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The objective of this pilot study was to generate data to support the development of an experimental model of hindgut acidosis to further understand its systemic consequences independently of rumen acidosis. Four ruminally fistulated multiparous Holstein cows (213 ± 11 d in milk) were subjected to 2 consecutive experimental periods (P1 and P2), separated by a 3-d washout. Experimental periods were 96 h long from the baseline to the final measurements but expanded over 5 calendar days (d 0–4). Abomasal infusions of saline and corn starch (2.8 kg/d) were performed for the first 72 h (d 0–3) of P1 and P2, respectively. Final measurements were performed 24 h after the end of the infusions (d 4). Each cow was used as its own control by comparing P2 to P1. Postruminal-intestinal permeability was assessed by Cr appearance in blood after a pulse dose administration of Cr-EDTA into the abomasum on d 2 (48 h after infusion initiation) of each period. Starch infusion during P2 was associated with a milk protein yield increase (3.3%) and a decrease in milk urea nitrogen (11%). Fecal dry matter increased (8.8%), and starch content tended to increase (∼2 fold) during P2. There was a period-by-day interaction for fecal pH as it decreased during starch infusion (1.3 pH points) but remained constant during P1. Although fecal lactate was not detectable during P1, it consistently increased during starch infusion. Fecal alkaline phosphatase activity also increased (∼17 fold) in association with starch infusion. Two hours after Cr-EDTA administration, blood Cr concentration was higher during starch infusion, resulting in a tendency for a treatment-by-hour interaction. Furthermore, blood d -lactate increased (∼2.5 fold), serum Cu decreased (18%), and blood urea nitrogen, cholesterol, and Ca tended to decrease (9.4%, 1.2%, and 2.4%, respectively), relative to P1. The current results suggest that hindgut acidosis was successfully induced by postruminal starch infusion, leading to gut damage and increased intestinal permeability. However, indications of systemic inflammation were not observed. The herein described preliminary results will require confirmation in a properly powered study. [ABSTRACT FROM AUTHOR]

While the importance of pH and short-chain fatty acids (SCFA) on rumen development are well-known, their impact on the small and large intestine are unclear. This study investigated how single-dose ruminal infusions with high or low short-chain fatty acid concentrations and high or low pH affect calves' productivity as well as physiological parameters associated with hindgut acidosis at 3-time points in 49 d. Holstein bull calves (n = 32) were individually housed and fed milk replacer (900 g/d) twice daily and calf starter and water ad libitum. At d 10 ± 3 of life, the rumens were fistulated and cannulated. At d 14 of life, calves were grouped by body weight and assigned in a 2 × 2 factorial arrangement of treatments: high or low SCFA concentration (285 vs. 10 mM) and high or low pH (6.2 vs. 5.2), creating 4 treatment groups: high SCFA concentration, high pH (HS-HP); high SCFA concentration, low pH (HS-LP); low SCFA concentration, high pH (LS-HP); and low SCFA concentration, low pH (LS-LP). On d 21, 35, 49, feces were sampled to calculate apparent total-tract digestibility, determinate organic acid concentrations (i.e., SCFA, BCFA and lactic acid), and pH. Afterward, the rumen was evacuated and underwent a single-dose infusion for 4 h with one of 4 treatment buffers. After completion of rumen infusion on d 49, calves were harvested, and the tissue weight and length, and digesta pH of the rumen, cecum, colon, and rectum were recorded along with the digesta pH of duodenum, jejunum, and ileum only at d 49 after dissection. Data were analyzed with main factors as fixed effects and repeated measures for weekly measurements. Treatments did not affect performance parameters such as feed intake, ADG, apparent total-tract digestibility and gut measurements. In the duodenum, jejunum, and ileum, HS-HP had a greater digesta pH than LS-HP, while the hindgut digesta pH was only affected by the SCFA concentration. High SCFA concentration increased the concentration of colonic isovaleric acid and fecal BCFA, while only colonic acetic acid and fecal lactic acid concentrations were affected by treatment. Fecal SCFA and BCFA concentrations increased mainly on d 35. In summary, 4 h of physiological buffer infusion in the rumen does not change apparent total-tract digestibility and gut measurements but does affect hindgut fermentation parameters (i.e., organic acid concentrations and digesta pH). In addition, calves can experience increased risks of hindgut acidosis around 35 d of life., (©, The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Many studies have shown a strong correlation between Hindgut Acidosis (HGA) and the occurrence of laminitis in horses; therefore, the early diagnosis of HGA is essential. In this study, we investigated changes in the plasma concentrations of lipopolysaccharide-binding protein (LBP) and serum amyloid A (SAA) as inflammatory markers in horses with laminitis. Sixteen healthy male Arabian horses that had cecal cannulation without visible laminitis or general symptoms were randomly divided into two groups. The horses were fed two different diets in a forage-to-concentrate ratio. Blood samples were collected on Days 1, 10, and 20. The primary objective of this study was to analyze plasma levels of LBP and SAA. Cecal specimens were obtained from each equine subject on three designated days: days 1, 10, and 20. The second objective was to assess the levels of pH and volatile fatty acids (VFA) in the samples. Throughout the study period, horses fed a high-concentrate diet exhibited a significantly elevated average lameness grade on days 10 and 20 compared to the initial stage (P < 0.001). On day 20, a significant increase in the concentration of SAA was observed in horses fed a high-concentrate diet, in contrast to the initial stage of the study. LBP levels in the plasma were significantly elevated on days 10 and 20 in horses fed a high-concentrate diet. Based on our findings, it is recommended that the evaluation of plasma LBP concentrations is more effective than SAA for the early identification of HGA in horses fed a high-grain diet. [ABSTRACT FROM AUTHOR]

The objectives of this study were to induce hindgut and metabolic acidosis via abomasal infusion of corn starch and β-hydroxybutyrate (BHB), respectively, and to determine the effects of these physiological states in early-lactation dairy cows. In a 6 × 6 Latin square design, 6 rumen-fistulated Holstein-Friesian dairy cows (66 ± 18 d in milk) were subjected to 5 d of continuous abomasal infusion treatments followed by 2 d of rest. The abomasal infusion treatments followed a 3 × 2 factorial design, with 3 levels of corn starch and 2 levels of BHB. The infusions were water as control, 1.5 kg of corn starch/d, 3.0 kg of corn starch/d, 8.0 mol BHB/d, 1.5 kg of corn starch/d + 8.0 mol BHB/d, or 3.0 kg of corn starch/d + 8.0 mol BHB/d. A total mixed ration consisting of 35.0% grass silage, 37.4% corn silage, and 27.6% concentrate (on a dry matter basis) was fed at 90% of ad libitum intake of individual cows. The experiment was conducted in climate respiration chambers to facilitate determination of energy and N balance. Fecal pH decreased with each level of corn starch infused into the abomasum and was 6.49, 6.00, and 5.15 with 0.0, 1.5, and 3.0 kg of corn starch/d, respectively, suggesting that hindgut acidosis was induced with corn starch infusion. No systemic inflammatory response was observed and the permeability of the intestine or hindgut epithelium was not affected by the more acidic conditions. This induced hindgut acidosis was associated with decreased digestibility of nutrients, except for crude fat and NDF, which were not affected. Induced hindgut acidosis did not affect milk production and composition and energy balance, but increased milk N efficiency. Abomasal infusion of BHB resulted in a compensated metabolic acidosis, which was characterized by a clear disturbance of acid-base status (i.e., decreased blood total CO 2 , HCO 3 , and base excess, and a tendency for decreased urinary pH), whereas blood pH remained within a physiologically normal range. Abomasal infusion of BHB resulted in increased concentrations of BHB in milk and plasma, but both remained well below the critical threshold values for subclinical ketosis. Induced compensated metabolic acidosis, as a result of abomasally infused BHB, increased energy retained as body fat, did not affect milk production and composition or inflammatory response, but increased intestinal permeability. [ABSTRACT FROM AUTHOR]

Next to rumen acidosis, other forms of acidosis may also affect lactational performance of cows. Therefore, the effects of hindgut acidosis, induced via abomasal infusion of ground corn, and metabolic acidosis, induced via abomasal infusion of NH 4 Cl, were studied in cows in early lactation. Observations were made on intake and digestibility of nutrients, lactation performance, energy and N partitioning, blood acid-base status, and rumen and hindgut fermentation characteristics. In a 6 × 6 Latin square design, 6 rumen-fistulated, second-lactation Holstein-Friesian dairy cows (48 ± 17 d in milk) were subjected to 5 d of continuous abomasal infusions of water as control, or solutions of 2.5 mol of NH 4 Cl/d, 5.0 mol of NH 4 Cl/d, 3.0 kg of ground corn/d, or the combination of ground corn with either of the 2 NH 4 Cl levels, followed by 2 d of rest. Treatment solutions were administered via peristaltic pumps through infusion lines attached to the rumen cannula plug and an abomasal infusion line with a flexible disk (equipped with holes to allow digesta passage) to secure its placement through the sulcus omasi. A total mixed ration consisting of 70% grass silage and 30% concentrate (on dry matter basis) was fed at 95% of ad libitum intake of individual cows. The experiment was conducted in climate respiration chambers to determine feed intake, lactation performance, and energy and N balance. Abomasal infusion of NH 4 Cl affected the acid-base status of the cows, but more strongly when in combination with abomasal infusion of ground corn. Metabolic acidosis (defined as a blood pH < 7.40, blood HCO 3 concentration < 25.0 mmol/L, and a negative base excess) was observed with 5.0 mol of NH 4 Cl/d, 3.0 kg of ground corn/d + 2.5 mol of NH 4 Cl/d, and 3.0 kg of ground corn/d + 5.0 mol of NH 4 Cl/d. Metabolic acidosis was associated with decreased milk lactose content, metabolic body weight, energy retained as protein, and fecal N excretion, and increased urine N excretion, and tended to decrease intake of nutrients. Digestibility of several nutrients increased with 5.0 mol of NH 4 Cl/d, likely as a result of decreased intake. Abomasal ground corn infusion resulted in hindgut acidosis, where fecal pH decreased from 6.86 without ground corn to 6.00 with ground corn, regardless of NH 4 Cl level. The decrease in fecal pH was likely the result of increased hindgut fermentation, evidenced by increased fecal volatile fatty acid concentrations. Hindgut acidosis was associated with decreased digestibility of nutrients, except for starch, which increased, and crude fat, which was not affected. No systemic inflammatory response was observed, suggesting that the hindgut epithelium was not severely affected by the more acidic conditions or barrier damage. Abomasal infusion of ground corn increased milk yield, milk protein and lactose yield, fecal N excretion, N use efficiency, and total energy retained as well as energy retained in fat, and reduced milk fat content and urine N excretion. [ABSTRACT FROM AUTHOR]

An adequate gastrointestinal barrier function is essential to preserve animal health and well-being. Suboptimal gut health results in the translocation of contents from the gastrointestinal lumen across the epithelium, inducing local and systemic inflammatory responses. Inflammation is characterized by high energetic and nutrient requirements, which diverts resources away from production. Further, barrier function defects and inflammation have been both associated with several metabolic diseases in dairy cattle and liver abscesses in feedlots. The gastrointestinal tract is sensitive to several factors intrinsic to the productive cycles of dairy and beef cattle. Among them, high grain diets, commonly fed to support lactation and growth, are potentially detrimental for rumen health due to their increased fermentability, representing the main risk factor for the development of acidosis. Furthermore, the increase in dietary starch associated with such rations frequently results in an increase in the bypass fraction reaching distal sections of the intestine. The effects of high grain diets in the hindgut are comparable to those in the rumen and, thus, hindgut acidosis likely plays a role in grain overload syndrome. However, the relative contribution of the hindgut to this syndrome remains unknown. Nutritional strategies designed to support hindgut health might represent an opportunity to sustain health and performance in bovines.

Aims The goal was to determine the effect of starch source (corn, oats and wheat) and concentration on: (i) total amylolytic bacteria, Group D Gram-positive cocci ( GPC), lactobacilli and lactate-utilizing bacteria, and (ii) fermentation by equine microbiota. Methods and Results When faecal washed cell suspensions were incubated with any substrate amylolytics increased over time. However, at 24 h there were 10 and 1000-fold more amylolytics with corn than wheat or oats respectively. Predominant amylolytics isolated were Enterococcus faecalis (corn, wheat) and Streptococcus bovis (oats). GPC increased with any substrate, but decreased during stationary phase in oats only. Lactobacilli decreased during stationary phase with corn only. By 24 h, oats had more lactate-utilizers and lactobacilli and fewer GPC than corn and wheat. More gas was produced from oats or wheat than from corn. Conclusions These results indicate that the growth of bacteria and fermentative capacity associated with starch metabolism is starch source dependent. Significance and Impact of the Study This study demonstrates a relationship between starch source and microbial changes independent of host digestion. However, future research is needed to evaluate the effect of starch source on the hindgut microbial community in vivo. [ABSTRACT FROM AUTHOR]

Abstract: Abrupt dietary transitions and feeding of rapidly fermentable diets are common practices in the horse industry and have been associated with digestive and metabolic disorders that can impair the performance of horses. The present study investigated the effect of dietary transition from pasture grazing to confinement with concentrate feeding, and back, on fecal pH and bacterial populations of Streptococcus spp and Lactobacillus spp. Six Thoroughbred fillies, previously grazing perennial ryegrass and white clover-based pasture, were housed in individual stalls and fed an increasing ratio of concentrate to conserved forages for 13 days (days 1-13), followed by an abrupt transition back to only pasture-grazing for 3 days (days 14-16). The concentrate was initially offered at 0.83 kg dry matter (DM)/d and increased to 5 kg DM/d, whereas ensiled alfalfa was initially offered at 0.61 kg DM/d, increasing to 1.22 kg DM/d. Meadow hay was initially offered at 6.73 kg DM/d, decreasing to 1.6 kg DM/d. Fecal specimens were collected daily for determination of pH, and every 2 days for quantitative analysis of Streptococcus spp and Lactobacillus spp. Mean fecal pH increased significantly from pasture baseline values (pH 6.18) during the initial confinement and supplementation on day 1 (6.37), day 2 (6.52), day 3 (6.58), and day 4 (6.43) (standard error of mean [SEM]: 0.056; P < .001). By day 5, mean fecal pH values had decreased to, and remained at, baseline values until the horses returned to pasture, when another increase occurred at day 15 (6.45). Fecal colony forming units (cfu) of Streptococcus spp and Lactobacillus spp increased linearly (r = 0.94; P < .001) from 6.0 and 6.1 log10 cfu/g on day -4, to 7.8 log10 cfu/g on day 14 (SEM: 0.2 P < .001), respectively. Fecal cfu decreased on return to a pasture-only diet (P < .001). In this study, the increment of bacterial populations was associated with a relatively stable fecal pH and highlights the difficulty in identifying the effects of dietary transition on the equine hindgut health, without microbial culture. [Copyright &y& Elsevier]

Lactic acid accumulation in the caecum and colon resulting from the fermentation of carbohydrates can lead to deleterious effects in ruminant and monogastric animals, including humans. In the present study, we examined the behavioural effects of two types of commonly consumed foods: soluble and fermentable carbohydrates (FCs). Thirty-six male Wistar rats were fed either a commercial rat and mouse chow, a soluble carbohydrate (SC)-based diet or an FC-based diet. Social interaction, anxiety, aggression and locomotor activity were examined by employing a social interaction test and a light/dark emergence test, while physical parameters of hindgut fermentation were examined after sacrifice, either 3 or 21 h after feeding. Results showed that anxiety (spending less time in the light compartment during the light/dark emergence test) and aggression (increased fighting during the social interaction test) were increased following raised concentrations of fermentation end products, such as lactic acid and volatile fatty acids (VFAs) in the caecum of rats. These associations occurred regardless of dopamine and 5-HT concentrations in the prefrontal cortex (PFC) and provide evidence supporting a general effect of FCs on behaviour. Possible mechanisms of action along with similarities between a rat and human model of acidosis are discussed. [Copyright &y& Elsevier]

Simple Summary: It is well established that the functions of the gastrointestinal tract go beyond the digestion and absorption of nutrients. For instance, its constant contact with the gastrointestinal microbes and components of the diet makes it a major player within the immune system. Preserving the gut's barrier function is essential to maintaining overall health and subsequently performance in farm animals. In cattle, multiple factors throughout their productive cycle can have negative consequences on gut health, including dietary changes. Most research in this topic has focused on rumen health, due to its critical role in digestion in bovines. However, it is increasingly evident that other sections of the gastrointestinal tract, such as the large intestine (also referred to as the hindgut), are similarly impacted by the same factors. Nutritional strategies aimed to promote rumen health have proven beneficial for overall health and performance in bovines. Targeting the hindgut might represent a window of opportunity for further improvement. An adequate gastrointestinal barrier function is essential to preserve animal health and well-being. Suboptimal gut health results in the translocation of contents from the gastrointestinal lumen across the epithelium, inducing local and systemic inflammatory responses. Inflammation is characterized by high energetic and nutrient requirements, which diverts resources away from production. Further, barrier function defects and inflammation have been both associated with several metabolic diseases in dairy cattle and liver abscesses in feedlots. The gastrointestinal tract is sensitive to several factors intrinsic to the productive cycles of dairy and beef cattle. Among them, high grain diets, commonly fed to support lactation and growth, are potentially detrimental for rumen health due to their increased fermentability, representing the main risk factor for the development of acidosis. Furthermore, the increase in dietary starch associated with such rations frequently results in an increase in the bypass fraction reaching distal sections of the intestine. The effects of high grain diets in the hindgut are comparable to those in the rumen and, thus, hindgut acidosis likely plays a role in grain overload syndrome. However, the relative contribution of the hindgut to this syndrome remains unknown. Nutritional strategies designed to support hindgut health might represent an opportunity to sustain health and performance in bovines. [ABSTRACT FROM AUTHOR]

Grass fructans can be fermented by Gram-positive bacteria (e.g., Streptococcus bovis ) in the equine hindgut, increasing production of lactic acid and decreasing pH. The degree of polymerization (DP) of fructans has been suggested to influence fermentation rates. The objective of the present study was to determine how DP impacts fermentation by equine fecal bacteria and a model S. bovis . Fecal microbes from three mares were harvested by differential centrifugation, washed, and resuspended in anaerobic media containing short-chain (SC; DP ≤ 10) or long-chain (LC) inulin (DP ≥ 23) from 0% to 2% wt/vol. After 24 hours of incubation (37°C), samples were collected for pH determination. Data were analyzed using the general linear models (GLM) procedure testing for the effect of treatment, concentration, and treatment × concentration (SAS v. 9.3). At all concentrations, the pH was lower in SC fermentations than in LC ( P < .0001, in all cases). To determine the effect of DP on S. bovis , cultures were grown (39°C, 9 hours) with 0.1%, 0.5%, or 1.3% SC or LC inulin. Optical density (600 nm) was determined by spectrophotometry. Maximum specific growth rates (μ) were determined by linear regression (2–5 hours). Data were analyzed using the one-way analysis of variance procedure (SAS v. 9.3). The final optical density (600 nm), μ, and yield were higher with SC than with LC fermentation ( P < .05). These results indicate that SC inulin may be more available for fermentation than LC inulin by equine fecal bacteria and S. bovis , specifically. [ABSTRACT FROM AUTHOR]