Canola meal or soybean meal as protein source and the effect of microencapsulated sodium butyrate supplementation in calf starter mixture. II. Development of the gastrointestinal tract.

The aim of this study was to assess the effect of protein source, either soybean meal (SM) or canola meal (CM), and microencapsulated sodium butyrate (MSB) supplementation in a pelleted starter mixture on the development of the gastrointestinal tract (GIT) in dairy calves. Twenty-eight bull calves (8.7 ± 0.8 d of age and 43.0 ± 4.4 kg; mean ± SD) were assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement: CM as a main source of protein without or with MSB or SM without or with MSB. Calves were fed starters ad libitum and exposed to a gradual weaning program, with weaning taking place on 51.7 ± 0.8 d of age. Calves were observed for an additional 3 wk after weaning and slaughtered on d 72.1 ± 0.9 of age, after which the GIT was dissected. Morphometric measurements were recorded, and samples for determination of ruminal fermentation, histology, gene expression, and brush border enzyme activities were collected. Canola meal use in the starter mixture increased abomasal tissue weight, jejunal tissue weight and length, and mRNA expression of SLC16A4 (formerly known as MCT4) and FFAR2 (GPR43) in the ruminal epithelium, and decreased ruminal ammonia and mRNA expression of SLC15A2 (PEPT2) and SLC6A14 (ATB0+) in the proximal small intestine and ileum, respectively. However, MSB inclusion in the starter mixture decreased ruminal papillae length, ruminal epithelial surface, and ruminal epithelium dry weight, while increasing mRNA expression of SLC16A1 (MCT1) in ruminal epithelia. Reduced ruminal surface area associated with MSB supplementation was the most apparent when MSB was combined with CM in the starter mixture. Additionally, MSB supplementation decreased the thickness of omasal epithelium, omasal epithelium living strata, and stratum corneum, and increased duodenal and ileal aminopeptidase A enzymatic activity and ileal aminopeptidase N enzymatic activity. Overall, CM might increase growth of the GIT of calves, particularly of the small intestine, but may negatively affect intestinal epithelium function and peptide and AA absorption. Supplementation of MSB has a negative effect on the ruminal and omasal epithelium development, particularly when combined in a starter mixture with CM.

Canola meal or soybean meal as protein source and the effect of microencapsulated sodium butyrate supplementation in calf starter mixture. I. Performance, digestibility, and selected blood variables.

Two studies were conducted to assess the effect of protein source and microencapsulated sodium butyrate (MSB) inclusion in pelleted starter mixtures on growth performance, gain to feed (G:F) ratio, nutrient digestibility, and selected blood metabolites in calves. In study 1, 28 Holstein bull calves (8.7 ± 0.8 d of age and 43.0 ± 4.4 kg; mean ± SD) were allocated to 1 of 4 treatments in a 2 × 2 factorial arrangement and fed a pelleted starter mixture containing canola meal (CM, 35% as fed) or soybean meal (SM, 24% as fed) as the main source of protein, with or without supplemental MSB (0.3% as fed). Starter mixtures were formulated to be similar for crude protein, Lys, and Met, and were fed ad libitum. Calves were weaned after 42 d of milk replacer feeding (51.7 ± 0.8 d of age) and observed for another 21 d. Furthermore, selected blood metabolites were measured on d 21, 42, and 63 of the study, and nutrient digestibility was measured after weaning. In study 2, 60 Holstein heifer calves (9.1 ± 0.8 d of age and 43.2 ± 4.2 kg) were assigned to the same treatments as in study 1. The calves were weaned after 49 d of milk replacer feeding (59.1 ± 0.8 d of age) and observed for an additional 14 d. Milk replacer and starter mixture intake and fecal score were recorded daily, whereas body weight (BW) was recorded weekly. In study 1, calves fed starter mixtures containing CM had or tended to have lesser preweaning starter intake, weaning average daily gain (ADG), weaning and overall G:F ratio, and postweaning total-tract dry matter digestibility, as opposed to those fed starter mixtures with SM. However, these differences did not affect overall starter intake, overall ADG, or final BW. Supplementation with MSB only tended to increase the preweaning starter mixture intake. In study 2, heifer calves that were fed starter mixtures with CM had greater cumulative starter intake after weaning, but the protein source in the starter mixture had no effect on ADG, BW, or G:F ratio. Inclusion of MSB in starter mixtures for calves tended to decrease postweaning starter mixture intake. In conclusion, use of CM or SM as the main source of protein in starter mixture resulted in similar growth performance of bull and heifer calves; however, CM use in starter mixtures reduced starter intake, ADG, and G:F ratio at least at some points of rearing. Supplementation of MSB had minor effects on the growth performance of 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.

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.

Effects of alternate day supplementation at two levels of energy on intake, rumen fermentation, and digestibility of beef heifers fed cool-season perennial grass hay.

A study was conducted to evaluate the effects of supplementing energy daily vs. on alternate days at levels that were 1.5 and 2 times the daily amount on DMI, rumen fermentation parameters, and apparent total tract digestibility of beef heifers fed grass hay. Four cannulated Hereford heifers (339 ± 11 kg) were randomly assigned over 4 periods to a 4 × 4 Latin square design. Heifers were fed a cool-season perennial grass (CSPG) hay (10% CP and 42% ADF) and supplemented with a pelleted feed formulated to provide 3.2 Mcal/kg of DE. Treatments consisted of a nonsupplemented control (CON) and 3 supplemented treatments where the supplement was offered daily at 0.6% BW (DLY) or on alternate days at 0.9% BW (LA) and 1.2% BW (HA). Heifers fed DLY had lower ( ≤ 0.04) CSPG hay DMI (7.1 vs. 8.1 kg/d) and mean ruminal pH (6.65 vs. 6.75) and greater ( < 0.01) total short-chain fatty acid (SCFA; 77.1 vs. 69.2 m) and NH-N (4.6 vs. 3.4 mg/dL) concentrations in ruminal fluid than CON heifers. The concentration of ruminal NH-N for LA (5.8 mg/dL) was greater ( < 0.01) than for DLY. Total tract DM digestibility was greater for DLY (52.5%; ≤ 0.03) than for CON (44.2%) and LA (49.7%), whereas no effects were found ( ≥ 0.11) for DLY vs. HA. When data was analyzed for days when LA and HA were supplemented, hay DMI was greater ( < 0.05) for DLY (7.3 kg/d) vs. HA (6.0 kg/d) but not different ( = 0.16) vs. LA (6.4 kg/d), mean ruminal pH of DLY (6.64) was greater vs. HA (6.59; = 0.04) and tended to be greater vs. LA (6.60; < 0.09), and total SCFA concentration of DLY (77.9 m) was lower ( < 0.01) vs. HA (88.2 m) and tended ( = 0.08) to be lower vs. LA (84.0 m). On days when LA and HA were not supplemented, hay DMI was not different ( ≥ 0.48) for DLY vs. LA and HA, mean ruminal pH was greater ( ≤ 0.03) for LA (6.79) and HA (6.85) compared with DLY (6.67), and total SCFA concentration of DLY (76.2 m) was not different ( = 0.15) vs. LA (67.5 m) but greater ( = 0.03) vs. HA (62.0 m). These results show that reducing the amount of supplement fed on alternate supplementation programs from 2 to 1.5 times the amount of daily programs can minimize the negative effects on rumen fermentation and forage DMI.

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.

Behavior and inflammation of the rumen and cecum in Holstein bulls fed high-concentrate diets with different concentrate presentation forms with or without straw supplementation.

Twenty-four individually housed Holstein bulls (395 ± 7.3 kg BW and 252 ± 3.1 d age) were exposed to a 2 × 2 factorial design (meal vs. pellets; with vs. without straw) to evaluate the effect of concentrate form and provision of straw in finishing diets on behavior and expression of rumen and cecum epithelium genes related to inflammation and behavior. Concentrate and straw consumption were recorded monthly and behavior (self-grooming, social, oral nonnutritive, tongue rolling, eating, drinking, ruminating, and lying) was recorded every two weeks. Bulls were slaughtered after 64 d of exposure to treatments, lesions on the rumen and liver were assessed, and samples of the rumen and cecum were collected. Straw supplementation tended ( = 0.08) to increase concentrate intake (8.0 vs. 7.4 ± 0.26 kg/d), increased ( < 0.01) the proportion of time ruminating (9.4 vs. 3.1 ± 1.02%), and decreased ( < 0.01) the occurrence of oral nonnutritive behaviors (0.52 vs. 1.34 ± 0.123 times/15 min) relative to bulls deprived of straw. Provision of straw increased ruminal pH, but the magnitude of the change was greater when the concentrate was provided as meal compared with pellets (interaction, < 0.05). When straw was not supplemented, all rumen samples had papillae fusion, whereas only 16.7% of bulls fed pellets and straw had papillae fusions (interaction, < 0.05). Vacuole grading of the rumen papillae was less ( < 0.01) in bulls provided straw compared with bulls without straw. For the ruminal epithelium, straw provision tended to increase the relative expression ratio of (which stimulates peptide YY, PYY, and serotonin secretion; = 0.06) and α (which modulates immune reactions and behavior; = 0.09) and increased and (tight junction proteins; < 0.05), along with ß and (proinflammatory cytokines; < 0.01) and ( < 0.01) in the rumen. Moreover, it also tended to increase the relative gene expression ratio of ß (an antimicrobial peptide; = 0.10) and ( = 0.10). Bulls fed pellets had a decreased ruminal relative expression ratio of α ( < 0.05). Bulls without straw had increased ( < 0.05) the cecum relative expression ratio of ß. In conclusion, the lack of straw supplementation in bulls fed high-concentrate diets modifies behavior and affects rumen macroscopic morphology and expression of epithelial genes that could be related to behavior and inflammation.

The effect of monensin concentration on dry matter intake, ruminal fermentation, short-chain fatty acid absorption, total tract digestibility, and total gastrointestinal barrier function in beef heifers.

In a 4 × 4 Latin square design (24-d periods), 4 ruminally cannulated Hereford × Angus/Simmental heifers were used to evaluate the effect of increasing levels of monensin concentration on DMI, ruminal fermentation, short-chain fatty acid (SCFA) absorption across the reticulorumen, and total tract barrier function. Heifers were fed a barley-based finishing diet (76% rolled barley grain, 12% barley silage, 8% mineral and vitamin supplement, and 4% canola meal) containing 0, 22, 33 or 48 mg/kg monensin. Urinary recovery of Cr-EDTA was used as an indicator of total tract barrier function (d 18 to 20). Days 20 to 23 were used to evaluate ruminal fermentation and total tract digestibility measurements, and SCFA absorption was measured using the temporarily isolated and washed reticulorumen technique on d 24. Data were analyzed using PROC MIXED of SAS with linear and quadratic contrasts to evaluate the effect of increasing monensin dose. Increasing monensin linearly decreased DMI (10.0, 9.9, 9.3, and 9.1 kg/d for diets containing 0, 22, 33 or 48 mg/kg monensin, respectively; = 0.01) but did not affect the variation in DMI among days. Urinary Cr-EDTA recovery was not ( ≥ 0. 61) affected by increasing dose of monensin, nor was ruminal pH (mean, minimum, maximum, duration less than 5.5, and area under curve; ≥ 0.21). The acetate-to-propionate ratio linearly decreased (1.9, 1.8, 1.4, and 1.3 for diets containing 0, 22, 33 or 48 mg/kg monensin, respectively; = 0.03) with increasing monensin. There was no response ( ≥ 0. 17) for the rate of SCFA absorption with monensin concentration. Total tract ethanol soluble carbohydrate digestibility linearly increased (77.2, 84.7, 88.0, and 94.0% for diets containing 0, 22, 33 or 48 mg/kg monensin, respectively; = 0.003) whereas starch digestibility quadratically responded (93.8, 93.9, 88.0, and 94.0% for diets containing 0, 22, 33 or 48 mg/kg monensin, respectively; < 0.001), where 33 mg/kg inclusion of monensin had a minimal value. The results from this study indicate that in addition to the known effects of monensin to reduce DMI and the acetate:propionate ratio, monensin inclusion does not affect ruminal pH, SCFA absorption, or total tract barrier function.

Effect of maturity at harvest for whole-crop barley and oat on dry matter intake, sorting, and digestibility when fed to beef cattle.

The objectives were to evaluate the effect of harvest maturity of whole-crop oat (Study 1) and whole-crop barley (Study 2) on forage intake and sorting, ruminal fermentation, ruminal digestibility, and total tract digestibility when fed to beef heifers. In Study 1, 3 ruminally cannulated heifers (417 ± 5 kg) were used in a 3 × 3 Latin square design with 24-d periods. Whole-crop oat forage harvested at the late milk (LMILK), hard dough (HD), or ripe (RP) stages was fed for ad libitum intake and heifers were supplemented (1% of BW) with alfalfa pellets, barley grain, canola meal, and a mineral and vitamin pellet. Maturity at harvest for whole-crop oat did not affect ( ≥ 0.058) forage intake, DE intake, amount of forage refused, ruminal short-chain fatty acid concentration, or digestibility of DM, OM, NDF, and ADF. Ruminal starch digestibility decreased ( < 0.001) from 92.6% at the LMILK stage to 90.0% at the RP stage, with total tract starch digestibility decreasing ( = 0.043) from 95.8% at the LMILK stage to 94.8% at the RP stage. Ruminal CP digestibility was reduced at the HD stage compared with the LMILK and RP stages ( < 0.001). Mean ruminal pH was greatest for the LMILK stage (6.36; = 0.003) compared with the HD and RP stages (6.30 and 6.28, respectively). In Study 2, 6 ruminally cannulated heifers (273 ± 16 kg) were used in a replicated 3 × 3 Latin square design with 24-d periods. Dietary treatments included ad libitum access to whole-crop barley harvested at the LMILK, HD, or RP stage and a constant rate (0.8% BW) of supplement containing alfalfa pellets, barley grain, canola meal, and a mineral and vitamin pellet. Dry matter intake, ruminal content mass, and feeding behavior were not affected by harvest maturity ( ≥ 0.16). There was a decrease in total tract digestibility of DM, OM, and NDF observed at the HD stage compared with the LMILK and RP stages ( ≤ 0.004). Ruminal NDF digestibility decreased from 69.7% at the LMILK stage to 54.4% at the HD stage and 54.9% at the RP stage ( = 0.001), whereas ruminal ADF digestibility decreased from 70.0% at the LMILK stage to 44.4% at the HD stage and 42.5% at the RP stage ( = 0.002). Minimum and mean ruminal pH were least for the LMILK stage, intermediate at the RP stage, and greatest at the HD stage ( = 0.016 and = 0.031, respectively). These data suggest that despite reductions in ruminal digestibility of NDF and ADF with advancing maturity, harvesting whole-crop oat and barley forage at the HD and RP stages of maturity did not negatively affect DMI, fermentation characteristics, or DE relative to whole-crop cereal forage harvested at the LMILK stage.

Relative contribution of ruminal buffering systems to pH regulation in feedlot cattle fed either low- or high-forage diets.

The relative contribution of ruminal short-chain fatty acid (SCFA) absorption and salivary buffering to pH regulation could potentially change under different dietary conditions. Therefore, the objective of this study was to investigate the effects of altering the ruminal supply of rapidly fermentable carbohydrate (CHO) on absorptive function and salivation in beef cattle. Eight heifers (mean BW±SD=410±14 kg) were randomly allocated to two treatments in a crossover design with 37-day periods. Dietary treatments were barley silage at 30% low forage (LF) or 70% high forage (HF) of dietary dry matter (DM), with the remainder of the diet consisting of barley grain (65% or 25% on a DM basis) and a constant level (5%) of supplement. The LF and HF diets contained 45.3% and 30.9% starch, and 4.1% and 14.0% physically effective fiber (DM basis), respectively. Ruminal pH was continuously measured from day 17 to day 23, whereas ruminal fluid was collected on day 23 to determine SCFA concentration. Ruminal liquid passage rate was determined on day 23 using Cr-ethylenediaminetetraacetic acid. Eating or resting salivation was measured by collecting masticate (days 28 and 29) or saliva samples (days 30 and 31) at the cardia, respectively. On days 30 and 31, the temporarily isolated and washed reticulo-rumen technique was used to measure total, and Cl--competitive (an indirect measure of protein-mediated transport) absorption of acetate, propionate and butyrate. As a result of the higher dietary starch content and DM intake, the ruminal supply of rapidly fermentable CHO, total ruminal SCFA concentration (118 v. 95 mM; P<0.001) and osmolality (330 v. 306 mOsm/kg; P=0.018) were greater in cattle fed LF compared with HF. In addition, feeding LF resulted in a longer duration (2.50 v. 0.09 h/day; P=0.02) and a larger area (0.44 v. 0.01 (pH×h)/day; P=0.050) that pH was below 5.5. There was no diet effect on total and Cl--competitive absorption (mmol/h and %/h) of acetate, propionate, butyrate and total SCFA (acetate+propionate+butyrate), but eating salivation was less (131 v. 152 ml/min; P=0.02), and resting salivation tended to be less (87 v. 104 ml/min; P=0.10) in cattle fed an LF diet. In summary, lower ruminal pH in cattle with greater rapidly fermentable CHO intake was attributed to an increase in SCFA production and decrease in salivation, which were not compensated for by an increase in epithelial permeability.

Effect of including high-lipid by-product pellets in substitution for barley grain and canola meal in finishing diets for beef cattle on ruminal fermentation and nutrient digestibility.

The objective was to determine the effect of replacing barley grain and canola meal with high-lipid by-product pellets (HLBP; 14.6% CP, 29.8% NDF, 9.0% fat, and 5.52 MJ NE/kg in DM) on DMI, ruminal fermentation, nutrient flow at the omasal canal, and nutrient digestibility. Four ruminally cannulated and ovariectomized Hereford × Gelbvieh heifers (initial BW of 631.9 ± 23.3 kg; mean ± SD) were used in a 4 × 4 Latin square design. Periods consisted of 28 d, including 10 d for diet transition, 11 d for dietary adaptation, and 7 d for measurements. Heifers were fed a typical finishing diet consisting of 89% of concentrate (barley grain and canola meal; CONT), 6% of barley silage, and 5% of mineral and vitamin supplement (on DM basis). Dietary treatments consisted of a CONT or diets where 30% (HLBP30), 60% (HLBP60), and 90% (HLBP90) of the barley grain and canola meal were replaced with HLBP. Dry matter intake was not affected by treatment ( > 0.10). Total short-chain fatty acid concentration and molar proportions of acetate, propionate, and butyrate ( > 0.10) among treatments and ruminal ammonia did not differ ( > 0.10) among treatments, and ruminal ammonia increased ( = 0.03) linearly with increasing HLBP inclusion rate in the diet. Mean and maximum pH increased, whereas the duration and area that pH was below 5.8, 5.5, and 5.2, thresholds used for mild, severe, and acute ruminal acidosis, respectively, decreased linearly ( ≤ 0.05) with increasing rates of inclusion of HLBP. Organic matter flow at the omasal canal increased linearly ( = 0.03) with increasing HLBP inclusion rate in the diet. However, OM digestibility coefficients and apparent ruminal NDF and ADF digestibility yielded negative values for some animals, especially those fed HLBP90, indicating that ruminal digestibility was underestimated. Total tract OM digestibility decreased linearly ( < 0.01) with increasing inclusion rates of HLBP. This study showed that HLBP inclusion in substitution for barley grain and canola meal linearly decreases the severity of ruminal acidosis in cattle fed a typical grain-based finishing diet. However, total tract nutrient digestibility was negatively affected.

Serosal-to-mucosal urea flux across the isolated ruminal epithelium is mediated via urea transporter-B and aquaporins when Holstein calves are abruptly changed to a moderately fermentable diet.

Urea transport (UT-B) proteins are known to facilitate urea movement across the ruminal epithelium; however, other mechanisms may be involved as well because inhibiting UT-B does not completely abolish urea transport. Of the aquaporins (AQP), which are a family of membrane-spanning proteins that are predominantly involved in the movement of water, AQP-3, AQP-7, and AQP-10 are also permeable to urea, but it is not clear if they contribute to urea transport across the ruminal epithelium. The objectives of this study were to determine (1) the functional roles of AQP and UT-B in the serosal-to-mucosal urea flux (Jsm-urea) across rumen epithelium; and (2) whether functional adaptation occurs in response to increased diet fermentability. Twenty-five Holstein steer calves (n=5) were assigned to a control diet (CON; 91.5% hay and 8.5% vitamin and mineral supplement) or a medium grain diet (MGD; 41.5% barley grain, 50% hay, and 8.5% vitamin and mineral) that was fed for 3, 7, 14, or 21 d. Calves were killed and ruminal epithelium was collected for mounting in Ussing chambers under short-circuit conditions and for analysis of mRNA abundance of UT-B and AQP-3, AQP-7, and AQP-10. To mimic physiologic conditions, the mucosal buffer (pH 6.2) contained no urea, whereas the serosal buffer (pH 7.4) contained 1 mM urea. The fluxes of (14)C-urea (Jsm-urea; 26 kBq/10 mL) and (3)H-mannitol (Jsm-mannitol; 37 kBq/10 mL) were measured, with Jsm-mannitol being used as an indicator of paracellular or hydrophilic movement. Serosal addition of phloretin (1 mM) was used to inhibit UT-B-mediated urea transport, whereas NiCl2 (1 mM) was used to inhibit AQP-mediated urea transport. Across treatments, the addition of phloretin or NiCl2 reduced the Jsm-urea from 116.5 to 54.0 and 89.5 nmol/(cm(2) × h), respectively. When both inhibitors were added simultaneously, Jsm-urea was further reduced to 36.8 nmol/(cm(2) × h). Phloretin-sensitive and NiCl2-sensitive Jsm-urea were not affected by diet. The Jsm-urea tended to increase linearly as the duration of adaptation to MGD increased, with the lowest Jsm-urea being observed in animals fed CON [107.7 nmol/(cm(2) × h)] and the highest for those fed the MGD for 21 d [144.2 nmol/(cm(2) × h)]. Phloretin-insensitive Jsm-urea tended to increase linearly as the duration of adaptation to MGD increased, whereas NiCl2-insensitive Jsm-urea tended to be affected by diet. Gene transcript abundance for AQP-3 and UT-B in ruminal epithelium increased linearly as the duration of MGD adaptation increased. For AQP-7 and AQP-10, gene transcript abundance in animals that were fed the MGD was greater compared with that of CON animals. These results demonstrate that both AQP and UT-B play significant functional roles in urea transport, and they may play a role in urea transport during dietary adaptation to fermentable carbohydrates.

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.

Short communication: Interrelationship between butyrate and glucose supply on butyrate and glucose oxidation by ruminal epithelial preparations.

The aim of this study was to determine whether dietary Na-butyrate supplementation affects butyrate and glucose oxidation by ruminal epithelial preparations and whether this effect can be acutely modulated by substrate (glucose and butyrate) supply. Eighteen Suffolk wether lambs (6 lambs/treatment) were blocked by body weight and, within block, randomly assigned to the control treatment (CON) or to diets containing differing Na-butyrate inclusion rates (1.58 or 3.16%) equating to 1.25 (B1.25), and 2.50% (B2.50) butyrate on a dry matter basis, respectively. All lambs received their diet for a period of 14 d. After dietary adaptation, lambs were killed and the ruminal epithelium was harvested from the ventral sac, minced finely, and used for in vitro incubations. Incubation medium contained either a constant concentration of glucose (4 mM) with increasing butyrate concentrations (0, 5, 15, 25, or 40 mM) or a constant butyrate concentration (15 mM) with increasing glucose concentrations (0, 1, 2, 4, or 8 mM) to allow for the evaluation of whether acute changes in the concentration of metabolic substrates affect the oxidation of glucose and butyrate. We observed no interactions between the in vivo and in vitro treatments. Increasing dietary butyrate supplementation linearly decreased glucose oxidation by ruminal epithelial preparations, but had no effect on butyrate oxidation. Increasing butyrate concentration in vitro decreased (cubic effect) glucose oxidation when butyrate concentration ranged between 5 and 15 mM; however, glucose oxidation was increased with a butyrate concentration of 40 mM. Butyrate oxidation decreased (cubic effect) as glucose concentration increased from 1 to 4 mM; however, butyrate oxidation increased when glucose was included at 8mM. The results of this study demonstrate that dietary butyrate supplementation can decrease glucose oxidation by the ruminal epithelium, but the relative supply of glucose and butyrate has a pronounced effect on substrate oxidation.

Supplemental butyrate does not enhance the absorptive or barrier functions of the isolated ovine ruminal epithelia.

Our objective was to determine if increasing the ruminal butyrate concentration would improve the selective permeability of ruminal epithelia. Suffolk wether lambs (n = 18) with an initial BW of 47.4 ±1.4 kg were housed in individual pens (1.5 × 1.5 m) with rubber mats on the floor. Lambs were blocked by initial BW into 6 blocks and, within block, were randomly assigned to either the control (CON) or 1 of 2 butyrate supplementation amounts (i.e., 1.25% or 2.50% butyrate as a proportion of DMI). With the exception of butyrate supplementation, all lambs were fed a common diet (90% concentrate and 10% barley silage). After a 14-d feeding period, lambs were killed, and ruminal epithelia from the ventral sac were mounted in Ussing chambers. To facilitate the Ussing chamber measurements, only 1 lamb was killed on an individual day. Thus, the starting date was staggered so that all lambs were exposed to the same experimental protocol. In Ussing chambers, epithelia were incubated using separate mucosal (pH 6.2) and serosal (pH 7.4) bathing solutions. Then 1-14C-butyrate (74 kBq/10 mL) was added to the mucosal side and was used to measure the mucosal-to-serosal flux (J(ms-butyrate)) in 2 consecutive 60-min flux periods with simultaneous measurement of transepithelial conductance (G(t)). During the first (challenge) flux period, the mucosal buffer solution was either acidified to pH 5.2 (ACID) or used as a control (pH 6.2; SHAM). Buffer solutions bathing the epithelia were replaced before the second flux period (recovery). Total ruminal short-chain fatty acid and butyrate concentrations were greater (P = 0.001) in lambs fed 2.50% compared with those fed 0% or 1.25% butyrate. The J(ms-butyrate) was less for lambs fed 1.25% and 2.50% butyrate [3.00 and 3.12 µmol/(cm2·h), respectively] than for CON [3.91 µmol/(cm2· h)]. However, no difference (P = 0.13)was observed for G(t). An ex vivo treatment × flux period interaction was detected (P = 0.003) for J(ms-butyrate), where no differences were present between ACID and SHAM during the challenge period, but the Jms-butyrate was less for ACID than for SHAM during recovery. These results indicate that large increases in the ruminal butyrate concentration decrease the selective permeability of the isolated ruminal epithelia.

Effects of feeding Fermenten on ruminal fermentation in lactating Holstein cows fed two dietary sugar concentrations.

This study was conducted to determine the effects of feeding Fermenten (Church and Dwight Co., Princeton, NJ) with or without dietary sucrose on ruminal fermentation, apparent total-tract nutrient digestibility, and nutrient utilization. Eight ruminally cannulated Holstein cows (163 +/- 55 d in milk; mean +/- standard deviation) were used in a replicated 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. Experimental diets were formulated with and without Fermenten (0 vs. 3.3% of dietary DM) at 2 dietary sugar concentrations (2.8 vs. 5.7%). Dietary treatment did not affect dry matter intake or apparent total-tract nutrient digestibility. Feeding Fermenten did not affect ruminal pH, but high-sugar diets tended to increase the daily minimum pH (5.61 vs. 5.42) and mean pH (6.17 vs. 6.30) compared with low-sugar diets. Ruminal ammonia concentration tended to be greater for cows fed Fermenten compared with control (18.1 vs. 15.9 mg/dL), but was not affected by dietary sugar concentration. Significant interactions between Fermenten and dietary sugar concentration were detected for some milk production responses. Fermenten treatment numerically increased milk fat yield (0.92 vs. 0.82 kg/d), 4% fat-corrected milk yield (24.3 vs. 21.9 kg/d), and milk energy output (18.2 vs. 16.4 Mcal/d) compared with control for cows fed low-sugar diets, but not for cows fed high-sugar diets. Increasing dietary sugar concentration did not enhance the effects of Fermenten, providing no support for the theory that synchronizing the availability of N and fermentable energy in the rumen improves nutrient utilization in lactating dairy cows.