Search

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

The objective of this study was to evaluate the influence of metabolizable protein (MP) level and supplemental rumen-protected methionine (RPM) on colostrum quality and passive immunity transfer from beef cows fed during late-gestation. One hundred and forty-seven pregnant Angus crossbred cows and heifers were randomly assigned to one of six dietary treatments based on a 3 x 2 factorial arrangement. Diets included feeding to 90%, 100% and 110% MP requirements (NRC, 2016), offered with (without) 9 g/d of RPM. Cattle were individually fed a partially mixed ration (60% haylage/40% straw for cows; 70% haylage/30% straw for heifers) with supplements top-dressed daily for approximately 56 d prior to calving. Immediately after calving, a colostrum sample was collected from each dam for analysis of milk components, total protein, and IgG concentrations. Two d post-calving, serum samples were collected from each calf for analysis of total protein and IgG concentrations. A refractometer was used to estimate total protein as a preliminary estimate of the transfer of maternal IgG and total IgG concentrations were later determined using Radial Immunodiffusion (RID). Data were analyzed as a completely randomized block design using Proc GLIMMIX in SAS. Level of MP, RPM, and their interaction did not influence concentrations of fat, protein, BHB or SCC in colostrum (P ≥ 0.12). Supplementation of RPM decreased concentrations of MUN (45.92 vs. 54.51 ±3.17 mg/dl; P = 0.04), but did not change IgG (14.66 vs. 15.90 ±0.87 g/dl; P = 0.29). While MP level during gestation did not affect total protein or IgG concentrations in calf serum (P ≥ 0.64), providing supplemental RPM decreased total protein (5.79 vs. 6.33 ±0.13 g/dl; P = 0.002) and IgG concentrations in calf serum (3.44 vs. 4.30 ±0.25 g/dl; P = 0.01). These results suggest that providing supplemental methionine for beef cows during gestation may alter colostrum quality and decrease serum protein and IgG in offspring.

A three-way factorial arrangement was used to assess impacts of protein/methionine nutrition during gestation and two lactational management systems on performance of cow-calf pairs pre-weaning. 140 crossbred beef cows were managed in drylot and randomly assigned to one of six nutritional treatments during the third trimester of gestation. Cows were fed to meet 110% (HP), 100% (MP), or 90% (LP) of metabolizable protein requirements for late-gestation (NRC, 2016), with(without) rumen-protected methionine (RPM) for 8 weeks prior to parturition. Post-partum, cow-calf pairs were managed in drylot (DL) and fed ad libitum, a ration formulated to meet lactational nutrient requirements, or rotationally grazed on pasture (PAS). Cow body weights (BW) and body condition scores (BCS) and calf BW were recorded at regular intervals. All data were analyzed using PROC GLIMMIX (SAS v9.4). HP cows were heaviest at calving (P = 0.02), but calf birthweight was unaffected by gestational nutrition (P > 0.19). Gestational nutrition did not impact cow conception rate (CR), or calf BW and ADG (P > 0.17). Lactational management system (PAS, DL) did not affect cow BCS or CR (P > 0.13), but impacted cow and calf BW and ADG. PAS calves were heavier, had greater ADG, and heavier weaning BW than DL calves (P < 0.02). This came at the expense of BW loss throughout lactation and lower ADG for PAS cows, versus BW gains and greater ADG for DL cows (P < 0.0001). An interaction between protein level and RPM supplementation was present for cow BW at calving and weaning, and BW change throughout lactation (P < 0.04), with tendencies for interactions for cow ADG and BCS (P < 0.09). Overall, prepartum protein/methionine supplementation did not affect calf performance prior to weaning, but may have affected cow performance during lactation. Rotationally grazing cow-calf pairs on pasture improved pre-weaning calf gains, but reduced cow gains throughout lactation.

The objective of this study was to investigate the role of protein-mediated transport pathways for short-chain fatty acid flux across the ruminal epithelium, using subacute ruminal acidosis (SARA) and feed restriction as models. Twenty-one Holstein steers (216.8 ± 31.4 kg BW) were individually housed and fed a total mixed ration (TMR) with a 50:50 forage:concentrate ad libitum for 5 d. After the 5 d diet adjustment period, calves were assigned 1 of 3 treatments: control (CTRL) calves were fed the TMR ad libitum on d 1, subacute ruminal acidosis calves were given 25% of their ad libitum DMI on d 1 and then given a barley grain challenge at 30% of ad libitum DMI on d2 (ACID) calves were given 25% of their ad libitum DMI on d 1 and then given a barley grain challenge at 30% of ad libitum DMI on d 2, and feed restriction (FR) calves were given 25% of their ad libitum DMI for 5 d. Reticuloruminal pH was continuously measured during the entire study. At the end of the study, rumen tissue was harvested and acetate and butyrate flux were measured. Selective inhibitors were used to differentiate total flux (TOTAL), protein-mediated flux (PMF), and passive diffusion flux (PDF). The duration that rumen pH was

The objectives of this study were to determine the effect of dietary inclusion [0%–50% of diet dry matter (DM)] and form (dry and modified wet) of corn distillers grains plus solubles (DGS) on pancreatic α-amylase and trypsin activities in calves. Feeding up to 50% DGS did not negatively impact pancreatic exocrine function.

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.

Agri-food supply chains in North America have become remarkably efficient, supplying an unprecedented variety of items at the lowest possible cost. However, the initial stages of the COVID-19 pandemic and the near-total temporary loss of the foodservice distribution channel, exposed a vulnerability that many found surprising. Instead of continued shortages, however, the agri-food sector has since moved back to near normal conditions with prices and production levels similar to those typically observed in years prior to the pandemic. Ironically, the specialization in most food supply chains designed for “just-in-time” delivery to specific customers with no reserve capacity, which led to the initial disruptions, may have also been responsible for its rapid rebound. A common theme in assessing the impacts across the six commodities examined is the growing importance of understanding the whole supply chain. Over the longer term, a continuation of the pandemic could push the supply chain toward greater consolidation of firms and diversification of products given the increasing option value of maintaining flexibility. Other structural changes will be felt through input markets, most notably labour, as the trend toward greater automation will continue to accelerate as a response to meeting concerns about a consistent supply of healthy and productive workers. The economic fall out from the pandemic may lead to greater concentration in the sector as some firms are not able to survive the downturn and changes in consumer food buying behaviour, including movement toward online shopping and enhanced demand for attributes associated with resiliency, such as local. On the other hand, online shopping may provide opportunities for small producers and processors to shorten supply chains and reach customers directly. In the long term, COVID-19 impacts on global commerce and developing country production are more uncertain and could influence poverty reduction. While COVID-19's impacts on North American agriculture should have minimal effect on the Sustainable Development Goals (SDGs) through food prices, the ongoing global trends in trade and agribusiness accelerated by the pandemic are relevant for achievement of the SDGs., Highlights • Initial stages of the COVID-19 pandemic exposed a vulnerability in agri-food sector supply chains. • Most sectors have since moved back to near normal conditions. • Importance of understanding the whole supply chain is growing. • The trend toward greater automation will continue to accelerate.

Fourteen Holstein bull calves were used in a randomized complete block design to investigate the effect of calf age and weaning on permeability of the gastrointestinal tract (GIT). Calves were randomly assigned to 1 of 2 treatments: (1) a weaning protocol that was initiated on d 35; WN; n=7), or (2) a control treatment where calves were not weaned (CON; n=7). Calves were bottle-fed milk replacer (150 g/L), in 3 equal portions/d targeting 15% of their body weight (BW) in liquid milk intake [approximately 21.1g/kg of BW/d, dry matter (DM) basis]. On d 35, the amount of milk replacer offered to WN calves was reduced to 7.5% of BW for 7 d before calves were weaned on d 42. On d 14, 28, and 42, calves were orally dosed with 500 mL of Cr-EDTA (179 mM Cr-EDTA solution) and housed in a metabolism crate to enable total urine collection and determination of total urinary Cr recovery as an indicator of total-tract permeability. On d 44, calves were killed and tissues from the rumen, omasum, duodenum, jejunum, ileum, cecum, and proximal and distal colon were collected, rinsed, and transported in buffer solution (pH 7.4 at 38.5°C). Tissues were incubated in Ussing chambers under short-circuit conditions with buffer solutions designed to mimic the mucosal and serosal energy source that would be available in vivo (glucose for tissues from the small intestine and short-chain fatty acids for tissues that would be exposed to fermentation; rumen, omasum, and large intestinal tissues). The serosal to mucosal flux of (14)C-mannitol and (3)H-inulin was measured for each region. Although we detected treatment × period interactions for BW and starter intake, dietary treatments did not differ within a week. Overall, the time that ruminal pH was5.5 was less before weaning than after weaning. We observed a differential response for the appearance of Cr in urine for WN and CON calves, where the appearance of Cr (mg/48 h) in urine decreased for both treatments from d 14 to 28, but increased from d 28 to 42 for WN, whereas Cr appearance continued to decrease for CON. The flux of mannitol and inulin did not differ between treatments but did differ among region of the GIT, with rumen, duodenum, and jejunum having the greatest permeability. These data suggest that permeability of the GIT decreases with age but weaning may disrupt this process. The rumen, duodenum, and jejunum appear to be the regions with greatest permeability.

Salim, H., Wood, K. M., Cant, J. P. and Swanson, K. C. 2015. Influence of feeding increasing levels of dry or modified wet corn distillers’ grains plus solubles in whole corn grain-based finishing diets on hepatic and renal mass, and glutathione peroxidase and urea cycle enzyme activities in finishing cattle. Can. J. Anim. Sci. 95: 407–415. Forty-two cross-bred steers (BW=357±5.8 kg) fed whole corn grain-based finishing diets were used in a completely randomized block (60, 120, or 180 d on feed) design (2×3 factorial arrangement of treatments plus control) to determine the effect of inclusion level [0 (control), 16.7, 33.3, and 50% of diet DM) and form (dry (DDGS) or modified wet (MWDGS)] of distillers’ grains plus solubles (DGS) on hepatic and renal glutathione peroxidase (GPx) and hepatic urea cycle enzyme activities. Kidney weight (g kg−1of BW) increased linearly (P=0.004) with increasing inclusion levels of DGS. There were no effects (P≥0.11) of dietary treatment on hepatic and renal GPx activity (U g−1, U mg−1of protein, and kU liver−1). Hepatic carbamoyl phosphate synthetase activity (kU liver−1and U kg−1of BW) tended to linearly increase (P=0.09 and P=0.10, respectively) with increasing inclusion level of DGS. Hepatic ornithine transcarbamoylase and argininosuccinate synthetase activity (kU liver−1and U kg−1of BW) increased linearly (P≤0.05) with increasing inclusion levels of DGS. These data indicate that steers adapt to feeding up to 50% DGS by increasing kidney mass and activity of urea cycle enzymes in liver to allow for clearance of excess nitrogen. Also, hepatic and renal GPx activity, as an indicator of Se status, is not affected when typical finishing diets are fed.

Wood, K. M., Montanholi, Y. R., Fitzsimmons, C. F., Miller, S. P., McBride, B. W. and Swanson, K. C. 2014. Characterization and evaluation of residual feed intake measured in mid- to late-gestation mature beef cows and relationships with circulating serum metabolites and linear body measurements. Can. J. Anim. Sci. 94: 499–508. To evaluate the use of residual feed intake (RFI) models measured in mid-to-late gestating beef cows, a dataset was used combining data from five experiments containing nine treatment and/or replicate groups for a total of 321 animal records. Investigations of RFI models included the effects of age, ultrasound measures of body composition, pregnancy corrected gain, and dietary treatment group. A subset of animals had serum analyzed for circulating metabolites (glucose, non-esterified fatty acids, urea, beta-hydroxybutyrate; n=227) and/or linear body measures (hip height and width, body length, body circumference at the heart, mid-body and at flank; n=114) for correlation analysis w...

In mid-to-late gestation, nutrient demand increases to meet the growth requirements of the conceptus and cows may alter metabolism in response to energy demands of pregnancy. By better understanding the metabolic role of pregnancy, there may be opportunities to better understand maintenance energy costs and improve overall feed efficiency. Eighteen mature Simmental/Angus crossbred cows, pregnant (PREG; n = 9) and nonpregnant (OPEN; n = 9), were used to investigate the effect of pregnancy on BW change, carcass traits, visceral organ mass, and circulating serum metabolites. Cows were blocked by day of expected parturition such that each block was slaughtered 4 to 5 wk before parturition. Cows were individually fed for ad libitum intake using Calan gates for 89 to 105 d. Cows were weighed, ultrasounded for rib (over the 12th and 13th rib) and rump fat, and a serum sample obtained at d 1, 56, and 3 to 5 d before slaughter. At slaughter, organs were removed, trimmed of fat, and weighed. Serum was analyzed for β-hydroxybutyrate (BHBA), NEFA, glucose, urea, total cholesterol, and triiodothyronine (T3). Tissue samples from liver, kidney, sternomandibularis muscle, ruminal papillae, pancreas, and small intestinal mucosa were collected at slaughter and snap frozen in liquid N. Western blots were conducted to quantify abundance of: proliferating cell nuclear antigen (PCNA), ATP synthase, ubiquitin, and Na(+)/K+ ATPase for all tissues; PPARγ, PPARγ coactivator 1α (PGC1-α), 5'-adenosine monophosphate-activated protein kinase (AMPK) and phosphorylated-AMPK (pAMPK) for liver, muscle, and rumen; phosphoenolpyruvate carboxykinase (PEPCK) for liver and kidney; and uncoupling protein 2 (UCP2) for liver. Data were analyzed using PROC MIXED in SAS as a replicated randomized complete block. Liver weights (actual, relative to BW, relative to HCW) were heavier (P ≤ 0.02) in OPEN. Rumen mass and kidney fat weight, both relative to BW, were also greater (P ≤ 0.04) in OPEN. On d 56 and at preslaughter, PREG cows had greater (P ≤ 0.04) BHBA, NEFA and urea concentrations and lower (P = 0.04) cholesterol concentration. Hepatic Na(+)/K+ ATPase abundance was greater (P = 0.04) in PREG cows. In rumen papillae, abundance of pAMPKα was increased (P = 0.006) in PREG cows. These data indicate that PREG cows may metabolize energy reserves and alter their metabolism to meet the energetic demands of the growing fetus.

Twenty-two nonlactating multiparous pregnant beef cows (639 ± 68 kg) were used to investigate the effect of dietary restriction on the abundance of selected proteins regulating cellular energy metabolism. Cows were fed at either 85% (n = 11; LOW) or 140% (n = 11; HIGH) of total NE requirements. The diet consisted of a haylage-based total mixed ration containing 20% wheat straw. Cows were slaughtered by block (predicted date of parturition), beginning 83 d after the initiation of dietary treatments and every week thereafter for 6 wk, such that each block was slaughtered at approximately 250 d of gestation. Tissue samples from liver, kidney, sternomandibularis muscle, ruminal papilli (ventral sac), pancreas, and small intestinal muscosa were collected at slaughter and snap frozen in liquid N2. Western blots were conducted to quantify abundance of proliferating cell nuclear antigen (PCNA), ATP synthase, ubiquitin, and Na/K+ ATPase for all tissues; PPARγ, PPARγ coactivator 1 α (PGC-1α), and 5´-adenosine monophosphate-activated protein kinase (AMPK) and the activated form phosphorylated-AMPK (pAMPK) for liver, muscle, and rumen; phosphoenolpyruvate carboxykinase (PEPCK) for liver and kidney; and uncoupling protein 2 (UCP2) for liver. Statistical analysis was conducted using Proc Mixed in SAS and included the fixed effects of dietary treatment, cow age, block, and the random effect of pen. Dietary treatments resulted in cows fed HIGH having greater (P ≤ 0.04) ADG and final BW than cows fed LOW. Abundance of ubiquitin in muscle was greater (P = 0.009) in cows fed LOW, and PCG-1 α in liver was greater (P = 0.03) in cows fed HIGH. Hepatic O2 consumption was greater in HIGH (P ≤ 0.04). Feed intake can influence the abundance of important metabolic proteins and suggest that protein degradation may increase in muscle from moderately nutrient restricted cows and that energy metabolism in liver increases in cows fed above NE requirements.

To determine effects of pregnancy (experiment 1) and plane of nutrition during pregnancy (experiment 2) on pancreatic digestive enzymes and morphology of insulin-containing cell clusters, beef cows...

Sixty cross-bred steers (Angus ×; n = 36 and Charolais ×; n = 24) were used in a split-plot design to investigate the effects of feeding corn (Zea mays) or sorghum (Sorghum bicolor) dried distillers grains plus solubles in growing and finishing diets on growth performance and carcass traits. Steers were randomly assigned to one of three dietary treatments used in both feeding periods: a control diet containing soybean meal (n = 20; CON), a diet containing 200 g/kg (DM basis) corn dried distillers grains + solubles (n = 20; CDDGS) and a diet containing 200 g/kg (DM basis) sorghum dried distillers grains + solubles (n = 20; SDDGS). Steers were fed a corn silage (CS) based grower diet (∼750/kg CS) for 56 d and then switched to a high grain finisher diet (150 g/kg CS). Feed intakes were measured using Insentec (n = 48) and Calan gate (n = 12) feeding systems. Animals were weighed every 28 d and slaughtered at an estimated backfat of 10 mm as estimated by ultrasound. Total trial average daily gain (ADG) was 1.56 kg/d ± 0.04 for CON, 1.54 kg/d ± 0.04 for CDDGS, and 1.51 kg/d ± 0.04 for SDDGS and did not differ (P>0.68) between treatments. Dietary treatment did not affect (P>0.14) dry matter intake (DMI) in the growing phase, although ADG was lower for SDDGS vs. CON (P=0.008) and CDDGS (P=0.02). There was a lower gain:feed in the growing phase for SDDGS vs. CDDGS (P=0.04). In the finishing phase, inclusion of corn or sorghum DDGS did not affect (P>0.41) ADG, DMI or G:F. However, fewer days on feed were required for SDDGS to reach the target backfat for slaughter than CDDGS (P=0.03) and CON (P=0.05). These results indicate that sorghum dried distillers grains plus solubles can be included at 200 g/kg inclusion level, similar to corn distillers grains plus solubles, in grower and finisher diets, without negatively influencing overall growth or carcass traits, although feeding SDDGS may result in reduced performance when corn silage based diets are fed and results in earlier fattening at a lighter body weight.

Seventy-one individually fed multiparous, pregnant crossbred beef cows [body weight (BW) ± SD; 730 ± 77.9 kg] were used to examine the effects of including crop residues in alfalfa/grass haylage-based rations on BW gain, fat deposition/loss and plasma metabolites. The haylage control ration (CON; n = 23) was modified to include either 40% (dry matter basis) wheat straw (WS; n = 24) or 40% corn stalklage (CS; n = 24). Cows were blocked by calving date and randomly assigned to each treatment and fed for 82 d leading up to the earliest calving date. On days 1, 40, and 82, cows were weighed, ultrasounded to measure subcutaneous backfat (BF) over the ribs, body condition scored (BCS) and plasma was collected. Calves from cows fed WS had greater (P = 0.02 ) weaning weights than cows fed CS, but did not differ (P = 0.23) from CON. CS cows had the lowest ADG (P

Twenty-four steers (initial body weight = 535 ± 5.0 kg) predominately of Angus breeding were used to determine the effect of dietary corn silage inclusion [20, 40, 60, or 80% of dry matter (DM)] on visceral mass, cellularity, and the protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen (PCNA) and ubiquitin. Steers were fed at similar energy levels (2.1 × NEm requirement). There were no significant treatment effects on specific visceral organ weights. Hepatic Na+/K+-ATPase expression linearly increased (P = 0.01) and ruminal Na+/K+-ATPase expression linearly decreased (P = 0.01) with increasing corn silage inclusion. Hepatic PCNA expression was quadratically affected (P = 0.05) with a decrease when corn silage inclusion increased from 20 to 60%, and an increase when corn silage inclusion increased from 60 to 80%. Renal ATP synthase (P = 0.02) and ubiquitin expression (P = 0.01) were quadratically affected in a similar pattern with an increase when corn silage inclusion increased from 20 to 60%, and a decrease when corn silage inclusion increased from 60 to 80%. These results indicate that different dietary corn silage inclusions, at similar dietary energy intake, may alter rumen, liver, and kidney energy expenditure, at least in part, through changes in specific metabolism rather than mass. Key words: Corn silage inclusion, visceral organ mass, cellular energy metabolism, steer

The objective of this study was to characterise the regional variation in the barrier function of the gastrointestinal tract in Holstein calves using the flux rates of mannitol and inulin as permeability markers and tissue conductance (Gt) as an electrophysiological indicator of barrier function. Six Holstein steer calves (6 months of age) fed a common diet were used. Calves were killed by captive bolt stunning and pithing, and tissues were collected from the rumen, omasum, duodenum, jejunum, ileum, caecum, proximal colon, and distal colon. Tissues were carefully washed using a pre-heated (38.5°C) buffer solution (pH 7.4) saturated with oxygen and then transported to the laboratory. The mucosa was prepared by hand stripping and mounted between two halves of an Ussing chamber (n = 3/region with an exposed surface area of 3.14 cm2 for rumen and omasum and 1 cm2 for all other tissues). All tissues were incubated under short-circuit conditions and exposed to a similar buffer solution except for the energy source; rumen, omasum, caecum, and colon tissues were incubated with buffer containing short-chain fatty acids while tissues from the small intestine were bathed in buffer containing glucose. The Gt and the serosal-to-mucosal flux rates of 14C-inulin and 3H-mannitol were measured as indicators of barrier function. The serosal-to-mucosal flux rate of mannitol was greatest (P < 0.001) in the jejunum [104.8 nmol/(cm2 × h)] and least in the rumen and omasum [20.3 and 18.6 nmol/(cm2 × h), respectively]. In contrast, the serosal-to-mucosal flux rate of inulin was greatest (P < 0.001) in the omasum [158.6 nmol/(cm2 × h)] followed by the rumen [87.3 nmol/(cm2 × h)] with no differences among the other regions [18.7 – 62.0 nmol/(cm2 × h)]. The Gt was greatest (P < 0.001) in the jejunum (34.6 mS/cm2) and least for the rumen (3.67 mS/cm2) and omasum (3.23 mS/cm2). The Gt was correlated with both inulin and mannitol flux rates in duodenum, caecum and proximal colon (P < 0.05); whereas, no such correlations existed in jejunum, ileum and distal colon. The Gt was correlated with the mannitol flux rate but not the inulin flux rate in rumen and omasum. For all regions but the rumen and omasum there was a positive correlation between mannitol and inulin flux rates. These data indicate that the translocation of a large molecule (inulin) across the omasum and rumen is greatest despite having an apparently tight epithelium based on Gt and mannitol flux rate, while the jejunum appears to have greatest potential for paracellular permeability.