D. L. Harmon

Evaluation of Nutrient Utilization in the Canine Using the Ileal Cannulation Technique

Nine mature mongrel dogs were used to evaluate a surgical technique for the cannulation of the terminal ileum and used in two experiments to determine the effect of carbohydrate source on starch and dry matter digestion. Dogs (16.2 +/- 2.0 kg body weight; means +/- SD) were fitted with an ileal T-cannula constructed of polyvinyl chloride pipe. The cannula was inserted into the terminal ileum approximately 10 cm proximal to the ileocecal junction and the cannula was exteriorized through a small incision on the right flank. Dogs recovered quickly from surgery (5d). A preliminary study using Cr:EDTA in the food indicated that sampling for 12 h postprandially allowed near complete representation of digesta flow for a meal; peak flow occurred 4-to 8-h postfeeding. Two experiments were performed evaluating the effect of carbohydrate source on ileal starch and dry matter digestibility. Dogs were fed two meals daily with Cr2O3 used as a digesta marker. Diets contained 67% extruded grain (corn, rice, oats or barley) and 33% canned meat supplement on a dry matter basis. Starch digestion was complete (> 98%) within the small intestine and was unaffected by carbohydrate source. In experiment 1, prececal and total tract dry matter digestibilities were higher for rice than corn, and in experiment 2, barley was higher than oats. The ileal T-cannula allows for measurement of small intestinal nutrient disappearance without the confounding effects of colonic microflora. This method may be useful when applied to the study of other nutrients in dogs.

Influence of fiber fermentability on nutrient digestion in the dog

Eight mature dogs (17.2 +/- 0.2 kg) surgically fitted with ileal T-cannulas were used in a replicated 4-x-4 Latin-square-design experiment to evaluate nutrient disappearance at the terminal ileum and through the digestive tract. Two fiber types, cellulose, a crystalline, slowly fermented fiber, and pectin, a soluble, rapidly fermented fiber, were fed in different increments, and the effects on nutrient availability were assessed. Treatments included 1) 100% cellulose, 2) 66% cellulose and 33% pectin, 3) 66% pectin and 33% cellulose, and 4) 100% pectin. Fiber was added at 10% of diet dry matter (DM). Diets were fed at 100% of ME for maintenance and offered at 0730 and 1730 h. All periods were 21 d, which included 3 d of diet transition and 7 d of adaptation. Daily DM intake was 210 +/- 5 g. Total tract and large-intestine DM digestibility increased linearly (P < 0.01) with increased pectin. These changes in DM digestion were largely the result of changes in fiber digestion. Fermentation of total dietary fiber in the large intestine went from less than zero to 39% of ileal flow (linear, P < 0.01). Total-tract crude-protein digestibility decreased linearly (P < 0.01) with increased pectin. This study demonstrated that fiber fermentability significantly affects digestion in the dog. Increasing fermentable fiber increased the digestion of DM and energy. However, increased fiber fermentability inversely affects crude protein digestibility. The lower crude-protein digestibility could be attributed to larger microbial protein excretion as a result of greater fermentation of pectin versus cellulose.

Factors affecting intestinal starch digestion in ruminants: A review

The process of starch assimilation in the ruminant is complex and remains an avenue by which increases in production efficiency can be gained. Ruminal starch digestion is typically 0.75–0.80 of starch intake. Starch that escapes fermentation and flows to the small intestine may be more resistant to enzymatic digestion and on average 0.35–0.60 of starch entering the small intestine is degraded there. Of the fraction that escapes small intestinal digestion an additional 0.35–0.50 is degraded in the large intestine. This suggests that limitations to small intestinal starch digestion do exist. This review summarizes available information describing the digestive and absorptive processes occurring in the small intestine with an emphasis on nutritional factors that influence these processes. A review of experiments measuring small intestinal starch digestion indicates that small intestinal digestion is either highly variable or poorly determined whereas ruminal and large intestinal digestion are much more clear...

The effects of an Aspergillus oryzae extract containing alpha-amylase activity on ruminal fermentation and milk production in lactating Holstein cows

The effects of an Aspergillus oryzae extract containing alpha-amylase activity (Amaize™, Alltech Inc., Nicholasville, KY) were examined in vivo and in vitro . A lactating cow study employed 20 intact and four ruminally fistulated Holstein cows in a replicated 4 × 4 Latin-square design to examine the effects of four concentrations of dietary Amaize™ extract on milk production and composition, ruminal fermentation and serum metabolite concentrations. The treatment diets contained 0, 240, 480 or 720 alpha-amylase dextrinizing units (DU) per kg of total mixed ration (TMR) (dry-matter basis). The supplemental alpha-amylase increased the yields of milk ( P = 0·02), fat ( P = 0·02) and protein ( P = 0·06) quadratically. The maximum milk yield was obtained when 240 DU per kg of TMR were offered. Ruminal in situ starch disappearance was not affected by alpha-amylase supplementation in lactating cows or ruminally cannulated steers. Supplemental alpha-amylase extract reduced the molar proportion of propionate in the rumen of steers ( P = 0·08) and lactating cows ( P = 0·04), and in rumen-simulating cultures ( P = 0·04). The supplement also increased the molar proportions of acetate ( P = 0·06) and butyrate ( P = 0·05), and the serum beta-hydroxybutyrate ( P = 0·01) and non-esterified fatty acid ( P = 0·03) concentrations in lactating cows. The improvements in milk production appear to be a consequence of the effects of alpha-amylase on ruminal fermentation and the potential changes in nutrient metabolism that result from them. We conclude that supplemental alpha-amylase may be given to modify ruminal fermentation and improve milk and component yield in lactating Holstein cattle.

Efficacy of chromium-yeast supplementation for growing beef steers

This experiment was conducted to determine the efficacy of feeding chromium yeast to growing beef steers. Animal growth, gain efficiency, and blood glucose kinetics were determined in 24 beef steers (initial body weight=253 ±4 kg) fed a corn silage-based diet supplemented with 0 (control), 100, 200, or 400 μg chromium from high-chromium yeast/kg of diet dry matter. Intravenous glucose tolerance tests (IVGTT) and intravenous insulin challenge tests (IVICT) were conducted at 3 and 6 weeks of chromium-yeast supplementation. There were minimal effects on plasma glucose kinetics during IVGTT and IVICT. There were tendencies for glucose clearance rate to increase (p=0.16) and half-life to decrease (p=0.14) during IVICT. However, chromium-yeast supplementation had no effect (p>0.24) on ADG and gain efficiency, suggesting that chromium-yeast supplementation to unstressed growing calves may not be beneficial.

Ruminal and abomasal starch hydrolysate infusions selectively decrease the expression of cationic amino acid transporter mRNA by small intestinal epithelia of forage-fed beef steers

Although cationic amino acids (CAA) are considered essential to maximize optimal growth of cattle, transporters responsible for CAA absorption by bovine small intestinal epithelia have not been described. This study was conducted to test 2 hypotheses: 1) the duodenal, jejunal, and ileal epithelia of beef cattle differentially express 7 mRNA associated with 4 mammalian amino acid (AA) transport activities: y(+) (CAT1), B(0,+) (ATB(0,+)), b(0,+) (b(0,+)AT and rBAT), and y(+)L (y(+)LAT1, y(+)LAT2, and 4F2hc), and 2) the expression of these mRNA is responsive to small intestinal luminal supply of AA substrates (derived from ruminal microbes) or glucose-derived energy (from starch hydrolysate, SH), or both. Eighteen ruminally and abomasally catheterized Angus steers (body weight = 260 +/- 17 kg) fed an alfalfa cube-based diet at 1.33 x net energy for maintenance requirement were assigned to 3 treatments (n = 6): ruminal and abomasal water infusion (control); ruminal SH and abomasal water infusion; and ruminal water and abomasal SH infusion. The dosage of SH infusion amounted to 20% of metabolizable energy intake. After 14 or 16 d of infusion, steers were slaughtered, duodenal, jejunal, and ileal epithelia were harvested, and total RNA was extracted. The relative amounts of mRNA expressed by epithelia were quantified using real-time reverse transcription-PCR. All 7 mRNA species were expressed by the epithelium from each region, but their abundance differed among the regions. Specifically, duodenal expression of CAT1 and ATB(0,+) mRNA was greater than jejunal or ileal expression; ileal expression of b(0,+)AT, rBAT, and y(+)LAT1 mRNA was greater than jejunal or duodenal expression, whereas the expression of y(+)LAT2 and 4F2hc mRNA did not differ among the 3 epithelia. With regard to SH infusion effect, ruminal infusion down-regulated or tended to down-regulate the jejunal expression of CAT1, rBAT, y(+)LAT2, and 4F2hc mRNA. Abomasal infusion down-regulated the jejunal expression of y(+)LAT2 mRNA and tended to down-regulate the jejunal expression of 4F2hc mRNA. This study characterized the pattern of CAA transporter mRNA expressed by growing beef cattle fed an alfalfa-based diet. Moreover, this study demonstrated that increasing the luminal supply of microbe-derived AA (by ruminal supplementation of SH) results in a reduced capacity of apical and basolateral membrane to transport of CAA, whereas increasing luminal glucose supply (by abomasal supplementation of SH) reduces only the basolateral transport capacity, assuming that CAA transporter mRNA content represents functional capacity.

Ergot alkaloids from endophyte-infected tall fescue decrease reticuloruminal epithelial blood flow and volatile fatty acid absorption from the washed reticulorumen.

An experiment was conducted to determine if ergot alkaloids affect blood flow to the absorptive surface of the rumen. Steers (n=8) were pair-fed alfalfa cubes and received ground endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum; E+) seed (0.015 mg ergovaline·kg BW(-1)·d(-1)) or endophyte-free tall fescue (E-) seed via the rumen cannula 2x daily for 7 d at thermoneutral (TN; 22°C) and heat stress (HS; 32°C) conditions. On d 8, the rumen was emptied and rinsed. A buffer containing VFA was incubated in the following sequence: control (CON), 15 μg ergovaline·kg BW(-1) (1×EXT) from a tall fescue seed extract, and 45 μg ergovaline·kg BW(-1) (3×EXT). For each buffer treatment there were two 30-min incubations: a 30-min incubation of a treatment buffer with no sampling followed by an incubation of an identical sampling buffer with the addition of Cr-EDTA and deuterium oxide (D2O). Epithelial blood flow was calculated as ruminal clearance of D2O corrected for influx of physiological water and liquid outflow. Feed intake decreased with dosing E+ seed at HS but not at thermoneutral conditions (TN; P<0.02). Dosing E+ seed decreased serum prolactin (P<0.005) at TN. At HS, prolactin decreased in both groups over the 8-d experiment (P<0.0001), but there was no difference in E+ and E- steers (P=0.33). There was a seed treatment×buffer treatment interaction at TN (P=0.038), indicating that E+ seed treatment decreased reticuloruminal epithelial blood flow at TN during the CON incubation, but the two groups of steers were not different during 1×EXT and 3×EXT (P>0.05). Inclusion of the extract in the buffer caused at least a 50% reduction in epithelial blood flow at TN (P=0.004), but there was no difference between 1×EXT and 3×EXT. There was a seed × buffer treatment interaction at HS (P=0.005), indicating that the reduction of blood flow induced by incubating the extract was larger for steers receiving E- seed than E+ seed. Volatile fatty acid flux was reduced during the 1×EXT and 3×EXT treatments (P<0.01). An additional experiment was conducted to determine the effect of time on blood flow and VFA flux because buffer sequence could not be randomized. Time either increased (P=0.05) or did not affect blood flow (P=0.18) or VFA flux (P>0.80), indicating that observed differences are due to the presence of ergot alkaloids in the rumen. A decrease in VFA absorption could contribute to the signs of fescue toxicosis including depressed growth and performance.

Constriction of bovine vasculature caused by endophyte-infected tall fescue seed extract is similar to pure ergovaline 1 2

Ergovaline has been extensively used to study vasoactive effects of endophyte- (Neotyphodium coenophialum) infected tall fescue (Lolium arundinaceum). However, initial results indicated that an extract of toxic tall fescue seed (E+EXT) is more potent than ergovaline alone in a right ruminal artery and vein bioassay. The E+EXT induced a greater contractile response than an equal concentration of ergovaline alone in the ruminal artery of heifers (P = 0.018). This led to a hypothesis that other compounds in the seed extract contribute to vasoconstriction. Thus, experiments were conducted to determine if vasoactivity of an E+EXT is different from a mixture of ergot alkaloids (ALK; ergovaline, ergotamine, ergocristine, ergocryptine, ergocornine, ergonovine, and lysergic acid) of similar concentrations and to determine if the vasoactivity of an E+EXT differs from an endophyte-free tall fescue seed extract (E-EXT). Segments of lateral saphenous vein and right ruminal artery and vein were collected from Holstein steers (n = 6) shortly after slaughter. Vessels were cleaned of excess connective tissue and fat and sliced into segments that were suspended in a multimyograph chamber with 5 mL of continually oxygenated Krebs-Henseleit buffer, equilibrated for 90 min, and exposed to a reference compound (120 mM KCl for ruminal vessels and 0.1 mM norepinephrine for saphenous vein). Increasing concentrations of each treatment (E+EXT, E-EXT, ALK, and ergovaline) were added to the respective chamber every 15 min after buffer replacement. Data were normalized as a percentage of maximal contractile response of the reference compound and fit to a sigmoidal concentration response curve. Ergovaline, ALK, and E+EXT induced similar responses in the saphenous vein, ruminal artery, and ruminal vein. The E+EXT displayed a smaller EC(50) (half maximal effective concentration) than ergovaline or ALK in the saphenous vein and ruminal vein (P < 0.008), but not the ruminal artery (P = 0.31). Extrapolated maximum response was greatest in the saphenous vein for ergovaline, least for E+EXT, and intermediate for ALK (P < 0.0001). The E-EXT did not induce a contractile response in any vessel tested (P > 0.1). Data from this study indicate that ergovaline is largely responsible for the locally induced vasoconstriction of bovine vasculature observed with endophyte-infected tall fescue.

Effect of ergot alkaloids on contractility of bovine right ruminal artery and vein.

Ergot alkaloids produced by the endophyte (Neotyphodium coenophialum) associated with tall fescue (Lolium arundinaceum) are implicated in the clinical signs of fescue toxicosis. These compounds were hypothesized to correspondingly affect foregut vasculature. The objective of this study was to determine vasoconstrictive potentials of ergovaline, ergotamine, ergocryptine, ergocristine, ergonovine, ergocornine, and lysergic acid on right ruminal artery and vein. Segments of right ruminal artery and vein were collected from the ventral coronary groove of predominantly Angus heifers (n = 10) shortly after slaughter and placed in a modified Krebs-Henseleit buffer on ice. Vessels were cleaned of excess connective tissue and fat, sliced into 2- to 3-mm segments, and suspended in a multi-myograph chamber with 5 mL of continuously oxygenated Krebs-Henseleit buffer (95%O(2)/5% CO(2); pH 7.4; 37°C). Arteries and veins were equilibrated to 1.0 and 0.5 g, respectively, for 90 min followed by the reference addition of 120 mM KCl. Increasing concentrations of each alkaloid were added to the respective chamber every 15 min after buffer replacement. Data were normalized as a percentage of the contractile response induced by KCl. Alkaloid (P < 0.0001), concentration (P < 0.0001), and vessel type (artery or vein; P = 0.004) affected contractility. No arterial response was observed until 10(-6) M for ergovaline and ergotamine; 10(-5) M for ergocryptine, ergocornine, and ergonovine; and 10(-4) M for ergocristine. Lysergic acid did not induce a contractile response in the ruminal artery. No venous contractile response was observed until concentrations of 10(-6) M for ergovaline, 10(-5) M for ergotamine, and 10(-4) M for ergocryptine and ergocristine were achieved. Lysergic acid, ergonovine, and ergocornine did not induce a contractile response in the ruminal vein. A greater arterial maximal response was observed for ergovaline (P < 0.0001), whereas the arterial and venous responses were not different for ergotamine (P = 0.16), ergocryptine (P = 0.218), and ergocristine (P = 0.425). These results indicate that ergot alkaloids associated with toxic endophyte-infected tall fescue are vasoactive and can potentially alter arterial blood supply and venous drainage from the bovine foregut.

PROTEIN SUPPLEMENTATION OF RUMINANTS CONSUMING LOW-QUALITY COOL- OR WARM-SEASON FORAGE: DIFFERENCES IN INTAKE AND DIGESTIBILITY

An in situ study (Exp. 1) using 4 ruminally cannulated steers (343 ± 11 kg of BW) in a completely randomized design was used to compare ruminal degradation characteristics of low-quality cool-season (C3; Kentucky bluegrass straw; Poa pratensis; 6.3% CP; DM basis) and warm-season (C4; tallgrass prairie; 5.7% CP; DM basis) forage. Four ruminally cannulated steers (252 ± 8 kg of BW; Exp. 2) and 4 wethers (38 ± 1 kg of BW; Exp. 3) were used in two 2 × 2 factorial arrangements of treatments to determine the influence of supplemental CP (CPSupp; soybean meal; 0.09 and 0.19% of BW, CP basis, for steers and lambs, respectively) on nutrient intake and digestion of C3 and C4 forages. Steers and wethers were allotted to separate 4 × 4 Latin squares that ran simultaneously with 20-d periods. In Exp. 1, C3 had a greater A fraction (fraction of total pool disappearing at a rate too rapid to measure) and effective degradability of DM and NDF compared with C4 (P < 0.01). In addition, C3 had a greater (P < 0.01) A fraction and effective degradability of N, whereas the C fraction (fraction of total pool unavailable in the rumen) was less (P < 0.01) than those for C4. Consequently, RDP accounted for 84.7% of total CP in C3 as compared with 66% for C4 (P < 0.01). In Exp. 2, a CPSupp × forage interaction (P < 0.01) was noted for forage and total DMI, with CPSupp increasing intake of C4 by 47% and intake of C3 forage by only 7%. Dry matter digestibility responded similarly, with a CPSupp × forage interaction (P = 0.05; CPSupp increased digestibility by 21% with C4 and by 9% with C3 forage). In addition, CPSupp × forage interactions were noted for ruminal liquid retention time (P = 0.02; CPSupp decreased retention by 3.6 h with C4 and by only 0.6 h with C3 forage) and particulate passage rate (P = 0.02; CPSupp increased passage by 46% with C4 and by 10% with C3 forage). As in Exp. 2, a CPSupp × forage interaction (P = 0.01; CPSupp increased digestibility by 18% with C4 and by 7% with C3 forage) was observed with DM digestibility in Exp. 3. In contrast, only N balance (P < 0.01) and N digestibility (P < 0.01) were affected by CPSupp. These data suggest that intake and digestion of low-quality C3 and C4 forages by ruminants are not similar and, more important, that the physiological response of ruminants to protein supplementation of low-quality forage is dependent on forage type.