Effects of prepartum concentrate feeding on reticular pH, plasma energy metabolites, acute phase proteins, and milk performance in grass silage-fed dairy cows

We investigated how concentrate feeding during the last 21 d of pregnancy affects reticular pH, inflammatory response, dry matter (DM) intake, and production performance of dairy cows. We hypothesized that adding concentrates to dairy cows' diet before calving reduces the decrease in reticular pH postpartum and thus alleviates inflammatory response. We also hypothesized that prepartum concentrate feeding increases DM intake postpartum and consequently improves milk performance. Two feeding experiments were conducted using a randomized complete block design. In each experiment, 16 multiparous Finnish Ayrshire cows were paired based on parity, expected calving date, body weight, and milk yield of the previous lactation. Within the pairs, cows were randomly allocated on one of the 2 dietary treatments 21 d before expected calving. In experiment 1 (Exp1), diets were ad libitum feeding of grass silage as a sole feed or supplemented with increasing amounts of concentrate offered separately (increased to 4 kg/d by d -7). In experiment 2 (Exp2), diets were ad libitum feeding of a total mixed ration containing either grass silage, barley straw, and rapeseed meal (64%, 28%, and 8% on DM basis, respectively) or grass silage, barley straw, and cereal-based concentrate mixture (49%, 29%, and 30% on DM basis, respectively). Following calving, all the cows were fed similarly and observed until d 56 postpartum. Feed intake and milk yield were recorded daily, and reticular pH was monitored continuously by reticular pH bolus. Blood samples were collected at the beginning of the experiments, 7 d before the expected calving date, 1 d (in Exp1) or 5 d (in Exp2), 10 d, and 21 d postpartum. In Exp1, concentrate feeding increased metabolizable energy intake and tended to increase DM and crude protein intake prepartum. Moreover, prepartum concentrate feeding increased the concentrations of plasma β-hydroxybutyrate and insulin, but differences in nonesterified fatty acids, glucose, or acute phase proteins were not observed. After calving, prepartum diet did not affect DM or nutrient intake, plasma energy metabolites, or milk production in Exp1. Although prepartum concentrate feeding increased reticular pH on the first day of lactation, it elevated plasma concentrations of serum amyloid-A and haptoglobin postpartum in the grass silage-based diet. In Exp2, adding concentrates to the diet based on a mixture of grass silage and straw did not affect prepartum DM intake or plasma concentrations of nonesterified fatty acids, glucose, or insulin. Adding concentrates to prepartum diet increased plasma concentration of β-hydroxybutyrate before calving as in Exp1. After calving, prepartum concentrate feeding increased DM and nutrient intake during the second week of lactation in Exp2, but no effects were observed thereafter. In contrast to our hypothesis, prepartum concentrate feeding decreased reticular pH after calving in Exp2, but no differences in inflammatory markers were observed. Based on this study, close-up concentrate feeding in diets based on grass silage with or without straw does not alleviate the decrease in reticular pH or mitigate inflammatory response postpartum.

Light microscopic observations of the ruminal papillae of cattle on diets with divergent forage to cereal ratios

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Characteristic histological change is associated with dietary cereal proportion.

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Immune-related cells are found in higher densities in cattle on lower cereal diets.

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Cereal proportion is associated with cell layer thickness, integrity, and sloughing.

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No benefit of Elastin Martius Scarlet Blue stain use over Haematoxylin and Eosin.

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Novel scoring system can differentiate groups by approximate dietary cereal level.

High levels of supplementation with cereal increases production rates in cattle but can increase incidence of disease, ranging from mild indigestion to acute ruminal acidosis and death. Therefore, there is motivation to determine biological markers which can be used to identify whether animals have been, or are being fed, sufficient or excessive cereals. This study aimed to describe light microscopic findings from animals being fed diverse dietary cereal proportions and to test the performance of a novel rumen epithelial scoring system. Rumen wall tissue samples were obtained from the abattoir from 195 cattle from 11 Scottish farms and processed for histological examination. Light microscopic examination was used to characterise ruminal epithelial response to dietary challenge. Secondary objectives included describing the distribution of immune-related cells in bovine ruminal epithelium and assessing the use of a modified Elastin Martius Scarlet Blue stain (EMSB) for histological examination of the rumen epithelium. Cells staining positive for cluster of differentiation 3 were distributed mainly in the lower layers of the stratum basale and were found in higher densities in animals offered lower cereal proportion diets. Cells staining positive for major histocompatibility complex class 2 (MHCII) were most common in perivascular locations and in the junction between the lower stratum basale and the propria-submucosa. The density of MHCII positive staining cells was higher in animals on lower cereal diets. The level of supplementation with cereal was also associated with the thickness of the stratum corneum (SCT) and stratum granulosum (SGT), the integrity of the stratum corneum and sloughing of cornified cells. There were no advantages in using EMSB stain over haematoxylin and eosin (H&E) in this scoring system. We concluded that a scoring system that included only SCT, SGT and a measure of the loss of appearance of intercellular space allowed differentiation of groups of animals according to the level of cereal supplementation.

Review: Rumen sensors: data and interpretation for key rumen metabolic processes

Rumen sensors provide specific information to help understand rumen functioning in relation to health disorders and to assist in decision-making for farm management. This review focuses on the use of rumen sensors to measure ruminal pH and discusses variation in pH in both time and location, pH-associated disorders and data analysis methods to summarize and interpret rumen pH data. Discussion on the use of rumen sensors to measure redox potential as an indication of the fermentation processes is also included. Acids may accumulate and reduce ruminal pH if acid removal from the rumen and rumen buffering cannot keep pace with their production. The complexity of the factors involved, combined with the interactions between the rumen and the host that ultimately determine ruminal pH, results in large variation among animals in their pH response to dietary or other changes. Although ruminal pH and pH dynamics only partially explain the typical symptoms of acidosis, it remains a main indicator and may assist to optimize rumen function. Rumen pH sensors allow continuous monitoring of pH and of diurnal variation in pH in individual animals. Substantial drift of non-retrievable rumen pH sensors, and the difficulty to calibrate these sensors, limits their application. Significant within-day variation in ruminal pH is frequently observed, and large distinct differences in pH between locations in the rumen occur. The magnitude of pH differences between locations appears to be diet dependent. Universal application of fixed conversion factors to correct for absolute pH differences between locations should be avoided. Rumen sensors provide high-resolution kinetics of pH and a vast amount of data. Commonly reported pH characteristics include mean and minimum pH, but these do not properly reflect severity of pH depression. The area under the pH × time curve integrates both duration and extent of pH depression. The use of this characteristic, as well as summarizing parameters obtained from fitting equations to cumulative pH data, is recommended to identify pH variation in relation to acidosis. Some rumen sensors can also measure the redox potential. This measurement helps to understand rumen functioning, as the redox potential of rumen fluid directly reflects the microbial intracellular redox balance status and impacts fermentative activity of rumen microorganisms. Taken together, proper assessment and interpretation of data generated by rumen sensors requires consideration of their limitations under various conditions.

Adaptive responses in short-chain fatty acid absorption, gene expression, and bacterial community of the bovine rumen epithelium recovered from a continuous or transient high-grain feeding

The feeding of high-grain diets to dairy cows commonly results in lowered pH and ruminal dysbiosis, characterized by changes in absorption dynamics of short-chain fatty acids (SCFA) across the reticuloruminal wall, epithelial function, and the epithelial bacteria community structure. Therefore, the present study evaluated the effect of high-grain feeding persistence on the absorption kinetics of reticuloruminal SCFA, gene expression in the rumen epithelium, and the associated shifts in the epithelial bacteria in cows recovering from either a long-term continuous high-grain feeding model or a long-term transient high-grain feeding model. In a crossover study design, 8 nonlactating Holstein cows were fed 60% concentrate either continuously for 4 wk (continuous) or with a 1-wk break in the second week of the high-grain feeding (transient). After the high-grain feeding, all animals were fed a diet of 100% forage (recovery) for an additional 8 wk. Rumen papilla biopsies and SCFA absorption measurements were taken at the start of the trial (baseline), after the 4-wk high-grain feeding (49 d), after 2-wk recovery forage feeding (63 d), and after 8-wk recovery forage (105 d). Absorption of SCFA was determined in vivo using the washed and isolated reticulorumen technique. Rumen papillae biopsies were used for adherent bacterial DNA and host RNA extraction. The epithelial bacteria were determined using Illumina MiSeq (Microsynth AG, Balgach, Switzerland) sequencing of the 16S rRNA gene. No significant effects of the high-grain feeding model were seen for bacterial diversity. However, bacterial diversity increased with time spent in the recovery forage feeding period regardless of feeding model. The relative abundance of Acidobacteria phyla and Acetivibrio spp. increased when animals were fed a transient high-grain feeding model. A trend toward increased CLDN4 expression was observed in the continuous model. Furthermore, there were interactions between feeding model and sampling day for gene targets CD14, DRA, NHE2, NHE3, and MCT2. When comparing length of recovery, in the continuous model increased relative absorption of SCFA was sustained at 63 d but dropped to baseline measurements at 105 d. A similar pattern was found with the transient model but it did not reach significance. The only gene target that was found to significantly correlate to relative absorption of SCFA was DRA (correlation coefficient ≤ -0.41). Whereas, genera Alkalibaculum, Anaerorhabdus, Coprococcus, and Dethiobacter all showed positive correlations to gene targets for pH regulation (NHE2 and NHE3) and SCFA uptake (MCT1) but negative correlations to SCFA absorption. We conclude that while the rumen absorption and epithelial bacteria were able to recover to baseline levels after 8 wk of forage feeding, the time needed for re-establishment of homeostasis in host gene expression is longer, especially when high-grain feeding is interrupted.

Feeding Diets Moderate in Physically Effective Fibre Alters Eating and Feed Sorting Patterns without Improving Ruminal pH, but Impaired Liver Health in Dairy Cows

The main challenge in dairy cattle feeding is to find a balance between the energy and physically effective fibre (peNDF), required to maintain rumen health. In an attempt to regulate the balance between energy intake and rumen buffering, we hypothesized that the content of peNDF in the diet modifies eating and feed sorting patterns of the cows. Sixteen lactating Simmental cows were switched from a diet high in peNDF, with which they were fed for one week, to a diet moderate in peNDF for four weeks. Data showed that during the moderate peNDF feeding the cows increased sorting for medium-sized particles and avoided both long and very fine particles. In addition, cows decreased their eating time per meal, but increased the number of meals per day, obviously attempting to decrease the amount of fermentable substrate per time unit while maintaining high levels of nutrient/energy intake. Although these changes during the moderate peNDF feeding went along with a lower diurnal variation of ruminal pH, feeding of the latter diet did not prevent ruminal pH drop and increased the level of all liver enzymes, indicating liver tissue damage. In conclusion, the altered eating, chewing, and sorting behaviour of the cows during the moderate peNDF feeding could not alleviate the deficiency in peNDF, which resulted in ruminal pH depression and impairment of liver health variables.

Transcriptome analysis of rumen epithelium and meta-transcriptome analysis of rumen epimural microbial community in young calves with feed induced acidosis

Many common management practices used to raise dairy calves while on milk and during weaning can cause rumen acidosis. Ruminal pH has long been used to identify ruminal acidosis. However, few attempts were undertaken to understand the role of prolonged ruminal acidosis on rumen microbial community or host health in young calves long after weaning. Thus, the molecular changes associated with prolonged rumen acidosis in post weaning young calves are largely unknown. In this study, we induced ruminal acidosis by feeding a highly processed, starch-rich diet to calves starting from one week of age through 16 weeks. Rumen epithelial tissues were collected at necropsy at 17 weeks of age. Transcriptome analyses on the rumen epithelium and meta-transcriptome analysis of rumen epimural microbial communities were carried out. Calves with induced ruminal acidosis showed significantly less weight gain over the course of the experiment, in addition to substantially lower ruminal pH in comparison to the control group. For rumen epithelial transcriptome, a total of 672 genes (fold-change, FC ≥ 1.5; adjusted-p ≤ 0.05) showed significant differential expression in comparison to control. Biological pathways impacted by these differentially expressed genes included cell signaling and morphogenesis, indicating the impact of ruminal acidosis on rumen epithelium development. rRNA read-based microbial classification indicated significant increase in abundance of several genera in calves with induced acidosis. Our study provides insight into host rumen transcriptome changes associated with prolonged acidosis in post weaning calves. Shifts in microbial species abundance are promising for microbial species-based biomarker development and artificial manipulation. Such knowledge provides a foundation for future more precise diagnosis and preventative management of rumen acidosis in dairy calves.

Synchronous and Time-Dependent Expression of Cyclins, Cyclin-Dependant Kinases, and Apoptotic Genes in the Rumen Epithelia of Butyrate-Infused Goats

In our previous study, we demonstrated that butyrate induced ruminal epithelial growth through cyclin D1 upregulation. Here, we investigated the influence of butyrate on the expression of genes associated with cell cycle and apoptosis in rumen epithelium. Goats (n = 24) were given an intra ruminal infusion of sodium butyrate at 0.3 (group B, n = 12) or 0 (group A, n = 12) g/kg of body weight (BW) per day before morning feeding for 28 days and were slaughtered (4 goat/group) at 5,7 and 9 h after butyrate infusion. Rumen fluid was analyzed for short chain fatty acids (SCFAs) concentration. Ruminal tissues were analyzed for morpho-histrometry and the expressions of genes associated with cell cycle and apoptosis. The results revealed that the ruminal butyrate concentration increased (P < 0.05) in B compared to group A. Morphometric analysis showed increased (P < 0.05) papillae size associated with higher number of cell layers in epithelial strata in B compared to A. Butyrate-induced papillae enlargement was coupled with enhanced mRNA expression levels (P < 0.05) of cyclin D1, CDK2, CDK4, and CDK6 (G₀/G1 phase regulators) at 5 h, cyclin E1 (G1/S phase regulator) at 7 h and cyclin A and CDK1 (S phase regulators) at 9 h post-infusion compared to A group. In addition, the mRNA expression levels of apoptotic genes, i.e., caspase 3, caspase 9 and Bax at 5 h post-infusion were upregulated (P < 0.05) in group B compared to group A. The present study demonstrated that butyrate improved ruminal epithelial growth through concurrent and time-dependent changes in the expressions of genes involved in cell proliferation and apoptosis. It seems that the rate of proliferation was higher than the apoptosis which was reflected in epithelial growth.

The effect of supplemental concentrate fed during the dry period on morphological and functional aspects of rumen adaptation in dairy cattle during the dry period and early lactation

Ten rumen-cannulated Holstein-Friesian cows were used to examine the effect of feeding supplemental concentrate during the dry period on rumen papillae morphology and fractional absorption rate (k_a) of volatile fatty acids (VFA) during the dry period and subsequent lactation. Treatment consisted of supplemental concentrate [3.0kg of dry matter (DM)/d] from 28d antepartum (ap) until the day of calving, whereas control did not receive supplemental concentrate. Cows were fed for ad libitum intake and had free access to the dry period ration (27% grass silage, 28% corn silage, 35% wheat straw, and 11% soybean meal on a DM basis) and, from calving onward, to a basal lactation ration (42% grass silage, 42% corn silage, and 16% soybean meal on a DM basis). From 1 to 3d postpartum (pp), all cows were fed 0.9kg DM/d of concentrate, which increased linearly thereafter to 8.9kg of DM/d on d 11 pp. At 28, 18, and 8d ap, and 3, 17, 31, and 45d pp, rumen papillae were collected and k_aVFA was measured in all cows. On average, 13.8 (standard deviation: 3.8) papillae were collected each from the ventral, caudodorsal, and caudoventral rumen sacs per cow per day. The k_aVFA was measured by incubating a standardized buffer fluid (45 L), containing 120mM VFA (60% acetic, 25% propionic, and 15% butyric acid) and Co-EDTA as fluid passage marker, in the evacuated and washed rumen. Treatment did not affect ap or pp DM and energy intakes or milk yield and composition. Treatment increased papillae surface area, which was 19 and 29% larger at 18 and 8d ap compared with 28d ap, respectively. Surface area increased, mainly due to an increase in papillae width. However, treatment did not increase k_aVFA at 18 and 8d ap compared with 28d ap. In the control group, no changes in papillae surface area or k_aVFA were observed during the dry period. In the treatment group, papillae surface area decreased between 8d ap and 3d pp, whereas no decrease was observed for control. From 3 to 45d pp, papillae surface area and k_aVFA increased for all cows by approximately 50%, but the ap concentrate treatment did not affect k_aVFA pp. In conclusion, the efficacy of supplemental concentrate during the dry period to increase papillae surface area and k_aVFA in preparation for subsequent lactation is not supported by the present study. Current observations underline the importance of functional measurements in lieu of morphological measurements to assess changes in the adapting rumen wall.

Concentrate diet modulation of ruminal genes involved in cell proliferation and apoptosis is related to combined effects of short-chain fatty acid and pH in rumen of goats

Short-chain fatty acids (SCFA) regulate cell proliferation and cell apoptosis in gastrointestinal tissue in vitro and in vivo. We have tested the hypothesis that a medium-concentrate intake induces mRNA abundance alterations of genes involved in cell proliferation and cell apoptosis in the rumen epithelium of goats, and that these changes in mRNA abundance are related to ruminal SCFA concentration and ruminal pH. Goats (n=16) were randomly allocated to 2 groups and fed either a low-concentrate (LC) diet (10% concentrate; n=8) or a medium-concentrate (MC) diet (35% concentrate; n=8) in 2 equal portions daily. The individually housed goats were fed separately with their respective diet for 3wk and were slaughtered 6h after the morning feed on d 22. In vivo, goats receiving the MC treatment exhibited a greater ruminal SCFA concentration (73.7mM) compared with those receiving the LC treatment (53.2mM), and the pH decreased from 6.9 to 6.5. The expression of proliferative genes of cyclin A, cyclin B1, cyclin D1, cyclin E1, CDK1, CDK2, CDK4, and CDK6 mRNA in the MC group was enhanced. The gene expression of apoptosis genes (caspase 3, caspase 8, caspase 9, p53, and Bax) was significantly higher, and the ratio of Bcl-2 to Bax (Bcl-2/Bax) expression was lower in the MC group than in the LC group. The same trend was observed in the population of apoptotic cells analyzed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. The cell density in the stratum germinativum of the MC group was significantly increased compared with that in the LC group. During primary culture of rumen epithelial cells, SCFA or pH treatment alone of the culture medium had significant effects on the expression of most of the genes tested in the present study. Furthermore, SCFA and pH exerted combined effects on the expression of cyclin A, cyclin B1, cyclin E1, CDK6, p53, Bcl-2, and Bcl-2/Bax. Thus, the MC diet induces alteration of gene expression of the genes that regulate both cell proliferation and apoptosis. These genes are regulated by combined effect of ruminal SCFA and ruminal pH.

The effects of a ration change from a total mixed ration to pasture on rumen fermentation, volatile fatty acid absorption characteristics, and morphology of dairy cows

To investigate the effect of the change from a concentrate and silage-based ration (total mixed ration, TMR) to a pasture-based ration, a 10-wk trial (wk 1-10) was performed, including 10 rumen- and duodenum-fistulated German Holstein dairy cows (182±24 d in milk, 23.5±3.5kg of milk/d; mean ± standard deviation). The cows were divided in either a pasture group (PG, n=5) or a confinement group (CG, n=5). The CG stayed on a TMR-based ration (35% corn silage, 35% grass silage, 30% concentrate; dry matter basis), whereas the PG was gradually transitioned from a TMR to a pasture-based ration (wk 1: TMR only; wk 2: 3 h/d on pasture wk 3 and 4: 12 h/d on pasture wk 5-10: pasture only). Ruminal pH, volatile fatty acids (VFA), NH3-N, and lipopolysaccharide (LPS) concentrations were measured in rumen fluid samples collected medially and ventrally on a weekly basis. Ruminal pH was continuously recorded during 1 to 4 consecutive days each week using ruminal pH measuring devices. In wk 1, 5, and 10, rumen contents were evacuated and weighed, papillae were collected from 3 locations in the rumen, and subsequently a VFA absorption test was performed. In the PG, mean rumen pH and molar acetate proportions decreased, and molar butyrate proportions increased continuously over the course of the trial, which can most likely be ascribed to an increased intake of rapidly fermentable carbohydrates. During the first weeks on a full grazing ration (wk 5-7), variation of rumen pH decreased, and in wk 5 a lower rumen content, papillae surface area, and potential for VFA absorption were observed. In wk 8 to 10, variation of rumen pH and total VFA concentrations increased again, and acetate/propionate ratio decreased. In wk-10 rumen content, papillae area and VFA absorption characteristics similar to initial levels were observed. Although continuous rumen pH assessments and LPS concentrations did not reveal an increased risk for subacute rumen acidosis (SARA) during the adaption period, histopathology of rumen papillae and potential for VFA absorption indicated a possible risk for rumen health. An increased risk for SARA was observed in wk 9 and 10 in the PG, but rumen LPS concentrations and histopathology were not adversely affected. Results of the present study suggest that after behavioral and metabolic adaptation to the transition from a TMR to a pasture-based ration, no adverse effects on rumen morphology and absorption capacity occurred, although rumen pH after adaptation to pasture indicated increased risk of SARA.

Identification of differentially expressed proteins in ruminal epithelium in response to a concentrate-supplemented diet

Ruminal epithelium adapts to dietary change with well-coordinated alterations in metabolism, proliferation, and permeability. To further understand the molecular events controlling diet effects, the aim of this study was to evaluate protein expression patterns of ruminal epithelium in response to various feeding regimes. Sheep were fed with a concentrate-supplemented diet for up to 6 wk. The control group received hay only. Proteome analysis with differential in gel electrophoresis technology revealed that, after 2 days, 60 proteins were significantly modulated in ruminal epithelium in a comparison between hay-fed and concentrate-fed sheep (P < 0.05). Forty proteins were upregulated and 20 proteins were downregulated in response to concentrate diet. After 6 wk of this diet, only 14 proteins were differentially expressed. Among these, 11 proteins were upregulated and 3 downregulated. To identify proteins that were modulated by dietary change, two-dimensional electrophoresis was coupled with liquid chromatography electrospray ionization mass spectrometry. The differential expression of selected proteins, such as esterase D, annexin 5, peroxiredoxin 6, carbonic anhydrase I, and actin-related protein 3, was verified by immunoblotting and/or mRNA analysis. The identified proteins were mainly associated with functions related to cellular stress, metabolism, and differentiation. These results suggest new candidate proteins that may contribute to a better understanding of the signaling pathways and mechanisms that mediate rumen epithelial adaptation to high-concentrate diet.

Population structure of rumen Escherichia coli associated with subacute ruminal acidosis (SARA) in dairy cattle

Previous studies indicated that only subacute ruminal acidosis (SARA), induced by feeding a high-grain diet, is associated with an inflammatory response and increased abundance of Escherichia coli in the rumen. We hypothesized that ruminal E. coli in grain pellet-induced SARA carried virulence factors that potentially contribute to the immune activation during SARA. One hundred twenty-nine E. coli isolates were cultured from the rumens of 8 cows (4 animals per treatment) in which SARA had been nutritionally induced by feeding a high-grain diet (GPI-SARA) or a diet containing alfalfa pellets (API-SARA). The population structure of the E. coli was evaluated with the ABD genotyping system and repetitive sequence-based (rep)-PCR fingerprinting. Twenty-five virulence factors were evaluated with PCR. Escherichia coli numbers were higher in the GPI-SARA treatment than in the API-SARA treatment. The genetic structure of the E. coli was significantly different between SARA challenge models. Isolates from GPI-control (46%), API-control (70%), and API-SARA (53%) were closely related and fell into one cluster, whereas isolates from GPI-SARA (54%) grouped separately. The ABD typing indicated a shift from an A-type E. coli population to a B1-type population only due to GPI-SARA. Of the 25 virulence factors tested, curli fiber genes were highly associated with GPI. Curli fibers were first identified in E. coli mastitis isolates and are potent virulence factors that induce a range of immune responses. Results suggest that under low rumen pH conditions induced by a grain diet, there is a burst in the number of E. coli with virulence genes that can take advantage of these rumen conditions to trigger an inflammatory response.

Change of ruminal sodium transport in sheep during dietary adaptation

Rumen adaptation plays an important role in the productive cycle of dairy cattle. In this study, the time course of functional rumen epithelium adaptation after a change from hay feeding (ad libitum) to a mixed hay/concentrate diet was monitored by measuring Na+ transport rates in Ussing chamber experiments. A total of 18 sheep were subjected to different periods of mixed hay/concentrate feeding ranging from 0 weeks (control; hay ad libitum) to 12 weeks (800 g hay plus 800 g concentrate per day in two equal portions). For each animal, the net absorption of sodium was measured following the mixed hay/concentrate feeding period. Net Na transport, Jnet, significantly rose from 2.15 +/- 0.43 (control) to 3.73 +/- 1.02 microeq x cm(-2) x h(-1) after one week of mixed hay/ concentrate diet, reached peak levels of 4.55 +/- 0.50 microEq x cm(-2) x h(-1) after four weeks and levelled out at 3.92 +/- 0.36 microeq x cm(-2) x h(-1) after 12 weeks of mixed feeding. Thus, 73% of functional adaptation occurred during the first week after diet change. This is in apparent contrast to findings that morphological adaptation takes approximately six weeks to reach peak levels. Hence, early functional adaptation to a mixed hay/concentrate diet is characterised by enhanced Na absorption rates per epithelial cell. Absorption rates are likely to be further enhanced by proliferative effects on the rumen epithelium (number and size of papillae) when concentrate diets are fed over longer periods of time. Early functional adaptation without surface area enlargement of the rumen epithelium appears to be the first step in coping with altered fermentation rates following diet change.

Subacute rumen acidosis in lactating cows: an investigation in intensive Italian dairy herds

Subacute rumen acidosis (SARA) represents one of the most important metabolic disorders in intensive dairy farms that affects rumen fermentations, animal welfare, productivity and farm profitability. The aim of the present study was to study the occurrence of SARA in intensive Italian dairy herds and to determine the relationship between diet composition, ruminal pH and short chain fatty acids (SCFA) concentration. Ten commercial dairy herds were investigated; twelve cows in each herd were selected randomly among animal without clinical signs of disease, with good body condition and between 5 and 60 day-in-milk (DIM), to perform rumenocentesis and obtain rumen fluid. Ruminal pH was determined immediately after sampling and concentration of SCFA in ruminal fluid was determined on samples after storage. An other objective of this research was to study in detail the effects of rumenocentesis on animal health: this study could confirm the extreme validity of this technique as ruminal sampling. Results were subject to anova and correlation analysis using SIGMA STAT 2.03. The results indicated the presence of SARA in three herds (more than 33% cows with rumen pH < 5.5), a critical situation (more than 33% cows with rumen pH < 5.8) in five farms and a normal rumen pH condition in two herds. In particular, dairy herds show on average SCFA concentration of 150, 145, 123 mmol/l for low pH, critical pH and normal pH herds respectively. There were not significant differences among diet composition even if herds with SARA showed a light discordance between initially chemistry composition and residual feed. In the affected herds it was not possible to understand the exact causes of SARA. Animal management seems to be one of the most important factors in developing SARA including total mixed ration preparation.

Physiology, regulation and multifunctional activity of the gut wall: a rationale for multicompartmental modelling

A rationale is given for a modelling approach to identify the mechanisms involved in the functioning and metabolic activity of tissues in the wall of the gastrointestinal tract. Maintenance and productive functions are discussed and related to the distinct compartments of the gastrointestinal tract and the metabolic costs involved. Functions identified are: tissue turnover; tissue proliferation; ion transport; nutrient transport; secretions of digestive enzymes, mucus and immunoglobulins; production of immune cells. The major nutrients involved include glucose, amino acids and volatile fatty acids.In vivomeasurements of net portal fluxes of these nutrients in pigs and ruminants are evaluated to illustrate the complexity of physiology and metabolic activity of the gastrointestinal tract. Experimental evidence indicates that high, but variable and specific, nutrient costs are involved in the functioning of the gastrointestinal tract.

Comparison of techniques to determine the clearance of ruminal volatile fatty acids

The objective of this experiment was to compare measurements of fractional clearance rates obtained by using an unlabeled valerate-CoEDTA technique with measurements obtained by using a (13)C-labeled volatile fatty acids (VFA) technique. The exponential decay rate of the (13)C/(12)C ratio after pulse-dosing (13)C-acetate, (13)C-propionate, or (13)C-butyrate into the rumen was compared with the decay rate of rumen valerate concentration following a simultaneous pulse dose. The unlabeled valerate, CoEDTA, and each labeled VFA, one at a time, were concurrently mixed with the evacuated ruminal content of 6 lactating cows in two 3 x 3 Latin squares. The clearance of VFA by passage to the omasum was assumed to be equivalent to the decay in ruminal Co concentration and was around 50% of the total clearance. Acetate, propionate, and butyrate had similar fractional clearance rates (31.2, 33.4, 30.4%/h, respectively), but propionate had a higher absorption rate (19.2%/h) than butyrate (14.2%/h). Linear regression determination coefficients using the valerate clearance rate as an estimator for acetate, propionate, and butyrate rumen clearance were 0.51, 0.56, and 0.99, respectively. In a second experiment, the (13)C-valerate fractional clearance rate estimate (33.7%/h) was similar to the estimate obtained with unlabeled valerate (35.0%/h) by the valerate-Co technique. No (13)C enrichment of rumen microbes was noted 4 h after the intraruminal infusion of (13)C-valerate. Fractional VFA absorption rate estimates obtained in both techniques were similar, although both were lower than estimates reported in the literature by other methods.

Effects of diet and osmotic pressure on Na+transport and tissue conductance of sheep isolated rumen epithelium

The intention of this study was to determine the effects of mucosal osmotic pressure on transport and barrier functions of the rumen epithelium of sheep, which were fed various diets: hay ad libitum, or 600, 1200 or 1800 g day(-1) of a supplemented diet plus hay ad libitum. The experiments were conducted by using the conventional Ussing chamber technique. Mucosal osmolarity was adjusted to 300 (control), 375 or 450 mosmol l(-1). Feeding of a supplemented diet led to a significant increase of mucosal to serosal Na+ transport and net Na+ transport, probably because of an increase of apical Na+-H+ exchange activity. An increase in mucosal osmotic pressure: (a) reduced net Na+ transport in all feeding groups, the remaining net Na+ transport being higher in tissues of sheep fed a supplemented diet; (b) increased transepithelial tissue conductance, this rise being smallest with a high intake of the supplemented diet; and (c) enhanced the serosal to mucosal Na+ transport in tissues of hay-fed sheep and sheep fed with 600 g day(-1) of the supplemented diet, while higher intakes of the supplemented diet (1200 and 1800 g) did not produce any effect. All these changes indicate a diet-dependent adaptation to luminal hypertonicity.

Transport of acetate and sodium in sheep omasum: mutual, but asymmetric interactions

We have studied the transport of acetate across the isolated epithelium of sheep omasum; no net transport was observed (J(ms) approximately = J(sm)) under Ussing chamber conditions. Low mucosal pH (pH 6.4) significantly enhanced J(ms) acetate and the transport rates of acetate increased linearly and significantly (r2=0.99) with the luminal acetate concentration. The presence of another short chain fatty acid (propionate) did not affect J(ms) acetate significantly. Neither addition of 1 mmol l(-1) DIDS to the mucosal side nor HCO3 replacement caused changes of J(ms) acetate; this does not support the assumption of acetate transport via anion exchange. Addition of 1 mmol l(-1) amiloride to the mucosal side significantly decreased acetate fluxes at high mucosal acetate concentration (100 mmol l(-1)) and low pH (6.4) indicating interaction between acetate uptake in the undissociated form, intracellular release of protons and activation of Na+/H+ exchange (NHE). However, the mutual interaction between Na transport via NHE and acetate transport is asymmetric. Stimulation or inhibition of Na transport via NHE is much more pronounced than the corresponding changes of acetate fluxes. Thus, the obtained results support the conclusion that acetate is transported via simple diffusion and probably predominantly in the protonated form, thereby explaining the positive and mutual interaction between Na transport and short chain fatty acids.

Intraruminal infusion of n-butyric acid induces an increase of ruminal papillae size independent of IGF-1 system in castrated bulls

The objective of this study was to explore morphological alterations of rumen papillae induced by n-butyric acid in relation to the insulin-like growth factor (IGF) system in adult castrated bulls. Three animals fitted with rumen cannula were fed twice daily at a low and high nutritional level (LL and HL), i.e., at 1.1 x maintenance (M) and 1.6 x M, respectively. Diets contained artificial dried grass and concentrate (74:26 and 52:48). Bulls received no (B0) or daily intraruminal infusions of 500 g n-butyric acid (B500) over 14 d. The infusion started 1 h after the morning feeding (9:00) and lasted for 3.5 h. Thus, four treatments (BOLL, B500LL, BOHL, and B500HL) were compared. Blood and rumen mucosa samples from the atrium ruminis were taken at the last day of each period. Length, width and surface of rumen papillae were greater (p < 0.001) in BOHL than in BOLL. Treatment with n-butyric acid resulted in an increase of the papillae surface of 20-40% (p = 0.047) for both nutritional levels as compared to periods without n-butyric acid treatments. The higher nutritional level and intraruminal n-butyric acid infusion induced epithelial cell death. The percentage of proliferative cells was doubled by n-butyric acid treatment. The mRNA of IGF-1 and IGF type 1 receptor (IGF-1R), as well as IGF-1R binding capacity were unaffected by butyric acid treatments. The abundance of IGF-1 mRNA tended to be lower (p = 0.1) and IGF-1R abundance was lower (p = 0.03) in response to the HL. The plasma IGF-1 concentration was lower with butyric acid treatment (p < 0.01), but was unaffected by the nutritional level. In conclusion, under described experimental preconditions of daily short-time intraruminal n-butyric acid infusion alterations of rumen papillae morphology is not mediated by ruminal IGF type 1 receptor and by local IGF-1 expression in papillae in castrated bulls.

Effect of ammonia on Na+ transport across isolated rumen epithelium of sheep is diet dependent

The cellular uptake of ammonia affects the intracellular pH (pHi) of polar and non-polar cells. A predominant uptake of NH3 and its intracellular protonation tend to alkalinise the cytoplasm, whereas a predominant uptake of NH4(+) acidifies the cytoplasm by reversing this reaction. Hence, the well-known absorption of ammonia across the rumen epithelium probably causes a change in the pHi. The magnitude and direction of this change in pHi (acid or alkaline) depends on the relative transport rates of NH3 and NH4(+). Consequently, the intracellular availability of protons will influence the activity of the Na(+)-H(+) exchanger, which could affect transepithelial Na(+) transport. The aim of the present study has been to test this possible interaction between ruminal ammonia concentrations and Na(+) transport. The term ammonia is used to designate the sum of the protonated (NH4(+)) and unprotonated (NH3) forms. Isolated ruminal epithelium of sheep was investigated by using the Ussing-chamber technique in vitro. The present results indicate that ammonia inhibits Na(+) transport across the rumen epithelium of hay-fed sheep, probably by binding intracellular protons and thus inhibiting Na(+)-H(+) exchange. By contrast, ammonia stimulates Na(+) transport in concentrate-fed and urea-fed sheep, which develop an adaptation mechanism in the form of an increased metabolism of ammonia in the rumen mucosa and/or an increased permeability of rumen epithelium to the charged ammonium ion (NH4(+)). Intracellular dissociation of NH4(+) increases the availability of protons, which stimulate Na(+)-H(+) exchange. This positive effect of ruminal ammonia on Na(+) absorption may significantly contribute to the regulation of osmotic pressure of the ruminal fluid, because intraruminal ammonia concentrations up to 40 mmol/l have been reported.

Subacute Ruminal Acidosis (SARA): a Review

Subacute ruminal acidosis (SARA) is likely to arise when an easily palatable, high-energy diet meets a ruminal environment not adapted to this type of substrate. Increase of short-chained fatty acids (SCFA) will occur. Eventually, this may result in a transient nadir of ruminal pH below 5.5. Two situations are likely to represent the risk of SARA. First, fresh lactating cows are confronted with a diet considerably differing from that in the dry-period. A diet change carried out too rapidly or without proper transition management will put the animals at risk. Secondly, further in lactation, inaccurate calculation of dry-matter-intake (DMI) leading to wrong roughage/concentrate ratio, an inadequate content of structure within the diet or mistakes in preparing of total mixed rations may produce SARA. The consequences of SARA are diverse and complex. Laminitis is regularly connected to SARA and the negative impact of organic acids on the ruminal wall may lead to parakeratosis enabling translocation of pathogens into the bloodstream provoking inflammation and abscessation throughout the ruminant body. Moreover, milk-fat depression (MFD) can be related to SARA. In order to achieve a proper diagnosis, SARA has to be understood as a herd-management problem. A screening of the herd for SARA by means of a rumenocentesis, performed on a sample-group, preferably 12 individuals, may reveal the presence of SARA. The herd screening should include the risk group suspected, preferably. The prevention of SARA applies to the principles of ruminant feeding. Careful transition management from the dry to the lactation period and control of fibre-content and ration quality should be more yielding than the use of buffers or antibiotic drugs.

Transfer of energy substrates across the ruminal epithelium: implications and limitations

The ruminal epithelium has an enormous capacity for the absorption of short-chain fatty acids (SCFAs). This not only delivers metabolic energy to the animal but is also an essential regulatory mechanism that stabilizes the intraruminal milieu. The epithelium itself, however, is endangered by the influx of SCFAs because the intracellular pH (pHi) may drop to a lethal level. To prevent severe cytosolic acidosis, the ruminal epithelium is able to extrude (or buffer) protons by various mechanisms: (i) a Na+/H+ exchanger, (ii) a bicarbonate importing system and (iii) an H+/monocarboxylate cotransporter (MCT). Besides pHi regulation, the MCT also provides the animal with ketone bodies derived from the intraepithelial breakdown of SCFAs. Ketone bodies, in turn, can serve as an energy source for extrahepatic tissues. In addition to SCFA uptake, glucose absorption has recently been identified as a potential way of eliminating acidogenic substrates from the rumen. At least with respect to SCFAs, absorption rates can be elevated when adapting animals to energy-rich diets. Although they are very effective under physiological conditions, the absorptive and regulatory mechanisms of the ruminal epithelium also have their limits. An increased number of protons during the state of ruminal acidosis can be eliminated neither from the lumen nor the cytosol, thus worsening dysfermentation and finally leading to functional and morphological alterations of the epithelial lining.

Short communication: Effect of subacute ruminal acidosis on in situ fiber digestion in lactating dairy cows

Subacute ruminal acidosis (SARA) was induced by replacing 25% of the total mixed ration intake [dry matter (DM) basis] with pellets consisting of 50% wheat and 50% barley. This reduced dietary forage content (DM basis) from 39.7 to 29.8% and increased the dietary concentrate content from 60.3 to 70.2%. Induction of SARA reduced the 24- and 48-h in situ neutral detergent fiber (NDF) degradabilities of grass hay numerically from 31.5% to 24.6% (P = 0.29) and from 51.3% to 36.9% (P < 0.05), respectively. The 24- and 48-h in situ NDF degradabilities of legume hay were reduced from 35.3 to 26.3% (P < 0.05) and from 49.0 to 35.8% (P < 0.05), respectively. The 24- and 48-h in situ NDF degradabilities of corn silage were reduced from 44.0 to 37.2% (P < 0.05) and from 56.1 to 44.8% (P < 0.05), respectively. This study suggests that induction of SARA by excess feeding of wheat/barley pellets reduces the rumen digestion of NDF from grass hay, legume hay, and corn silage.

Pathophysiology of grass tetany and other hypomagnesemias. Implications for clinical management

Magnesium is an essential mineral with many physiologic and biochemical functions. Surprisingly, Mg homeostasis is not regulated by a hormonal feedback system, but simply depends on inflow (absorption) from the gastrointestinal tract and outflow (endogenous secretion, requirement for milk production, uptake by tissues). Any surplus (inflow greater than outflow) is excreted via urine. Conversely, if the outflow (mainly milk secretion and endogenous loss) exceeds inflow, hypomagnesemia occurs because of the lack of hormonal mechanisms of homeostasis. The major reason for insufficient inflow is a reduced absorption of Mg from the forestomachs. Recent studies from our laboratory and data from the literature permit the proposal of a putative transport model for the secondary active transport of Mg across the rumen epithelium. This model includes two uptake mechanisms across the luminal membrane (PD-dependent and PD-independent) and basolateral extrusion via a Na/Mg exchange. The well-known negative interaction between ruminal K concentration and Mg absorption can be explained on the basis of this model: an increase of ruminal K depolarizes the potential difference of the luminal membrane, PDa, and as the driving force for PD-dependent (or K-sensitive) Mg uptake. Because Na deficiency causes an increase of K concentration in saliva and ruminal fluid, Na deficiency should be considered a potentially important risk factor. The data obtained from in vitro and in vivo studies on the association of Mg transport, changes of ruminal K concentration, and PDa are extensive and confirm the model, if the ruminal Mg concentrations are below 2 to 3 mM. It is further proposed by the model that the PD-independent Mg uptake mechanism is primarily working at high ruminal Mg concentration (above 2 mM). Mg absorption becomes more and more independent of ruminal K with increasing Mg concentration, which can be considered as an explanation for the well-known prophylaxis of hypomagnesemia by increasing oral Mg intake. Fermentation products, NH4+ and SCFA, influence Mg absorption. The possible meaning regarding the pathogenesis of hypomagnesemia is not quite clear. A sudden increase of ruminal NH4+ should be avoided, because high NH4+ concentrations transiently reduce Mg absorption. The most prominent signs of hypomagnesemia are excitations and muscle cramps, which are closely correlated with the Mg concentration in the CSF. It is suggested that the clinical signs are caused by spontaneous activation of neurons in the CNS at low Mg concentrations, which leads to tetany. Prophylactic measures are discussed in context with the known effects on ruminal Mg absorption.

Morphological and functional development of the rumen in the calf: influence of the time of weaning. 1. Morphological development of rumen mucosa

The objective of this study was to determine whether the nutritional regimen of rearing calves would influence the morphometric and histological development of rumen mucosa. Twelve male Holstein calves 7 d of age were assigned to three groups of 4 animals each: milk group (I), early weaned (6 weeks) group (II) and late weaned (9 weeks) group (III). All animals received additional solid feed. Animals of group I were slaughtered after 6 weeks of age, whereas those in groups II and III were slaughtered after 9 weeks of age. At slaughter, the ruminal digesta amounted to 2035 g (milk group), 3092 g (late weaned group) and 5374 g (early weaned group). The differences in the ruminal molar percentage of SCFA were not significant. There was a trend for lower pH and higher SCFA concentrations in the order late weaned, early weaned and milk fed animals (pH: 6.4, 6.6 and 6.7, respectively; SCFA: 96, 87 and 77 mmol/l, respectively). The mean length (1.07 mm in milk group, 1.45 mm in late weaned group and 1.87 mm in early weaned group), width (0.43, 0.58 and 0.71 mm, respectively) and surface of papillae (190, 232 and 241 mm2/cm2 mucosa, respectively) increased with both the age of the animals and the elevated intake of solid feed, whereas the number of papillae (210, 140 and 92 per cm2 mucosa, respectively) decreased. In both milk-fed groups type A and B corneal cells were present in the Stratum corneum, whereas in the earlier weaned calves type C-cells could be also seen. These findings indicate a more advanced stage of development of the rumen epithelium in the earlier weaned calves fed higher amounts of concentrate and hay.

Attachment of different Escherichia coli strains to cultured rumen epithelial cells

The attachment to fully characterized primary rumen epithelial cell cultures of Escherichia coli strains isolated from different animal species and expressing F1-F4 or F17 fimbriae was examined. As the cell cultures contained stratified (keratinized) and non-stratified (non-keratinized) cells which grew either confluently or non-confluently, the strength of attachment of the different bacterial strains was assessed in relation to the differentiation state of the cells. Thus, strains having F1 fimbriae attached to all types of cultured cells, while strains with F2 and F3 fimbriae did not bind at all. E. coli strains having F4 or F17 fimbriae attached only to non-keratinized cells, particularly to confluent areas. As membrane glycosylation is known to change with differentiation (keratinization), our results suggest that the attachment of fimbriated E. coli strains which were capable of binding to rumen cells was more likely to be dependent on differentiation than the host specificity of the bacteria.

Influence of dietary concentrate to forage ratio on the development of rumen mucosa in calves

Effects of structural and non-structural carbohydrates on the development of rumen fermentation and ruminal mucosa in calves were examined during the weaning period. Barley/soybean meal (SBM) group was fed a concentrate starting from 2 weeks of age, whereas alfalfa group received a mixture of concentrate and alfalfa hay in which the proportion of the latter was gradually increased from 20% to 70% between weeks 2 and 9 of age. The total volatile fatty acid concentration in rumen fluid of calves increased with age, but at 9 weeks there were no significant differences between the two diets (barley/SBM group 153 mmol/l, alfalfa group 150 mmol/l). Rumen papillae at 9 weeks of age, as compared to 6 weeks of age, were longer and fewer in number per square centimetre mucosa, with larger cut surface. This resulted in a higher surface of papillae per square centimetre mucosa at 9 weeks (barley/SBM group 286 mm2/cm2, alfalfa group 245 mm2/cm2) than at 6 weeks of age (barley/SBM group 217 mm2/cm2, alfalfa group 198 mm2/cm2). At 9 weeks of age, the pH (barley/SBM 5.0, alfalfa 5.7), the acetate to propionate ratio (barley/SBM 2.2, alfalfa 3.2) as well as the length of the papillae in the ventral ruminal sac (barley/SBM 1.96 mm, alfalfa 2.37 mm) were increased in the alfalfa group when compared to the barley/SBM group (P < 0.1). In the former group, the proportion of butyrate revealed significantly increased values at 4 and 6 weeks of age. In animals of the barley/SBM group at 9 weeks of age, characteristic protrusions with proliferated thick epithelium occurred on the papillae and increased the surface for absorption. On the epithelium (Stratum corneum) desquamating cells with parakeratosis could be observed. In the alfalfa group the papillae of the ventral ruminal sac were longer, without protrusions. The morphotypes of the adhering rumen microflora differed between the groups. It can be concluded that feeding greater amounts of non-structural carbohydrates increases the surface for absorption of the rumen epithelium in calves. The absence of hyperkeratosis and rumenitis in the barley/SBM group indicated that there is no reason to limit high starch diets in the early weaning period of calves.

Feed-induced changes in transport across the rumen epithelium

The effect of feeding strategy on rumen epithelial growth and transport capacity were studied in sixteen dairy cows. There was a significant effect of feeding strategy on transport of butyrate, sodium and chloride ions, which could not be explained by changes in epithelial surface area, structure or resistance.

SCFA transport in the forestomach of ruminants

Short-chain fatty acids are the main end-products of microbial metabolism in the forestomach of ruminants. SCFA produced by the microorganisms are rapidly absorbed across forestomach epithelia and can cover up to 80% of the energy requirement of the animal. Although there is a great concentration gradient for SCFA between the forestomach content and the blood favoring passive transport, (secondary) active transport mechanisms are likely involved in SCFA permeation across the epithelia. (Secondary) active SCFA transport seems to be mediated by an anionic exchange system. The system interacts with other anions like chloride and bicarbonate. Similar to the large intestine of various species, SCFA can stimulate sodium transport probably by activating a Na+/H+ exchange located in the apical membrane. However, in contrast to the large intestine, SCFA transport itself seems to be independent from sodium. Part of the absorbed SCFA does not reach the blood side in the original form because it is metabolized in the epithelial cell. Metabolism, in turn, influences SCFA transport.

Bovine acidosis: implications on laminitis

Bovine lactic acidosis syndrome is associated with large increases of lactic acid in the rumen, which result from diets that are high in ruminally available carbohydrates, or forage that is low in effective fiber, or both. The syndrome involves two separate anatomical areas, the gastrointestinal tract and body fluids, and is related to the rate and extent of lactic acid production, utilization, and absorption. Clinical manifestations range from loss of appetite to death. Lactic acid accumulates in the rumen when the bacteria that synthesize lactic acid outnumber those that utilize lactic acid. The systemic impact of acidosis may have several physiological implications, including laminitis, a diffuse aseptic inflammation of the laminae (corium). Although a nutritional basis for the disease exists, etiology includes a multitude of interactive factors, such as metabolic and digestive disorders, postpartum stress, and localized trauma, which lead to the release of vasoactive substances that trigger mechanisms that cause degenerative changes in the foot. The severity of laminitis is related to the frequency, intensity, and duration of systemic acidotic insults on the mechanisms responsible for the release of vasoactive substance. The critical link between acidosis and laminitis appears to be associated with a persistent hypoperfusion, which results in ischemia in the digit. Management of acidosis is critical in preventing laminitis. High producing dairy herds attempting to maximize energy intake are continually confronted with subclinical acidosis and laminitis. Management of feeding and husbandry practices can be implemented to reduce incidence of disease.

Influence of food deprivation on SCFA and electrolyte transport across sheep reticulorumen

Net absorption rates for SCFA, sodium, chloride, magnesium, and water were measured in the temporarily isolated and washed reticulorumen of sheep. The animals were either fed hay ad lib. plus concentrates once daily or were deprived of food for two days. Food deprivation led to decreased net absorption of all the substances tested. Comparing the solutes, the relative decreases varied between 43% (butyrate) and 56% (acetate). The decrease in solute absorption was accompanied by diminished water absorption. It is concluded that the reduction in absorption may be beneficial for the animal in that energy consumption is diminished and the reservoir function of the forestomach will be maintained longer. However, the reduced absorptive capacity may lead to a deficiency of magnesium, which is thought to be absorbed mainly by the forestomachs.

Influences of extracellular matrix components on the growth and differentiation of ruminal epithelial cells in primary culture

Primary cultures of ovine ruminal epithelial cells were made to study the influence of collagen types I and IV out of medium supplementation with various hormones and Na-n-butyrate on cell morphology and growth characteristics. Both collagen type I and type IV led to increased cell proliferation with the stimulatory effect being more pronounced in collagen IV. In cultures grown on collagen I, both non-stratified and stratified colonies were found, whereas cultures grown on collagen IV showed predominantly stratified growth. Cells in both stratified and non-stratified colonies were positive for cytokeratin antibody. In non-stratified colonies, positive staining with fibronectin antibodies (FN-15) was found in a network over and around the cells. It is suggested that the non-stratified ruminal epithelial cells are in some respects similar to a 'non-differentiating keratinocyte' strain, derived from newborn foreskin epidermis. Cells in stratified colonies bound Ulex europaeus (UEAI) lectin which has been shown to be specific for differentiated epithelial cells in ruminal mucosa. Supplementation of culture medium with glucagon and insulin increased the total cell-overgrown area of collagen I cultures, whereas this effect was absent in cultures grown on collagen IV. In both cultures grown on collagen I or IV, hydrocortisone led to an increase in total cell-overgrown area, whereas Na-n-butyrate inhibited proliferation.

Subclinical ketosis in dairy cows

Subclinical ketosis is defined as a preclinical stage of ketosis. The peak prevalence of subclinical ketosis occurs during the fourth week of lactation. Herd-related factors, breed, parity, and season are other important determinants. Subclinical ketosis can be revealed by determining levels of plasma glucose, plasma NEFA and blood, and milk or urine ketone body concentration. There are theoretical and practical advantages of using milk ketone bodies. Most authors are agreed on approximate lower and upper borderlines for subclinical ketosis. The risk of an outbreak of clinical symptoms has been evaluated by some authors. Most authors have found significant negative relationships between energy balance and ketone body concentration. Some disagreement may be attributable to the fact that the diets used in different experiments can have different glucogenic potential, even if the energy content is the same. This affects the relationship between energy balance and ketone body concentration, as the ketone body level is influenced by both the energy balance and plasma glucose. Feeding silage with high butyric acid content increases the risk of subclinical ketosis. There are indications that cows with the highest milk yield directly after calving are at greatest risk for developing ketosis. Increased ketone body level secondarily reduces milk production, a decrease that has been quantified by some authors. Subclinical ketosis causes delayed reproductive functions return to normal after calving, increased intervals from calving to first and last service, and an increased frequency of ovarian cysts. The routine determination of milk acetone levels in control programs can be used to evaluate the status of individual cows, to indicate the energy feeding in early lactation at a herd level, and to evaluate sires for breeding. The heritability and the tendency toward a positive genetic correlation between milk acetone and milk yield have also been discussed, as have aspects of nutritional prevention. Factors such as energy- and protein-rich roughage, tasty high-energy concentrates, suitable feeding during the dry period, and division of the concentrates into at least four meals are considered to be important.