Ardacin for steers grazing endophyte-free fescue pasture: effects on live weight gain, forage intake, nitrogen and fiber digestion, ruminal fluid kinetics, ruminal fermentation, and serum hormones and metabolites.

Growth and digestion studies were conducted to evaluate the use of ardacin as a feedgrade antibiotic for enhancing digestive function and growth in grazing steers. In Exp. 1, 90 yearling steers (average initial BW of 248 kg) used in a randomized complete block design (block = weight group) grazed fescue pasture without supplementation (CON) or with daily supplements (DM basis) of .4% of BW supplemental ground corn (CRN) or .4% of BW supplemental corn supplying 120 mg of ardacin (ARD). In Exp. 2, 12 ruminally and duodenally cannulated steers and three ruminally cannulated steers (Hereford x Angus; average BW of 347 kg) were used to evaluate the effects of the same supplements used in Exp. 1 on ruminal fermentation and digestion. In Exp. 1, ARD-supplemented steers weighed more (P < .01) at the conclusion of the study than CRN steers, which together weighed more (P < .01) than CON steers. Average daily gain was greater (P < .10) in supplemented than in CON steers; ARD steers had greater (P < .01) ADG than CRN steers. In Exp. 2, forage intake and harvesting efficiency did not vary (P > .10) with supplementation or type of supplement, but total intake reflected (P = .03) the addition of corn to the forage diet. Addition of ardacin increased (P = .02) ruminal pH compared with CRN steers. Ardacin decreased ruminal molar proportions of acetate and increased (P = .01) propionate proportions when compared with CRN steers. Total tract N digestibility was affected (P < .10) by supplementation and by addition of ardacin to the diet. Addition of ardacin to the ground corn supplement increased ADG, in part by enhancing acetate:propionate ratios and increasing N digestion.

Supplemental cracked corn or wheat bran for steers grazing endophyte-free fescue pasture: effects on live weight gain, nutrient quality, forage intake, particulate and fluid kinetics, ruminal fermentation, and digestion.

Two experiments were conducted with beef steers (Exp. 1, average BW of 580 kg; Exp. 2, average BW of 247 kg) to evaluate the use of no supplements (CON) or daily supplementation with (OM basis) .34% of BW of cracked corn (CORN), .34% of BW of wheat bran (WBBW), or .48% of BW of wheat bran (WBISO; calculated to be isocaloric to CORN) on digestive responses (Exp. 1) and live weight gain (Exp. 2). In Exp. 1, type of supplement did not affect (P > .10) the dietary fiber or N constituents, but in vitro OM disappearance of the forage differed (P < .10) with supplementation and type of supplement fed. Supplemented steers consumed less (P < .05) forage and total OM. Particulate passage, fluid passage, and ruminal pH were not affected (P > .10) by supplementation. Ruminal NH3 N concentration showed (P < .05) a treatment x sampling time interaction and, in general, WBBW and WBISO steers had greater ruminal NH3 N than CORN and CON steers. Total VFA concentrations and molar proportions of propionate were lower (P < .10) in CON steers than in supplemented steers; no differences were noted (P > .10) among supplemented steers. Molar proportions of acetate were lower (P = .01) in supplemented steers than in CON steers and were greater (P = .03) in WBBW steers than in WBISO steers. Butyrate molar proportions were lower (P < .05) in CON steers than in supplemented steers and differed (P < .10) with type and quantity of supplement supplied. In situ forage NDF disappearance at 6, 9, and 24 h after feeding and rate of disappearance were greater (P < .05) in CON steers than in supplemented steers. In Exp. 2, CON steers weighed less (P = .01) than supplemented steers, CORN steers weighed more (P = .08) than wheat bran-supplemented steers, and WBISO steers weighed more (P = .02) than WBBW steers; ADG for 90 d followed a similar response. Results suggest that supplementation of wheat bran rather than corn did not seem to stop the reduction in forage intake or OM digestion associated with corn supplementation.

Supplemental protein for beef cattle grazing dormant intermediate wheatgrass pasture: effects on nutrient quality, forage intake, digesta kinetics, grazing behavior, ruminal fermentation, and digestion.

Sixteen ruminally cannulated yearling beef cattle (British x British; average BW = 295 +/- 25 kg; three steers and one heifer per treatment) grazing dormant intermediate wheatgrass (Thinopyrum intermedium Host) were allotted to four treatments: 1) no supplement (CON); 2) alfalfa hay (ALF; .52% of BW); 3) cottonseed meal (CSM; .22% of BW); and 4) corn gluten meal-wheat bran feed (CGMWBF; .36% of BW). Supplements were formulated (DM basis) so that intakes were isonitrogenous and were provided once daily (0700). Sampling periods were in February (FEB; .96% N in masticate), March (MAR; 1.06% N in masticate), and April (APR; 1.12% N in masticate) following an initial 21-d adaptation period. Daily grazing time was 1.1 to 1.5 h longer (P < .05) for CON cattle than for supplemented cattle. Forage OM intake (OMI) was not altered (P > .15) by supplemental protein; however, total OMI was greater (P < .04) for supplemented than for unsupplemented cattle. Harvesting efficiency (grams of OM intake-kilogram of BW-1.minute spent grazing-1) was greater (P < .05) for cattle fed CSM than for those fed CGF or CON; cattle fed ALF were intermediate in harvesting efficiency. Ruminal fluid kinetics, in situ rate and extent of NDF digestion, and total VFA concentration were not influenced (P > .10) by type of supplemental protein. Ruminal NH3 N concentration exhibited a treatment x sampling time interaction (P < .05). Type of protein supplement did not seem to affect most digestion measures; however, harvesting efficiency was influenced by supplement type.

Steers grazing intermediate wheatgrass at various stages of maturity: effects on nutrient quality, forage intake, digesta kinetics, ruminal fermentation, and serum hormones and metabolites.

Six ruminally cannulated Holstein steers (average BW of 495 +/- 5 kg) grazed a 32-ha, nonirrigated, intermediate wheatgrass (Thinopyrum intermedium Host) pasture from April 10 through December 7. Sample collections were conducted in May, June, September, and November 1989. Total masticate N decreased (P < .05) and bound N increased (P < .05) with advancing forage maturity. Masticate in vitro OM disappearance was lower (P < .05) in November (40.5%) than in May (62.0%). Organic matter intake (grams/kilogram of BW) decreased (P < .05) at each sampling date (May = 35.7, June = 26.8, September = 20.0, November = 14.9). Correspondingly, particulate passage rate decreased and gastrointestinal mean retention time increased (P < .05) with advancing forage maturity. Extent and rate of NDF digestion were greater (P < .05) during May and June than during September and November. Ruminal NH3 N and total VFA concentrations were greater (P < .05) during May and June than during September and November. Advancing forage maturity did not alter (P > .10) serum growth hormone concentrations; however, nonesterified fatty acid concentrations were greater (P < .05) during September and November than during May and June. Serum insulin-like growth factor I decreased (P < .05) with advancing forage maturity. Seasonal changes in forage intake and ruminal fermentation suggest that animal performance might be increased if supplemental energy is provided early in the growing season of intermediate wheatgrass; however, supplemental protein would likely be needed as wheatgrass matures.

Forage intake and digestion by cattle grazing midgrass prairie rangeland or sideoats grama/sweetclover pasture.

In mid-May, beef cattle fitted with esophageal (four steers/pasture) or ruminal and duodenal cannulas (six heifers/pasture; 274 +/- 6 kg BW +/- SE) grazed midgrass prairie (excellent range condition; PRAIRIE) or a seeded mixture of sideoats grama (48% of pasture DM) and sweetclover (6% of pasture DM; Bouteloua curtipendula [Michx.] Torr./Melilotus officinalis [L.] Lam.; PASTURE). Masticate NDF, ADF, and in vitro OM disappearance did not differ (P > .11) between forage types (average = 66.6, 36.1, and 58.8% of OM). Only N differed (P = .02) between PRAIRIE (2.1) and PASTURE (2.4% of OM). Extents of in situ OM and N disappearance were greater (P < .05) and rate of N disappearance between 12 and 36 h was slower (P < .10) from PRAIRIE than from PASTURE masticate. Based on in situ data, the ruminally degraded N: ruminally degraded OM (grams/kilogram) ratio differed (P < .05) between PRAIRIE (22) and PASTURE (25). Ruminal ammonia N concentration (milligrams/deciliter) was less (P = .02) for PRAIRIE (2.8) than for PASTURE (3.8). Forage OM intake and fecal OM output did not differ (P > .72; average = 8,207 and 3,380 g/d), but duodenal OM flow tended (P = .13) to be greater (PRAIRIE = 4,892, PASTURE = 5,170 g/d) in cattle grazing PASTURE. Apparent and true ruminal OM digestion did not differ between forage types (P > .18; average = 38.3 and 48.5%). Nitrogen intake, nonammonia N, and forage N flow at the duodenum were greater (P < .04) for PASTURE (198 vs 171, 242 vs 210, and 162 vs 135 g/d) than for PRAIRIE. Microbial N flow (average = 78 g/d) and microbial efficiency (average = 20 g of microbial N/kg of OM truly fermented) did not differ (P > .25) between forage types. Apparent and true ruminal N digestion did not differ (P > .65; average = -26.6 and 19.3%) between forage types. Flow of nonammonia N was in excess relative to digestible OM intake; hence, digestible OM intake seemed to be first-limiting for performance by cattle grazing either forage type.

Supplemental methionine and time of supplementation effects on ruminal fermentation, digesta kinetics, and in situ dry matter and neutral detergent fiber disappearance in cattle.

Two experiments were conducted to study the effects of methionine supplementation on ruminal fermentation and digesta kinetics. In Exp. 1, nine ruminally cannulated beef heifers (average initial BW = 527 kg) in a crossover design were fed low-quality grass hay and cottonseed meal with or without 11.4 g of supplemental methionine (polysaccharide-coated). Particulate and fluid kinetics, rate of DM and NDF disappearance, ruminal VFA and NH3 N concentrations, and pH were not altered (P > .10) by supplemental methionine; however, ruminal purine concentration was greater (P < .05) in methionine-supplemented heifers than in unsupplemented heifers. In Exp. 2, 12 ruminally cannulated Holstein steers (average initial BW = 622 kg) grazing a fescue pasture were allotted to one of three groups: no supplemental methionine (CON) or 11.4 g of supplemental methionine fed at 0700 (AM) or at 1200 (PM). Forage intake, particulate kinetics, ruminal fluid kinetics, pH, VFA, and NH3 N concentrations were not altered (P > .10) by supplemental methionine or supplementation time. In situ rate of DM and NDF disappearance was greater (P < .05) in supplemented steers than in CON steers; AM steers exhibited faster (P < .05) rates than PM steers. Overall, methionine supplementation of low-quality forage increased ruminal purine concentration but did not alter in situ fermentation or digesta passage, whereas supplementation at 0700, but not at 1200, of steers grazing fescue forage increased rate of NDF fermentation.

Time of daily supplementation for steers grazing dormant intermediate wheatgrass pasture.

To compare the effects of time of daily protein supplementation on grazing behavior, forage intake, digesta kinetics, ruminal fermentation, and serum hormones and metabolites, 12 ruminally cannulated Holstein steers (449 and 378 kg average initial and final BW, respectively) were allotted to three groups. Treatments consisted of CON = no supplement, AM = cottonseed meal (.25% of BW) at 0600, and PM = cottonseed meal (.25% of BW) at 1200. Steers grazed a dormant (1.1% N) intermediate wheatgrass (Thinopyrum intermedium Host) pasture. Sampling trials occurred in December, January, and February. Supplementation altered (P = .01) time spent grazing; CON steers grazed approximately 1.5 h longer than supplemented steers. Supplemented steers lost less (P = .02) BW (-40 kg) than CON steers (-75 kg) did. Supplementation did not alter (P greater than .15) forage OM intake; however, total OM intake was greater (P = .01) for supplemented steers (22.3 g/kg of BW) than for CON (18.4 g/kg of BW) steers. Supplementation did not affect (P greater than .15) digesta kinetics. Extent of in situ NDF (96 h) and rate (%/h) of disappearance for supplemented steers was greater (P = .01) than for CON steers. Across all periods, ruminal NH3 N and total VFA concentrations were lower (P = .01) for CON steers than for supplemented steers. Serum insulin (ng/mL) concentration was lower (P = .03) and concentration of serum growth hormone (ng/mL) was higher (P = .02) for CON steers than for supplemented steers. Cottonseed meal supplementation enhanced utilization of intermediate wheatgrass; however, supplementation time had minimal effects on the variables measured.

Effects of cottonseed meal supplementation time on ruminal fermentation and forage intake by Holstein steers fed fescue hay.

Four ruminally cannulated Holstein steers (average BW 303 kg) were used in a 4 x 4 Latin square design digestion trial to study the influence of daily cottonseed meal (CSM; 1.6 g of CP/kg of BW) supplementation time on forage intake and ruminal fluid kinetics and fermentation. Steers were housed individually in tie stalls and were fed chopped fescue hay on an ad libitum basis at 0600 and 1400. Treatments were 1) control, grass hay only (CON) and grass hay and CSM fed once daily at 2) 0600 (EAM) 3) 1000 (MAM), or 4) 1400 (PM). Ruminal NH3 N concentrations reflected a time of supplementation x sampling time interaction (P less than .05); CON steers had the lowest (P less than .05) ruminal NH3 N concentrations at all times other than at 0600, 1000, 1200, and 2400, when they did not differ (P greater than .05) from at least one of the supplemented groups. Forage intake, ratio of bacterial purine:N, rate of DM and NDF disappearance, and ruminal fluid kinetics were not influenced (P greater than .05) by supplementation time. Total ruminal VFA differed (P less than .05) between CON and supplemented steers, as well as among supplemented steers (linear and quadratic effects P less than .05). Acetate, propionate, and valerate proportions were influenced (P less than .05) by a sampling time X supplementation time interaction. Under the conditions of this study, greater peak ammonia concentrations with morning supplementation than with afternoon supplementation did not stimulate ruminal fermentation or rate of NDF disappearance.

Influence of ruminal or duodenal soybean oil infusion on intake, ruminal fermentation, site and extent of digestion, and microbial protein synthesis in beef heifers consuming grass hay.

Six heifers (two Hereford X Jersey, four Hereford X Longhorn; average BW 278 kg) cannulated at the rumen and duodenum and fed a grass hay (fescue/orchardgrass) diet were used in a replicated 3 X 3 Latin square. Treatments were either no infusion (C), 150 ml of duodenally infused soybean oil (DI), or 150 ml of ruminally infused soybean oil (RI)/heifer twice daily for a total daily infusion of 300 ml of soybean oil. Periods of the Latin square included 18 d for adaptation and 5 d for collection. Forage OM, ADF, NDF, and N intakes were not affected (P greater than .10) by soybean oil infusion. Ruminal (P = .11) and total tract (P less than .10) OM digestibilities were decreased by RI compared with C or DI, but ADF and NDF digestibilities were not affected by treatment. Duodenal N (P less than .05) and microbial N flows were increased (P less than .10) for C and RI compared with DI. Microbial efficiency (g of N/kg of OM truly fermented) was improved (P less than .10) by RI compared with DI but did not differ (P greater than .10) from C. Ruminal pH was lower (P less than .05) with RI than with either C or DI. Ruminal NH3 N, total VFA, and acetate were not affected (P greater than .10) by treatment. Propionate (mol/100 mol) was greater (P less than .05) with RI than with DI and C, but the proportion of butyrate did not differ among treatments. These data indicate minimal direct benefits for improving forage usage as a result of soybean oil infusion with a 100% grass diet; however, animals should realize benefits from additional dietary energy provided by infused lipid.

Influence of branched-chain fatty acid supplementation on voluntary intake, site and extent of digestion, ruminal fermentation, digesta kinetics and microbial protein synthesis in beef heifers consuming grass hay.

Four heifers (British x British; average BW 372 kg) cannulated at the rumen and duodenum and consuming a grass hay (fescue-orchardgrass) diet were used in a 4 x 4 Latin square and supplemented with four levels (0, 20, 40, and 60 g.head-1.d-1) of supplemental four- and five-carbon VFA (BCFA). Forage OM, ADF, NDF and N intakes and digestibilities were not affected (P greater than .10) by BCFA supplementation. Likewise, duodenal N (microbial, feed and ammonia) flows and microbial efficiency were not altered (P greater than .10) by BCFA supplementation. Neither particulate and fluid passage rate nor in situ rate of NDF digestion was affected (P greater than .10) by treatment. Ruminal pH, ammonia concentrations and total VFA concentrations were similar (P greater than .10) among treatments. Ruminal proportions of acetate and propionate were not affected (P greater than .10) by treatment; however, butyrate responded in a cubic (P less than .05) fashion to BCFA, with the lowest proportion of butyrate at the 40 g BCFA feeding level. A time x treatment interaction (P less than .05) was noted for isobutyrate, isovalerate and valerate proportions; they were increased as a function of BCFA dosage at 2 to 8 h postdosing. Supplemental four- and five-carbon VFA had no effect on digestion and fermentation of grass hay. Supplementation of low-quality roughages with BCFA is not justified.

Influence of soybean meal and sorghum grain supplementation on intake, digesta kinetics, ruminal fermentation, site and extent of digestion and microbial protein synthesis in beef steers grazing blue grama rangeland.

Six beef steers (British x Brahman) cannulated at the rumen, duodenum and ileum (avg wt 334 kg) and three mature steers (British x British) cannulated at the esophagus were used in a replicated 3 x 3 latin square design and fed no supplement (C), .5 kg soybean meal (SBM) or .5 kg steam-flaked sorghum grain (SFS).head-1.d-1 (DM basis) while grazing blue grama rangeland. Periods of the latin square included a minimum of 14 d for adaptation and 11 d for esophageal masticate collection and digesta sampling. In September, October and November, respectively, forage collected by esophageally cannulated steers averaged 74.5, 88.8 and 71.0% grasses; 2.06, 1.53 and 1.77% N and 68.3, (P greater than .10) by treatment, but total N intake was greater (P less than .05) for SBM vs C and SFS treatments. No differences (P greater than .10) were detected among treatments in OM, NDF, ADF and N digestibilities in the rumen, small intestine or hindgut, but total tract OM digestibility was greater (P less than .10) for SBM and SFS than for C, and total tract N digestibility was greater (P less than .10) for SBM than for C or SFS. Duodenal ammonia N flow was greater (P less than .05) when SBM was fed that when SFS and C were fed, but microbial N and non-ammonia, non-microbial N flows and microbial efficiency were not altered by treatment. Likewise, ileal N flow was not affected (P greater than .10) by treatment. Particulate passage rate, gastrointestinal mean retention time, forage in vitro OM disappearance and in situ rate of forage NDF digestion also were not affected (P greater than .10) by treatments. Ruminal fluid volume was greater (P less than .05) for SFS vs SBM and C treatments, but no differences were noted in fluid dilution rate. Ruminal fluid ammonia concentration was greater (P less than .05) when SBM was fed than when SFS and C were fed (13.5, 9.9 and 8.7 mg/dl, respectively), whereas pH and total VFA concentrations were not different (P greater than .10). Proportion of acetate in ruminal fluid was less (P less than .10) for SBM and SFS than for C. Small amounts of supplemental SBM and SFS had little effect on forage intake, ruminal fermentation and site of digestion but both increased total tract OM digestion in steers grazing blue grama rangeland.

Influence of cottonseed meal supplementation on voluntary intake, ruminal and cecal fermentation, digesta kinetics and serum insulin and growth hormone in mature ewes fed prairie hay.

To determine the influence of protein supplementation on intake and fermentation of low-quality hay, six ruminal- and cecal-cannulated Rambouillet ewes (avg wt 43.6 kg) in a crossover design were given ad libitum access to prairie hay with or without 80 g of cottonseed meal (CSM) X head-1 X d-1. Voluntary hay intake was measured the last 7 d of each 18-d period. Ruminal, cecal and blood samples were collected at 0, 1 (except cecal), 3, 6, 9, 12, 15, 18, 21 and 24 h post-supplementation on d 14 of each period to measure fluid dilution rate, fermentation characteristics and serum concentrations of insulin and growth hormone. An intraruminal dose of Yb-labeled hay, followed by fecal sampling on d 15 through 18, was used to measure particulate passage rate. Voluntary intake of prairie hay was increased (P less than .04) from 23.7 to 28.3 g/kg of body weight by CSM supplementation. Particulate passage rate constants did not differ (P greater than .15) between supplemented (3.76%/h) and control (3.72%/h) ewes, and total mean retention time was not altered (P greater than .15) by CSM supplementation. Ruminal retention time of particulates did not differ (P greater than .15) between treatments; however, intestinal transit time was faster (P less than .03; 18.1 vs 22.6 h) in supplemented than in control ewes. Estimated gastrointestinal dry matter fill was greater (P less than .05; 14.3 vs 12.9 g/kg body weight) in supplemented ewes. Ruminal fluid volume did not differ (P greater than .15) between treatments; however, supplemented ewes tended to have faster fluid dilution rates (P less than .14) and fluid outflow rates (P less than .11) than control ewes. Cecal fluid volume, dilution rate and outflow rate did not differ (P greater than .15) between groups. Ruminal and cecal pH and total volatile fatty acids were similar between treatments. Similarly, cottonseed meal supplementation did not affect (P greater than .15) ruminal or cecal ammonia concentrations. Molar proportions of ruminal and cecal individual fatty acids were not affected (P greater than .15) by CSM supplementation. Feeding cottonseed meal increased (P less than .05) serum insulin, decreased (P less than .07) serum growth hormone and increased (P less than .06) serum free fatty acids, but did not influence (P greater than .15) either serum urea N or glucose concentrations. Cottonseed meal supplementation in ewes fed prairie hay caused increased hay intake but had minimal effects on ruminal and cecal fermentation.