Potential of selected plant extracts to control severe subacute ruminal acidosis in vitro as compared with monensin.

BACKGROUND: In recent years, researchers have become increasingly interested in developing natural feed additives that can stabilize ruminal pH and thus prevent or eliminate the risk of severe subacute rumen acidosis. Herein, 3 experiments were conducted using a semi-automated in vitro gas production technique. In the experiment (Exp.) 1, the efficacy of 9 plant extracts (1.5 mg/ml), compared to monensin (MON; 12 µg/ml), to counteract ruminal acidosis stimulated by adding glucose (0.1 g/ml) as a fermentable carbohydrate without buffer was assessed for 6 h. In Exp. 2, cinnamon extract (CIN) and MON were evaluated to combat glucose-induced acidosis with buffer use for 24 h. In Exp. 3, the effect of CIN and MON on preventing acidosis when corn or barley grains were used as substrate was examined. RESULTS: In Exp. 1, cinnamon, grape seeds, orange, pomegranate peels, propolis, and guava extracts significantly increased (P < 0.05) pH compared to control (CON). Both CIN and MON significantly increased the pH (P < 0.001) but reduced cumulated gas production (P < 0.01) compared to the other treatments. In Exp. 2, the addition of CIN extract increased (P < 0.01) pH value compared to CON at the first 6 h of incubation. However, no significant differences in pH values between CIN and CON at 24 h of incubation were observed. The addition of CIN extract and MON decreased (P < 0.001) lactic acid concentration and TVFA compared to CON at 24 h. The CIN significantly (P < 0.01) increased acetate: propionate ratio while MON reduced it. In Exp. 3, both CIN and MON significantly increased (P < 0.05) ruminal pH at 6 and 24 h and reduced lactic acid concentration at 24 h compared to CON with corn as substrate. However, CIN had no effect on pH with barley substrate at all incubation times. CONCLUSIONS: It can be concluded that CIN can be used effectively as an alternative antibiotic to MON to control ruminal acidosis when corn is used as a basal diet.

Subacute ruminal acidosis in dairy herds: Microbiological and nutritional causes, consequences, and prevention strategies.

Dairy cattle are frequently fed high-concentrate (HC) diets in modern intensive feeding systems, especially in the transition period. During this period, cows face many alterations that include hormonal changes and shifting to a lactating state. Switching to a HC diet that may disrupt the ruminal microbiota balance can lead to subacute ruminal acidosis (SARA). Moreover, the main factor shaping the rumen microbiota is dietary composition, especially the ratio of starch to fibrous carbohydrates. Feeding highly fermentable carbohydrate diets after adaptation to forage diets leads to a rumen fermentation rate that exceeds rumen absorption and buffering rates, resulting in a reduction in ruminal pH. As a result of Gram-negative bacterial cell lysis, an increase in harmful ruminal bacterial metabolites, including lipopolysaccharide, lactic acid, and histamine, is observed. The interactions between the host immune system and the ruminal microbiota play an essential role in many physiological processes and the development of the disorder. Progress in DNA sequencing and bioinformatics platforms provides new opportunities to investigate the composition of ruminal microbes and yields unique advances in understanding ecology of the rumen. Subacute ruminal acidosis is linked with a change in the ruminal microbiota structure and richness and with other metabolic disorders; such as rumenitis, milk fat depression, laminitis, and liver abscesses. Therefore, this review aims to explore a better understanding of the crosstalk between diet and microbiota in the prevalence of rumen acidosis and its consequences, which is crucial for control strategies such as feeding management, and supplementation with thiamine, prebiotics, and probiotics.

The effect of sodium butyrate supplementation on ruminal and fecal pH and serum lipopolysaccharide-binding protein after ruminal acidosis challenge in nonlactating cows.

The objective of this study was to evaluate effects of sodium-butyrate supplementation on gastrointestinal function and the inflammatory response to ruminal acidosis (RA) challenge in cows. Four nonlactating cows with a rumen cannula were assigned to two treatments in a crossover design. Treatments were ruminal administration of sodium-butyrate (BUT) or control (CON). Sodium-butyrate was provided as Gustor BP70 and administered at a butyrate dose of 0.04% per kg body weight. The CON premix was made by replacing sodium-butyrate with wheat bran. Experimental periods were 28 days long with 21-day washout period separating the treatments. On Day 25 of each period, corn starch was ruminally administered at 0.7% per kg body weight as RA challenge. After RA challenge, ruminal pH was lower, and endotoxin concentration was higher for cows provided with BUT than those with CON, but the increase in fecal starch and the decrease in fecal pH were attenuated by BUT. The effect of butyrate supplementation on serum lipopolysaccharide-binding protein after RA challenge was not found. From these findings, butyrate supplementation mitigated rectal acidosis by reducing the flux of fermentable carbohydrate into the large intestine. An anti-inflammatory effect of butyrate was not observed, possibly due to lower pH and higher endotoxin concentration in the rumen.

Potential protective effects of thiamine supplementation on the ruminal epithelium damage during subacute ruminal acidosis.

In ruminants, the ruminal epithelium not only has the function of absorbing nutrients but also is an important tissue to prevent harmful substances in the rumen from entering the blood circulation. Thus, the normal function of ruminal epithelium is critical for ruminants. However, subacute ruminal acidosis induced by high-concentrate diets often damages the barrier function of ruminal epithelium in ruminants. Recently, many studies have shown that dietary supplementation with thiamine is an effective method to alleviate subacute ruminal acidosis. In order to provide theoretical reference for the in-depth study of subacute ruminal acidosis and the application of thiamine in the future, this review introduces the effects of subacute ruminal acidosis on morphological structure, inflammatory response, and tight junction of ruminal epithelium. In addition, this paper summarizes the role of thiamine in maintaining ruminal epithelial function of ruminants during subacute ruminal acidosis challenge.

Effects of calcium-magnesium carbonate and calcium-magnesium hydroxide as supplemental sources of magnesium on microbial fermentation in a dual-flow continuous culture.

Supplemental sources of Mg can also aid in ruminal pH regulation due to their alkaline properties. Magnesium oxide (MgO) is the most common source of Mg for ruminants and can help controlling ruminal pH; however, the alkaline potential of other sources of Mg has not been evaluated. We aimed to evaluate the inclusion of calcium-magnesium carbonate (CaMg(CO3)2) and calcium-magnesium hydroxide (CaMg(OH)4) alone or in combination as supplemental sources of Mg in corn silage-based diets and its impact on ruminal microbial fermentation. We hypothesized that inclusion of CaMg(OH)4 would allow for ruminal fermentation conditions resulting in a greater pH compared to the inclusion of CaMg(CO3)2. Four treatments were defined by the supplemental source of Mg in the diet: 1) Control (100% MgO, plus sodium sesquicarbonate as a buffer); 2) CO3 [100% CaMg(CO3)2]; 3) OH [100% CaMg(OH)4]; and 4) CO3/OH [50% Mg from CaMg(CO3)2, 50% Mg from CaMg(OH)4]. Nutrient concentration was held constant across treatments (16% CP, 30% NDF, 1.66 Mcal NEl/kg, 0.67% Ca, and 0.21% Mg). Four fermenters were used in a 4 × 4 Latin square design with four periods of 10 d each. Samples were collected for analyses of nutrient digestibility, soluble Mg, VFA, and NH3, while pH was measured at 0, 1, 2, 4, 6, 8, and 10 h post morning feeding to estimate % time when pH was below 6 (pH-B6) and area under the pH curve for pH below 6.0 (pH-AUC). Bacteria pellets were harvested for 15N analysis and estimates of N metabolism. Treatment effects were analyzed with the mixed procedure of SAS, while effects of using either CaMg(CO3)2 or CaMg(OH)4 as Mg source in comparison to Control treatment were evaluated by orthogonal contrasts. Similar pH-related variables were observed for Control, OH, and CO3/OH treatments, which had smaller pH-AUC and pH-B6 than CO3 (P ≤ 0.01). Butyrate molar proportion was greater in Control and CO3/OH than in CO3 and OH (P = 0.04). Orthogonal contrasts showed lower flow of bacterial N (P = 0.04), lower butyrate molar proportion (P = 0.08) and greater pH-AUC (P = 0.05) for diets with CaMg(CO3)2 in comparison with the Control. Concentration of soluble Mg in ruminal fluid (P = 0.73) and nutrient digestibility (P ≥ 0.52) were similar across treatments. Under the conditions of this experiment, using CaMg(OH)4 alone or combined with CaMg(CO3)2 allowed for a less acidic ruminal fermentation pattern than a diet with only CaMg(CO3)2.

Optimum roughage proportion in barley-based feedlot cattle diets: growth performance, feeding behavior, and carcass traits.

High grain diets are fed to finishing beef cattle to maximize animal performance in a cost-effective manner. However, a small amount of roughage is incorporated in finishing diets to help prevent ruminal acidosis, although few studies have examined optimum roughage inclusion level in barley-based diets. The objective of the study was to evaluate the effects of roughage proportion in barley-based finishing diets on growth performance, feeding behavior, and carcass traits of feedlot cattle. Crossbred beef steers (n = 160; mean body weight ± SD, 349.7 ± 21.4 kg) were allocated to 20 pens that were assigned randomly to four dietary treatments (five pens of eight steers per treatment). The treatment diets contained barley silage at 0%, 4%, 8%, and 12% of dietary dry matter (DM). The remainder of the diets (DM basis) consisted of 80%, 76%, 72%, and 68% barley grain, respectively, 15% corn dried distiller's grains, 5% mineral and vitamin supplement, and 32 mg monensin/kg diet DM. The diets were fed as total mixed rations for ad libitum intake (minimum of 5% refusal) once per day. Cattle were weighed on 2 consecutive days at the start and end of the experiment and on 1 d every 3 wk throughout the experiment (124 d). Two pens for each treatment group were equipped with an electronic feeding system (GrowSafe Systems Ltd., Calgary, Alberta) to monitor feed intake and feeding behavior of individual cattle. The data for dry matter intake (DMI), average daily gain (ADG), gain:feed (G:F) ratio, and carcass traits were analyzed as a completely randomized design with fixed effect of barley silage proportion and pen replicate as experimental unit. Feeding behavior data were analyzed similarly, but with animal as experimental unit. Averaged over the study, DMI increased linearly (11.1, 11.3, 11.7, 11.8 kg/d; P = 0.001) as barley silage proportion increased from 0%, 4%, 8%, and 12% of DM, but ADG was not affected (carcass-adjusted,1.90, 1.85, 1.87, 1.89 kg/d; P ≥ 0.30). Consequently, G:F ratio decreased linearly (carcass-adjusted, 168.9, 163.8, 158.5, 160.6 g/kg DMI; P = 0.023). When averaged over the study, proportion of barley silage in the diet had no linear or quadratic effects (P > 0.10) on meal frequency, duration of meals, intermeal duration, or meal size, but eating rate decreased linearly with increasing silage proportion (P = 0.008). There was no diet effect on liver abscesses (P ≥ 0.92), and effects on carcass characteristics were minor or nonexistent. We conclude that increasing the proportion of barley silage in a feedlot finishing diet at the expense of barley grain to minimize the incidence of ruminal acidosis may decrease feed conversion efficiency.

Thiamine ameliorates inflammation of the ruminal epithelium of Saanen goats suffering from subacute ruminal acidosis.

This study aimed to examine the role of thiamine in the local inflammation of ruminal epithelium caused by high-concentrate diets. Eighteen mid-lactating (148 ± 3 d in milk; milk yield = 0.71 ± 0.0300 kg/d) Saanen goats (body weight = 36.5 ± 1.99 kg; body condition score = 2.73 ± 0.16, where 0 = emaciated and 5 = obese) in parity 1 or 2 were selected. The goats were randomly divided into 3 groups (n = 6/group): (1) control diet (concentrate:forage 30:70), (2) high-concentrate diet (HC; concentrate:forage 70:30), and (3) high-concentrate diet with 200 mg of thiamine/kg of dry matter intake (THC; concentrate:forage 70:30). Goats remained on experimental diets for 8 wk. On the last day of 8 wk, ruminal and blood samples were collected to determine ruminal parameters, endotoxin lipopolysaccharide, and blood inflammatory cytokines. Goats were slaughtered to collect ruminal tissue to determine gene and protein expression of toll-like receptor 4 (TLR4) signaling pathways. Thiamine supplementation increased ruminal pH (6.03 vs. 5.42) compared with the HC group. Propionate (21.08 vs. 31.61 mM), butyrate (12.08 vs. 19.39 mM), lactate (0.52 vs. 0.71 mM), and free lipopolysaccharide (42.16 vs. 55.87 × 103 endotoxin units/mL) concentrations in ruminal fluid were lower in THC goats compared with HC goats. Similar to plasma interleukin 1ß (IL-1ß) concentration (209.31 vs. 257.23 pg/mL), blood CD8+ percentage (27.57 vs. 34.07%) also decreased in response to thiamine. Compared with HC goats, THC goats had lower ruminal epithelium activity of the enzymes myeloperoxidase and matrix metalloproteinase (MMP) 2 and 9. In contrast to HC, THC had downregulated mRNA expression of nuclear factor-κB (NFKB), TLR4, IL1B, MMP2, and MMP9 in ruminal epithelium. Thiamine supplementation led to lower relative protein expression of IL-1ß, NF-κB unit p65, and phosphorylated NF-κB unit p65 in ruminal epithelium. Taken together, these results suggest that thiamine supplementation mitigates HC-induced local inflammation and ruminal epithelial disruption.

Graded replacement of corn grain with molassed sugar beet pulp modulates the fecal microbial community and hindgut fermentation profile in lactating dairy cows.

High starch lactation diets not only enhance the risk of subacute ruminal acidosis but also of hindgut acidosis, which increases the risk of dysbiosis and the depression of fiber degradation. We recently showed that replacing corn with molassed sugar beet pulp (Bp) improved fiber degradation in high-producing dairy cattle, possibly because of an improvement of rumen and hindgut conditions for microbes by Bp feeding. However, little is known about the effects of high inclusion rates of Bp on hindgut microbes and fermentation. Thus fecal grab samples were taken from 18 high-yielding Simmental cows after 28 d of feeding 3 different levels of Bp (n = 6) for bacterial 16S rRNA amplicon sequencing. In addition, the reticular pH was continuously monitored with indwelling sensors and eating and ruminating behavior was evaluated with noseband sensors. The Bp inclusion rates were 0 g/kg (i.e., no Bp inclusion as control, CON), 120 g/kg (12Bp), or 240 g/kg (24Bp) replacing corn grain and limestone on a dry matter basis. The amount of time spent eating and ruminating was unaffected by Bp level, and the daily fluctuation in the reticular pH was reduced by 25% with Bp inclusion from 0.8 in the CON diet to 0.6 in 24Bp fed animals. Also, the fecal pH tended to increase with dietary Bp inclusion. Fecal acetate production showed a quadratic tendency with the lowest concentration (58.9%) of the total short-chain fatty acid in the 12Bp treatment. Inclusion of Bp up to 24% of the diet decreased the fecal butyrate proportion by 27%. The Shannon diversity index was increased from 5.50 to 8.09 with dietary Bp inclusion indicating increased species diversity. Of the 200 most abundant operational taxonomic units, 25 were increased by dietary Bp inclusion, whereas 15 were decreased and 7 were quadratically affected. The second most abundant group was proposed taxon "CF231" of the family Paraprevotellaceae. Although it accounted for only 2.52% of the operational taxonomic units in the CON diet, it was increased by 64% with dietary Bp inclusion. The largest relative change in the abundance was found for the genus Fibrobacter that increased more than 14-fold from 0.04% (CON) to 0.66% (24Bp). In conclusion, feeding molassed sugar beet pulp as partial substitution of corn up to 240 g/kg is a viable alternative that promotes ruminal and hindgut fermentation by supporting physiological pH and bacterial diversity.

Effects of active dried Saccharomyces cerevisiae on ruminal fermentation and bacterial community during the short-term ruminal acidosis challenge model in Holstein calves.

We investigated the effects of active dried Saccharomyces cerevisiae (ADSC) on ruminal pH, fermentation, and the fluid bacterial community during the short-term ruminal acidosis challenge. Five rumen-fistulated male Holstein calves (147.0 ± 5.8 kg of body weight; 3.6 ± 0.2 mo of age) were used in a crossover design, and 0 g (control group, n = 5) or 2 g (SC group, n = 5) of ADSC (1 × 1010 cfu/g) was administered twice daily for 21 consecutive days. Calves were fed a high-forage diet during the first 15 d (d -14 to d 0; prechallenge), a high-grain diet for 2 d (d 1 and 2; ruminal acidosis challenge), and a high-forage diet for 4 d (d 3 to 6; postchallenge). Ruminal pH was measured continuously. Rumen fluid samples were collected once daily (0800 h) on d 0, 3, 4, and 6 and twice daily (0800 and 1100 h) on d 1 and 2. Bacterial DNA was extracted from fluid samples collected on d 0 and 3. The 24-h and 1-h mean ruminal pH was significantly depressed during the ruminal acidosis challenge in each group, although the changes were more severe in the SC group, consistent with a significant increase in lactic acid on d 2 (1100 h) compared with d 0 and a significantly higher proportion of butyric acid on d 2 (1100 h) compared with the control group. Feeding a high-grain diet caused a decrease in bacterial diversity due to high acidity in both groups. The relative abundances of the genus Bifidobacterium and operational taxonomic unit (OTU) 3 (Bifidobacterium species) increased significantly in both groups but were higher in the SC group. Correlation analyses indicated that OTU3 (Bifidobacterium species) were positively correlated with lactic acid concentration and that OTU1 (Prevotella species) and OTU5 (Succinivibrio species) were correlated with the proportion of butyric acid. These results suggest that ADSC supplementation induced the intense decreases in ruminal pH by increased butyric and lactic acid production through a high-grain diet fermentation by rumen fluid bacterial species during the short-term ruminal acidosis challenge in Holstein calves after weaning.

Symposium review: The importance of the ruminal epithelial barrier for a healthy and productive cow.

The stratified squamous ruminal epithelium is the main site for absorption of key nutrients (e.g., short-chain fatty acids; SCFA) and electrolytes (e.g., sodium and magnesium). The absorptive function has to be highly selective to prevent simultaneous entry of microbes and toxins from the rumen into the blood. As such, epithelial absorption is primarily transcellular, whereas the paracellular pathway appears rather tightly sealed. A network of tight junction (claudin-1, claudin-4, and occludin) and tight junction-associated proteins (e.g., zonula occludens) accomplishes the latter. When microbial fermentation activity is high such as with highly fermentable diets, rumen epithelial functions are often challenged by acidity, high osmolarity, toxins (e.g., endotoxin and histamine), and immune mediators (inflammatory mediators and cytokines) released during local and systemic inflammation. Epithelial damage by low pH in combination with high luminal SCFA concentrations is not immediately reversible and may initially aggravate upon return to physiological pH. In contrast, barrier opening upon hyperosmolarity is acutely transient. The initial insults set by luminal acidity and SCFA and the increasing concentrations of microbial-associated molecular patterns such as lipopolysaccharides are key factors that trigger inflammation not only in the rumen but also in the hindgut (cecum and colon), which reach out to the liver and other organs, causing systemic inflammation. Low feed intake during parturition, transportation, heat stress, or disease is the second most relevant challenge for the ruminal epithelial barrier. The barrier opening is usually only transient and quickly restored upon refeeding. Due to a rapid, dose-dependent, and prolonged decrease in absorption capacity for SCFA, however, any feed restriction increases the odds for postrestriction subacute ruminal acidosis. Inflammation due to acidosis can be alleviated by supplemental thiamine, yeasts, and plant bioactive (phytogenic) compounds. Butyrate is used in weaning calves to support ruminal barrier development; however, excess butyrate may promote hyperkeratosis, parakeratosis, and epithelial injury in the fully developed rumen of adult cows. Further research is needed to enhance the understanding of the various factors that counteract barrier impairment and help barrier restoration during acidogenic feeding, especially when concurring with unavoidable periods of feed restriction.

Supplementation of a clay mineral-based product modulates plasma metabolomic profile and liver enzymes in cattle fed grain-rich diets.

Grain-rich diets often lead to subacute ruminal acidosis (SARA) impairing rumen and systemic cattle health. Recent data suggest beneficial effects of a clay mineral (CM)- based product on the rumen microbiome of cattle during SARA. This study sought to investigate whether the CM supplementation can counteract SARA-induced perturbations of the bovine systemic health. The study used an intermittent diet-induced SARA-model with eight dry Holstein cows receiving either no additive as control or CM via concentrates (n=8 per treatment). Cows received first a forage diet (Baseline) for 1 week, followed by a 1-week SARA-challenge (SARA 1), a 1-week recovery phase (Recovery) and finally a second SARA-challenge for 2 weeks (SARA 2). Cows were monitored for feed intake, reticular pH and chewing behavior. Blood samples were taken and analyzed for metabolites related to glucose and lipid metabolism as well as liver health biomarkers. In addition, a targeted electrospray ionization-liquid chromatography-MS-based metabolomics approach was carried out on the plasma samples obtained at the end of the Baseline and SARA 1 phase. Data showed that supplementing the cows' diet with CM improved ruminating chews per regurgitated bolus by 16% in SARA 1 (P=0.01) and enhanced the dry matter intake during the Recovery phase (P=0.05). Moreover, the SARA-induced decreases in several amino acids and phosphatidylcholines were less pronounced in cows receiving CM (P≤0.10). The CM-supplemented cows also had lower concentrations of lactate (P=0.03) and biogenic amines such as histamine and spermine (P<0.01) in the blood. In contrast, the concentration of acylcarnitines with key metabolic functions was increased in the blood of treated cows (P≤0.05). In SARA 2, the CM-cows had lower concentrations of the liver enzymes aspartate aminotransferase and γ-glutamyltransferase (P<0.05). In conclusion, the data suggest that supplementation of CM holds the potential to alleviate the negative effects of high-grain feeding in cattle by counteracting multiple SARA-induced perturbations in the systemic metabolism and liver health.

Thiamine status, metabolism and application in dairy cows: a review.

As the co-enzyme of pyruvate dehydrogenase and α-ketoglutarate dehydrogenase, thiamine plays a critical role in carbohydrate metabolism in dairy cows. Apart from feedstuff, microbial thiamine synthesis in the rumen is the main source for dairy cows. However, the amount of ruminal thiamine synthesis, which is influenced by dietary N levels and forage to concentrate ratio, varies greatly. Notably, when dairy cows are overfed high-grain diets, subacute ruminal acidosis (SARA) occurs and results in thiamine deficiency. Thiamine deficiency is characterised by decreased ruminal and blood thiamine concentrations and an increased blood thiamine pyrophosphate effect to >45 %. Thiamine deficiency caused by SARA is mainly related to the increased thiamine requirement during high grain feeding, decreased bacterial thiamine synthesis in the rumen, increased thiamine degradation by thiaminase, and decreased thiamine absorption by transporters. Interestingly, thiamine deficiency can be reversed by exogenous thiamine supplementation in the diet. Besides, thiamine supplementation has beneficial effects in dairy cows, such as increased milk and component production and attenuated SARA by improving rumen fermentation, balancing bacterial community and alleviating inflammatory response in the ruminal epithelium. However, there is no conclusive dietary thiamine recommendation for dairy cows, and the impacts of thiamine supplementation on protozoa, solid-attached bacteria, rumen wall-adherent bacteria and nutrient metabolism in dairy cows are still unclear. This knowledge is critical to understand thiamine status and function in dairy cows. Overall, the present review described the current state of knowledge on thiamine nutrition in dairy cows and the major problems that must be addressed in future research.

População de protozoários ruminais em novilhos zebuínos alimentados com ou sem volumoso / Population of Protozoa in zebu steers fed with or without bulk

This study aimed to quantify and identify the profile of the rumen protozoa population of beef steers fed with or without roughage. Nellore crossbred steers raised in extensive system on lignified tropical pastures with mineral supplementation and steers confined for 60 days only receiving pelletized concentrate and whole corn kernels were evaluated. After slaughter, rumen fluid was collected and one ml aliquots were diluted in nine ml formaldehyde solution at 10%. The counts of small, medium and large protozoa were held in Sedgewick Rafter chambers and identification of genus was possible after staining lugol and optical microscope with a 40X objective. The concentration of rumen protozoa positively correlated with pH ruminal. Cattle fed without roughage had significantly lower rumen protozoa population (P<0.05). Animals fed roughage had higher occurrence of Dasytrichia genus, Charonina, Entodinum, Diplodinium, Ostracodinium and Epidinium while those fed without bulk, the Buetschilia, Isotricha, Eodinium, Polyplastron, Elyplastron, Metadinium and Enoploplastron were the most frequent genus.(AU)

Effects of corn silage particle size, supplemental hay, and forage-to-concentrate ratio on rumen pH, feed preference, and milk fat profile of dairy cattle.

Two experiments (Exp.) were conducted to study effects of feeding long or short corn silage total mixed rations (TMR) on rumen pH, feed preference, and dairy cow performance and to determine the rate of recovery from grain-induced subacute ruminal acidosis (SARA). Both experiments utilized a crossover design with 12 lactating, multiparous, Holstein cows each (including 4 ruminally cannulated cows) and consisted of two 26-d periods. Each period consisted of 12d of adaptation followed by 14d of data collection. Each period was divided into 4 phases: adaptation, d 1 to 12; baseline, d 13 to 14; challenge, d 15 to 19; and recovery, d 20 to 26. Treatments in Exp. 1 were TMR based on corn silage with long (L) or short (ST) particle size in a 65:35 forage-to-concentrate (F:C) diet. Treatments in Exp. 2 were TMR based on corn silage with short (SH) or long (LH) particle size in a 65:35 F:C diet with 3.3% (DM basis) orchardgrass hay offered as a supplement to the diet. In both experiments, during the challenge phase cows received a 50:50 F:C diet to initiate SARA. Animals were housed individually, milked twice per day, and fed once per day for 10% refusal rate on an as-fed basis. Data were analyzed using PROC MIXED of SAS. Feeding L and LH diets increased acetate-to-propionate ratio in the rumen, which resulted in the maintenance of a ratio >2 from the start of the SARA challenge through recovery. In Exp. 1, feeding long corn silage TMR resulted in lower milk fat concentration on the third day of the challenge, whereas cows fed short corn silage TMR had lower milk fat concentration on the final day of the challenge compared with d 13. Providing supplemental hay to cows fed TMR based on long or short corn silage in Exp. 2 prevented acidosis when cows were challenged with a high-grain diet. Milk fat concentrations substantially decreased during the challenge phase in both diets supplemented with hay, but feeding LH did not lower milk fat concentrations until d 20 compared with d 17 for cows fed SH. Under the conditions of these experiments, cows selected for shorter particles compared with longer particles, despite the rumen challenge. However, when feeding a 50:50 F:C diet, feeding long corn silage TMR or supplementing the diet with grass hay increased rumen pH, acetate-to-propionate ratio in the rumen, and rate of recovery from SARA.

The effects on ruminal pH and serum haptoglobin after feeding a grain-based supplement to grazing dairy cows as a partial mixed ration or during milking.

Ruminal pH and serum concentrations of haptoglobin (Hp) were measured in order to assess the risk of subacute ruminal acidosis (SARA) in grazing cows offered rolled wheat grain twice daily in the dairy at milking (Control group; n= 64), or as a partial mixed ration (PMR group; n= 64) on a feedpad. Cows were allocated various levels of the supplement (8, 10, 12 or 14 kg dry matter/day). Ruminal pH was measured in 16 rumen-fistulated cows (eight PMR and eight Control group cows), using indwelling pH meters, recording every 10 min for 14 days. Serum Hp was analysed in samples collected from 125 cows. No differences in ruminal pH or serum Hp concentration were found between treatment groups, or levels of feeding. It was concluded that, using ruminal pH patterns and Hp as markers of SARA at the feeding levels used in this study, there were no differences between grazing cows fed the supplement either as grain in the dairy or as a PMR fed on a feedpad.

Feeding lactating dairy cattle long hay separate from the total mixed ration can maintain dry matter intake during incidents of low rumen pH.

The objective of this study was to investigate effects of offering dry hay of different quality and length on rumen pH and feed preference in lactating dairy cows. Eight rumen-cannulated Holstein cows (104 ± 34 d in milk, body weight of 601 ± 116 kg, and parity of 2.38 ± 1.69; mean ± standard deviation) were used in a replicated 4 × 4 Latin square design. Each period encompassed 21 d divided into 5 phases: adaptation (d 1 to 14), with ad libitum total mixed ration (TMR); baseline (d 15 to 17), with ad libitum TMR; restricted feeding (d 18), with cows fed for 75% of baseline dry matter intake; challenge (d 19), with 4 kg (as-fed) of finely ground wheat mixed into the digesta of each cow via rumen cannula before feeding; and recovery (d 20 to 21), with ad libitum TMR. Cows were assigned to squares by parity and randomly assigned to treatments. Treatments were 5.2% low-quality hay TMR (CL), 5.2% high-quality hay TMR (CH; both hays were chopped and included in TMR), TMR with 5.2% supplemental long low-quality hay (TMR+L), and TMR with 5.2% supplemental long high-quality hay (TMR+H; both hays were unprocessed and fed separate from TMR).Low-quality hay contained 8.6% crude protein and 67.1% neutral detergent fiber, whereas high-quality hay contained 14.4% crude protein and 56.2% neutral detergent fiber. Animals were housed individually, milked twice per day, and fed once per day for 10% refusal rate. Data were analyzed using PROC MIXED of SAS (SAS Institute Inc., Cary, NC). Subacute ruminal acidosis challenge decreased weighted average rumen pH from 5.72 to 5.51. Cows fed TMR+L had higher rumen pH compared with CL and TMR+H on d 19. During d 20, cows fed chopped hay had higher rumen pH than cows fed supplemental long hay. Cows fed supplemental long hay had greater dry matter intake during baseline and challenge days compared with when hay was chopped and included in the TMR. Minimal differences among diets were found for TMR particle size selection during the challenge day; however, cows had a greater preference for high-quality long hay during recovery days. Milk production averaged 38.3 kg/d and did not differ among treatments. Fat, protein, and lactose yields were also not different among treatments. Milk fatty acid profile was altered by treatment. The TMR+L and CH treatments increased production of cis-9,trans-11 conjugated linoleic acid. Results of this study indicate that feeding TMR plus supplemental long hay can maintain dry matter intake during incidents of and recovery from periods of low ruminal pH.

Incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing.

The objective of this study was to determine the incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing. Steers were purchased from a local auction market (n = 250; mean ± SD; 330 ± 20.0 kg initial BW) and were grouped together with 28 steers fitted with a ruminal cannula (248 ± 25.5 kg initial BW). Steers were randomly allocated to 1 of 8 pens (3 to 4 cannulated steers per pen with a total of 35 steers/pen). The feeding period (143 d) was divided into 4 phases: backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), and the first (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of finishing. The BKGD diet contained (% DM) barley silage (45.7%), barley grain (41.6%), canola meal (4.2%), and a pelleted mineral and vitamin supplement (8.5%). Steers were transitioned to a finishing diet containing (% DM) barley silage (5%), barley grain (80.9%), canola meal (4.9%), and a pelleted mineral and vitamin supplement (9.2%) using 4 transition diets. Feed was offered to achieve 5% refusals (as-is basis). Ruminal pH was recorded in cannulated steers every 10 min throughout the study, and feed refusals and BW were recorded at 2 wk intervals. Mean ruminal pH (P < 0.01) was 6.4, 6.3, 6.2, and 6.0 ± 0.01 during the BKGD, TRAN, FIN1, and FIN2, respectively. The duration (P < 0.01) pH < 5.5 was 4.1, 12.1, 78.7, and 194 ± 9.4 min/d during BKGD, TRAN, FIN1, and FIN2, respectively. Using a threshold of ruminal pH < 5.5 for at least 180 min to diagnose ruminal acidosis, incidence was defined as the number of times steers experienced ruminal acidosis during each period and prevalence was defined as the percentage of steers that experienced acidosis during each period. On average, the incidence rate (P < 0.01) of ruminal acidosis was 0.1, 0.3, 6.7, and 14.8 ± 0.97 episodes during BKGD, TRAN, FIN1, and FIN2, respectively. In the same order, the prevalence (P < 0.01) was 0.7, 1.7, 15.4, and 37.8 ± 2.0%. Based on multiple regression, factors associated with prevalence of ruminal acidosis and the duration pH < 5.5 were feeding phase (P < 0.01) and DMI (P < 0.01). Overall, the greatest incidence, prevalence, and severity of ruminal acidosis were observed towards the end of the finishing phase and were associated with days on feed and DMI.