Ruminant Nutrition Symposium: Role of fermentation acid absorption in the regulation of ruminal pH

Dietary supplements during the cold season increase rumen microbial abundance and improve rumen epithelium development in Tibetan sheep

Livestock on the Qinghai-Tibetan Plateau are faced with extreme harsh winters and are often in negative energy balance during this period. Dietary supplementation can improve growth performance of Tibetan sheep and, consequently, we hypothesized that it would also increase microbial abundance and rumen epithelium development. To test this hypothesis, we examined the effect of feed supplementation during the cold season on rumen microbes, fermentation, epithelium development, and absorptive capability in Tibetan sheep. Eighteen 1-yr-old ewes (BW = 29.4 ± 1.79, kg) were offered oat hay ad libitum for 60 d and divided randomly into three groups: 1) no supplement; control group (CON); 2) urea-molasses lick block supplement (BS); and 3) concentrate feed supplement (CS). The ADG of CS ewes (143.3, g/d) was greater (P < 0.05) than BS ewes (87.9, g/d), which was greater (P < 0.05) than CON ewes (44.5, g/d). Serum concentrations of GH, IGF-1, and IGF-2 in the CS and BS groups were greater than in the CON group (P < 0.05). Greater relative abundance of protozoa, Ruminococcus albus, Fibrobacter succinogenes, Streptococcus bovis, and Ruminobacter amylophilus was observed in the CS and BS groups than in the CON group (P < 0.05), and relative abundances of rumen fungi, Butyrivibrio fibrisolvens, and Prevotella ruminicola in the CS group were greater than in the BS and CON groups (P < 0.05). Ruminal total VFA, ammonia, and microbial protein concentrations in the CS and BS groups were greater than in the CON group (P < 0.05), and in the CS group were greater than in the BS group (P < 0.05). Ruminal papillae width and surface area in the CS and BS groups were greater than in the CON group (P < 0.05), while in the CS group were greater than in the BS group (P < 0.05). The mRNA expressions of IGFBP5, NHE1 (sodium/hydrogen antiporter, isoform 1), DRA (downregulated in adenoma), and Na+/K+-ATPase (sodium/potassium ATPase pump) in ruminal epithelium were greater in the CS and BS groups than in the CON group (P < 0.05), and in the CS group was greater than in the BS group (P < 0.05), while NHE3 (sodium/hydrogen antiporter, isoform 3), MCT1 (monocarboxylate transporter 1), and MCT4 (monocarboxylate transporter 4) mRNA expressions in the CS group were greater than in the BS and CON groups (P < 0.05). It was concluded that supplementing Tibetan sheep during the cold season increases rumen microbial abundance and improves fermentation parameters, rumen epithelium development, and absorptive capability.

Effects of tributyrin supplementation on ruminal microbial protein yield, fermentation characteristics and nutrients degradability in adult Small Tail ewes

Two trials were conducted to assess the effects of tributyrin (TB) supplementation on ruminal microbial protein yield and fermentation characteristics in adult sheep. In an in vitro trial, substrate was made to offer TB at 0, 2, 4, 6, and 8 g/kg on a dry matter (DM) basis and incubated for 48 hr. In an in vivo trial, 45 adult ewes were randomly assigned by initial body weight (55 ± 5 kg) to five treatments of nine animals over an 18-day period. Total mixed ration was made to offer TB to ewes at 0, 2, 4, 6, and 8 g/kg on a DM basis. The in vitro trial showed that TB enhanced apparent degradation of DM (p = .009), crude protein (p < .001), neutral detergent fiber (p = .007) and acid detergent fiber (p = .010) and increased methanogenesis (p < .001), respectively. The in vivo trial showed that TB decreased DM intake (p < .001) and enhanced rumen microbial N synthesis (p < .001), respectively. Both in vitro and in vivo trials showed that TB increased total volatile fatty acid concentration and enhanced fibrolytic enzyme activity. The results indicated that TB might exert positive effects on microbial protein yield and fermentation in the rumen.

Effect of dietary energy substrate and days on feed on apparent total tract digestibility, ruminal short-chain fatty acid absorption, acetate and glucose clearance, and insulin responsiveness in finishing feedlot cattle

The objective of this study was to determine the effect of dietary energy substrate and days on feed on apparent total tract digestibility, ruminal fermentation, short-chain fatty acid (SCFA) absorption, plasma glucose and acetate clearance rates, and insulin responsiveness. Eight ruminally cannulated, crossbred growing heifers were randomly allocated to 1 of 2 dietary treatments. The control (CON) diet consisted of 75.2% barley grain, 9.8% canola meal, 9% mineral and vitamin supplement, and 6% barley silage (DM basis). To evaluate the effect of energy source, a high-lipid, high-fiber byproduct pellet (HLHFP) was included in the diet by replacing 55% of the barley grain and 100% of canola meal. The study consisted of 4 consecutive 40-d periods (P1 to P4), with data and sample collection occurring in the last 12 d of each period. Dry matter intake tended ( = 0.10) to decrease by period and HLHFP-fed heifers tended to eat less ( = 0.09). The ADG of the CON was greater than that of the HLHFP during P1 and P4 (treatment × period, = 0.02). Heifers fed HLHFP tended to have greater mean ruminal pH (6.10 vs. 5.96; = 0.07) than heifers fed the CON, but pH was not affected by period. The CON heifers had a greater digestibility for DM, OM, CP, and NDF ( ≤ 0.03), and the digestibility for DM and OM linearly increased ( = 0.01) and for CP, NDF, and starch quadratically increased ( ≤ 0.04) with advancing period. Total SCFA concentration in the rumen was greater ( < 0.01) for the CON than for the HLHFP (141.6 vs. 128.1 m). The molar proportion of acetate and isobutyrate linearly increased and butyrate and valerate linearly decreased ( ≤ 0.05) with advancing periods. The rate of valerate absorption tended to increase (linear, = 0.06) and the ruminal liquid passage rate tended to decrease (linear, = 0.08) with advancing period. The arterial clearance rate of acetate tended to quadratically increase ( = 0.06) with period, whereas the clearance rate of glucose was not affected by treatment or period. Both fasting plasma insulin and the area under the insulin curve in response to glucose infusion linearly increased ( = 0.04) with period. These data suggest that partially replacing barley grain with HLHFP negatively affects total tract digestibility and performance. Moreover, with advancing days on feed, digestibility and insulin resistance increases without changes in ruminal pH and plasma metabolite clearance rates.

Prevalence and magnitude of acidosis sequelae to rice-based feeding regimen followed in Tamil Nadu, India

Background and Aim

In Tamil Nadu, a southern state of India, rice is readily available at a low cost, hence, is cooked (cooking akin to human consumption) and fed irrationally to cross-bred dairy cattle with poor productivity. Hence, a study was carried out with the objective to examine the prevalence of acidosis sequelae to rice-based feeding regimen and assess its magnitude.

Materials and Methods

A survey was conducted in all the 32 districts of Tamil Nadu, by randomly selecting two blocks per districts and from each block five villages were randomly selected. From each of the selected village, 10 dairy farmers belonging to the unorganized sector, owning one or two cross-bred dairy cows in early and mid-lactation were randomly selected so that a sample size of 100 farmers per district was maintained. The feeding regimen, milk yield was recorded, and occurrence of acidosis and incidence of laminitis were ascertained by the veterinarian with the confirmative test to determine the impact of feeding cooked rice to cows.

Results

It is observed that 71.5% of farmers in unorganized sector feed cooked rice to their cattle. The incidence of acidosis progressively increased significantly (p<0.05) from 29.00% in cows fed with 0.5 kg of cooked rice to 69.23% in cows fed with more than 2.5 kg of cooked rice. However, the incidence of acidosis remained significantly (p<0.05) as low as 9.9% in cows fed feeding regimen without cooked rice which is suggestive of a correlation between excessive feeding cooked rice and onset of acidosis. Further, the noticeable difference in the incidence of acidosis observed between feeding cooked rice and those fed without rice and limited intake of oil cake indicates that there is a mismatch between energy and protein supply to these cattle. Among cooked rice-based diet, the incidence of laminitis increased progressively (p<0.05) from 9.2% to 37.9% with the increase in the quantum of cooked rice in the diet.

Conclusion

The study points out the importance of protein supplementation in rice-based feeding regimen to set right the mismatched supply between nitrogen and fermentable organic matter in the rumen. This research has practical implications for animal health, welfare, nutrition, and management.

Invited review: Current perspectives on eating and rumination activity in dairy cows

Many early studies laid the foundation for our understanding of the mechanics of chewing, the physiological role of chewing for the cow, and how chewing behavior is affected by dietary characteristics. However, the dairy cow has changed significantly over the past decades, as have the types of diets fed and the production systems used. The plethora of literature published in recent years provides new insights on eating and ruminating activity of dairy cows. Lactating dairy cows spend about 4.5 h/d eating (range: 2.4-8.5 h/d) and 7 h/d ruminating (range: 2.5-10.5 h/d), with a maximum total chewing time of 16 h/d. Chewing time is affected by many factors, most importantly whether access to feed is restricted, intake of neutral detergent fiber from forages, and mean particle size of the diet. Feed restriction and long particles (≥19 mm) have a greater effect on eating time, whereas intake of forage neutral detergent fiber and medium particles (4-19 mm) affects rumination time. It is well entrenched in the literature that promoting chewing increases salivary secretion of dairy cows, which helps reduce the risk of acidosis. However, the net effect of a change in chewing time on rumen buffing is likely rather small; therefore, acidosis prevention strategies need to be broad. Damage to plant tissues during mastication creates sites that provide access to fungi, adhesion of bacteria, and formation of biofilms that progressively degrade carbohydrates. Rumination and eating are the main ways in which feed is reduced in particle size. Contractions of the rumen increase during eating and ruminating activity and help move small particles to the escapable pool and into the omasum. Use of recently developed low-cost sensors that monitor chewing activity of dairy cows in commercial facilities can provide information that is helpful in management decisions, especially when combined with other criteria. Although accuracy and precision can be somewhat variable depending on sensor and conditions of use, relative changes in cow behavior, such as a marked decrease in rumination time of a cow or sustained low rumination time compared with a contemporary group of cows, can be used to help detect estrus, parturition, and some illnesses. This review provides a comprehensive understanding of the dietary, animal, and management factors that affect eating and ruminating behavior in dairy cows and presents an overview of the physiological importance of chewing with emphasis on recent developments and practical implications for feeding and managing the modern housed dairy cow.

Effect of short-chain fatty acids on the expression of genes involved in short-chain fatty acid transporters and inflammatory response in goat jejunum epithelial cells

Short-chain fatty acids (SCFAs) produced by microbial fermentation of dietary fibers are utilized by intestinal epithelial cells to provide an energy source for the ruminant. Although the regulation of mRNA expression and inflammatory response involved in SCFAs is established in other animals and tissues, the underlying mechanisms of the inflammatory response by SCFAs in goat jejunum epithelial cells (GJECs) have not been understood. Therefore, the objective of the study is to investigate the underlying mechanisms of the effects of SCFAs on SCFA transporters and inflammatory response in GJECs. These results showed that the acetate, butyrate, and SCFA concentration were markedly reduced in GJECs (p < 0.01). In addition, the propionate concentration was significantly decreased in GJECs (p < 0.05). The mRNA abundance of monocarboxylate transporter 1 (MCT1), MCT4, NHE1, and putative anion transporter 1 (PAT1) was elevated (p < 0.05) by 20 mM SCFAs at pH 7.4 compared with exposure to the pH group. The anion exchanger 2 (AE2) was increased (p < 0.05) by 20 mM SCFAs at pH 6.2. The mRNA abundance of vH⁺ ATPase B subunit (vH⁺ ATPase) was attenuated by SCFAs. For inflammatory responses, IL-1β and TNF-α were increased with SCFAs (p < 0.05). In addition, IκBα involved in NF-κB signaling pathways was disrupted by SCFAs. Consistently, p-p65 signaling molecule was enhanced by adding SCFAs. However, IL-6 was attenuated by adding SCFAs (p < 0.05). Furthermore, p-ErK1/2 mitogen-activated protein kinase (MAPK) signaling pathway was downregulated by adding SCFAs. In conclusion, these novel findings demonstrated that mRNA abundance involved in SCFA absorption is probably associated to SCFAs and pH value, and mechanism of the inflammatory response by SCFAs may be involved in NF-κB and p-ErK1/2 MAPK signaling pathways in GJECs. These pathways may mediate protective inflammation response in GJECs.

Ureases in the gastrointestinal tracts of ruminant and monogastric animals and their implication in urea-N/ammonia metabolism: A review

Urea in diets of ruminants has been investigated to substitute expensive animal and vegetable protein sources for more than a century, and has been widely incorporated in diets of ruminants for many years. Urea is also recycled to the fermentative parts of the gastrointestinal (GI) tracts through saliva or direct secretory flux from blood depending upon the dietary situations. Within the GI tracts, urea is hydrolyzed to ammonia by urease enzymes produced by GI microorganisms and subsequent ammonia utilization serves the synthesis of microbial protein. In ruminants, excessive urease activity in the rumen may lead to urea/ammonia toxicity when high amounts of urea are fed to animals; and in non-ruminants, ammonia concentrations in the GI content and milieu may cause damage to the GI mucosa, resulting in impaired nutrient absorption, futile energy and protein spillage and decreased growth performance. Relatively little attention has been directed to this area by researchers. Therefore, the present review intends to discuss current knowledge in ureolytic bacterial populations, urease activities and factors affecting them, urea metabolism by microorganisms, and the application of inhibitors of urease activity in livestock animals. The information related to the ureolytic bacteria and urease activity could be useful for improving protein utilization efficiency in ruminants and for the reduction of the ammonia concentration in GI tracts of monogastric animals. Application of recent molecular methods can be expected to provide rationales for improved strategies to modulate urease and urea dynamics in the GI tract. This would lead to improved GI health, production performance and environmental compatibility of livestock production.

Effect of ruminal acidosis and short-term low feed intake on indicators of gastrointestinal barrier function in Holstein steers

The objective of this study was to determine effect of ruminal acidosis (RA) and low feed intake [LFI] on the regional barrier function of the gastrointestinal tract. Twenty-one Holstein steers were fed for ad libitum intake for 5 d (control [CON]), fed at 25% of ad libitum intake for 5 d (LFI), or provided 2 d of ad libitum intake followed by 1-d of feed restriction (25% of ad libitum intake), 1 d where 30% of ad libitum dry matter intake (DMI) was provided as pelleted barley followed by the full allocation (RA) and fed for ad libitum intake the following day. Tissues and digesta from the rumen, omasum, duodenum, jejunum, ileum, cecum, proximal, and distal colon were collected. Permeability was assessed using the mucosal-to-serosal flux of inulin (JMS-inulin) and mannitol (JMS-mannitol). Digesta pH was 0.81, 0.63, and 0.42 pH units less for RA than CON in the rumen, cecum, and proximal colon; while, LFI had pH that was 0.47 and 0.36 pH units greater in the rumen and proximal colon compared to CON. Total ruminal short-chain fatty acid (SCFA) concentration were less for LFI (92 mM; P = 0.010) and RA (87 mM; P = 0.007) than CON (172 mM) steers. In the proximal colon, the proportion of butyrate (P = 0.025 and P = 0.022) and isobutyrate (P = 0.019 and P = 0.019) were greater, and acetate (P = 0.028 and P = 0.028) was less for LFI and RA, respectively, when compared to CON steers. Ruminal papillae length, width, perimeter, and surface area were 1.21 mm, 0.78 mm, 3.84 mm, and 11.15 mm2 less for LFI than CON; while, RA decreased papillae width by 0.52 mm relative to CON. The JMS-mannitol was less for LFI steers than CON in the proximal colon (P = 0.041) and in the distal colon (P = 0.015). Increased gene expression for claudin 1, occludin, tight-cell junction protein 1 and 2, and toll-like receptor 4 were detected for LFI relative to CON in the rumen, jejunum, and proximal colon. For RA steers, expression of toll-like receptor 4 in the rumen, and occludin and tight-cell junction protein 1 were greater in the jejunum than CON. An acute RA challenge decreased pH in the rumen and large intestine but did not increase tissue permeability due to increases in the expression of genes related to barrier function within 1 d of the challenge. Steers exposed to LFI for 5 d had reduced ruminal SCFA concentrations, smaller ruminal papillae dimensions, and increased tissue permeability in the proximal and distal colon despite increases for genes related to barrier function and immune function.

Invited review: Mineral absorption mechanisms, mineral interactions that affect acid-base and antioxidant status, and diet considerations to improve mineral status

Several minerals are required for life to exist. In animals, 7 elements (Ca, P, Mg, Na, K, Cl, and S) are required to be present in the diet in fairly large amounts (grams to tens of grams each day for the dairy cow) and are termed macrominerals. Several other elements are termed microminerals or trace minerals because they are required in much smaller amounts (milligrams to micrograms each day). In most cases the mineral in the diet must be absorbed across the gastrointestinal mucosa and enter the blood if it is to be of value to the animal. The bulk of this review discusses the paracellular and transcellular mechanisms used by the gastrointestinal tract to absorb each of the various minerals needed. Unfortunately, particularly in ruminants, interactions between minerals and other substances within the diet can occur within the digestive tract that impair mineral absorption. The attributes of organic or chelated minerals that might permit diet minerals to circumvent factors that inhibit absorption of more traditional inorganic forms of these minerals are discussed. Once absorbed, minerals are used in many ways. One focus of this review is the effect macrominerals have on the acid-base status of the animal. Manipulation of dietary cation and anion content is commonly used as a tool in the dry period and during lactation to improve performance. A section on how the strong ion theory can be used to understand these effects is included. Many microminerals play a role in the body as cofactors of enzymes involved in controlling free radicals within the body and are vital to antioxidant capabilities. Those same minerals, when consumed in excess, can become pro-oxidants in the body, generating destructive free radicals. Complex interactions between minerals can compromise the effectiveness of a diet in promoting health and productivity of the cow. The objective of this review is to provide insight into some of these mechanisms.

Comparative assessment of probiotics and monensin in the prophylaxis of acute ruminal lactic acidosis in sheep

Background

Acute ruminal lactic acidosis (ARLA) is a major nutritional and metabolic disorder usually characterized by excessive or non-adapted intake of diets rich in nonstructural carbohydrates. Feed additives that regulate the ruminal environment have been used to prevent ARLA, such as ionophores and, more recently, yeast culture. Thus, we aimed to compare the efficacy of a yeast-based culture (Saccharomyces cerevisiae) with that of monensin sodium in the prevention of ARLA in sheep. Eighteen male, crossbred, rumen-cannulated sheep were randomly distributed into three groups of six animals: control, yeast culture and monensin. Thirty days after the start of supplementation with yeast culture (4 × 10⁹ cfu/animal/day of S. cerevisiae) and monensin (33 mg/kg of total dry matter intake), 15 g/kg BW of sucrose was administered directly into the rumen of the animals to induce ARLA. Samples of blood and ruminal fluid were collected at the following time points: at baseline (T0 h) immediately before the induction of ARLA; 6 h (T6 h); 12 h (T12 h); 18 h (T18 h); 24 h (T24 h); 36 h (T36 h); and 48 h (T48 h) after ARLA induction.

Results

Ruminal pH was higher in monensin group at T12 h and in yeast culture group at T36 h when compared to control group. Lower values of L-Lactate were found at yeast culture group at T24 h and T36 h. Monensin showed prophylactic effect by decreasing the rate of ruminal pH decline and occasionally reducing ruminal acidosis, whereas probiotics resulted in less accumulation of lactic acid in the rumen and a lower degree of systemic acidosis.

Conclusion

The use of yeast culture can be beneficial in the prevention and treatment of ARLA in sheep, because it can effectively reduce the accumulation of lactic acid, and thereby increase ruminal pH and reduce ruminal osmolarity. On the other hand, monensin showed prophylactic effect by decreasing the rate of ruminal pH decline and occasionally reducing ruminal acidosis, however, it did not directly prevent these conditions.

A look at the smelly side of physiology: transport of short chain fatty acids

Fermentative organs such as the caecum, the colon, and the rumen have evolved to produce and absorb energy rich short chain fatty acids (SCFA) from otherwise indigestible substrates. Classical models postulate diffusional uptake of the undissociated acid (HSCFA). However, in net terms, a major part of SCFA absorption occurs with uptake of Na⁺ and resembles classical, coupled electroneutral NaCl transport. Considerable evidence suggests that the anion transporting proteins expressed by epithelia of fermentative organs are poorly selective and that their main function may be to transport acetate^-, propionate^-, butyrate^- and HCO₃^- as the physiologically relevant anions. Apical uptake of SCFA thus involves non-saturable diffusion of the undissociated acid (HSCFA), SCFA^-/HCO₃^- exchange via DRA (SLC26A3) and/or SCFA^--H⁺ symport (MCT1, SLC16A1). All mechanisms lead to cytosolic acidification with stimulation of Na⁺/H⁺ exchange via NHE (SLC9A2/3). Basolaterally, Na⁺ leaves via the Na⁺/K⁺-ATPase with recirculation of K⁺. Na⁺ efflux drives the transport of SCFA^- anions through volume-regulated anion channels, such as maxi-anion channels (possibly SLCO2A1), LRRC8, anoctamins, or uncoupled exchangers. When luminal buffering is inadequate, basolateral efflux will increasingly involve SCFA^-/ HCO₃^- exchange (AE1/2, SCL4A1/2), or efflux of SCFA^- with H⁺ (MCT1/4, SLC16A1/3). Furthermore, protons can be basolaterally removed by NHE1 (SCL9A1) or NBCe1 (SLC4A4). The purpose of these transport proteins is to maximize the amount of SCFA transported from the tightly buffered ingesta while minimizing acid transport through the epithelium. As known from the rumen for many decades, a disturbance of these processes is likely to cause severe colonic disease.

Improving ruminal fermentation and nutrient digestibility in dairy steers by banana flower powder-pellet supplementation

The present study aimed to investigate the effect of banana flower powder pellet (BAFLOP pellet) on nutrient digestibility, rumen ecology and microorganism population. Four rumen-fistulated dairy steers of 200 ± 20 kg bodyweight were randomly assigned to receive four dietary treatments according to a 4 × 4 Latin square design. The treatments were as follows: control (T1), NaHCO3 supplementation at 20 g/kg of total dry-matter feed intake (DMI; T2), BAFLOP-pellet supplementation at 20 g/kg of DMI (T3) and BAFLOP-pellet supplementation at 40 g/kg of DMI (T4). All cattle were fed roughage–concentrate mix (30 : 70 ratio) at 25 g/kg bodyweight. Standard management protocols were employed during the experimental periods. The results showed that nutrient digestibility was increased in steers supplemented with NaHCO3 and BAFLOP pellets at 40 g/kg DMI (P < 0.05). Although ruminal temperature and blood urea nitrogen were not influenced by dietary supplementation, ruminal pH was increased (P < 0.05) in steers supplemented with NaHCO3 and BAFLOP pellets at 40 g/kg DMI. In addition, NaHCO3 supplementation increased bacterial and protozoal populations, whereas populations of fungal zoospores were similar among treatments. Supplementation with BAFLOP pellets at 40 g/kg DMI increased the bacterial count, whereas protozoal numbers were similar to those in the control group (P < 0.05). On the basis of the present findings, BAFLOP-pellet supplementation improved nutrient digestibility, ruminal pH and microbial population, without having any adverse effects on voluntary feed intake. The present study showed promising results for BAFLOP pellets (40 g/kg DMI) as a rumen dietary buffering agent, suggesting that these pellets could be used a replacement for sodium bicarbonate in ruminants fed high-concentrate diets.

Transcriptome analysis of ruminal epithelia revealed potential regulatory mechanisms involved in host adaptation to gradual high fermentable dietary transition in beef cattle

Background

The transition from a high forage to a highly fermentable diet can induce digestive disorders in the rumen. To date, the host mechanisms that regulate the adaption to such dietary transition are largely unknown. To understand the molecular mechanisms involved in such phenomena, RNA-sequencing was performed to identify the changes in the transcriptome of ruminal epithelia during gradual transition from a diet containing 0% to 89% grain.

Results

In total, the expression of 11,044, 11,322 and 11,282 genes were detected in ruminal epithelia of beef heifers (n = 15) fed 0%, 72% and 89% barley grain diet, respectively. The transcriptome profiles of rumen epithelia differed between low grain diet (LGD) (0% grain) and high grain diet (HGD) (72% and 89%), and HGD tended to reduce the expression of genes involved in epithelial catalytic and binding activities. When diet was changed from 72% to 89% grain, the mean ruminal pH change was significantly different among individual heifers with five of them decreased (down group (DG); from 6.30±0.09 to 5.87±0.15, P < 0.01) and five of them increased (up group (UG); from 5.84±0.42 to 6.35±0.37, P < 0.05). The functional analysis of differentially expressed (DE) genes revealed inhibited “Immune response of leukocytes”, “Attraction of phagocytes”, and “Cell movement of leukocytes” (P < 0.05) functions (Z-score = −2.2, −2.2 and −2.0, respectively) in DG, and inhibited “Concentration of lipid” and “Proliferation of epithelial cells” functions in UG (Z-score = −2.0, and −1.8, respectively). In addition, the expression of genes involved in ketogenesis (HMGCL) and lipid synthesis (SREBF2, FABP4) was increased in DG, while the expression of ketogenesis (ACAT2, HMGCS) and cholesterol synthesis related genes (HMGC and FDPS) were deceased in UG. Furthermore, the upstream regulators were found to be involved in the regulation of immune response and cell cycle progress, and SNP (g.46834311A > G) in FABP4 was identified between two groups of animals (P < 0.1).

Conclusion

The identified genes, upstream regulators, and SNP could be potential genetic markers that may account for the varied individual ruminal pH responses to the dietary transition stress.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4317-y) contains supplementary material, which is available to authorized users.

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).

Short-Chain Fatty Acid Transporters: Role in Colonic Homeostasis

Short-chain fatty acids (SCFA; acetate, propionate, and butyrate) are generated in colon by bacterial fermentation of dietary fiber. Though diffusion in protonated form is a significant route, carrier-mediated mechanisms constitute the major route for the entry of SCFA in their anionic form into colonic epithelium. Several transport systems operate in cellular uptake of SCFA. MCT1 (SLC16A1) and MCT4 (SLC16A3) are H+-coupled and mediate electroneutral transport of SCFA (H+: SCFA stoichiometry; 1:1). MCT1 is expressed both in the apical membrane and basolateral membrane of colonic epithelium whereas MCT4 specifically in the basolateral membrane. SMCT1 (SLC5A8) and SMCT2 (SLC5A12) are Na+-coupled; SMCT1-mediated transport is electrogenic (Na+: SCFA stoichiometry; 2:1) whereas SMCT2-mediated transport is electroneutral (Na+: SCFA stoichiometry; 1:1). SMCT1 and SMCT2 are expressed exclusively in the apical membrane. An anion-exchange mechanism also operates in the apical membrane in which SCFA entry in anionic form is coupled to bicarbonate efflux; the molecular identity of this exchanger however remains unknown. All these transporters are subject to regulation, notably by their substrates themselves; this process involves cell-surface receptors with SCFA as signaling molecules. There are significant alterations in the expression of these transporters in ulcerative colitis and colon cancer. The tumor-associated changes occur via transcriptional regulation by p53 and HIF1α and by promoter methylation. As SCFA are obligatory for optimal colonic health, the transporters responsible for the entry and transcellular transfer of these bacterial products in colonic epithelium are critical determinants of colonic function under physiological conditions and in disease states. © 2018 American Physiological Society. Compr Physiol 8:299-314, 2018.

The effect of different physical forms of starter feed on rumen fermentation indicators and weight gain in calves after weaning

The aim of the study was to determine the effect of different physical forms of starter feed on rumen fermentation indicators of calves after weaning and their weight gain. The experiment was performed with Czech Fleckvieh calves after weaning. The calves were fed ad libitum completely pelleted starter feed or texturized starter feed with chopped straw. The rumen fluid samples were collected after a month of feeding the starter feeds. The calves were weighed monthly. The pH, total acidity, total volatile fatty acids, acetate, propionate, butyrate, lactic acid, ammonia and the number of rumen ciliate protozoa were determined in the rumen fluid samples. The calves receiving the starter feed with straw showed significantly higher rumen pH (6.24 ± 0.51 vs. 5.58 ± 0.30), total volatile fatty acids (98.02 ± 20.46 vs. 61.40 ± 26.51 mmol/l), molar proportion of acetate (61.20 ± 4.87 vs. 50.53 ± 4.66%), and the acetate:propionate ratio (2.38 ± 0.53 vs. 1.34 ± 0.18) and lower molar proportion of propionate (26.55 ± 4.48 vs. 37.92 ± 3.58%) compared with the calves receiving pelleted starter feed. Average daily gain of the calves did not differ significantly. The feeding of starter feed with chopped straw compared with the pelleted starter feed led to better development of the rumen fermentation evaluated by rumen pH, by total volatile fatty acids production, and by the proportion and ratio of acetic and propionic acids. The feeding of starter feed with chopped straw reduced the occurrence of subacute ruminal acidosis in the weaned calves.

Invited review: Practical feeding management recommendations to mitigate the risk of subacute ruminal acidosis in dairy cattle

Rumen health is of vital importance in ensuring healthy and efficient dairy cattle production. Current feeding programs for cattle recommend concentrate-rich diets to meet the high nutritional needs of cows during lactation and enhance cost-efficiency. These diets, however, can impair rumen health. The term "subacute ruminal acidosis" (SARA) is often used as a synonym for poor rumen health. In this review, we first describe the physiological demands of cattle for dietary physically effective fiber. We also provide background information on the importance of enhancing salivary secretions and short-chain fatty acid absorption across the stratified squamous epithelium of the rumen; thus, preventing the disruption of the ruminal acid-base balance, a process that paves the way for acidification of the rumen. On-farm evaluation of dietary fiber adequacy is challenging for both nutritionists and veterinarians; therefore, this review provides practical recommendations on how to evaluate the physical effectiveness of the diet based on differences in particle size distribution, fiber content, and the type of concentrate fed, both when the latter is part of total mixed ration and when it is supplemented in partial mixed rations. Besides considering the absolute amount of physically effective fiber and starch types in the diet, we highlight the role of several feeding management factors that affect rumen health and should be considered to control and mitigate SARA. Most importantly, transitional feeding to ensure gradual adaptation of the ruminal epithelium and microbiota; monitoring and careful management of particle size distribution; controlling feed sorting, meal size, and meal frequency; and paying special attention to primiparous cows are some of the feeding management tools that can help in sustaining rumen health in high-producing dairy herds. Supplementation of feed additives including yeast products, phytogenic compounds, and buffers may help attenuate SARA, especially during stress periods when the risk of a deficiency of physically effective fiber in the diet is high, such as during early lactation. However, the usage of feed additives cannot fully compensate for suboptimal feeding management.

Increases in the expression of Na+ /H+ exchanger 1 and 3 are associated with insulin signalling in the ruminal epithelium

Na⁺ /H⁺ exchanger (NHE), which catalyses the exchange of extracellular Na⁺ for intracellular H⁺ , is of importance in the maintenance of Na⁺ and pH homoeostasis for rumen epithelial cells. Studies in ruminants showed that high concentrate diets could increase the expression of NHE in ruminal epithelium. Results of recent studies further indicated that insulin, as an important hormone closely related to dietary concentrate, could enhance the expression of NHE. In this study, we have investigated the mechanisms of insulin regulating the expression of NHE in rumen epithelial cells and its potential role in dietary modulation of NHE expression in ruminal epithelium of cows. In primary culture, insulin increased phosphorylation of ERK 1/2 and AKT in rumen epithelial cells. However, this promotion was diminished by insulin receptor inhibitor. Insulin also stimulated NHE1 and NHE3 expression. But this increase was suppressed by insulin receptor inhibitor, ERK inhibitor and AKT inhibitor. In the present animal experiment, NHE1 and NHE3 expression increased in rumen epithelium of cows ingesting a high concentrate diet (HC, 60% concentrate), accompanied by increased insulin concentration in plasma, compared to those feeding a low concentrate diet (LC, 20% concentrate). Furthermore, the phosphorylation of ERK1/2 and AKT was higher in the rumen epithelium of the HC group than those in the LC group. Collectively, these results indicate that diet-dependent change of NHE1 and NHE3 abundance was mediated, at least in part, by plasma insulin through the ERK and AKT pathway.

Physically adjusted neutral detergent fiber system for lactating dairy cow rations. II: Development of feeding recommendations

The objective of this work was to leverage equations derived in a meta-analysis into an ensemble modeling system for estimating dietary physical and chemical characteristics required to maintain desired rumen conditions in lactating dairy cattle. Given the availability of data, responsiveness of ruminal pH to animal behaviors, and the chemical composition and physical form of the diet, mean ruminal pH was chosen as the primary rumen environment indicator. Physically effective fiber (peNDF) is defined as the fraction of neutral detergent fiber (NDF) that stimulates chewing activity and contributes to the floating mat of large particles in the rumen. The peNDF of feedstuffs is typically estimated by multiplying the NDF content by a particle size measure, resulting in an estimated index of effectiveness. We hypothesized that the utility of peNDF could be expanded and improved by dissociating NDF and particle size and considering other dietary factors, all integrated into a physically adjusted fiber system that can be used to estimate minimum particle sizes of TMR and diet compositions needed to maintain ruminal pH targets. Particle size measures of TMR were limited to those found with the Penn State particle separator (PSPS). Starting with specific diet characteristics, the system employed an ensemble of models that were integrated using a variable mixture of experts approach to generate more robust recommendations for the percentage of dietary DM material that should be retained on the 8-mm sieve of a PSPS. Additional continuous variables also integrated in the physically adjusted fiber system include the proportion of material (dry matter basis) retained on the 19- and 8-mm sieves of the PSPS, estimated mean particle size, the dietary concentrations of forage, forage NDF, starch, and NDF, and ruminally degraded starch and NDF. The system was able to predict that the minimum proportion of material (dry matter basis) retained on the 8-mm sieve should increase with decreasing forage NDF or dietary NDF. Additionally, the minimum proportion of dry matter material on the 8-mm sieve should increase with increasing dietary starch. Results of this study agreed with described interrelationships between the chemical and physical form of diets fed to dairy cows and quantified the links between NDF intake, diet particle size, and ruminal pH. Feeding recommendations can be interpolated from tables and figures included in this work.

Growth performance, rumen fermentation, bacteria composition, and gene expressions involved in intracellular pH regulation of rumen epithelium in finishing Hu lambs differing in residual feed intake phenotype

The objective of this study was to evaluate the effect of residual feed intake (RFI) on rumen function in finishing lambs. A total of 60 male Hu lambs (average initial BW = 25.2 ± 2.5kg) were used and were offered a pelleted high-concentrate diet, of which the forage to concentrate ratio was 25:75. Individual feed intake was recorded over a period of 42 d, then 10 lambs with the lowest RFI and the highest RFI were selected, respectively. The rumen fluid used for fermentation variables and relative abundance of bacteria measurement was obtained on d 10 and 20 after RFI measurement. At the end of this experiment, the selected lambs were slaughtered and rumen epithelium and liver tissues were collected for RNA extraction. Low-RFI lambs had lower ( < 0.01) DMI and greater ( < 0.05) G:F than the high-RFI ones, while the RFI groups did not differ in ADG and BW ( > 0.05). Additionally, RFI was positively ( = 0.57; < 0.01) correlated with DMI and negatively ( = -0.53; < 0.05) correlated with G:F. Total VFA and individual VFA decreased ( < 0.05) over time. The concentrations of total VFA, acetate, valerate, isobutyrate, isovalerate, and rumen pH ( > 0.05) were not affected by RFI classification. Nonetheless, low-RFI group lambs had a greater ( < 0.05) concentration of propionate, a lower ( < 0.05) concentration of butyrate, and a lower ( < 0.05) acetate to propionate ratio compared with the high-RFI group. There was a significant ( < 0.05) effect of RFI on the relative abundance of and . The relative abundance of , , and decreased ( < 0.05) over time in high-RFI group. And the relative abundance of in high-RFI group was greater ( < 0.05) than its low-RFI counterpart. Furthermore, RFI had no effect ( > 0.05) on gene expression associated with intracellular pH regulation (, , , , , , , and ) in rumen epithelium and β-hydroxybutyrate metabolism () in both rumen epithelium and liver tissues. In conclusion, even though low-RFI lambs had lower DMI, however, the number of was lower. Additionally, there was no difference in gene expressions level associated with intracellular pH regulation in rumen epithelium between RFI groups.

Effects of dissolved carbon dioxide on the integrity of the rumen epithelium: An agent in the development of ruminal acidosis

The carbon dioxide released and dissolved in rumen fluid may easily permeate across the epithelial cell membrane. Thus, we hypothesized that CO₂ may act as proton carrier and induce epithelial damage under acidotic conditions. Ovine ruminal epithelia were mounted in Ussing chambers under short-circuit conditions. The serosal buffer solution had a constant pH of 7.4 and was gassed either with 100% oxygen or with carbogen (95% O₂ /5% CO₂ ). The mucosal solution was gassed with either 100% oxygen or 100% carbon dioxide. The mucosal pH was lowered stepwise from 6.6 to 5.0 in the presence or absence of short-chain fatty acids (SCFA). The transepithelial conductance (G_t ) as an indicator of epithelial integrity and the short-circuit current (I_sc ) as an indicator of active electrogenic ion transfer were continuously monitored. At an initial mucosal pH of 6.6, there was no significant difference in G_t between the treatment groups. In the absence of both SCFA and CO₂ , G_t remained constant when the mucosal solution was acidified to pH 5.0. In the presence of SCFA, mucosal acidification induced a significant rise in G_t when the solutions were gassed with oxygen. A small increase in G_t was observed in the mucosal presence of CO₂ . However, no difference in final G_t was observed between SCFA-containing and SCFA-free conditions under carbon dioxide gassing during stepwise mucosal acidification. The SCFA+proton-induced increase in G_t could also be minimized by serosal gassing with carbogen. Because of the SCFA+proton-induced changes in G_t and their attenuation by CO₂ , a protective role for mucosally available carbon dioxide may be assumed. We suggest that this effect may be due to the intraepithelial conversion of carbon dioxide to bicarbonate. However, the serosal presence of CO₂ at a physiological concentration may be sufficient to protect the epithelia from SCFA+proton-induced damage for a certain period of time.

Generation and Characterization of Acid Tolerant Fibrobacter succinogenes S85

Microorganisms are key components for plant biomass breakdown within rumen environments. Fibrobacter succinogenes have been identified as being active and dominant cellulolytic members of the rumen. In this study, F. succinogenes type strain S85 was adapted for steady state growth in continuous culture at pH 5.75 and confirmed to grow in the range of pH 5.60–5.65, which is lower than has been reported previously. Wild type and acid tolerant strains digested corn stover with equal efficiency in batch culture at low pH. RNA-seq analysis revealed 268 and 829 genes were differentially expressed at pH 6.10 and 5.65 compared to pH 6.70, respectively. Resequencing analysis identified seven single nucleotide polymorphisms (SNPs) in the sufD, yidE, xylE, rlmM, mscL and dosC genes of acid tolerant strains. Due to the absence of a F. succinogenes genetic system, homologues in Escherichia coli were mutated and complemented and the resulting strains were assayed for acid survival. Complementation with wild-type or acid tolerant F. succinogenes sufD restored E. coli wild-type levels of acid tolerance, suggesting a possible role in acid homeostasis. Recent genetic engineering developments need to be adapted and applied in F. succinogenes to further our understanding of this bacterium.

Effect of increasing the proportion of dietary concentrate on gastrointestinal tract measurements and brush border enzyme activity in Holstein steers

The aim of this study was to determine the time course for adaptation of the reticulo-rumen, omasum, abomasum, and small intestine in response to an abrupt increase in the proportion of grain in the diet. Adaptive responses include tissue and digesta mass, small intestinal length, and brush border enzyme activity in the duodenum, proximal jejunum, and ileum. Twenty-five Holstein steers (213 ± 23 kg; 5 to 7 mo of age) were blocked by body weight, and within block were randomly assigned to 1 of 5 treatments: the control diet (CTRL; 92% chopped grass hay and 8% mineral and vitamin supplement on a dry matter basis) or a moderate grain diet (MGD; 50% chopped grass hay, 42% rolled barley grain, and 8% mineral and vitamin supplement) that was fed for 3 (MGD3), 7 (MGD7), 14 (MGD14), or 21 d (MGD21). Dry matter intake was limited to 2.25% of body weight to ensure that changes in dry matter intake did not confound the results. On the last day of the dietary exposure, steers were slaughtered 2 h after feeding. Reticulo-rumen tissue mass and ruminal epithelium mass in the ventral sac of the rumen were not affected by the MGD. Wet reticulo-ruminal digesta mass decreased from CTRL to MGD7 and then increased, but reticulo-ruminal digesta dry matter mass did not differ between treatments. Omasal mass, omasal tissue mass, and omasum digesta mass decreased linearly with the number of days fed MGD, but abomasal tissue mass tended to increase linearly. Duodenal tissue mass tended to increase linearly, and ileal length increased linearly with the number of days fed MGD. Lactase activity in the proximal jejunum increased linearly and maltase activity in duodenum tended to increase linearly with days fed MGD. Aminopeptidase N activity in the proximal jejunum increased cubically with days fed MGD, and dipeptidylpeptidase IV activity in ileum tended to decrease from CTRL to MGD14 and then tended to increase. Adaptation to a diet with a greater proportion of concentrate involves changes in the mass and length of regions of the gastrointestinal tract and brush border enzyme activity. These changes take place gradually over at least 3 wk.

Review: Sugar beets as a substitute for grain for lactating dairy cattle

Dairy cows are customarily given grains and highly digestible byproduct ingredients as additions to forage to support milk production. In many parts of the world growing seasons are short, and the grain crops that can be grown may not provide adequate yields. Sugar beets, on the other hand are relatively hardy, and dry matter yields surpass the yields of most grain crops. There are however, perceptions that beets may not be suitable as a feed ingredient due to the fact that the storage form of carbohydrate is sugar rather than starch. With little analytical support, sugar has been rejected in many feeding programs with the view that sugar reduces rumen pH, fiber digestion and microbial yield. This review explores available facts revolving around these concerns. Information regarding the feeding of sugar beets is provided and the use of sugar beets as a partial replacement for grain is proposed.

Sodium Butyrate Ameliorates High-Concentrate Diet-Induced Inflammation in the Rumen Epithelium of Dairy Goats

To investigate the effect of sodium butyrate on high-concentrate diet-induced local inflammation of the rumen epithelium, 18 midlactating dairy goats were randomly assigned to 3 groups: a low-concentrate diet group as the control (concentrate:forage = 4:6), a high-concentrate (HC) diet group (concentrate:forage = 6:4), and a sodium butyrate (SB) group (concentrate:forage = 6:4, with 1% SB by weight). The results showed that, with the addition of sodium butyrate, the concentration of lipopolysaccharide (LPS) in rumen fluid (2.62 × 10⁴ ± 2.90 × 10³ EU/mL) was significantly lower than that in the HC group (4.03 × 10⁴ ± 2.77 × 10³ EU/mL). The protein abundance of pp65, gene expression of proinflammatory cytokines, and activity of myeloperoxidase (MPO) and matrix metalloproteinase (MMP)-2,9 in the rumen epithelium were significantly down-regulated by SB compared with those in the HC group. With sodium butyrate administration, the concentration of NH3-N (19.2 ± 0.890 mM) in the rumen fluid was significantly higher than that for the HC group (12.7 ± 1.38 mM). Severe disruption of the rumen epithelium induced by HC was also ameliorated by dietary SB. Therefore, local inflammation and disruption of the rumen epithelium induced by HC were alleviated with SB administration.

Epimural bacterial community structure in the rumen of Holstein cows with different responses to a long-term subacute ruminal acidosis diet challenge

Subacute ruminal acidosis (SARA) is a prevalent metabolic disorder in cattle, characterized by intermittent drops in ruminal pH. This study investigated the effect of a gradual adaptation and continuously induced long-term SARA challenge diet on the epimural bacterial community structure in the rumen of cows. Eight rumen-cannulated nonlactating Holstein cows were transitioned over 1 wk from a forage-based baseline feeding diet (grass silage-hay mix) to a SARA challenge diet, which they were fed for 4 wk. The SARA challenge diet consisted of 60% concentrates (dry matter basis) and 40% grass silage-hay mix. Rumen papillae biopsies were taken at the baseline, on the last day of the 1-wk adaptation, and on the last day of the 4-wk SARA challenge period; ruminal pH was measured using wireless sensors. We isolated DNA from papillae samples for 16S rRNA gene amplicon sequencing using Illumina MiSeq. Sequencing results of most abundant key phylotypes were confirmed by quantitative PCR. Although they were fed similar amounts of concentrate, cows responded differently in terms of ruminal pH during the SARA feeding challenge. Cows were therefore classified as responders (n = 4) and nonresponders (n = 4): only responders met the SARA criterion of a ruminal pH drop below 5.8 for longer than 330 min/d. Data showed that Proteobacteria, Firmicutes, and Bacteroidetes were the most abundant phyla, and at genus level, Campylobacter and Kingella showed highest relative abundance, at 15.5 and 7.8%, respectively. Diversity analyses revealed a significant increase of diversity after the 1-wk adaptation but a decrease of diversity and species richness after the 4-wk SARA feeding challenge, although without distinction between responders and nonresponders. At the level of the operational taxonomic unit, we detected diet-specific shifts in epimural community structure, but in the overall epimural bacterial community structure, we found no differences between responders and nonresponders. Correlation analysis revealed significant associations between grain intake and operational taxonomic unit abundance. The study revealed major shifts in the 3 dominating phyla and, most importantly, a loss of diversity in the epimural bacterial communities during a long-term SARA diet challenge, in which 60% concentrate supply for 4 wk was instrumental rather than the magnitude of the drop of ruminal pH below 5.8.

Intramammary infusion of Escherichia coli lipopolysaccharide negatively affects feed intake, chewing, and clinical variables, but some effects are stronger in cows experiencing subacute rumen acidosis

Feeding high-grain diets increases the risk of subacute rumen acidosis (SARA) and adversely affects rumen health. This condition might impair the responsiveness of cows when they are exposed to external infectious stimuli such as lipopolysaccharide (LPS). The main objective of this study was to evaluate various responses to intramammary LPS infusion in healthy dairy cows and those experimentally subjected to SARA. Eighteen early-lactating Simmental cows were subjected to SARA (n = 12) or control (CON; n = 6) feeding conditions. Cows of the control group received a diet containing 40% concentrates (DM basis) throughout the experiment. The intermittent SARA feeding regimen consisted in feeding the cows a ration with 60% concentrate (DM basis) for 32 d, consisting of a first SARA induction for 8 d, switched to the CON diet for 7 d, and re-induction during the last 17 d. On d 30 of the experiment, 6 SARA (SARA-LPS) and 6 CON (CON-LPS) cows were intramammary challenged once with a single dose of 50 μg of LPS from Escherichia coli (O26:B6), whereas the other 6 SARA cows (SARA-PLA) received 10 mL of sterile saline solution as placebo. To confirm the induction of SARA, the reticular pH was continuously monitored via wireless pH probes. The DMI remained unchanged between SARA and CON cows during the feeding experiment, but was reduced in both treatment groups receiving the LPS infusion compared with SARA-PLA, whereby a significant decline was observed for cows of the SARA-LPS treatment (-38%) compared with CON-LPS (-19%). The LPS infusion did not affect the reticuloruminal pH dynamics, but significantly enhanced ruminal temperature and negatively affected chewing behavior. The ruminal temperature increased after the LPS infusion and peaked about 1 h earlier in SARA-LPS cows compared with the cows of the CON-LPS treatment. Moreover, a significant decline in milk yield was found in SARA-LPS compared with CON-LPS following the LPS infusion. Cows receiving LPS had elevated somatic cell counts, protein, and fat contents in milk as well as decreased lactose contents and pH following the LPS infusion, whereby the changes in milk constituents were more pronounced in SARA-LPS than CON-LPS cows. Rectal temperature and pulse rate were highest 6 h after LPS infusion, but rumen contractions were not affected by the LPS infusion. The data suggest that a single intramammary LPS infusion induced fever and negatively affected feed intake, chewing activity, rectal temperature, and milk yield and composition, whereby these effects were more pronounced in SARA cows.

Rapid Fermentable Substance Modulates Interactions between Ruminal Commensals and Toll-Like Receptors in Promotion of Immune Tolerance of Goat Rumen

Whether dietary non-fiber carbohydrate (NFC), a rapid fermentable substance, affects immune homeostasis of rumen through the modulation of interactions of ruminal microbiota and epithelial toll-like receptors (TLRs) remains unclear. A combination of 16S rRNA amplicon sequencing and quantitative PCRs was applied to study the synergetic responses of ruminal microbiota and epithelial TLRs to the dietary NFC switch from 15 to 31% in the goat model. The results showed that the 31% NFC diet caused the radical increases on the richness and diversity of rumen microbiota. The phylum Verrucomicrobia was most significantly expanded, whereas opportunistic pathogens, namely Rikenella, Anaeroplasma, and Olsenella, were significantly decreased. In rumen epithelium, the significantly increased expressions of TLR1, 6, 10 were associated with the significantly decreased expressions of pro-inflammatory cytokines interleukin-1beta (IL-1ß), IL-6, and anti-inflammatory cytokine IL-10. Constrained correlation analysis indicated that the increased abundance of commensal bacteria in Verrucomicrobia subdivision 5 contributed to the upregulation of TLR10 expression. Finally, the significantly increased concentrations of rumen short-chain fatty acids (SCFAs), coupled with the significantly upregulated expressions of epithelial genes related to SCFA absorption were observed in goats fed with 31% NFC diet. Thus, the NFC-induced expansion of rumen microbiota promoted epithelium tolerance by enhancement of the intensity of TLR10 signaling. The newly established equilibrium benefited to the transport of ruminal energy substances into the blood.