Extent of butyrate metabolism by bovine ruminoreticulum epithelium and the relationship to absorption rate

Effect of increased intake of concentrates and sodium butyrate supplementation on ruminal epithelium structure and function in growing rams

Increased ruminal butyrate production is considered to have a positive impact on rumen epithelium growth and function. However, excessive ruminal butyrate production may affect the rumen negatively, particularly when the rumen is already challenged with low pH. The aim of this study was to determine the effect of the inclusion of concentrates in the diet and sodium butyrate (SB) supplementation on ruminal epithelium growth and function in growing rams. Forty-two rams (27.8 ± 7.3 kg; 9-14 months of age) were allocated into six treatments and fed a diet with low (22.5% of diet DM; LOW) or high (60% of diet DM; HIGH) inclusion of concentrates in combination with no (SB0), 1.6% (SB1.6) or 3.2% (SB3.2) of diet DM inclusion of SB. There was no impact of the investigated factors on papilla dimensions and mucosa surface area, either in the atrium ruminis or ventral rumen (P ≥ 0.11). Stratum corneum thickness was higher for HIGH compared to LOW treatments (P ≤ 0.04), independently of the location in the rumen. In the atrium ruminis, the epithelium and living strata thickness quadratically increased due to SB supplementation for LOW treatments but quadratically decreased for HIGH treatments (concentrate inclusion × butyrate supplementation interaction; P ≤ 0.03); conversely, in the ventral sac of the rumen, a thicker epithelium was observed due to both increased concentrate inclusion in the diet and SB supplementation (P < 0.01) but living strata thickness was increased only by SB supplementation (linear effect; P < 0.01). The epithelium damage index in the ventral sac of the rumen was higher for LOW compared to HIGH treatments (P = 0.02). Increased inclusion of concentrates in the diet increased mRNA expression of monocarboxylate transporter 1 in both the epithelium of the atrium ruminis and ventral rumen, occludin in the epithelium of the atrium ruminis and downregulated in adenoma in the epithelium of the ventral rumen (P ≤ 0.02). Protein expression of claudin-4 in the epithelium of the ventral rumen was the highest for the HIGH/SB1.6 and HIGH/SB3.2 treatments (significant effect of interaction between main effects; P < 0.01). Under the conditions of the current study, increased intake of concentrates had mostly positive effects on ruminal epithelium in growing rams, and the same was observed for the effect of SB supplementation. However, the effect of SB supplementation was at least partially affected by the inclusion of concentrates in the diet.

Rumen microbiota and its relation to fermentation in lactose-fed calves

In our previous studies, we revealed the effect of lactose inclusion in calf starters on the growth performance and gut development of calves. We conducted the present study as a follow-up study to identify the shift in rumen microbiota and its relation to rumen fermentation when calves are fed a lactose-containing starter. Thirty Holstein bull calves were divided into 2 calf starter treatment groups: texturized calf starter (i.e., control; n = 15) or calf starter in which starch was replaced with lactose at 10% (i.e., LAC10; n = 15) on a dry matter basis. All calves were fed their respective treatment calf starter ad libitum from d 7, and kleingrass hay from d 35. Rumen digesta were collected on d 80 (i.e., 3 wk after weaning) and used to analyze rumen microbiota and fermentation products. There was no apparent effect of lactose feeding on the α-diversity and overall composition of rumen microbiota. Amplicon sequencing and real-time PCR quantification of the 16S rRNA gene confirmed that the abundance of butyrate-producing bacteria (i.e., Butyrivibrio group and Megasphaera elsdenii) did not differ between the control and LAC10 groups. Conversely, the relative abundance of Mitsuokella spp., which produce lactate, succinate, and acetate, was significantly higher in the rumen of calves that were fed lactose, whereas the lactate concentration did not differ between the control and LAC10 groups. These findings suggest that the lactate production can be elevated by an increase of Mitsuokella spp. and then converted into butyrate, not propionate, since the proportion of propionate was lower in lactose-fed calves. In addition, we observed a higher abundance of Coriobacteriaceae and Pseudoramibacter-Eubacterium in the LAC10 group. Both these bacterial taxa include acetate-producing bacteria, and a positive correlation between the acetate-to-propionate ratio and the abundance of Pseudoramibacter-Eubacterium was observed. Therefore, the higher abundance of Coriobacteriaceae, Mitsuokella spp., and Pseudoramibacter-Eubacterium in the rumen of lactose-fed calves partially explains the increase in the proportion of rumen acetate that was observed in our previous study.

Altering the ratio of dietary palmitic and oleic acids affects nutrient digestibility, metabolism, and energy balance during the immediate postpartum in dairy cows

This article is the second from an experiment that determined the effects of altering the dietary ratio of palmitic (C16:0) and oleic (cis-9 C18:1) acids on digestibility, production, and metabolic responses of dairy cows during the immediate postpartum. This article elaborates on the effect of these diets on nutrient digestibility, energy balance, and metabolism. Fifty-six multiparous cows were used in a randomized complete block design and randomly assigned to 1 of 4 treatments fed from 1 to 24 d in milk. The treatments were: (1) control (CON) diet not supplemented with fatty acids (FA); (2) diet supplemented with a FA blend containing 80% C16:0 and 10% cis-9 C18:1 (80:10); (3) diet supplemented with a FA blend containing 70% C16:0 and 20% cis-9 C18:1 (70:20); and (4) diet supplemented with a FA blend containing 60% C16:0 and 30% cis-9 C18:1 (60:30). The FA supplement blends were added at 1.5% of diet dry matter by replacing soyhulls in the CON diet. Three preplanned contrasts were used to compare treatment differences: (1) CON versus FA-supplemented diets, (80:10 + 70:20 + 60:30)/3; (2) the linear effect of cis-9 C18:1 inclusion in diets; and (3) the quadratic effect of cis-9 C18:1 inclusion in diets. The FA-supplemented diets increased digestibility of dry matter, neutral detergent fiber, 18-carbon FA, and total FA compared with CON. We observed a tendency for an interaction between treatment and time for the digestibility of 18-carbon and total FA because the difference in digestibility between CON and 60:30 treatments tended to increase over time. Increasing dietary cis-9 C18:1 increased linearly the digestibility of dry matter, neutral detergent fiber, 16-carbon, 18-carbon, and total FA. Interestingly, total absorbed FA was positively related to milk, milk fat yield, energy-corrected milk, plasma insulin, and albumin, and negatively related to plasma nonesterified FA (NEFA) and body weight loss. The FA-supplemented diets increased intake of digestible energy, metabolizable energy, and net energy for lactation compared with CON. Compared with CON, FA-supplemented diets increased milk energy output and tended to increase negative energy balance. Increasing dietary cis-9 C18:1 increased intake of digestible energy, metabolizable energy, and net energy for lactation. Although increasing dietary cis-9 C18:1 did not affect milk energy output and energy for maintenance, increasing dietary cis-9 C18:1 improved energy balance. Compared with CON, FA-supplemented diets increased plasma insulin, but we did not observe differences between CON and FA-supplemented diets for NEFA and albumin. Increasing cis-9 C18:1 in FA treatments linearly decreased plasma NEFA and tended to linearly increase insulin and β-hydroxybutyrate. During the carryover period, no treatment differences in blood metabolites were observed. Our results indicate that feeding FA supplements containing C16:0 and cis-9 C18:1 during the immediate postpartum period increased nutrient digestibility, energy intake, and milk energy output compared with a non-fat-supplemented control diet. Increasing dietary cis-9 C18:1 increased energy intake, reduced markers of body fat mobilization, and improved energy balance during the immediate postpartum.

Hyperglycemia-stimulating diet induces liver steatosis in sheep

Hepatic steatosis is strongly associated with chronic liver disease and systemic metabolic disorder. Adipose lipolysis is a recognized principal source of intrahepatic fat in various metabolic disorders, including non-alcoholic fatty liver disease. We hypothesized that, in the premorbid state, hepatic de novo lipogenesis (DNL) driven by excess carbohydrates abundance might play a more significant role. We employed a novel nutritional model in sheep of two distinct carbohydrates abundances. During 4 months of the dietary treatment, lambs were monitored for metabolic and terminal liver parameters. Lambs grown on the high-calorie (HC) diet were consistently more hyperglycemic and hyperinsulinemic than lambs grown on the lower-calorie (LC) diet (P < 0.0001). As a result, the HC lambs developed systemic- (HOMA-IR of 7.3 vs. 3.1; P < 0.0001), and adipose- (ADIPO-IR of 342.7 vs. 74.4; P < 0.0001) insulin resistance, significant adiposity (P < 0.0001), and higher plasma triglycerides (P < 0.05). Circulating leukocytes in the HC lambs had higher mRNA expression levels of the proinflammatory markers CCL2 (P < 0.01) and TNF-alpha (P < 0.04), and IL1B trended higher (P < 0.1). Remarkably, lambs on the HC diet developed substantial liver steatosis (mean fat content of 8.1 vs. 5.3% in the LC group; P < 0.0001) with a higher histological steatosis score (2.1 vs. 0.4; P < 0.0002). Hepatic steatosis was most-strongly associated with blood glucose and insulin levels but negatively correlated with circulating fatty acids-indicating a more significant contribution from hepatic DNL than from adipose lipolysis. Sheep may prove an attractive large-animal model of fatty liver and metabolic comorbidities resulting from excess carbohydrate-based energy early in life.

The bovine epimural microbiota displays compositional and structural heterogeneity across different ruminal locations

Dairy cattle are globally important agricultural animals. Central to their biology is the rumen, which houses an essential microbial community, or microbiome, important for providing nutrition from otherwise host-inaccessible dietary components. The rumen environment is noted for its substantial spatial heterogeneity, as illustrated by the stratification into ruminal solid and liquid phases. A third microbiota found directly attached to the ruminal epithelium (the epimural microbiota) also exists but is less well understood because of challenges in sampling the ruminal epithelium. As a result, our understanding of the epimural microbiota is based on analyses of cannulated animals sampled at a single location-the ventral sac-and does not account for other ruminal locations, which may have importance for overall rumen function. To address this knowledge gap, we hypothesize that the epimural microbiota at different ruminal locations differs due to known morphological, physiological, and functional differences across the geographic spread of the rumen epithelium. Here, we characterized bacterial epimural communities at different sites within 8 lactating Holstein dairy cows using 16S rRNA gene sequencing. Four different sites were sampled via rumen tissue biopsy: cranial sac (CS), ventral sac (VS), caudodorsal blind sac (CDBS), and caudoventral blind sac (CVBS). We found that locations differed in both epimural bacterial community structure and composition, with the CDBS community displaying the greatest diversity. Across all sampling sites, epimural bacterial communities were dominated by members of the phyla Bacteroidetes, Firmicutes, and Proteobacteria. Bacteria within Prevotellaceae, Butyrivibrio, Campylobacter, Mogibacterium, and Desulfobulbus all showed high relative sequence abundance and differential distributions according to sample location. There appears to be a core epimural microbiota present across all locations in all cows, although relative abundance was highly variable. The difference in relative abundance in epimural microbial communities, perhaps influenced by host physiology and the diversity within rumen contents, likely has important consequences for nutrition acquisition and general health. To the best of our knowledge, this work represents the first characterization of the ruminal epimural microbiota across different epithelial locations for any bovine ruminant.

Invited review: Use of butyrate to promote gastrointestinal tract development in calves

Promotion of microbial butyrate production in the reticulorumen is a widely used method for enhancing forestomach development in calves. Additional acceleration of gastrointestinal tract (GIT) development, both the forestomach and lower parts of the GIT (e.g., abomasum, intestine, and also pancreas), can be obtained by dietary butyrate supplementation. For this purpose, different sources (e.g., butyrate salts or butyrins), forms (e.g., protected or unprotected), methods (e.g., in liquid feed or solid feed), and periods (e.g., before or after weaning) of butyrate administration can be used. The aim of this paper was to summarize the knowledge in the field of butyrate supplementation in feeds for newborn calves in practical situations, and to suggest directions of future studies. It has been repeatedly shown that supplementation of unprotected salts of butyrate (primarily sodium salt) in milk replacer (MR) stimulates the rumen, small intestine, and pancreas development in calves, with a supplementation level equating to 0.3% of dry matter being sufficient to exert the desired effect on both GIT development and growth performance. On the other hand, the effect of unprotected butyrins and protected forms of butyrate supplementation in MR has not been extensively investigated, and few studies have documented the effect of butyrate addition into whole milk (WM), with those available focusing mainly on the growth performance of animals. Protected butyrate supplementation at a low level (0.3% of protected product in DM) in solid feed was shown to have a potential to enhance GIT development and performance of calves fed MR during the preweaning period. Justification of this form of butyrate supplementation in solid feed when calves are fed WM or after weaning needs to be documented. After weaning, inclusion of unprotected butyrate salts in solid feed was shown to increase solid feed intake, but the effect on GIT development and function has not been determined in detail, and optimal levels of supplementation are also difficult to recommend based on available reports. Future studies should focus on comparing different sources (e.g., salts vs. esters), forms (e.g., protected vs. unprotected), and doses of supplemental butyrate in liquid feeds and solid feeds and their effect not only on the development of rumen, abomasum, and small intestine but also the omasum and large intestine. Furthermore, the most effective source, form, and dose of supplemental butyrate in solid feed depending on the liquid feed program (e.g., MR or WM), stage of rearing (e.g., pre- or postweaning), and solid composition (e.g., lack or presence of forage in the diet) need to be determined.

Effect of butyrate infusion into the rumen on butyrate flow to the duodenum, selected gene expression in the duodenum epithelium, and nutrient digestion in sheep

The aim of the study was to determine the effect of butyrate infusion into the rumen on butyrate flow to the duodenum, expression of short-chain fatty acid (SCFA) transporters (monocarboxylate transporter-1, -2, and -4) and receptors (G protein coupled receptor-41 and -43) in the duodenal epithelium and nutrient digestion in sheep. Eight wethers (39.0 ± 3.00 kg; mean ± SD) with ruminal and T-shape duodenal cannulas were allocated to 4 × 4 replicated Latin square design with each experimental period lasting for 21 d (12 d of adaptation and 9 d for data and sample collection). Experimental treatments were: 1) distilled water infusion into the rumen (CONT); 2) 15 g/d of butyric acid infusion into the rumen (BUT15); 3) 30 g/d of butyric acid infusion into the rumen (BUT30); and 4) 45 g/d of butyric acid infusion into the rumen (BUT45). The daily dose of butyrate was infused into the rumen via the rumen cannula, with 200 mL of solution of butyric acid and distilled water, at a constant rate (0.1389 mL/min) throughout the day using a peristaltic pump. Correspondingly, 200 mL/d of distilled water was infused into the rumen of CONT. The wethers were fed daily 900 g of chopped meadow hay and 200 g of concentrate in two equal meals at 0600 and 1800 h. Butyrate infusion into the rumen did not affect total SCFA concentration in the rumen fluid ( > 0.11). Molar proportion of butyrate in total SCFA linearly increased, and molar proportion of acetate and isovalerate linearly decreased ( ≤ 0.02) with an increasing amount of butyrate infused into the rumen. The molar proportion of butyrate in total SCFA in the duodenal digesta linearly increased ( < 0.01), and butyrate flow to duodenum tended to linearly increase ( = 0.06) with an increasing dose of exogenous butyrate delivered to the rumen. Butyrate infusion into the rumen did not affect ( ≥ 0.14) the mRNA expression of monocarboxylate transporter-2 and -4 and G protein coupled receptor-43 in the duodenal epithelium. The G protein coupled receptor-41 and monocarboxylate transporter-1 mRNA expression in the duodenal epithelium was very low in many of the analyzed samples. Digestibility of organic matter, neutral detergent fiber, and acid detergent fiber in the stomach (forestomach and abomasum) decreased for BUT15 and BUT30 and then increased for BUT45 (quadratic, ≤ 0.04); however, neither digestibility in the intestine nor total tract digestibility differed between treatments ( ≥ 0.10).

Milk fatty acid composition as an indicator of energy status in Holstein dairy cows

Abstract. Transition dairy cows often enter a stage of negative energy balance during which the utilization of energy reserves is reflected in the milk fatty acid (FA) composition. In this study, metabolic status was evaluated by measuring milk FA, ruminal short-chain FA (RSCFA), and serum biochemical parameters in Holstein cows. Samples (milk, rumen contents, and blood) were collected around days 30 (early) and 150 (middle) of lactation, and rumen contents and blood samples were collected 30 days before calving (dry). Fatty acids were extracted and FA composition was determined. Glucose, triacylglycerols, total cholesterol, low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C), beta-hydroxybutyric acid (BHB), and non-esterified fatty acid (NEFA) concentrations were determined in serum samples. Lower percentages of saturated FA in milk and higher percentages of monounsaturated FA, polyunsaturated FA, and C18:1n-9 were observed in early lactation compared to mid-lactation. In rumen higher concentrations of propionic acid were determined at mid-lactation compared to early lactation. Acetic and butyric acid concentrations showed no significant differences between sampling intervals. In serum higher glucose concentrations were observed during the dry period and mid-lactation than during early lactation. Lower BHB and higher NEFA concentrations were noted during early lactation compared to mid-lactation and the dry period. Total cholesterol, LDL-C, HDL-C and triacylglycerols showed no significant differences between sampling intervals. The results of the present study suggest that determination of milk FA is a potential indicator of energy status in dairy cows.

Digestive development in neonatal dairy calves with either whole or ground oats in the calf starter

A series of 3 trials was conducted to determine effects of whole or ground oats in starter grain on reticulorumen fermentation and digestive system development of preweaned calves. Male Holstein calves (43.1±2.3kg at birth; n=8, 9, and 7 for trials 1, 2, and 3, respectively) were housed in individual pens in a heated facility; bedding was covered with landscape fabric to prevent consumption of bedding by the calves. In trials 1 and 2 only, calves were fitted with rumen cannulas by wk 2 of life. In all trials, a fixed amount of starter (containing 25% oats either ground and in the pellet or whole) was offered daily; orts were fed through the cannula in trials 1 and 2. Calves were randomly assigned to an all-pelleted starter or pellets plus whole oats. Rumen contents (trials 1 and 2) were sampled weekly at -8, -4, 0, 2, 4, 8, and 12 h after grain feeding for determination of pH and volatile fatty acids. Calves were killed 3 wk (trial 1) or 4 wk (trials 2 and 3) after grain was offered; organs were harvested, emptied, rinsed, and weighed to gauge digestive organ development. Starter intake was not different between treatments. Weekly measurements of rumen digesta pH did not change and only subtle changes were observed in molar proportions of individual volatile fatty acids. Molar proportion of butyrate and pH linearly decreased with age, whereas acetate proportion increased. Reticulorumen weight and papillae length tended to be greater for calves fed pelleted starter, whereas abomasum weight was greater for calves fed pellets plus whole oats. Fecal particle size and starch content were greater for calves fed pellets plus whole oats. Under the conditions of this study, physical form of oats in starter grain did not affect rumen fermentation measurements; greater rumen weight and papillae length in calves fed pelleted starter may be the result of greater nutrient availability of ground oats. Under the conditions of this study with young calves on treatments for <4 wk, increasing particle size of the starter by feeding whole oats did not affect rumen fermentation nor did it improve digestive system development.

Effects of cooked molasses licking block supplementation pre- and post-partum on feed intake, suckling lamb performance, milk yield and milk quality in dairy sheep. Part 1

This study tested the nutritional benefit of a supplement offered freely to dairy sheep over a period from 60 days before lambing to 60 days after lambing, at stall and grazing. Thirty Sarda dairy sheep on Day 90 of gestation, homogeneous for age, parity number, bodyweight (BW) and body condition score (BCS), were allocated to one of two groups: control (Ctr) or treated (Cry). Over 120 days, both groups received ryegrass hay and concentrate indoors. After weaning, the ewes also had access to pasture for 6 h/day. Throughout the experimental period, the Cry group had ad libitum access to a cooked molasses licking block. No significant differences were observed between the groups in forage, concentrate and total DM intake. During the experiment, the reduction in BCS in early lactation tended to be slower in the Cry than in Ctr group (Ptrend < 0.09), whereas no significant effects were seen on BW. Lamb performance tended to be improved by Cry in terms of liveweight of litter size per sheep (9.65 vs 8.22 kg for Cry and Ctr, respectively; P < 0.07), whereas no significant effects were observed on milk yield and composition, except for a trend for increased fat content in the Cry versus Ctr group (6.15% vs 5.95%, respectively; P < 0.08). Cry ewes had higher blood cholesterol concentrations than did Ctr ewes (1.96 vs 1.63 mmol/L; P < 0.01). Because there were no differences between feed intake at stall and the estimated total DM intake at stall and during grazing between the two groups, the better performance of the Cry group could be explained by an increase of feed use efficiency at the digestive and/or metabolic level.

Epithelia of the ovine and bovine forestomach express basolateral maxi-anion channels permeable to the anions of short-chain fatty acids

It has long been established that the absorption of short-chain fatty acids (SCFA) across epithelia stimulates sodium proton exchange. The apically released protons are not available as countercations for the basolateral efflux of SCFA anions and a suitable transport model is lacking. Patch clamp and microelectrode techniques were used to characterize an anion conductance expressed by cultured cells of the sheep and bovine rumen and the sheep omasum and to localize the conductance in the intact tissue. Cells were filled with a Na-gluconate solution and superfused with sodium salts of acetate, propionate, butyrate, or lactate. Reversal potential rose and whole cell current at +100 mV decreased with the size of the anion. Anion-induced currents could be blocked by diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS), NPPB (200 μmol l(-1)), or pCMB (1 mmol l(-1)). In patches of bovine ruminal cells, single channels were observed with a conductance for chloride (327 ± 11 pS), acetate (115 ± 8 pS), propionate (102 ± 10 pS), butyrate (81 ± 2 pS), and gluconate (44 ± 3 pS). Channels expressed by sheep rumen and omasum were similar. Microelectrode experiments suggest basolateral localization. In conclusion, forestomach epithelia express basolateral maxi-anion channels with a permeability sequence of chloride > acetate > propionate > butyrate. SCFA absorption may resemble functionally coupled transport of NaCl, with the Na(+)/K(+)-ATPase driving the basolateral efflux of the anion through a channel. Since protons are apically extruded, the model accurately predicts that influx of buffers with saliva is essential for the pH homeostasis of the ruminant forestomach.

Microbial butyrate and its role for barrier function in the gastrointestinal tract

Butyrate production in the large intestine and ruminant forestomach depends on bacterial butyryl-CoA/acetate-CoA transferase activity and is highest when fermentable fiber and nonstructural carbohydrates are balanced. Gastrointestinal epithelia seem to use butyrate and butyrate-induced endocrine signals to adapt proliferation, apoptosis, and differentiation to the growth of the bacterial community. Butyrate has a potential clinical application in the treatment of inflammatory bowel disease (IBD; ulcerative colitis). Via inhibited release of tumor necrosis factor α and interleukin 13 and inhibition of histone deacetylase, butyrate may contribute to the restoration of the tight junction barrier in IBD by affecting the expression of claudin-2, occludin, cingulin, and zonula occludens poteins (ZO-1, ZO-2). Further evaluation of the molecular events that link butyrate to an improved tight junction structure will allow for the elucidation of the cofactors affecting the reliability of butyrate as a clinical treatment tool.

Effect of increasing ruminal butyrate absorption on splanchnic metabolism of volatile fatty acids absorbed from the washed reticulorumen of steers

Four steers fitted with a ruminal cannula and chronic indwelling catheters in the mesenteric artery, mesenteric vein, hepatic portal vein, hepatic vein, and the right ruminal vein were used to study the absorption and metabolism of VFA from bicarbonate buffers incubated in the temporarily emptied and washed reticulorumen. Portal and hepatic vein blood flows were determined by infusion of p-aminohippurate into the mesenteric vein, and portal VFA fluxes were calibrated by infusion of isovalerate into the ruminal vein. The steers were subjected to four experimental treatments in a Latin square design with four periods within 1 d. The treatments were Control (bicarbonate buffer) and VFA buffers containing 4, 12, or 36 mmol butyrate/kg of buffer, respectively. The acetate content of the buffers was decreased with increasing butyrate to balance the acidity. The butyrate absorption from the rumen was 39, 111, and 300 +/- 4 mmol/h for the three VFA buffers, respectively. The ruminal absorption rates of propionate (260 +/- 12 mmol/h), isobutyrate (11.4 +/- 0.7 mmol/h), and valerate (17.3 +/- 0.7 mmol/h) were not affected by VFA buffers. The portal recovery of butyrate and valerate absorbed from the rumen increased (P < 0.01) with increasing butyrate absorption and reached 52 to 54 +/- 4% with the greatest butyrate absorption. The liver responded to the increased butyrate absorption with a decreasing fractional extraction of propionate and butyrate, and with the greatest butyrate absorption, the splanchnic flux was 22 +/- 1% and 18 +/- 1% of the absorbed propionate and butyrate, respectively. The increased propionate and butyrate release to peripheral tissues was followed by increased (P < 0.05) arterial concentrations of propionate (0.08 +/- 0.01 mmol/kg) and butyrate (0.07 +/- 0.01 mmol/kg). Arterial insulin concentration increased (P = 0.01) with incubation of VFA buffers compared with Control and was numerically greatest with the greatest level of butyrate absorption. We conclude that the capacity to metabolize butyrate by the ruminal epithelium and liver is limited. If butyrate absorption exceeds the metabolic capacity, it affects rumen epithelial and hepatic nutrient metabolism and affects the nutrient supply of peripheral tissues.

Feeding lactose increases ruminal butyrate and plasma beta-hydroxybutyrate in lactating dairy cows

Ruminal fermentation of lactose increases molar proportions of butyrate, which is metabolized by the ruminal epithelium to beta-hydroxybutyrate (BHBA). To determine the effects of dietary whey, and specifically lactose, on concentrations of ruminal and blood volatile fatty acids (VFA) and blood BHBA, 8 Holstein and 4 Brown Swiss multiparous cows (210 +/- 33 d in milk) were blocked by breed and randomly assigned to one of three 4 x 4 Latin squares. Treatments were control (CON; 7.1% of dietary dry matter [DM] as cornstarch), liquid whey (WHEY; 9.4% of diet DM) containing 70% lactose on a DM basis, low lactose (LOLAC; 7.1% lactose), or high lactose (HILAC; 14.3% lactose). Diets contained 53% forage as corn silage, alfalfa hay, and grass hay (DM basis) and a corn and soybean meal-based concentrate. Average dietary percentage of crude protein and energy density (Mcal/kg net energy for lactation) were 16.8 and 1.47, respectively. Feeding lactose increased DM intake. Milk production and composition were not affected by diet with the exception of decreased urea nitrogen in milk from cows fed lactose. Greater proportions of ruminal propionate were observed in cows fed CON relative to those fed WHEY and LOLAC. Increasing dietary lactose increased proportions of ruminal butyrate and decreased acetate and branched-chain VFA. Concurrent with the increase in ruminal butyrate concentrations, there was an increase in plasma BHBA as lactose in the diet increased. Concentrations of VFA in plasma were not affected by diet with the exception of the branched-chain VFA, which were increased in cows fed LOLAC compared with WHEY. These data indicate lactose fermentation increases proportions of ruminal butyrate and plasma BHBA in lactating dairy cows; however, the observed increase in plasma BHBA is not sufficient to subject cows to ketosis.

Refinements in primary rumen epithelial cell incubation techniques

The objectives of this study were to 1) determine if the number of rumen epithelial cells in primary cell incubation affects the rate of metabolite production, and 2) determine the optimum mode of data expression to standardize reporting criteria. Sections of rumen epithelial tissue were excised from five Holstein heifers and subjected to serial tryptic digestion to isolate cells. Isolated cells had a mean viability of 86% (+/- 1.29) and were incubated at concentrations of 0.5, 1, 5, 10, 20, and 40 million cells per flask. Oxidation of [1-14C]butyrate to 14CO2 and production of acetoacetate (ACAC), beta-hydroxybutyrate (BHBA), lactate, and pyruvate were measured for cell dilution comparisons. Cell number, cell dry matter, cell crude protein, epithelial wet tissue weight, body weight, and metabolic body weight were measured to generate 12 different forms of data expression. Coefficients of variation were calculated for each type of expression. Expressing data per cell number resulted in the lowest variation. Oxidation of [1-14C]butyrate to 14CO2 and pyruvate production per million cells did not significantly differ between treatments for 90-min incubation. Acetoacetate and lactate concentrations were greatest at 0.5 and 1 million cells/flask, respectively, with no differences between 5 to 40 million cells/flask. Production of BHBA for 1 million cells/flask was greater than 0.5 and 40 million cells/flask, but did not change between cell concentrations 5 to 20 million. The BHBA:ACAC concentration ratios for 0.5 and 1 million cell dilutions were both 1.1 to 1 indicating low mitochondrial redox potentials. Concomitantly, lactate:pyruvate ratios for 0.5 and 1 million cells were greater than other cell dilutions, indicating a high cytosolic redox potential. The suggested range of rumen epithelial cells to include in incubations is 5 to 20 million cells/flask. This will minimize experimental error associated with using low cell numbers and the potential for reduced metabolite production caused by incubating large cell quantities. When rumen tissue taken from animals of the same species, size, and stage of development; data adjusted by cell number is preferred. However, it is recommended that cell protein, cell DM, and animal metabolic weight be included to facilitate future comparison between species and laboratories.

Portal recovery of short-chain fatty acids infused into the temporarily-isolated and washed reticulo-rumen of sheep

The present study was undertaken to study the metabolism of short-chain fatty acids (SCFA) by the reticulo-ruminal epithelium and the portal-drained viscera (PDV) under in vivo conditions with no interference from the metabolism of the rumen microbes. The technique of temporary isolation of the reticulo-rumen was applied to wethers implanted with catheters in a mesenteric artery, the hepatic portal vein and the right ruminal vein. Portal blood flow was measured by downstream dilution of p-aminohippuric acid; the PDV uptake of arterial acetate, as well as the whole-body irreversible loss rate (ILR) of acetate, was estimated by [2-(13)C]acetate infusion into the right ruminal vein. The sheep were maintained with a bicarbonate-buffered solution of SCFA in the reticulo-rumen along with continuous intraruminal infusion of SCFA for 4 h. The portal appearance of SCFA of non-reticulo-ruminal origin was estimated before and after the infusion protocol. Of the acetate absorbed by the sheep, 89 (SE 5), 109 (SE 7) and 101 (SE 7)% was recovered as portal net appearance of acetate, portal net appearance of acetate corrected for PDV uptake of arterial acetate and increase in the ILR of acetate respectively. Of the propionate, isobutyrate, butyrate, isovalerate and valerate absorbed by the sheep, 95 (SE 7), 102 (SE 9), 23 (SE 3), 48 (SE 5) and 32 (SE 4)% respectively was recovered as portal net appearance. In contrast to current concepts, the present study showed that the reticulo-ruminal epithelium metabolizes none (or only a small proportion) of the acetate and propionate absorbed from the rumen. This observation could lead to the more efficient use of results obtained with multi-catheterized animals to quantify the net metabolite output of the rumen microbes.

Absorption and metabolism of short-chain fatty acids in ruminants

Short-chain fatty acids (SCFA), viz. acetate, propionate and butyrate are quantitatively important substrates in ruminant energy metabolism. In the reviewed literature, 16 44% of ME intake was recovered as portal appearance of SCFA. This is considerably lower than expected when related to the estimated intragastric flux of SCFA. The discrepancy is caused by portal drained viscera metabolism of arterially abundant metabolites e.g., acetate and the metabolism of acetate and butyrate to acetoacetate and D-3-hydroxybutyrate in the absorptive epithelia. Even though considerable variations between experiments on acetate and propionate appearance are found, there seems to be a great deal of evidence that the proportion of gastrointestinally produced acetate and propionate absorbed to the portal blood is 50-75%. The portal recovery of butyrate has been found to be between 10 and 36% dependent on intraruminal infusion rate. It is concluded that major parts of acetate and propionate are directly absorbed to the portal vein. The true absorption rate of acetate can only be estimated by taking the portal drained viscera metabolism of arterial acetate into account. Butyrate is generally found to have a low recovery in the portal vein, but the production of D-3-hydroxybutyrate seems to be underestimated in major parts of the literature. It is therefore necessary to measure portal appearance as well as portal drained viscera metabolism to assess the quantitative as well as the qualitative contribution of SCFA and SCFA metabolites to whole animal metabolism.

Relationship between fermentation acid production in the rumen and the requirement for physically effective fiber

The content of ruminally fermented OM in the diet affects the fiber requirement of dairy cattle. Physically effective fiber is the fraction of feed that stimulates chewing activity. Chewing, in turn, stimulates saliva secretion. Bicarbonate and phosphate buffers in saliva neutralize acids produced by fermentation of OM in the rumen. The balance between the production of fermentation acid and buffer secretion is a major determinant of ruminal pH. Low ruminal pH may decrease DMI, fiber digestibility, and microbial yield and thus decrease milk production and increase feed costs. Diets should be formulated to maintain adequate mean ruminal pH, and variation in ruminal pH should be minimized by feeding management. The fraction of OM that is fermented in the rumen varies greatly among diets. This variation affects the amount of fermentation acids produced and directly affects the amount of physically effective fiber that is required to maintain adequate ruminal pH. Acid production in the rumen is due primarily to fermentation of carbohydrates, which represent over 65% of the DM in diets of dairy cows and have the most variable ruminal degradation across diets. The non-fiber carbohydrate content of the diet is often used as a proxy for ruminal fermentability, but this measure is inadequate. Ruminal fermentation of both nonfiber carbohydrate and fiber is extremely variable, and this variability is not related to the nonfiber carbohydrate content of the diet. The interaction of ruminally fermented carbohydrate and physically effective fiber must be considered when diets for dairy cattle are evaluated and formulated.

Effects of the ratio of ruminal propionate to butyrate on milk yield and blood metabolites in dairy cows

Four Ayrshire cows (mean = 56 DIM) were used in a 4 x 4 Latin square design to study the effects of the ratio of propionate to butyrate in the rumen on milk yield, milk composition, and blood metabolites. The cows were fed a basal diet (16.2% CP, 43.4% NDF) consisting of 50% grass silage, 6% grass hay, and 44% concentrate (percentage of DM). The diet supplied 44 Mcal/d of metabolizable energy and was supplemented with isoenergetic infusions of VFA (4.5 Mcal/d). Propionate (900 g/d) was replaced gradually with 33, 67, and 100% of butyrate on an energy basis. Replacement of propionate with butyrate in the infusate decreased propionate and increased butyrate concentrations in ruminal fluid and in blood plasma. Yields of milk and lactose decreased, and yield of milk fat increased, as butyrate increased. Milk fat content increased, and lactose content decreased, as butyrate increased. Increased ruminal supply of butyrate decreased plasma glucose concentration and increased blood ketone body concentration. When only butyrate was infused (750 g/d), either liver metabolism was changed or tissue mobilization was increased, as indicated by the increased production of long-chain milk fatty acids and increased plasma concentrations of acetate, Gly, and branched-chain AA. An increase in ruminal butyrate supply at the expense of propionate adversely affected milk yield and the repartitioning of nutrients between milk components. At a high percentage, increased butyrate might also adversely affect the overall metabolism of the cow.

Effect of increasing ruminal butyrate on milk yield and blood constituents in dairy cows fed a grass silage-based diet

The effects of increased ruminal supply of butyrate on milk yield, milk composition, and blood metabolites were studied in four lactating cows in a 4 x 4 Latin square design. The basal diet comprised grass silage, hay, and concentrate (34:22:42, DM basis) and was supplemented with isoenergetic VFA infusions (3.58 Mcal/d). A 3:1 molar mixture of acetate and propionate was replaced gradually with butyrate at the rates of 0, 200, 400, or 600 g/d. When the amount of infused butyrate increased, isobutyrate, butyrate, and isovalerate in plasma and acetoacetate and beta-hydroxybutyrate in whole blood increased linearly, but plasma glucose concentration decreased. The latter was associated with a trend toward higher plasma urea concentration, suggesting that more AA were used for gluconeogenesis as the supply of propionate decreased and that of butyrate increased. Milk yield was not changed. The concentrations of milk fat and protein increased, and that of lactose decreased linearly, with the rate of butyrate infusion. Milk fat yield increased, and lactose yield tended to decrease, with increased butyrate infusion. These results indicate that changes in the supply of butyrate do not affect markedly milk yield in cows yielding less than 20 kg/d but cause marked changes in milk composition. The increase in ruminal butyrate supply increased ketogenesis and decreased gluconeogenesis in the liver of lactating dairy cows.

Absorption of volatile fatty acids from the rumen of lactating dairy cows as influenced by volatile fatty acid concentration, pH and rumen liquid volume

The effect of rumen liquid volume, pH and concentration of volatile fatty acids (VFA) on the rates of absorption of acetic, propionic and butyric acids from the rumen was examined in lactating dairy cows. Experimental solutions introduced into the emptied, washed rumen comprised two different volumes (10 or 30 l), four levels of pH (4.5, 5.4, 6.3, 7.2) and three levels of individual VFA concentrations (20, 50 or 100 mM-acetic, propionic or butyric acid). All solutions contained a total of 170 mM-VFA and an osmotic value of 400 mOsmol/l. Absorption rates were calculated from the disappearance of VFA from the rumen corrected for passage with liquid phase to the omasum. An increase in initial fluid pH caused a reduction in fractional absorption rates of propionic and butyric acids. Increasing the initial pH from 4.5 to 7.2 reduced fractional absorption rates of acetic, propionic and butyric acids from 0.35, 0.67 and 0.85 to 0.21, 0.35 and 0.28/h respectively. The fractional absorption rates of all VFA were reduced (P < 0.05) by an increase in initial rumen volume. The fractional absorption rate of acetic acid was lower (P < 0.05) at an initial concentration of 20 mM than of 50 mM. The fractional absorption rate of propionic acid tended (P < 0.10) to decrease as the level of concentration increased while fractional absorption rate of butyric acid was not affected by butyric acid concentration. These results indicate that relative concentrations of VFA in rumen fluid might not represent relative production rates and that attempts to estimate individual VFA production from substrate digestion must take account of pH and VFA concentration.

Effect of dietary forage:grain ratio on blood constituents in dairy cows

Forty-nine primiparous and 44 multiparous lactating Holstein cows were used to study the effect of five dietary forage: grain ratios on blood constituents. Blood samples were collected in wk 2, 3, 4, 6, 8, 12, and 16 of lactation and were analyzed for glucose, urea, beta-hydroxybutyrate, and FFA. Increasing the percentage of forage in the diet decreased blood glucose concentration. Glucose levels were low at the beginning of lactation and increased as DMI increased. Increasing percentage of forage in the diet did not affect blood urea concentration. Increasing forage in the diet from 38.2 to 98.2% increased beta-hydroxybutyrate concentrations threefold during the first 4 wk of lactation in both primiparous and multiparous cows. The concentration of plasma FFA was higher in all the treatments at the beginning of lactation and decreased as lactation advanced. Dietary forage:grain ratio did not affect plasma FFA.

In vitro production of beta-hydroxybutyrate from 1,3-butanediol by bovine liver, rumen mucosa, and kidney

A model ketosis can be produced in dairy cows by restricting feed intake plus feeding 1,3-butanediol. Increases in D-beta-hydroxybutyrate in blood result from metabolism of the 1,3-butanediol, but the site of metabolism has not been established. In vitro production of D-beta-hydroxybutyrate from butyrate and from isomers of 1,3-butanediol was measured in bovine liver, rumen papillae, and kidney cortex, all obtained at slaughter from nonlactating, nonpregnant Holstein cows. Production of D-beta-hydroxybutyrate from butyrate by the tissues was greatest for liver and rumen and much less for kidney. Only liver, however, produced appreciable amounts of D-beta-hydroxybutyrate from R-, S-, or RS-1,3-butanediol, and rates were maximal at substrate concentrations of 5 mM. Production of D-beta-hydroxybutyrate from R-1,3-butanediol by liver was greater than from S-1,3-butanediol. In vitro rates of production of D-beta-hydroxybutyrate were consistent with liver being the primary tissue involved in the metabolism of 1,3-butanediol, and capacity of the liver probably is sufficient to account for metabolism of 1,3-butanediol when 1 kg is fed daily to dairy cows.

Metabolic effects of intraruminal administration of 1,3-butanediol or tributyrin in lactating goats

Acute effects of dietary 1,3-butanediol and tributyrin on concentrations of glucose, beta-hydroxybutyrate, and insulin in plasma were compared in lactating goats. In Experiment 1, glucose was decreased by intraruminal administration of 75 or 150 g of 1,3-butanediol or by 84 or 168 g of tributyrin. Tributyrin caused transient hyperglycemia immediately after administration. beta-Hydroxybutyrate was increased in a dose-dependent manner by tributyrin and increased independently of dose by 1,3-butanediol. Tributyrin, but not 1,3-butanediol. Tributyrin, but not 1,3-butanediol, caused large increases of insulin in plasma. In Experiment 2, 75 g of 1,3-butanediol or 84 g of tributyrin administered intraruminally decreased glucose, whereas 73 g of butyric acid (pH 5.6) increased glucose compared with water or 25.6 g of glycerol. All treatments produced transient hyperglycemia immediately after administration. Tributyrin, butyric acid, or 1,3-butanediol greatly increased beta-hydroxybutyrate compared with administration of water or glycerol. Concentrations of beta-hydroxybutyrate in both experiments increased more slowly for 1,3-butanediol than for tributyrin. Both 1,3-butanediol and tributyrin decreased glucose and increased beta-hydroxybutyrate. Because 1,3-butanediol does not stimulate increases of insulin in plasma, it may be more desirable than tributyrin for inducing metabolic changes characteristic of lactation ketosis.

Volatile fatty acid uptake and propionate metabolism in ruminant hepatocytes

Previous reports have demonstrated that butyrate inhibits metabolism of propionate by liver cells isolated from sheep and goats. Our objectives were to examine some possible mechanisms for this inhibition and to test for this inhibition in the bovine animal. Incorporation of label from 2.5 mM [2-(14)C]propionate into glucose (nmol propionate/mg cell DM/h) in the presence of 0, 1.25, and 2.5 mM butyrate was 107, 66, and 62 by goat hepatocytes and 79, 25, and 29 by calf hepatocytes; therefore, butyrate inhibited propionate metabolism at least as effectively in calves as in goats. In goat hepatocytes 1.25 mM butyrate reduced 1.25 mM propionate uptake to 46% of control, and 1.25 mM [2-(14)C] propionate incorporation into glucose to 44% of control. Propionate had no effect on butyrate uptake. Isovalerate and valerate tended to be cleared from the media to a greater extent than butyrate but had no effect on propionate uptake. Therefore, inhibition of propionate conversion to glucose by butyrate is specific and is not due to a general competition among VFA for metabolism. Butyrate inhibits hepatic propionate utilization generally, not specifically propionate conversion to glucose. Butyrate also inhibited propionate utilization by goat liver homogenates, indicating that butyrate inhibits propionate metabolism at a step subsequent to propionate transport across the hepatocyte plasma membrane.

Propionate absorption and metabolism in the rabbit hindgut

Propionate disappearance from the loops of the hindgut in the rabbit was evaluated by measuring variations in the concentration of propionate in caecocolonic loops and differences in the arterial and venous plasma. In vivo metabolism in gut and liver tissues was studied after introduction of (1-14C) propionate into the caecocolonic loops. The rate of disappearance from the loops was always quantitatively significant but was greater in the proximal colon. Hindgut tissue metabolised propionate and the intensity of the metabolism varied with the segment studied; the proximal colon showed by far the highest propionate consumption. Radioactivity was found in a certain number of free amino acids, organic acids, sugars, lipid soluble substances and proteins. Propionate is an efficient respiratory fuel for the colonocyte and a good precursor for gluconeogenesis.

Occurrence, absorption and metabolism of short chain fatty acids in the digestive tract of mammals

Short chain fatty acids (SCFA) also named volatile fatty acids, mainly acetate, propionate and butyrate, are the major end-products of the microbial digestion of carbohydrates in the alimentary canal. The highest concentrations are observed in the forestomach of the ruminants and in the large intestine (caecum and colon) of all the mammals. Butyrate and caproate released by action of gastric lipase on bovine milk triacylglycerols ingested by preruminants or infants are of nutritional importance too. Both squamous stratified mucosa of rumen and columnar simple epithelium of intestine absorb readily SCFA. The mechanisms of SCFA absorption are incompletely known. Passive diffusion of the unionized form across the cell membrane is currently admitted. In the lumen, the necessary protonation of SCFA anions could come first from the hydration of CO2. The ubiquitous cell membrane process of Na+-H+ exchange can also supply luminal protons. Evidence for an acid microclimate (pH = 5.8-6.8) suitable for SCFA-protonation on the surface of the intestinal lining has been provided recently. This microclimate would be generated by an epithelial secretion of H+ ions and would be protected by the mucus coating from the variable pH of luminal contents. Part of the absorbed SCFA does not reach plasma because it is metabolized in the gastrointestinal wall. Acetate incorporation in mucosal higher lipids is well-known. However, the preponderant metabolic pathway for all the SCFA is catabolism to CO2 except in the rumen wall where about 80% of butyrate is converted to ketone bodies which afterwards flow into bloodstream. Thus, SCFA are an important energy source for the gut mucosa itself.

Propionate and butyrate metabolism in rat or sheep hepatocytes

The capacities of isolated hepatocytes to metabolize volatile fatty acids have been compared in rat and sheep hepatocytes. In both species, acetate utilization in vitro was quite limited. Significant species differences for propionate and butyrate consumption were found: propionate utilization by rat hepatocytes was relatively limited and plateaued at about 0.8-1.0 mM, whereas butyrate utilization was approx. 2-times higher. In contrast, ruminant hepatocytes exhibited a lower rate of butyrate utilization, but propionate metabolism was much more active than in rat liver cells. With relatively low concentrations of substrates (max. 2 mM), only propionate, compared to lactate or alanine, had a significant glucogenicity with hepatocytes from fed sheep. In both species, butyrate inhibited propionate consumption, although to a larger extent in sheep. The conversion of [2-14C]propionate to glucose by sheep hepatocytes was inhibited by 2 mM butyrate (60%) or ammonia (30%); 1 mM oleate or 10 mM glucose were ineffective. The basal rate of ammonia utilization by sheep hepatocytes was much lower than in rat and was unaffected upon addition of ornithine. Ammonia metabolism was markedly enhanced by butyrate and, in contrast to rat liver cells, also by propionate.

Absorption and metabolism of the volatile fatty acids in the hind-gut of the rabbit

Volatile fatty acids (VFA) absorption in the large intestine of the anaesthetized rabbit was evaluated by measuring variations in the concentration of VFA in intestinal loops and plasma arteriovenous differences. Metabolic conversions were studied using [1-14C]acetate, [1-14C]propionate and [3,4-14C]butyrate. The hind-gut tissues metabolized the three VFA, although this metabolism varied with the segment studied. Butyrate was the best respiratory fuel for the colonic wall, followed by propionate; acetate participated also, but it was mainly converted to glutamate. The liver was the main organ metabolizing absorbed propionate and butyrate; acetate was available for extrahepatic tissue metabolism. For the rabbit, VFA represented about 40% of the maintenance energy requirement.

The ketogenic effect of glucose in rumen epithelium of ovine (Ovis aries) and bovine (Bos taurus) origin

In experiments with rumen epithelium incubated in vitro the ratio of 3-hydroxybutyrate: acetoacetate produced was similar to the ratio reported for portal blood, and the ratio ketogenesis: oxidized to CO2 of butyrate was also close to values reported in vivo. Ovine and bovine epithelium incubated with butyrate differed significantly by the values of about 12-17 and 4-7 obtained for the ratio of 3-hydroxybutyrate: acetoacetate. Increasing levels of butyrate in the incubation medium resulted in a decreasing proportion of butyrate oxidized to CO2 and an increasing proportion of ketogenesis. The addition of glucose to butyrate in the incubation medium significantly increased the rate of ketogenesis from butyrate by ovine and bovine tissues. The addition of glucose to butyrate in the incubation medium significantly decreased the rate of butyrate oxidation to CO2 by ovine and bovine tissues. The ketogenic effect of glucose was also apparent in perfused rumen epithelium with butyrate at the mucosal side and glucose at the serosal side.

The effects of intraruminal infusions of sodium bicarbonate, ammonium chloride and sodium butyrate on urea metabolism in sheep

1. Three sheep fitted with rumen cannulas were fed hourly a daily ration of 1000 g pelleted-grass cubes, and during four successive 2-week periods were intraruminally infused (0·45 l/d) with solutions containing sodium chloride (0·47 mol/d), sodium bicarbonate (0·47 mol/d), ammonium chloride (0·47 mol/d) and sodium butyrate (0·47 mol/d). Each solution, except that for NaHCO3, was adjusted to pH 7 before infusion, and provided equal sodium intakes for sheep in all periods.

2. In the final week of each infusion period, a balance trial was conducted and on separate days each sheep was continuously infused with [14C]urea and NaH14CO3 intravenously and NaH14CO3 intraruminally. Carbon transfer rates between blood urea, blood bicarbonate and rumen fluid bicarbonate were calculated from the specific radioactivity of urea and bicarbonate samples and isotope infusion rates during each experimental period.

3. There was no significant effect of intraruminal infusions on N balance, and with the exception of sheep in fused with NH4Cl, all sheep utilized apparently digested N with similar efficiency for N retention. Sheep infused with NH4Cl (6·2 g N/d) excreted the equivalent of 93% of the infused N as urea in urine.

4. Infusion of NaHCO3. NH4Cl and sodium butyrate significantly (P < 0·05) increased the rurnen fluid concentrations of bicarbonate, ammonia and butyric acid respectively, and all infusions significantly (P < 0·05) increased total volatile fatty acid concentrations. Both NaHCO3 and sodium, butyrate significantly (P < 0·05) increased the pH of rumen fluid There was no significant effect of infusion on the proportions of propionic acid or the osmolality of rumen fluid.

5. Intraruminal infusions of NH4Cl significantly (P < 0·05) increased and infusion of sodium butyrate significantly (P < 0·05) decreased plasma urea concentrations. Sheep infused with NH4Cl had higher rates of urea synthesis and urinary urea excretion compared with sheep on the other treatments, and a significantly (P < 0·05) lower proportion of urea synthesized by these sheep was degraded in the digestive tract. Sheep infused with sodium butyrate degraded a significantly (P < 0·05) greater amount (3·2 g N/d) and proportion (0·24) of total urea synthesis in the rumen than did sheep infused with NaCl. Corresponding values for the control (NaCl) sheep were 1·5 g N/d and 0·13 respectively. There was no significant effect of other infusions on the amount of urea recycled to the rumen or on the distribution of total urea degradation between the rumen and lower digestive tract. Plasma urea clearance to the rumen was significantly (P < 0·05) increased during sodium butyrate infusion, and the clearance of urea to the lower digestive tract was significantly (P < 0·05) decreased during NH4Cl infusion.

6. The mechanism by which urea entry into the rumen is regulated by rumen metabolite levels is discussed.

The effect of rumen epithelial development on metabolic activities and ketogenesis by the tissue in vitro

1. An investigation was made on oxygen consumption, glucose and lactate uptake and ketogenesis from butyrate by rumen epithelium in vitro from lambs at various stages of development. 2. Oxygen uptake was decreased by about 35% and glucose uptake by about 90% between 2 weeks and 1/2 year of age. 3. The uptake of L-lactate and the utilization of butyrate as a substrate for respiration were increased during epithelial development. 4. The production of D(-)-3-hydroxybutyrate and acetoacetate from butyrate by the epithelium was largely increased between 4 to 10 weeks of age, independently of rumen fermentation. 5. A synergistic effect of glucose on the production of D(-)-3-hydroxybutyrate and on total ketone bodies from butyrate by the epithelium was observed. It accounted to 40-80% over butyrate depending on the stage of epithelial development.

[The effect of nutritional factors on the ruminal mucosa. 3. Condition of the mucosa after infusion of propionic acid, acetic acid and butyric acid]

Three non-lactating cows (Deutsches Schwarzbuntes Rind) with large ruminal fistulas were fed coarsely structured food. Within a trial period of 21 weeks infusion periods lasting 3 weeks alternated with equally long control periods (K). During the 3 infusion periods, 8.4 mMol of propionic acid (P), 14.8 mMol of acetic acid (E) and 4,5 mMol of butyric acid (B) per kg liveweight per day were administered through the fistula, the total quantity being 19 litres of solution. In the periods K1...4 the ruminal fluid contained an average of 68 Mol% E, 19 Mol% P, 13 Mol% B (maximum of 10.25 mMol free fatty acids (FFS) per 100 ml, minimum pH 6.4). In the course of the 10 hrs of infusion the Mol percentages of the particular acids infused increased to 27% P (maximum of 11.14 mMol FFS per 100 ml, minimum pH 6.4) or 79% E (maximum of 12,99 mMol FFS per 100 ml, minimum pH 6.0 (5.5)) or 25% B (maximum of 10.34 mMol FFS per 100 ml, minimum pH 6.0 (5.5)). Infusions of E and B had the most pronounced effect on the ruminal mucosa compared with the K periods. All fatty acids increased the process of keratinization and decreased the size of cell nuclei in the stratum basale. As specific effect, P infusions produced a thickening of the lamina propria; B infusions caused a thickening of the stratum germinativum (proliferative effect) while e infusions led to a drastically reduced thickness of villi (antiproliferative effect) due to reductions in the stratum germinativum and the lamina propria. According to the morphological situation high specific mucosal function is suggested during the B-period. The mucosa appeared quite normal during all periods investigated, with the exception of the E period, where hyperkeratosis, atrophy and necrosis were observed in 34% of the sample. Changes in the state of the mucosa appeared as early as 1 week after the beginning of the respective trial periods. Keratin consolidation was the primary cause for chemically induced keratosis. The development of hyperkeratosis seemed to be favoured if low pH values occurred in the rumen in combination with small amounts of metabolites inducing proliferation, both representing synergistic factors.

Volatile fatty acid metabolism by rumen mucosa from cattle fed hay or grain

Effects of an all-grain versus an all-hay diet on metabolic activity of rumen mucosa of cattle were investigated. After diets had been fed for 3 to 4 mo, rumen papillae were collected at slaughter from the dorsal rumen sac and incubated with one of various volatile fatty acids. Rates of substrate utilization were in the order: n-butyrate greater than n-valerate approximately propionate greater than iso-butyrate approximately iso-valerate. Over-all, papillae from hay-fed steers utilized greater amounts of volatile fatty acids. Dietary treatment did not significantly affect extent of conversion of volatile fatty acids to lactate and to ketone bodies. Lactate was the major metabolite from propionate and n-valerate. Ketone body formation accounted for more than 90% of n-butyrate uptake by papillae. Ketone formation from n-valerate was restricted to beta-hydroxybutyrate while that from iso-valerate was essentially acetoacetate plus acetone. Metabolic systems in rumen mucosa of physiologically mature ruminants seem to adapt little to varying individual volatile fatty acids available for absorption in vivo.

[Studies of the influence of nutritional factors on the ruminal mucosa. 1. Structure and functional state of the ruminal mucosa after feeding of extreme rations and abrupt change in nutrition]

Different rations were used in successive experimental periods (Dried green feeds (I), fresh green feed from sugar beet tops (II), concentrates (III, IV), and maize silage (V), to test the effect they have on the structure and oxidative functions of the ruminal mucosa in cattle. Rations I, II, IV, and V were both energy and protein equivalent. Biopsy specimens from ruminal papillae were taken on the day when rations were suddenly changed and on the 21st and 22nd day of the feeding period; they were then investigated histologically and manometrically. It was found that some characteristics, (viz. the type and thickness of the stratum corneum, the thickness of epithelia, the size of cell nuclei in the stratum basale of the epitheliumas well as the state of the lamina propria and the oxygen uptake were subject to alterations depending on nutrition. Nutrition with energy-equivalent, but otherwise extremely different diets representing particular types of rations led to the development of different and quite specific functional states of the ruminal mucosa. All these functional states of the mucosa were found to be within the limits of normality but seemed to have a definitely more favourable functional effect in the case of rations I and IV than in the case of rations II and V. The feeding of concentrates (III, V) increased the energy intake to an amount of 6.6 kEFr, i.e. double that of the other rations, and brought about changes in quantitative parameters. These, in turn, indicated that proliferative and oxidative processes had been stimulated. Changes of this kind were accompanied by increases in the concentration of volatile fatty acids in the ruminal fluid which rose from a maximum of 9 mMol per 100 ml (ration IV) to 12.5 mMol per 100 ml (ration III). Immediately after any change in nutrition brought about by a change of rations, processes of adaptation occurred in the ruminal mucosa. A balanced state of the mucosa was again achieved after a period of not more than 3 weeks.