The effects of ruminal acidosis on volatile fatty acid absorption and plasma activities of pancreatic enzymes in lambs

Influence of vasoactive intestinal polypeptide on growth performance, nutrient digestibility, nitrogen balance, and digestive enzyme activity in lambs

This study evaluated if vasoactive intestinal polypeptide (VIP) influences growth performance, nutrient digestibility, nitrogen balance, and digestive enzyme activity. Sixteen wether lambs (69.6 ± 1.9 kg) were housed in individual pens, adapted to a corn grain-based diet, and randomly assigned to 2 treatment groups. Lambs were injected intraperitoneally every other day for 28 d with saline (0.9% NaCl) containing no VIP (n = 8; control) or containing VIP (n = 8; 1.3 nmol/kg body weight [BW]). All lambs were transferred to individual metabolic crates for the final 7 d of the experiment to measure nitrogen balance and nutrient digestibility. At the end of the treatment period, lambs were slaughtered, and pancreatic tissue, small intestinal tissue, and rumen fluid were collected for protein, digestive enzymes, ruminal pH, and volatile fatty acid (VFA) analyses. Lambs treated with VIP had greater final BW, average daily gain, and gain:feed (P = 0.01, 0.05, 0.03, respectively). No differences between treatment groups were observed (P ≥ 0.25) for nutrient intake, digestibility, nitrogen retention, ruminal pH, and VFA concentrations. Moreover, VIP treatment did not influence (P ≥ 0.19) plasma glucose, urea N, and insulin concentrations. Treatment with VIP increased (P = 0.03) relative cecum weight (g/kg BW) and decreased (P = 0.05) relative brain weight. Pancreatic and intestinal digestive enzyme activities, except for duodenal maltase (P = 0.02), were not influenced (P ≥ 0.09) by VIP treatment. These data suggest that the administration of VIP may have potential to improve average daily gain and gain:feed in lambs fed grain-based diets.

Thiamine modulates intestinal morphological structure and microbiota under subacute ruminal acidosis induced by a high-concentrate diet in Saanen goats

Ruminant animals are generally fed with starch-rich grain as the main energy source, and the incidence of metabolic diseases such as subacute ruminal acidosis (SARA) is high due to the intensive farming. Thiamin has been reported to alleviate SARA caused by high-concentrate diets, but the exact mechanism is not well understood. The goal of this study was to examine the role of thiamine in intestinal inflammation and microbiota caused by high-concentrate diets. The SARA model was induced by low neutral detergent fibre/starch ration to study the effects of thiamine on intestinal tissue structure and microbiota. 18 mid-lactation (148 ± 3 d in milk; milk yield = 0.71 ± 0.0300 kg/d) Saanen goats (BW = 36.5 ± 1.99 kg; body condition score = 2.73 ± 0.16, where 1 = emaciated and 6 = obese) in parities 1 or 2 were selected. The goats were randomly divided into three groups with six replicates: (1) control diet (C; concentrate:forage 30:70), (2) high-concentrate diet (H; concentrate:forage 70:30), and (3) high-concentrate diet with 200 mg of thiamine/kg of DM intake (H + T;concentrate:forage 70:30). The experimental period was lasted for 56 d. The small and large intestine, expression of inflammatory factor genes, tight junction protein genes, total antioxidant capacity, and intestinal microbiota were measured. The results showed that SARA was observed in treatment H, whereas rumen fluid pH was improved in treatment H + T. Treatment H + T also significantly repaired the intestinal tissue structure damaged by SARA, improved the total antioxidant capacity of the small intestinal mucosa, reduced mRNA expression of inflammatory factors in the small intestine tissue, and increased the mRNA expression of tight junction genes in small intestine tissue. The high-concentrate diet reduced the diversity of intestinal microbiota. When thiamine is added to the high-concentrate diet, the relative abundance of intestinal Firmicutes and beneficial bacteria represented by Lactobacilli were upregulated, and the relative abundance of Proteus, a marker of intestinal dysbacteriosis, returned to normal. In conclusion, thiamine supplementation could alleviate the damage to the intestinal tissue structure and microbial environment caused by SARA condition in dairy goats fed a high-concentrate diet.

Diagnosis and Management of Rumen Acidosis and Bloat in Feedlots

Ruminal acidosis and ruminal bloat represent the most common digestive disorders in feedlot cattle. Ruminants are uniquely adapted to digest and metabolize a large range of feedstuffs. Although cattle have the ability to handle various feedstuffs, disorders associated with altered ruminal fermentation can occur. Proper ruminal microorganism adaptation and a consistent substrate (ration) help prevent digestive disorders. Feed bunk management, sufficient ration fiber, consistent feed milling, and appropriate response to abnormal weather are additional factors important in prevention of digestive disorders. When digestive disorders are suspected, timely diagnosis is imperative.

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.

Butyric acid stimulates bovine neutrophil functions and potentiates the effect of platelet activating factor

Increased short-chain fatty acid (SCFA) production is associated with subacute ruminal acidosis (SARA) and activation of inflammatory processes. In humans and rodents, SCFAs modulate inflammatory responses in the gut via free fatty acid receptor 2 (FFA2). In bovines, butyric acid is one of the most potent FFA2 agonists. Its expression in bovine neutrophils has recently been demonstrated, suggesting a role in innate immune response in cattle. This study aimed to evaluate if butyric acid modulates oxidative and non-oxidative functions or if it can potentiate other inflammatory mediators in bovine neutrophils. Our results showed that butyric acid can activate bovine neutrophils, inducing calcium (Ca(2+)) influx and mitogen-activated protein kinase (MAPK) phosphorylation, two second messengers involved in FFA2 activation. Ca(2+) influx induced by butyric acid was dependent on the extracellular and intracellular Ca(2+) source and phospholipase C (PLC) activation. Butyric acid alone had no significant effect on reactive oxygen species (ROS) production and chemotaxis; however, a priming effect on platelet-activating factor (PAF), a potent inflammatory mediator, was observed. Butyric acid increased CD63 expression and induced the release of neutrophil granule markers matrix metalloproteinase-9 (MMP-9) and lactoferrin. Finally, we observed that butyric acid induced neutrophil extracellular trap (NET) formation without affecting cellular viability. These findings suggest that butyric acid, a component of the ruminal fermentative process, can modulate the innate immune response of ruminants.

Pathophysiological evaluation of subacute ruminal acidosis (SARA) by continuous ruminal pH monitoring

Evaluation of the radio‐transmission pH‐measurement system for monitoring the ruminal pH and subacute ruminal acidosis (SARA) in cattle is described. This is done in order to reveal the possible application of this system for detection and pathophysiological research of SARA by continuous ruminal pH measurement. The possibility of using this system for assessment of the ruminal pH in SARA cattle, and the presence of negative correlation between the ruminal pH and ruminal temperature in heathy and SARA cattle were determined. In addition, the 16S rRNA gene pyrosequencing analysis showed that the ruminal microbial community was simpler in SARA cattle, and the bacterial numbers in SARA cattle were lower than those in healthy hay‐fed cattle. Concentrate feeding might have reduced the diversity of the ruminal microbial community. Changes in the ruminal microbial community of SARA cattle might be related to the changes in ruminal pH followed by the decrease in the number of some bacteria. Continuous monitoring of the ruminal pH using the radio‐transmission pH‐measurement system would be applied for detection and prevention of SARA in the field and pathophysiological research of SARA, including ruminal zymology and bacteriology, which have been determined previously by sampling of the ruminal fluid and measuring of ruminal pH.

Total mixed ration pellets for light fattening lambs: effects on animal health

Fifty male Merino lambs (6 to 8 weeks, 14.1 kg; n=10 per group) were used to study the effect of feeding system: barley straw in long form and concentrate pellets in separate troughs (Control), ad libitum alfalfa supplemented with concentrate in separate troughs (Alfalfa) or including various levels of ground barley straw in concentrate pellets (B05, B15 and B25 for 50, 150 and 250 g barley straw/kg), on rumen characteristics, acid-base status, blood cell counts and lymphocyte stimulation. Alfalfa lambs had the heaviest digestive tract contents, highest rumen pH values, lowest volatile fatty acid concentration, highest papillae counts and best mucosa colour and the greatest blood pCO2 values, lowest sodium and chloride and highest potassium concentrations (P<0.05). Including ground barley straw in the concentrate pellet or providing straw in long form separately from the concentrate reduces rumen pH and darkens ruminal mucosa as compared with alfalfa-fed lambs, thus affecting acid-base status.

Duodenal supply of glutamate and casein both improve intestinal starch digestion in cattle but by apparently different mechanisms

Greater postruminal flows of protein increase small intestinal starch digestion in cattle. Our objective was to determine if small intestinal starch digestion is increased by duodenal supplementation of AA. We fed 5 duodenally and ileally cannulated steers a low-starch soybean hull-based diet in 5 × 5 Latin square designs and provided continuous duodenal infusion of raw cornstarch in combination with AA or casein and measured small intestinal starch digestion. In Exp. 1 treatments were continuous duodenal infusion of 1) no supplement (control), 2) casein (400 g/d), 3) crystalline AA similar in amount and AA composition to the casein (CASAA), 4) crystalline nonessential AA similar to those provided by casein, or 5) crystalline essential AA similar to those provided by casein. In Exp. 2 treatments were continuous duodenal infusion of 1) no supplement (control), 2) casein (400 g/d), 3) Glu (133 g/d), 4) Phe and Trp plus Met (30.4, 6.5, and 17.5 g/d, respectively; PTM), or 5) a combination of Glu and PTM. Duodenal infusion of casein increased (P ≤ 0.05) small intestinal starch digestion. When CASAA was infused, small intestinal starch digestion was similar (P = 0.30) to casein infusion. Infusion of only nonessential AA tended to increase (P = 0.14) small intestinal starch digestion relative to the control, but infusion of essential AA alone did not affect (P = 0.84) small intestinal starch digestion. In addition, infusion of casein or CASAA increased ileal flows of ethanol-soluble starch (small-chain α-glycosides), but nonessential AA alone were not different than the control. Duodenal infusion of Glu increased (P ≤ 0.05) small intestinal starch digestion, whereas PTM did not. Neither Glu nor PTM increased ileal flow of ethanol-soluble starch, but Glu and PTM provided together tended (P = 0.07) to increase ileal flows of small chain α-glycosides. Our data suggest that Glu alone can increase small intestinal starch digestion in cattle similar to casein, but increases in small intestinal starch digestion in response to Glu are not associated with an increase in ileal flows of small chain α-glycosides.

Duration of time that beef cattle are fed a high-grain diet affects the recovery from a bout of ruminal acidosis: short-chain fatty acid and lactate absorption, saliva production, and blood metabolites

This study was conducted to determine if the duration of time that beef cattle are fed a high-grain diet affects short-chain fatty acid (SCFA) absorption, saliva production, and blood metabolites before, during, and following an induced bout of ruminal acidosis. Sixteen Angus heifers were assigned to 1 of 4 blocks and within block to 1 of 2 treatments designated as long adapted (LA) or short adapted (SA). Long adapted and SA heifers were fed a backgrounding diet [forage:concentrate (F:C) = 60:40] for 33 and 7 d, respectively, and then transitioned over 20 d to a high-grain diet (F:C = 9:91) with the timing of dietary transition staggered such that the LA and SA heifers were fed the high-grain diet for 34 and 8 d, respectively, before inducing ruminal acidosis. Ruminal acidosis was induced by restricting feed to 50% of DMI:BW for 24 h followed by an intraruminal infusion of ground barley at 10% DMI:BW. Heifers were then given their regular diet allocation 1 h after the intraruminal infusion. Data were collected during an 8 d baseline period (BASE), on the day of the acidosis challenge (CHAL), and during 2 consecutive 8 d recovery periods (REC1 and REC2). When pooled across periods, the fractional rates of propionate (42 vs. 34%/h; P = 0.045) and butyrate (45 vs. 36%/h; P = 0.019) absorption, measured using the isolated and washed reticulorumen technique, were greater for LA than SA heifers. Moreover, overall, LA heifers tended to have greater absolute rates of butyrate absorption (94 vs. 79 mmol/h; P = 0.087) and fractional rates of total SCFA absorption (37 vs. 32%/h; P = 0.100). Treatment × period interactions for lactate absorption (P = 0.024) and serum D-lactate concentration (P = 0.003) were detected with LA heifers having greater D-lactate concentrations during CHAL and greater fractional rates of lactate absorption during REC1 than SA. The absolute and fractional absorption of acetate, propionate, and butyrate increased between REC1 and REC2, with intermediate values for BASE (P ≤ 0.05). Although fractional rates of SCFA absorption were low during REC1, saliva production (P = 0.018) increased between BASE and REC1, with intermediate values for REC2. These results suggest that the duration of time that animals are fed a high-grain diet may increase propionate, butyrate, and lactate absorption, and that cattle may decrease SCFA absorption and increase saliva production shortly after an acute bout of ruminal acidosis.

The duration of time that beef cattle are fed a high-grain diet affects the recovery from a bout of ruminal acidosis: dry matter intake and ruminal fermentation

This study was conducted to determine if the duration of time cattle are fed a high-grain diet affects their susceptibility to and recovery from ruminal acidosis. Sixteen Angus heifers (BW ± SEM, 261 ± 6.1 kg) were assigned to 1 of 4 blocks and fed a backgrounding diet consisting of 60% barley silage, 30% barley grain, and 10% supplement (DM basis). Within block, cattle were randomly assigned to 1 of 2 treatments differing in the number of days they were fed the high-grain diet before an acidosis challenge: 34 d for long adapted (LA) and 8 d for short adapted (SA). All heifers were exposed to the same 20 d dietary transition to a high-grain diet containing 9% barley silage, 81% barley grain, and 10% supplement (DM basis). Ruminal acidosis was induced by restricting feed to 50% of DMI:BW for 24 h followed by an intraruminal infusion of ground barley at 10% DMI:BW. Heifers were then given their regular diet allocation 1 h after the intraruminal infusion. Data were collected during an 8-d baseline period (BASE), on the day of the acidosis challenge (CHAL), and during 2 consecutive 8-d recovery periods (REC1 and REC2). Acidosis induction increased daily duration (531 to 1,020 min/d; P < 0.001) and area (176 to 595 (min × pH)/d; P < 0.001) that ruminal pH was <5.5 relative to BASE. Relative to BASE, inducing acidosis also increased the daily mean (0.3 to 11.4 mM; P = 0.013) and maximum (1.3 to 29.3 mM; P = 0.008) ruminal fluid lactate concentrations. There was no effect of dietary treatment on ruminal pH, lactate, or short-chain fatty acid (SCFA) concentrations (P > 0.050). However, during BASE and CHAL, SA heifers experienced greater linear (P = 0.031), quadratic (P = 0.016), and cubic (P = 0.008) coefficients for the duration of time that pH was <5.5. In addition, a treatment × day interaction for the duration that pH was <5.5 during REC1 suggested that LA cattle tended to recover from the challenge more rapidly than SA cattle (P = 0.085). Regression analysis confirmed that the LA heifers experienced a quicker linear (P = 0.019) recovery from induced acidosis over time. These results indicate adaptation of the ruminal epithelium continues with advancing time as evidenced by more stable ruminal pH both before and after an induced bout of acute ruminal acidosis but does not affect susceptibility of cattle to ruminal acidosis.

Isolation, identification and growth determination of lactic acid-utilizing yeasts from the ruminal fluid of dairy cattle

Ruminal organic acid production, especially lactic acid, can be modified by feeding cattle highly concentrated diets, which have been shown to adversely affect dairy cattle health. Therefore, the use of lactic acid-utilizing organisms is considered to be a potential method for controlling lactic acid levels. This study was conducted to isolate and identify lactic acid-utilizing yeasts from the ruminal fluid of dairy cattle and to determine the specific growth rate and generation time when using lactic acid as a carbon source instead of glucose. Seventeen yeast isolates were examined in this study. Yeasts isolated from dairy cattle that were fed a high cassava pulp diet (HCP) had higher specific growth rates and shorter generation times than yeasts isolated from dairy cattle that were fed a high-concentrate diet (HC) and a mixed diet (M). The three most effective yeasts in terms of specific growth rate and generation time were Pichia kudriavzevii, Candida rugosa and Kodamaea ohmeri, with 99, 100 and 99% nucleotide identities, respectively. These three isolates could be used as potential probiotics in dairy cattle diets.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates that yeasts isolated from the ruminal fluid of dairy cattle can utilize lactic acid as a carbon and energy source for growth. The isolated yeasts can be used as probiotic supplements for dairy cattle that are fed highly concentrated diets to reduce ruminal lactic acid production.

Effects of an extract of plant flavonoids (Bioflavex) on rumen fermentation and performance in heifers fed high-concentrate diets

To study the effects of an extract of plant flavonoids [Bioflavex (FL)] in cattle fed high-concentrate diets, 2 experiments were designed. In the first experiment, the effects of Bioflavex on the development of rumen acidosis was evaluated in 8 Holstein-Friesian crossbreed heifers (451 kg; SEM 14.3 kg of BW) using a crossover design. Each experimental period lasted 22 d; from d 1 to 20, the animals were fed rye grass, on d 21 the animals were fasted, and on d 22, rumen acidosis was induced by applying 5 kg of wheat without [

CONTROL

(CTR) heifers who did not receive Bioflavex] or with flavonoids [heifers who received FL; 300 mg/kg DM] through a rumen cannula. Rumen pH was recorded continuously (from d 19 to d 22). On d 22, average rumen pH was significantly (P < 0.01) higher in the FL animals (6.29; SEM = 0.031) than it was in the CTR heifers (5.98; SEM = 0.029). After the wheat application, the rumen VFA concentration increased (P < 0.01), the proportion of acetic acid decreased (P < 0.01), and lactate concentration (mmol/L) increased, but the increase was not as great (P = 0.09) in the FL as it was in the CTR heifers (0.41 to 1.35 mmol/L; SEM = 0.24). On d 22, Streptococcus bovis and Selenomonas ruminantium titers increased after the wheat application, but Megasphaera elsdenii titers increased (P < 0.05) only in the FL heifers. In the second experiment, the effect of Bioflavex on the performance and rumen fermentation in finishing heifers was evaluated. Forty-eight Fleckvieh heifers (initial BW = 317 kg; SEM = 5.34) were used in a completely randomized design. Heifers were assigned to 1 of 4 blocks based on their BW and, within each block, assigned to 1 of 2 pens (6 heifers/pen). In addition, 16 heifers (2/pen) were rumen cannulated. Individual BW and group consumption of concentrate and straw were recorded weekly until the animals reached the target slaughter weight. Supplementation with FL did not affect ADG, feed consumption, or feed conversion ratio. Rumen pH and molar proportions of propionate were greater (P < 0.01) and acetate proportion was less in the FL (P < 0.01) than they were in the CTR heifers. Flavonoid supplementation might be effective in improving rumen fermentation and reducing the incidence of rumen acidosis. This effect of flavonoids may be partially explained by increasing the numbers of lactate-consuming microorganisms (e.g., M. elsdenii) in the rumen.

An increase in dietary non-structural carbohydrates alters the structure and metabolism of the rumen epithelium in lambs

Steele, M. A., Greenwood, S. L., Croom, J. and McBride, B. W. 2012. An increase in dietary non-structural carbohydrates alters the structure and metabolism of the rumen epithelium in lambs. Can. J. Anim. Sci. 92: 123–130. This study investigated the effect of a grain challenge on the structure and metabolism of the rumen epithelium in lambs. In a randomized design, lambs (n = 8) received either a control diet [30% dry matter (DM) grain], or a diet of increasing amounts of grain to a maximum inclusion of 79% of DM for 12 d prior to slaughter. Rumen papillae were collected from the ventral sac on day 13 and prepared for histological and gene expression analyses. All lambs fed the high-grain diet were diagnosed with ruminal parakeratosis as the thickness of the corneum was higher (P<0.01) compared with control lambs (51.0±2.3 vs. 17.3±2.5 µm). Plasma beta-hydroxybutyric acid concentrations increased linearly (P<0.05) with increased grain consumption compared with the control. However, the relative mRNA expression of the ketogenic enzyme 3-hydroxy-3-methyl-glutaryl CoA-synthase (HMGCS2) in rumen papillae was not different between treatments. The expression of cholesterolgenic enzyme HMGCS1 was down-regulated by 0.70±0.06 (P<0.05) fold in lambs fed the high-grain diet compared with the control. These results suggest that a short-term grain challenge in lambs is associated with altered rumen epithelium metabolism and structural changes indicative of ruminal parakeratosis.

Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle

McAllister, T. A., Beauchemin, K. A., Alazzeh, A. Y., Baah, J., Teather, R. M. and Stanford, K. 2011. Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle. Can. J. Anim. Sci. 91: 193–211. Direct-fed microbials (DFM) have been employed in ruminant production for over 30 yr. Originally, DFM were used primarily in young ruminants to accelerate establishment of the intestinal microflora involved in feed digestion and to promote gut health. Further advancements led to more sophisticated mixtures of DFM that are targeted at improving fiber digestion and preventing ruminal acidosis in mature cattle. Through these outcomes on fiber digestion/rumen health, second-generation DFM have also resulted in improvements in milk yield, growth and feed efficiency of cattle, but results have been inconsistent. More recently, there has been an emphasis on the development of DFM that exhibit activity in cattle against potentially zoonotic pathogens such as Escherichia coli O157:H7, Salmonella spp. and Staphylococcus aureus. Regulatory requirements have limited the microbial species within DFM products to organisms that are generally recognized as safe, such as lactic acid-producing bacteria (e.g., Lactobacillus and Enterococcus spp.), fungi (e.g., Aspergillus oryzae), or yeast (e.g., Saccharomyces cerevisiae). Direct-fed microbials of rumen origin, involving lactate-utilizing species (e.g., Megasphaera elsdenii, Selenomonas ruminantium, Propionibacterium spp.) and plant cell wall-degrading isolates of Butyrivibrio fibrisolvens have also been explored, but have not been commercially used. Development of DFM that are efficacious over a wide range of ruminant production systems remains challenging because[0] comprehensive knowledge of microbial ecology is lacking. Few studies have employed molecular techniques to study in detail the interaction of DFM with native microbial communities or the ruminant host. Advancements in the metagenomics of microbial communities and the genomics of microbial–host interactions may enable DFM to be formulated to improve production and promote health, responses that are presently often achieved through the use of antimicrobials in cattle.

A single mild episode of subacute ruminal acidosis does not affect ruminal barrier function in the short term

Twenty-four German Merino sheep (72.3±10.1 kg of body weight) were fed an all-hay diet and assigned to either the subacute ruminal acidosis (SARA) treatment (n=17) or sham treatment (n=7). The SARA sheep were orally dosed with a 2.2 M glucose solution to supply 5 g of glucose/kg of body weight, whereas sham sheep received an equal volume of water. Ruminal pH was measured for 48 h before and 3 h after the oral dose. Sheep were then killed and ruminal epithelia from the ventral sac were mounted in Ussing chambers. The serosal-to-mucosal flux rate of partially (3)H-labeled mannitol (J(mannitol-SM)), an indicator of barrier function, was measured while epithelia were exposed to 3 sequential in vitro measurement periods lasting 1 h each. The measurement periods consisted of baseline, challenge, and recovery periods and were interspersed by 30-min periods for treatment equilibration. Baseline conditions were pH 6.1 (mucosal solution) and pH 7.4 (serosal solution) with a bilateral osmolarity of 293 mOsm/L. During the challenge period, the mucosal side of the epithelia was exposed to either an acidotic challenge (pH 5.2, osmolarity 293 mOsm/L) or an osmotic challenge (pH 6.1, osmolarity 450 mOsm/L); a third group served as control (pH 6.1, osmolarity 293 mOsm/L). The mucosal buffer solution was replaced for the recovery period. In vivo, sheep on the SARA treatment had lower mean (5.77 vs. 6.67) and nadir (5.48 vs. 6.47) ruminal pH for the 3h following the oral drench compared with sham sheep, indicating the successful induction of SARA with the oral glucose dose. Despite the marked reduction in pH in vivo, induction of SARA had no detectable effects on the baseline measurements of J(mannitol-SM), tissue conductance (G(t)), and short-circuit current (I(sc)) in vitro. However, reducing mucosal pH to 5.2 in vitro had negative effects on epithelial barrier function in the recovery period, including increased J(mannitol-SM), increased G(t), and decreased I(sc). The osmotic challenge increased J(mannitol-SM) and G(t) and decreased I(sc) during the challenge period, which was reversible in the recovery period except for slight reduction in I(sc). Interactions between the in vitro treatment and measurement period were detected for J(mannitol-SM), G(t), and I(sc). These data indicate that a mild episode of SARA (nadir pH, 5.48; duration ruminal pH <5.8, 111 min relative to the 180-min measurement period) does not affect ruminal epithelial barrier function immediately after the episode but that a rapid and more severe acidification (pH 5.2) in vitro increases epithelial permeability following the insult.

Effect of feeding combinations of wet distillers grains and wet corn gluten feed to feedlot cattle

Three experiments were conducted to evaluate the use of combinations of wet corn gluten feed (WCGF) and wet distillers grain plus solubles (WDGS) in dry-rolled and high-moisture corn-based finishing diets for beef cattle. In Exp. 1, 250 steers (BW = 343 +/- 13.5 kg) were fed 5 treatments consisting of a corn-based, control diet with 0% coproducts, and diets including 30% WCGF, 30% WDGS, 15% WCGF plus 15% WDGS, or 30% WCGF plus 30% WDGS. No associative effects resulted from feeding 15% WCGF plus 15% WDGS; DMI, ADG, and G:F were intermediate between steers fed WCGF or WDGS at 30% of diet DM. Feeding coproducts in combinations at 30 and 60% of diet DM increased ADG, G:F, and final BW (P < 0.05) compared with the corn-based diet. In Exp. 2, 280 yearling steers (BW = 370 +/- 0.45 kg) were used to evaluate feeding 0, 25, 50, or 75% coproducts as a combination of 50% WCGF:50% WDGS (DM basis). Additional diets were fed containing decreased alfalfa hay at 5, 2.5, and 0% (DM basis) as coproduct blend inclusions increased at 25, 50, and 75% (DM basis), respectively. No interactions were observed between alfalfa hay and coproduct blend levels, and no effects on ADG or G:F (P > 0.21) were observed due to alfalfa hay. Intake, ADG, and G:F responded quadratically (P < 0.05) across coproduct levels, with the greatest ADG and G:F at 25 and 50% blend, and similar ADG and G:F for the 0 and 75% blend levels. In Exp. 3, 504 steers (BW = 376 +/- 16 kg) were fed to evaluate 0, 10, 15, 20, 25, and 30% (DM basis) WDGS in diets containing 30% WCGF (DM basis) as well as a control diet with no coproducts. The inclusion of 30% WCGF in the diets increased DMI, ADG, and G:F (P < 0.05) when compared with control. Response to inclusion level of WDGS tended to be quadratic for DMI (P = 0.12), quadratic for ADG (P = 0.05), and no effect for G:F (P = 0.96). Greatest ADG was achieved with 15 to 20% WDGS inclusion in diets containing 30% WCGF. The use of combinations of WCGF and WDGS in finishing diets resulted in similar or improved steer performance compared with corn, suggesting replacement of corn with coproduct combinations up to 75% diet DM is possible if a roughage source is fed.

Repeated ruminal acidosis challenges in lactating dairy cows at high and low risk for developing acidosis: ruminal pH

The primary objective of this experiment was to determine whether lactating dairy cows that are at high (HR) or low (LR) risk for experiencing ruminal acidosis, because of their diet and stage of lactation, differ in their response to an acidosis challenge. A secondary objective was to determine whether the severity of acidosis changes with repeated challenges. The experiment was a completely randomized design with 2 groups (risk scenarios, HR vs. LR) and 3 periods corresponding to 3 repeated acidosis challenges. Eight lactating ruminally cannulated cows were assigned to 1 of 2 groups: HR, early lactation cows fed a 45% forage diet, or LR, midlactation cows fed a 60% forage diet. Cows were exposed to 3 acidosis challenges, each separated by 14 d. The challenge consisted of restricting total mixed rations to 50% of ad libitum intake for 24 h, followed by a 1-h meal of 4 kg of ground barley-wheat before allocating the total mixed rations. Ruminal pH was measured continuously for 9 of the 14 d each period using an indwelling system. Subacute acidosis (SARA) was described at 2 thresholds: pH <5.8 and pH <5.5. As expected, HR cows had lower ruminal pH profiles (curves) compared with LR cows: mean pH (5.81 vs. 6.21) and nadir pH (5.13 vs. 5.53). The HR cows also experienced SARA to a greater extent than LR cows during the experiment (pH <5.8, 10.6 vs. 3.5 h/d; pH <5.5, 5.9 vs. 1.6 h/d). The pH profiles of cows in both risk categories decreased with each challenge period; mean pH was 6.13, 6.03, 5.77, and nadir pH was 5.52, 5.34, and 5.14 in periods 1, 2, and 3, respectively. The challenges caused a similar decrease in pH for cows in both risk categories, but because the HR cows had a lower baseline pH, they experienced more severe SARA with each subsequent challenge. Feed restriction the day before administering the acidosis challenge caused ruminal pH to gradually increase. On the challenge day, the entire grain allotment was consumed by all cows in period 1, six cows in period 2, and only 3 cows in period 3. The pH plummeted immediately after each grain challenge. Ruminal pH remained very low during the first day after the challenge for all cows, but LR cows began their recovery more quickly than HR cows. Regardless of risk category, with each successive challenge, the pH decrease on the challenge day was more severe: nadir pH on the challenge day was 5.19, 5.07, and 4.90 and duration of SARA (pH <5.8) was 12.2, 13.4, and 15.8 h/d in periods 1, 2, and 3. This study indicates that cows become more prone to acidosis over time even though they decrease intake of the challenge grain to avoid acidosis. The severity of each subsequent bout of acidosis increases, especially for cows fed diets low in physically effective fiber and at high acidosis risk. Therefore, a bout of acidosis that occurs due to improper feed delivery or poor diet formulation can have long-term consequences on cow health and productivity.

The monitoring, prevention and treatment of sub-acute ruminal acidosis (SARA): a review

Sub-acute ruminal acidosis (SARA) has become an increasing problem in well-managed, high yielding dairy herds and the monitoring of groups of cows for signs of the condition is now crucial. Rumenocentesis may be ethically questionable but the technique remains the most reliable means of diagnosing SARA. Continuous measurement of ruminal pH may however be possible in the future. Parameters reflecting the metabolic acidosis caused by SARA are also promising tools, and measurement of milk fat content may be useful in individual mid-lactation cows although it is less valuable for bulk tank milk samples. The prevention of SARA includes the establishment of feeding and management guidelines seeking to minimize rumen acidotic load. Regular monitoring may facilitate early recognition of the condition and limit economic losses. Some degree of SARA may however be inevitable and presents a challenge to the dairy industry as consumers become increasingly concerned about the welfare of production animals.

Nutrient synchrony: sound in theory, elusive in practice

The concept of improving animal performance by going beyond simply meeting requirements and synchronizing ruminal availability of protein and energy has been with us for at least 3 decades. Although theoretically appealing, research and field results have not supported this approach to diet formulation. Why? Essential to successful ruminal synchrony is the ability to predict available amounts and fates of diverse substrates. The substrates come from varied sources; their efficiencies of use and yields of products are affected by inherent properties, interactions, transformations, and passage. However, substrate quality and availability in the rumen are affected only in part by diet. For example, NPN, true protein, and peptides are contributed by diet and intraruminal recycling, with additional endogenous NPN contributions by the cow. Changes in factors that alter the rate or extent of substrate fermentation, such as the rate of passage or ruminal pH, can alter nutrient yield from the rumen and must be accounted for in order for synchrony to work. Our ability to estimate ruminally available substrate is also challenged by normal variation in feed composition and imprecision in component and digestibility analyses. Current in vitro assays may not be adequate to accurately describe the digestibility of feed components in vivo in mixed diets. There are some indications that the amount or pattern of supply of fermentable carbohydrate has a greater impact on microbial production and efficiency than does the pattern of protein supply. Animal responses to modifications in the supply of true protein from the rumen may be masked if additional protein is oxidized by tissues or if AA from endogenous sources cover deficiencies. Animal factors, such as response to immune challenge and sustained damage to tissues, will also affect partitioning of nutrients for production and may alter an animal's response to changes in nutrient supply. With the array of factors internal and external to the diet that must be considered, "synchrony" implies a greater deliberate precision in diet manipulation than may be currently possible to effect. Perhaps we should consider balance. Within the rumen and cow, can we generate conditions so that needed substrates or nutrients are available from the diet or accessible from endogenous resources to meet requirements and enhance productivity and efficiency? This approach involves the whole animal, rather than only the rumen and feed we offer to the cow.

Ruminal acidosis in beef cattle: the current microbiological and nutritional outlook

Ruminal acidosis continues to be a common ruminal digestive disorder in beef cattle and can lead to marked reductions in cattle performance. Ruminal acidosis or increased accumulation of organic acids in the rumen reflects imbalance between microbial production, microbial utilization, and ruminal absorption of organic acids. The severity of acidosis, generally related to the amount, frequency, and duration of grain feeding, varies from acute acidosis due to lactic acid accumulation, to subacute acidosis due to accumulation of volatile fatty acids in the rumen. Ruminal microbial changes associated with acidosis are reflective of increased availability of fermentable substrates and subsequent accumulation of organic acids. Microbial changes in the rumen associated with acute acidosis have been well documented. Microbial changes in subacute acidosis resemble those observed during adaptation to grain feeding and have not been well documented. The decrease in ciliated protozoal population is a common feature of both forms of acidosis and may be a good microbial indicator of an acidotic rumen. Other microbial factors, such as endotoxin and histamine, are thought to contribute to the systemic effects of acidosis. Various models have been developed to assess the effects of variation in feed intake, dietary roughage amount and source, dietary grain amount and processing, step-up regimen, dietary addition of fibrous byproducts, and feed additives. Models have been developed to study effects of management considerations on acidosis in cattle previously adapted to grain-based diets. Although these models have provided useful information related to ruminal acidosis, many are inadequate for detecting responses to treatment due to inadequate replication, low feed intakes by the experimental cattle that can limit the expression of acidosis, and the feeding of cattle individually, which reduces experimental variation but limits the ability of researchers to extrapolate the data to cattle performing at industry standards. Optimal model systems for assessing effects of various management and nutritional strategies on ruminal acidosis will require technologies that allow feed intake patterns, ruminal conditions, and animal health and performance to be measured simultaneously in a large number of cattle managed under conditions similar to commercial feed yards. Such data could provide valuable insight into the true extent to which acidosis affects cattle performance.

Adaptation of beef cattle to high-concentrate diets: performance and ruminal metabolism

The diet adaptation period is widely considered a critical period of time in which nutritional management practices can promote or impair subsequent performance and health. Performance studies indicate that adapting feedlot cattle with incremental increases in dietary concentrate, from approximately 55 to 90% of diet DM, in 14 d or less, while allowing ad libitum access to the diet, generally results in reduced performance during adaptation or over the entire feeding period. However, the number of cattle involved in these studies does not allow insight into the frequencies of metabolic disorders associated with the management practices tested. Adapting cattle by restricting the quantity of higher-concentrate diets offered shows promise for improving production efficiency, but further development is needed for application in commercial feedlots. Evidence suggests considerable diversity in the ability of animals to cope with ingested cereal grain, and indicates that diet adaptation procedures should affect the frequency of health-impaired or low-performing cattle in a pen. Individuals that seem to effectively regulate voluntary feed intake during adaptation generally display a steady increase in DMI as dietary concentrate is increased. These data also highlight a seemingly counterproductive, repeating cycle of overconsumption, followed by a pronounced reduction in ruminal pH, by cattle that appear to cope less favorably with grain adaptation. At least a portion of this diversity may relate to the maintenance of protozoal populations. Increases in amylolytic bacteria seemed to follow the increment of additional concentrate. Protozoa were most numerous when the diet contained approximately 60% concentrate, and lactate-utilizing bacteria increased more markedly when the diet contained more than approximately 70% concentrate. Available in vivo data suggest that the number of lactate-utilizing bacteria may reach a plateau for a given diet composition after 2 to 7 d, but thorough assessments of the time course of events using modern techniques are lacking. Further research is needed to characterize how the quantity and frequency of increases in cereal grain consumption, reflective of industry practices, impact microbial dynamics, and to identify the biological features that allow certain animals to adapt more readily to high-concentrate diets.

Subacute ruminal acidosis induces ruminal lipopolysaccharide endotoxin release and triggers an inflammatory response

Subacute ruminal acidosis (SARA) was induced in 3 rumen fistulated Jersey steers by offering them different combinations of wheat-barley pellets and chopped alfalfa hay. Steers were offered 4, 5, and 6 kg/d of pelleted concentrate and 6, 5, and 4 kg/d of chopped alfalfa hay for diets 1, 2, and 3, respectively, during 5-d treatment periods and were fed chopped alfalfa hay between treatment periods. Inducing SARA increased blood concentrations of haptoglobin and serum amyloid-A. Dry matter intake of concentrate and hay decreased from d 1 to 5 in each period. Subacute ruminal acidosis was induced in all steers during d 4 and 5 when concentrate was fed, with ruminal pH remaining below 5.6 for an average of 187 and 174 min/d on these days. Lipopolysaccharide concentration increased significantly during periods of grain feeding compared with times when only hay was fed. Inducing SARA by feeding wheat-barley pellets activated a systemic inflammatory response in the steers.

Effect of rapid or gradual grain adaptation on subacute acidosis and feed intake by feedlot cattle1,2

The effects of grain adaptation protocol on subacute acidosis and feed intake by cattle were studied in a completely randomized experiment using 12 crossbred heifers (384 +/- 25 kg BW). The dietary proportion of concentrate was increased from 40 to 90% (DM basis) either by rapid adaptation (65% concentrate diet fed for 3 d) or by gradual adaptation (five intermediate diets containing 48.3, 56.7, 65.0, 73.3, and 81.7% concentrate, fed for 3 d each). Feed intake and ruminal pH (by indwelling ruminal electrodes) were monitored over 20 d. Mean daily pH variables did not differ (P > or = 0.10) between treatments on any of the 3 or 4 d that 65 or 90% concentrate was fed. Variances of a number of pH variables were greater (P < 0.05) for rapidly adapted heifers than for those on the gradual adaptation protocol during adaptation to 65 and 90% concentrate. Mean hourly pH did not differ over the first 24 h of adaptation to 65% concentrate, but variance of hourly pH tended (P < 0.10) to be greater for rapidly adapted than for gradually adapted heifers for eight of the first 24 h. On the first day of feeding 90% concentrate, ruminal pH tended (P = 0.07) to be less at 11 and 12 h after feeding with rapid adaptation than with gradual adaptation. Variance of hourly pH increased steadily in rapidly adapted heifers from 6 h after feeding onward. Ruminal VFA concentration and osmolality did not differ between treatments. Ruminal lactate concentration was < 1 mM, except in two rapidly adapted heifers and one gradually adapted heifer after introduction to 90% concentrate. Adaptation method did not affect DMI or day-to-day variation in DMI. Detection of acidosis was associated with increased variance in ruminal pH variables. A range of individual responses to grain challenge was observed, but current management strategies for preventing acidosis in pens of cattle are based on responses of the most susceptible individuals. A better understanding of factors governing individual responses to acidotic challenge may allow for the development of more effective acidosis prevention practices.