruminal vein (CV = 11%), second by rigorous corrections on instantaneous blood flow data (CV = 13.5%), or by a combination of both (CV = 9.5%). Corrections did not modify the conclusions of the analysis of variance concerning the treatment effect, but reduced the residual variance and eliminated the negative hepatic artery blood flow values. At the hindquarters level, corrections allowed us to approach the aortic blood flows of animals in a similar 'quietly standing' state. They decreased the daily variability (from 22 to 8%) and enabled the detection of a treatment effect, which was not shown by observed data.

Net transfer of urea and ammonia across the ruminal wall of sheep.

Texel wethers (68 +/- 2.5 kg BW) fitted with catheters in the ruminal veins and a mesenteric artery, blood flow probes on ruminal arteries, and a ruminal cannula were fed 500 g of orchardgrass hay every 12 h. During the last third of the feeding cycle, intraruminal injections were performed to evaluate the effect of urease activity, osmolality, and concentrations of NH3, butyrate, and CO2 in the rumen on urea and NH3 fluxes across the rumen wall. At pH 6.7, NH3 absorption increased with NH3 and butyrate concentrations in the rumen, and to a lesser extent with CO2 concentration. The increase in ruminal blood flow associated with CO2 and butyrate increase was always greater than the increase in NH3 absorption. Increasing ruminal osmolality slightly decreased NH3 absorption. Ruminal NH3 concentration and ruminal blood flow seemed to be the main determinant of NH3 absorption. Decreasing urease activity in the rumen decreased urea net transfer. The net transfer of urea to the rumen was stimulated by CO2. High concentrations of NH3 (330 mg of N/L) and butyrate (25 mM) in the rumen decreased urea net uptake, whereas osmolality (up to 420 mOsmol/L) did not affect it. Modifications in ruminal blood flow or water net movement across the ruminal wall did not seem to account for the effect of CO2, NH3, and butyrate on urea net uptake.

Net flux of metabolites across the ruminal wall of sheep fed twice a day with orchardgrass hay.

Four Texel wethers (68 +/- 2.5 kg BW) fitted with catheters in the ruminal veins and a mesenteric artery, blood flow probes around ruminal arteries, and a ruminal cannula were used to determine meal-related variations and daily significance of net flux across the ruminal wall of urea and ammonia (NH3), VFA, D-beta-hydroxybutyrate (D beta HOB), lactate, and glucose. Sheep were fed every 12 h with orchardgrass hay (430 g of DM/meal; 611 g of digestible OM/kg of DM and 23.6 g of N/kg of DM). Apart from lactate and glucose, the fluxes of studied metabolites were significantly affected by time after morning feeding. Maximum absorption of VFA and NH3 were observed at the end of the meal; however, 5 h after the meal VFA absorption was still high, whereas NH3 absorption had decreased to the prefeeding level. Net release of D beta HOB was greater during the 2 h after the meal than during the rest of the time. Urea net transfer decreased during the meal, and thereafter it increased to the 5th h after feeding, at which time it was twofold higher than at prefeeding. The difference in net flux across the ruminal wall of urea and NH3 was linearly correlated with NH3 concentration in the ruminal fluid. Daily urea and NH3 net transfer were -2.10 and 3.76 g of N/d, respectively. The VFA net appearance in the ruminal veins was 1.167, .226, and .014 mol/d for acetate, propionate, and butyrate, respectively. Daily net release of D beta HOB, lactate, and glucose by the rumen wall was .153, .093, and -.012 mol/d, respectively.

Technical note: ruminal vein catheterization and continuous blood flow measurement in ruminal arteries of sheep.

Eight wethers were used to test the technique. Silicone rubber catheters were introduced into both ruminal veins so that their tips lay a few centimeters from the splenic vein. Arterial blood flow to the rumen was measured by an ultrasonic transit-time flow meter with 3-mm probes implanted around the left and right ruminal arteries. No loss of patency of the venous catheters was observed before slaughter (2 to 6 mo after surgery). There was no evidence of extensive vascular trauma due to catheterization at postmortem examination. In vivo calibration of the flow probes showed that reliable measurements could be made until at least 6 mo after implantation. With an accurate method of blood flow measurement in ruminal arteries and guaranteed long-term catheter patency, it would be possible to make reliable estimates of nutrient uptake across the ruminal wall of sheep over an experimental period of several months.

Wool production and blood supply to skin and other tissues in sheep.

Quantitative measurements of blood flow (BF) to skin and several other tissues were made using radioactive microspheres in conscious sheep. The sheep were from established flocks that had been selectively bred for greater (Fleece plus) or lesser (Fleece minus) wool production. The BF rate per unit area of wool-bearing skin was significantly greater in the Fleece plus (n = 9) than in the Fleece minus (n = 6) group, but the correlation between skin BF and the wool growth rate in individual animals was modest (r = .581). There was a strong, positive correlation (r = .813) between wool production and pineal BF. Other tissues that exhibited significant BF differences between the two groups included adrenal glands and fat, which were greater in Fleece plus sheep, and thyroid glands, reticulum, rumen, and extremity skin (non-wool-bearing), which were lesser in Fleece plus sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Artérias dos estômagos de fetos de bovinos da raça Nelore / Stomach arteries in Nelore bovines

Foi pesquisado o comportamento dos ramos arteriais destinados aos estômagos de fetos de bovinos da raça Nelore. Foram utilizados 30 fetos, os quais tiveram suas artérias injetadas a partir da aorta com látex Neoprene e dissecadas. De acordo com as observaçöes realizadas, o rúmen recebia ramos arteriais (artérias ruminais) derivados da artéria esplênica, a qual supria também o retículo (artéria reticular) através de colateral originado a partir da artéria ruminal esquerda. O omaso recebia irrigaçäo sanguínea a partir da artéria gástrica esquerda, a qual emitia um ou mais ramos para os sacos craniais do rúmen, e na curvatura do abomaso dava origem a artéria gastroepiplóica esquerda. As artérias gástricas direita e esquerda e as artérias gastroepiplóicas direita e esquerda anastomosaram-se entre si, respectivamente na pequena e grande curvaturas do abomaso