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We previously demonstrated that postruminal casein infusion and exogenous glucagon-like peptide 2 (GLP-2) administration independently stimulated growth and carbohydrase activity of the pancreas and jejunal mucosa in cattle. The objective of the current study was to profile the jejunal mucosal transcriptome of cattle using next-generation RNA sequencing in response to postruminal casein infusion and exogenous GLP-2. Twenty-four Holstein steers [250 ± 23.1 kg body weight (BW)] received a continuous abomasal infusion of 3.94 g raw corn starch/kg of BW combined with either 0 or 1.30 g casein/kg of BW for 7 d. Steers received subcutaneous injections at 0800 and 2000 h to provide either 0 or 100 μg GLP-2/kg of BW per day. At the end of the 7-d treatment period, steers were slaughtered for collection of the jejunal mucosa. Total RNA was extracted from jejunal mucosal tissue, strand-specific cDNA libraries were prepared, and RNA sequencing was conducted to generate 150-bp paired-end reads at a depth of 40 M reads per sample. Differentially expressed genes (DEG), KEGG pathway enrichment, and gene ontology enrichment were determined based on the FDR-corrected P-value (padj). Exogenous GLP-2 administration upregulated (padj < 0.05) 667 genes and downregulated 1,101 genes of the jejunal mucosa. Sphingolipid metabolism, bile secretion, adherens junction, and galactose metabolism were among the top KEGG pathways enriched with upregulated DEG (padj < 0.05) in response to exogenous GLP-2 administration. The top gene ontologies enriched with upregulated DEG (padj < 0.05) in response to exogenous GLP-2 administration included nutrient metabolic processes, brush border and bicellular tight junction assembly, and enzyme and transporter activities. Exogenous GLP-2 administration increased or tended to increase (padj < 0.10) brush border carbohydrase (MGAM, LCT, TREH), hexose transporter (SLC5A1, SLC2A2), and associated transcription factor (HNF1, GATA4, KAT2B) mRNA expression of the jejunal mucosa. Gene ontologies and KEGG pathways that were downregulated (padj < 0.05) in response to exogenous GLP-2 were related to genetic information processing. Postruminal casein infusion downregulated (padj < 0.05) 7 jejunal mucosal genes that collectively did not result in enriched KEGG pathways or gene ontologies. This study highlights some of the transcriptional mechanisms associated with increased growth, starch assimilation capacity, and barrier function of the jejunal mucosa in response to exogenous GLP-2 administration. [ABSTRACT FROM AUTHOR]

To better understand mechanisms of serotonin‐ (5‐HT) mediated vasorelaxation, isolated lateral saphenous veins from cattle were assessed for vasoactivity using myography in response to increasing concentrations of 5‐HT or selective 5‐HT receptor agonists. Vessels were pre‐contracted with 1 × 10−4 M phenylephrine and exposed to increasing concentrations of 5‐HT or 5‐HT receptor agonists that were selective for 5‐HT1B, 5‐HT2B, 5‐HT4, and 5‐HT7. Vasoactive response data were normalized as a percentage of the maximum contractile response induced by the phenylephrine pre‐contraction. At 1 × 10−7 M 5‐HT, a relaxation was observed with an 88.7% decrease (p < 0.01) from the phenylephrine maximum. At 1 × 10−4 M 5‐HT, a contraction was observed with a 165% increase (p < 0.01) from the phenylephrine maximum. Increasing concentrations of agonists selective for 5‐HT2B, 5‐HT4, or 5‐HT7 resulted in a 27%, 92%, or 44% (p < 0.01) decrease from the phenylephrine maximum, respectively. Of these 5‐HT receptor agonists, the selective 5‐HT4 receptor agonist resulted in the greatest potency (−log EC50) value (6.30) compared with 5‐HT2B and 5‐HT7 receptor agonists (4.21 and 4.66, respectively). To confirm the involvement of 5‐HT4 in 5‐HT‐mediated vasorelaxation, blood vessels were exposed to either DMSO (solvent control) or a selective 5‐HT4 antagonist (1 × 10−5 M) for 5‐min prior to the phenylephrine pre‐contraction and 5‐HT additions. Antagonism of the 5‐HT4 receptor attenuated the vasorelaxation caused by 5‐HT. Approximately 94% of the vasorelaxation occurring in response to 5‐HT could be accounted for through 5‐HT4, providing strong evidence that 5‐HT‐mediated vasorelaxation occurs through 5‐HT4 activation in bovine peripheral vasculature. [ABSTRACT FROM AUTHOR]

Simple Summary: There is rising interest globally in reducing the use of antibiotics in livestock feeding regimens. Phytogenic feed additives have been evaluated for their potential use to replace compounds such as ionophores in finishing cattle diets. The effects of saponin-containing extracts from Yucca schidigera (YSE) on ruminal fermentation, average daily gain, and feed efficiency appear to be similar to monensin; however, YSE is not approved for the control or prevention of coccidiosis in cattle. Therefore, the objectives of this study were to evaluate sources and levels of anti-coccidial compounds and saponins, individually or in combination, on in vitro and in vivo ruminal fermentation and CH4 production. In summary, the combination of decoquinate with YSE did not influence in vivo CH4 production but tended to increase ruminal propionate proportion. Monensin inclusion decreased in vitro CH4 production and the acetate:propionate. Increasing saponin inclusion increased the propionate proportion in vitro but was not accompanied by a reduction in CH4 production. Four experiments were conducted to evaluate sources of anti-coccidial compounds and phytogenic saponin extracts on in vitro and in vivo ruminal fermentation and CH4 production at multiple inclusion levels. In experiment 1, eight steers were fed either a finishing diet or a finishing diet supplemented with 0.5 mg/kg BW decoquinate (DCQ) and 3.33 mg/kg BW Yucca schidigera extract (YSE), and respiratory gas exchange was measured. In experiment 2, four ruminally-cannulated steers were fed the same treatments as experiment 1, and ruminal fermentation was evaluated. Anti-coccidial sources (experiment 3; monensin, DCQ, amprolium) and saponin sources (experiment 4; YSE, Quillaja saponaria extract) and levels were evaluated for effects on in vitro ruminal fermentation and CH4 production. DCQ + YSE supplementation did not influence (p ≥ 0.24) in vivo respiratory gas consumption/production, in situ DM degradation, or liquid passage kinetics. Ruminal propionate proportion tended to increase (p = 0.09) with DCQ + YSE. Monensin decreased (p ≤ 0.04) in vitro acetate:propionate and CH4 production; saponin supplementation linearly increased (p < 0.01) propionate proportion but did not influence (p ≥ 0.38) in vitro CH4 production. Saponins and non-antibiotic anti-coccidials did not influence in vitro or in vivo CH4 production with finishing diets. [ABSTRACT FROM AUTHOR]

Increased efficiency of nutrient utilization can potentially be gained with increased starch digestion in the small intestine in ruminants. However, ruminants have quantitative limits in the extent of starch disappearance in the small intestine. The objective is to explore the nutritional and physiological constraints that contribute to limitations of carbohydrate assimilation in the ruminant small intestine. Altered digesta composition and passage rate in the small intestine, insufficient pancreatic α-amylase and/or small intestinal carbohydrase activity, and reduced glucose absorption could all be potentially limiting factors of intestinal starch assimilation. The absence of intestinal sucrase activity in ruminants may be related to quantitative limits in small intestinal starch hydrolysis. Multiple sequence alignment of the sucrase-isomaltase complex gives insight into potential molecular mechanisms that may be associated with the absence of intestinal sucrase activity, reduced capacity for intestinal starch digestion, and limitations in the efficiency of feed utilization in cattle and sheep. Future research efforts in these areas will aid in our understanding of small intestinal starch digestion and glucose absorption to optimize feeding strategies for increased meat and milk production efficiency. [ABSTRACT FROM AUTHOR]

Consumption of high-grain diets by cattle can result in large quantities of starch that flow to the small intestine for potential enzymatic digestion. However, small intestinal starch digestion is potentially limited because of insufficient activity of pancreatic and/or small intestinal carbohydrases. Studies suggest regulation of carbohydrase activity is complex in cattle and perhaps uncoordinated in response to luminal carbohydrate flow. The objective of this experiment was to use postruminal casein infusion and exogenous glucagon-like peptide 2 (GLP-2) administration, known stimulators of pancreatic and small intestinal function, to evaluate their effects on pancreatic and small intestinal carbohydrase activities. Twenty-four Holstein steers [250 ± 23 kg body weight (BW)] were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments. Steers were fed an alfalfa cube-based diet to limit dietary starch intake. Steers received a continuous abomasal infusion of 4 g/kg of BW of raw corn starch combined with either 0 or 1.33 g/kg of BW of casein for 7 d. Steers received subcutaneous injections in two portions daily of excipient (0.5% bovine serum albumin) or 100 μg/kg of BW GLP-2. This resulted in four treatments: control, casein, GLP-2, and casein + GLP-2. At the end of the 7-d treatment period, steers were slaughtered for pancreatic and small intestinal tissue collection. Data were analyzed using the GLM procedure of SAS. Postruminal casein infusion increased (P = 0.03) pancreatic mass by 12.6%, total pancreatic a-amylase activity by 50%, and postruminal starch disappearance from 96.7% to 99.3%. Exogenous GLP-2 increased (P < 0.01) total small intestinal mass and small intestinal mucosal mass by 1.2 kg and 896 g, respectively. Relative to control, GLP-2 and casein + GLP-2 treatments increased (P = 0.04) total small intestinal a-glucosidase activity (sum of maltase, isomaltase, glucoamylase) by 83.5%. Total small intestinal maltase, isomaltase, and glucoamylase activity was 90%, 100%, and 66.7% greater for GLP-2 and casein + GLP-2 steers compared with control. The use of postruminal casein infusion and exogenous GLP-2 administration resulted in four distinct carbohydrase activity phenotypes. Relative to control, casein increased pancreatic a-amylase activity, GLP-2 increased small intestinal a-glucosidase activity, and the combination of casein and GLP-2 increased both pancreatic a-amylase activity and small intestinal a-glucosidase activity. This approach provides a novel in vivo animal model to selectively increase endogenous carbohydrase activity to overcome complications of coordinating carbohydrase activity with luminal nutrient flows. This model could be useful to understand physiological mechanisms that might improve small intestinal starch assimilation and efficiency of cattle consuming high-grain diets. [ABSTRACT FROM AUTHOR]

Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine peripheral and visceral vasculature. Ergovaline acts as both an agonist and an antagonist in bovine gut blood vessels through serotonin (5-HT) receptors and it appears that the type of action could be influenced by the extent of ERV exposure. Because it was unclear how the duration of ERV exposure influences 5-HT-mediated vasoactivity, experiments were designed to evaluate how simultaneous or prior ERV exposure influenced 5-HT-mediated vasoactivity of mesenteric artery (MA) and vein (MV) segments from Holstein steers (n = 10). Isolated vessel segments were incubated in Krebs-Henseleit buffer containing 0, 0.01, or 0.1 mM ERV for 24-h befoe the 5-HT doseresponse or exposed to fixed concentrations of 0, 0.01, or 0.1 mM ERV simultaneously during the 5-HT dose-response. Vessels were suspended in chambers of a multi-myograph containing 5 mL of continuously oxygenated Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were exposed to increasing concentrations of 5-HT (5 × 10-8 M to 1 × 10-4 M) every 15 min and contractile responses were normalized as a percentage of the maximum contractile response induced by 120 mM KCl reference addition. Two-way analysis of variance was used to separately analyze data for each vessel type and duration of exposure using the MIXED procedure of SAS for the main effects of 5-HT and ERV concentration and the 5-HT × ERV concentration interaction. When 5-HT concentration increased from 5 ' 10-8 M to 1 ' 10-6 M, simultaneous addition of 0.1 mM ERV increased (P < 0.01) the contractile response of MV compared with additions of 0 mM ERV and 0.01 mM ERV. At 1 ' 10-4 M 5-HT, the simultaneous presence of 0.01 mM ERV and 0.1 mM ERV decreased (P < 0.01) the contractile response of both MA and MV compared with 0 mM ERV addition. As 5-HT concentrations increased, the contractile response increased (P < 0.01) in both MA and MV with no previous ERV exposure, but decreased in MA and MV with 24-h prior exposure to 0.01 mM ERV and 0.1 mM ERV. These data demonstrate that the duration of ERV exposure influences 5-HT-mediated vasoconstriction and likely vasorelaxation in bovine mesenteric vasculature. If ERV and 5-HT exposure occur simultaneously, ERV can act as a partial agonist of 5-HT-mediated vasoconstriction. If 5-HT exposure occurs after blood vessels have had prior ERV exposure, it appears that 5-HT may induce vasorelaxation of blood vessels. More research is needed to identify receptors and mechanisms involved with 5-HT-mediated vasoconstriction and vasorelaxation before and after exposure to ERV. This will aid in the development of strategies for alleviating symptoms of sustained vasoconstriction that occur during fescue toxicosis in ruminants. [ABSTRACT FROM AUTHOR]

Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine vasculature by interacting with serotonin (5-HT) receptors. Ergovaline acts as a partial agonist of 5-HT2A-mediated vasoconstriction. The duration of ERV exposure affects 5-HT-mediated vasoactivity of mesenteric blood vessels. If ERV and 5-HT exposure occur simultaneously, ERV can increase 5-HT-mediated vasoconstriction. If 5-HT exposure occurs after blood vessels have had prior ERV exposure, increasing levels of 5-HT can induce vasorelaxation of blood vessels. To better understand mechanisms of 5-HT-mediated vasorelaxation, lateral saphenous veins from steers (n = 5) were assessed for vasoactivity in response to increasing concentrations of selective 5-HT receptor agonists Isolated vessel segments were suspended in chambers of a multi-myograph containing 5 mL of continuously oxygenated Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were pre-contracted with 1×10-4 M phenylephrine and exposed to increasing concentrations of 5-HT or 5-HT receptor agonists that were selective for 5-HT1B, 5-HT2B, 5-HT4, and 5-HT7. Vasoactive response data were normalized as a percentage of the maximum contractile response induced by the phenylephrine pre-contraction. Increasing concentrations of 5-HT resulted in divergent vasoconstriction and vasorelaxation responses that were dose-dependent. Serotonin caused an 86.3% increase (P < 0.01) in relaxation activity at 1×10-7 M and 5-HT caused a 166% increase (P < 0.01) in contraction activity at 1x10-4 M. Increasing concentrations of the selective 5-HT1B agonist did not result in any vasoactive response. Increasing concentrations of agonists selective for 5-HT2B, 5-HT4, or 5-HT7 resulted in a 27.3%, 91.6%, or 43.9% (P < 0.01) increase in maximal vasorelaxation activity. Of these 5-HT receptor agonists, the selective 5-HT4 receptor agonist resulted in the lowest -log IC50 value (6.30) compared with 5-HT2B and 5-HT7 receptor agonists (4.21 and 4.66, respectively). To confirm the involvement of 5-HT4 in 5-HT-mediated vasorelaxation, blood vessels were exposed to either DMSO (control), a selective 5-HT2A antagonist (1×10-5M), or selective antagonists of 5-HT2A and 5-HT4 simultaneously for 5-min before the precontraction with phenylephrine and additions of 5-HT. Antagonism of the 5-HT2A receptor did not result in increased vasorelaxation activity compared with control. Antagonism of the 5-HT2A receptor and 5-HT4 receptor simultaneously inhibited vasorelaxation activity and increased (P < 0.01) the maximal contractile response occurring at 1×10-4 M by 47% compared with control. Approximately 84% of the maximal vasorelaxation activity occurring in response to 5-HT could be accounted for through 5-HT4. These data provide strong evidence that 5-HT4 is the primary receptor involved with 5-HT-mediated vasorelaxation in bovine lateral saphenous vein. More research is needed to determine if 5-HT4-mediated vasorelaxation is responsible for relaxation responses observed in blood vessels with prior ERV exposure. This will aid in the development of strategies for alleviating symptoms of sustained vasoconstriction that occur during fescue toxicosis in ruminants. [ABSTRACT FROM AUTHOR]

To examine the effects of nutrient restriction during midgestation to late gestation on maternal and fetal digestive enzyme activities, 41 singleton ewes (48.3 ± 0.6 kg of BW) were randomly assigned to dietary treatments: 100% (control; CON; n = 20) or 60% of nutrient requirements (restricted; RES; n = 21) from day 50 until day 90 (midgestation). At day 90, 14 ewes (CON, n = 7; RES, n = 7) were euthanized. The remaining ewes were subjected to treatments of nutrient restriction or remained on a control diet from day 90 until day 130 (late gestation): CON-CON (n = 6), CON-RES (n = 7), RES-CON (n = 7), and RES-RES (n = 7) and were euthanized on day 130. The fetal and maternal pancreas and small intestines were weighed, subsampled, and assayed for digestive enzyme activity. One unit (U) of enzyme activity is equal to 1 µmol of product produced per minute for amylase, glucoamylase, lactase, and trypsin and 0.5 µmol of product produced per minute for maltase and isomaltase. Nutrient restriction during midgestation and late gestation decreased (P < 0.05) maternal pancreatic and small intestinal mass but did not affect fetal pancreatic or small intestinal mass. Maternal nutrient restriction during late gestation decreased (P = 0.03) fetal pancreatic trypsin content (U/pancreas) and tended to decrease (P < 0.08) fetal pancreatic trypsin concentration (U/g), specific activity (U/g protein), and content relative to BW (U/kg of BW). Nutrient restriction of gestating ewes decreased the total content of α-amylase (P = 0.04) and tended to decrease total content of trypsin (P = 0.06) and protein (P = 0.06) in the maternal pancreas on day 90. Nutrient restriction during midgestation on day 90 and during late gestation on day 130 decreased (P = 0.04) maternal pancreatic α-amylase-specific activity. Sucrase activity was undetected in the fetal and maternal small intestine. Nutrient restriction during late gestation increased (P = 0.01) maternal small intestinal maltase and lactase concentration and tended to increase (P = 0.06) isomaltase concentration. Realimentation during late gestation after nutrient restriction during midgestation increased lactase concentration (P = 0.04) and specific activity (P = 0.05) in the fetal small intestine. Fetal small intestinal maltase, isomaltase, and glucoamylase did not respond to maternal nutrient restriction. These data indicate that some maternal and fetal digestive enzyme activities may change in response to maternal nutrient restriction. [ABSTRACT FROM AUTHOR]

Ractopamine hydrochloride (RAC) is a β-adrenergic agonist that functions as a repartitioning agent to improve muscling in feedlot cattle. Many studies have investigated the effects of RAC on growth performance and carcass characteristics; however, there is minimal information about the influence of RAC on feeding behavior. Sixty-nine steers (body weight [BW] = 364 ± 3.9 kg) predominately of Angus and Simmental breeding were subjected to a 126-d (n = 46) or 154-d (n = 23) feeding period and randomly assigned to one of two treatment groups: supplementation to provide 0 (CON; n = 34) or 267 ± 4.9 mg/d of RAC (n = 35). Ractopamine was provided as Optaflexx 45 at 0.024% of the diet (dry matter [DM] basis; Elanco Animal Health, Greenfield, IN). Dietary treatments were fed the final 42 d in the feed yard (treatment period). Feeding behavior and growth performance were measured using radio frequency identification tags and the Insentec feeding system. Following the final day of treatment, steers were slaughtered and carcass measurements were recorded. Data were analyzed using MIXED models in SAS. There were no differences in BW, average daily gain (ADG), DM intake (DMI), gain:feed ratio (G:F), or feeding behavior during the pretreatment period (P > 0.44). Ractopamine supplementation increased G:F during the treatment period (P = 0.02) and during the total period (P = 0.03) and tended to increase ADG during the treatment and total period (P ≤ 0.08). DMI was not affected during the treatment or total period (P > 0.67). Eating time per visit, per meal, and per day were decreased (P < 0.02) in steers supplemented with RAC during the treatment period. DMI per minute was increased (P = 0.02) in steers supplemented with RAC. Hot carcass weight, dressing percentage, and 12th rib fat were not influenced by RAC supplementation. Ractopamine supplementation decreased marbling (P = 0.008) and kidney, pelvic, and heart percentage (P = 0.04) and increased longissimus muscle area (P = 0.01). These data demonstrate that RAC supplementation for 42 d improves feed efficiency, increases the rate of DMI without altering DMI, and increases muscling in finishing cattle. [ABSTRACT FROM AUTHOR]

Ergot alkaloids from endophyte- infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum) induce vasoconstriction. Previous work has shown that serotonin receptor subtype, 5HT2A, is present in bovine ruminal (R) and mesenteric (M) vasculature, plays a role in vasoconstriction, and could be influenced by ergot alkaloids. To determine the influence of ergot alkaloids on 5HT2A, the vasoactivity of an agonist selective for 5HT2A, (4-bromo-3,6-dimethoxybenzocyclobuten- 1-yl) methylamine HCl (TCB-2), was evaluated using bovine ruminal and mesenteric arteries and veins (RA, RV, MA, MV) that were exposed to ergovaline (ERV) prior to or during the TCB-2 additions. Ruminal and mesenteric blood vessel segments were collected, cleaned, and cut into 2- to 3-mm cross-sections. Vessel segments were incubated in Krebs-Henseleit buffer containing 0, 0.01 or 1 μM ERV for 2 h prior to TCB-2 dose response or exposed to ERV concentrations simultaneously during TCB-2 dose response. For the dose response portion of the study, vessels were suspended in a multimyograph containing 5 mL of continuously oxygenated Krebs–Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were exposed to increasing concentrations of TCB-2 every 15 min and contractile response data were normalized as a percentage of the maximum contractile response induced by 120 mM KCl reference. Analysis of variance was evaluated separately for each vessel and each ERV exposure experiment using the mixed models procedure of SAS for effects of TCB-2 and ERV concentrations. All blood vessels with previous ERV exposure had significantly lower contractile responses to TCB-2 (P < 0.01). All blood vessels with simultaneous exposure to 1 μM ERV had higher (P < 0.01) contractile responses at lower concentrations of TCB-2. Simultaneous ERV addition at 1 × 10−4 M TCB-2 did not affect contractility of RV, MA, MV (P > 0.05), but decreased contractility of RA (P < 0.01). These results indicate that ergopeptine alkaloid exposure influences contractility of bovine ruminal and mesenteric blood vessels through serotonin receptor subtype 5HT2A by acting as both an agonist and antagonist. Additional work is needed to determine if ergot alkaloids like ERV simply occupy receptor binding sites competitively, or influence receptor internalization to cause the observed divergent responses. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate different combinations of one-carbon metabolites [OCM: rumen-protected methionine (RPM), rumenprotected choline (RPC), folate (FA), vitamin B12 (B12)] on pancreatic and jejunal carbohydrase activity at d 14 of the estrous cycle in beef heifers. Thirty Angus heifers were fed a high-roughage diet and assigned to treatments: 0% RPM + 0 g/d RPC + saline injection (0XNEG), 0.08% RPM + 60 g/d RPC + saline injection (0XPOS), 0.08% RPM + 60 g/d RPC + 80 mg FA + 5 mg B12 (0.5X), 0.08% RPM + 60 g/d RPC + 160 mg FA + 10 mg B12 (1X), or 0.08% RPM + 60 g/d RPC + 320 mg FA + 20 mg B12 (2X). Dietary treatments were fed for 14 d and FA and B12 injections were given on d 0 and 7 of the estrous cycle with tissues collected on d 14. The effect of RPM+RPC supplementation was evaluated using a contrast statement comparing 0XNEG vs. others. Polynomial contrasts were used to determine effects of FA+B12 dose. Protein concentration and carbohydrase activities of the pancreas and jejunum were not influenced (P=0.21) by RPM+RPC supplementation. Pancreatic protein concentration responded cubically (P< 0.01) to FA+B12 dose where pancreatic protein concentration was lesser for 0.5X compared with other treatments. Likewise, pancreatic a-amylase activity responded cubically (P< 0.01) to increasing FA+B12 dose because pancreatic a-amylase activity was lesser for 0.5X (182 U/g) compared with 0XPOS (350 U/g), 1X (347 U/g), and 2X (412 U/g). Jejunal protein concentration and maltase and glucoamylase activities were not influenced (P=0.29) by FA+B12 dose. Jejunal isomaltase activity tended to decrease linearly (P=0.07) with increasing FA+B12 dose. These findings suggest that the balance of different OCM could be important for regulation of pancreatic protein turnover and a-amylase activity. USDA is an equal opportunity provider and employer. [ABSTRACT FROM AUTHOR]

The objectives of my dissertation research are to develop strategies to increase the efficiency of finishing beef production by optimizing the site and extent of starch digestion, improving flaking quality and consistency, and reducing methane emissions. Post-flaking sampling and handling techniques such as sifting steam-flaked corn samples with a sieve (P < 0.01), air equilibration time (P < 0.01), and storage temperature during shipping (P < 0.01) all influenced enzymatic starch availability of steam-flaked corn. Inducing starch retrogradation of steam-flaked corn decreased the rate (P < 0.01), but not the extent (P = 0.80), of ruminal dry matter degradation and thus, energetic efficiency was predicted to increase by up to 3.4% because of increased postruminal flow and digestion of starch in the small intestine. If producing steam-flaked corn is not feasible for smaller capacity feedlots, finely ground corn has a similar ruminal starch solubility to steamflaked corn (38.1% vs. 44.4, respectively, P > 0.05), suggesting an alternative processing method to increase feeding value in finishing diets. Duodenal infusion of glucoamylase (fungal origin) increased (P = 0.02) small intestinal starch disappearance in steers, while duodenal infusion of porcine a-amylase did not (P = 0.41), supporting the hypothesis that small intestinal carbohydrases are the primary hydrolytic limit to small intestinal starch digestion. Comparative sequencing analyses revealed a missing region of the stalk region of the sucrase-isomaltase protein sequence (AA 47-60) which is important for intracellular sorting of the sucrase subunit to the apical membrane. The absence of this region of the protein likely explains the absence of intestinal sucrase activity and quantitative limitations of starch digestion in the ruminant small intestine. Feeding decoquinate with Yucca schidigera extract for 7-d decreased (P < 0.01) ruminal acetate proportion and tended to increase ruminal (P = 0.08) propionate proportion, suggesting potential for hydrogen shifts which could contribute to reductions in methane emissions with longer feeding periods. The findings of my dissertation research provide: 1) post-flaking sampling and handling recommendations for commercial feedlots and laboratories to improve estimates of starch availability and flaking consistency, 2) a mechanistic target (sucrase-isomaltase) for limitations in small intestinal starch digestion, 3) practical feeding strategies to shift the site of starch digestion to the small intestine to increase feed efficiency (retrogradation), 4) new processing alternatives for small feedlot producers (fine ground corn inclusion), and 5) new information on how combinations of feed additives could potentially decrease methane production in feedlot cattle. [ABSTRACT FROM AUTHOR]