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Gypsum has been shown to reduce runoff on soils prone to crust formation in the southeastern United States. Increased infiltration from gypsum applications could therefore help reduce runoff P and other nutrient losses from application of broiler litter (BL), a nutrient-rich fertilizer. In rainfall simulation experiments in June 2009 and May 2011, runoff and nutrient (N, P, Ca, Mg) losses in runoff were compared among treatments consisting of 0, 2.2, 4.5, and 9.0 Mg ha⁻¹ flue gas desulfurization gypsum (FGDG) combined with 13.5 Mg ha⁻¹ of BL and two control treatments of (0–0) and (9.0–0.0) Mg ha⁻¹ (FGDG-BL). A randomized block design with three replications was set up on a Cecil (Typic Kanhapludult) soil growing Coastal bermudagrass (Cynodon dactylon L.) for hay near Watkinsville, Georgia. Amendments were applied each April from 2009 to 2011. A reduction in runoff of 30% each year from the (9.0–13.5) compared with the (0–0) treatment was not statistically significant. Gypsum was effective in reducing concentration and load in one of the two study years: P and NH₄–N in 2009 (up to 83%) and NO₃–N in 2011 (up to 73%). A combination of factors related to weather extremes, timing of FGDG and BL applications, and their implication on soil and vegetation responses at different landscape positions might have caused the different responses between years. Additional studies focused on isolating the impacts of such factors would be helpful to ascertain the effectiveness of multiyear applications of FGDG as a best management practice to reduce P and other nutrient losses in soils of the southeastern United States.

Switchgrass (Panicum virgatum L.; SG) may have CP below recommended concentrations for feeding ruminants that limit animal performance when cut as hay and fed as the sole diet. Three experiments were conducted to determine the influence of white clover (Trifolium repens. L.) at 0, 15, and 30% of DM (Exp. 1), or alfalfa (Medicago sativa L.) at 0, 25, and 50% of DM with either headed SG (Exp. 2) or vegetative SG (Exp. 3) on steer DMI (kg/100 kg of BW) and DM digestion (g/kg). Eating behavior (Exp. 1) and masticated feed characteristics (Exp. 2 and 3) were also examined. Steer (Bos taurus L.) DM digestion of SG (Exp. 1) increased linearly (P < 0.01) from 544 g/kg on SG to 584 g/kg when clover composed 30% of the offered diet. However, steer DMI of headed SG (Exp. 2) was 1.61 kg/100 kg of BW with a DM digestion of 480 g/kg when fed alone, and both increased linearly (P < 0.01) to 2.68 kg/100 kg of BW and 578 g/kg, respectively, when alfalfa composed 50% of the offered diet. The DM digestion of vegetative SG (Exp. 3) increased linearly (P = 0.09) from 541 when fed alone to 575 g/kg when alfalfa composed 50% of the offered diet. The CP of masticated feed (Exp. 2 and 3) increased linearly (P < 0.01) and NDF decreased linearly (P < 0.01) with increasing alfalfa. Perennial legumes can be a useful source of CP in SG hay diets.

Year-round grazing in animal production systems has potential in the mid-Atlantic United States. Tall fescue [Lolium arundinaceum (Schreb.) S. J. Darbysh.] is generally the cool-season perennial and bermudagrass [Cynodon dactylon (L.) Pers.] is the warm-season perennial in these systems. This study evaluated yellow bluestem (Bothriochloa ischemum L.; YBS) and Coastal panicgrass (Panicum amarum var. amarulum; CPG) for their quality and productivity with a tall fescue-bermudagrass system (BGS) as a control. Steer ADG (kg/d) was less (P = 0.05) in the BGS (0.66) than the mean of 0.77 from YBS (0.68) and CPG (0.86), which differed (P = 0.02). Steer ADG (kg/d) in spring (0.95) was greater (P < 0.01) than summer (0.53), but pasture species interacted with season (P = 0.02). The ADG of CPG was stable across season (from 0.97 to 0.76 kg/d), whereas BGS or YBS declined from 0.97 and 0.92, respectively, to 0.37 and 0.49 kg/d. Dietary in vitro true OM disappearance was similar among species (P = 0.29) and seasons (P = 0.62), averaging 803 g/kg; however, DMI (kg/d per 100 kg of BW) was least (P = 0.05) from the BGS (2.64) compared with YBS (2.97) and CPG (3.40) (P = 0.09). The BGS was stocked greater (P < 0.01) at 12.3 compared with 6.2 and 4.9 steers/ha for YBS and CPG, respectively. Adjusting for days tall fescue was grazed (23%) still favored the BGS. No difference in steer gain (P = 0.95) and effective feed units (P = 0.54) occurred between YBS and CPG (473 and 2,754 kg/ha).

Tall fescue (Festuca arundinacea Schreb.) is a well-adapted perennial pasture species utilized across the north-south transition zone of the United States. This 3-yr trial evaluated the influence of three forage masses (FM) on steer and pasture responses for spring (April to July) and fall (October) growths. Spring FM averaged 1450 kg ha ―1 (Short), 3032 kg ha ―1 (Medium), and 3812 kg ha ―1 (Tall) for the three treatments. Canopy in vitro true organic matter disappearance (ITOD) decreased linearly from Short (797 g kg ―1 ) to Tall (771 g kg ―1 ). Steer daily gains (0.88 kg) and gains per hectare (392 kg ha ―1 yr ―1 ) were not altered by FM, but the mean number of steers per hectare decreased linearly from Short (8.2 steers ha ―1 ) to Tall (6.1 steers ha ―1 ) as did effective feed units per hectare (2256 to 1712 kg ha ―1 yr ―1 ). Canopies were predominately leaf (53%) and averaged 847 g kg ―1 ITOD with estimates similar among FM treatments. Diet ITOD declined linearly from Short (870 g kg ―1 ) to Tall (839 g kg ―1 ) as did crude protein (CP) (from 235 to 192 g kg ―1 ). In the fall, FM averaged 1556, 3228, and 3494 kg ha ―1 for the three FM treatments. Canopy ITOD averaged 774 g kg ―1 and was not altered by FM. Canopy leaves averaged 60% with an ITOD of 864 g kg ―1 and were similar among FM treatments. Diets selected averaged 834 g kg ―1 ITOD and 233 g kg ―1 CP and were not altered by FM. Tall fescue pasture free of toxic endophyte needs to be effectively utilized to enhance production and can be managed flexibly in grazing systems.

In situ and in vitro experiments were performed to assess the effects of solar radiation and predation by indigenous microflora on the relative die-off rates of a toxigenic strain of Escherichia coli 0157:H7, commensal E. coli, and fecal enterococci in surface waters from ponds in agricultural watersheds. The objective of these experiments was to discern a mechanism of persistence of E. coli 0157:H7 in surface waters compared to fecal indicator bacteria. Results of these experiments indicated that E. coli and fecal enterococci were affected by both insolation and apparent predation; whereas E. coli 0157:H7 appeared to be resistant to both of these environmental stressors. The number of days to reach 99% die-off (T99-values) for E. coli 0157:H7 was significantly greater than that for the indicator bacteria. The capacity to prolong die-off may be connected to the apparent persistence of E. coli 0157:H7 in surface waters.

Management strategies to accommodate switchgrass (Panicum virgatum L.) in production systems have been reported but impact of variation in forage mass (FM) on animal responses and pasture stands are lacking. This 4-yr study assessed canopy and stand characteristic and steer (Bos taurus) responses when 'Kanlow' switchgrass was continuously and variably stocked to produce Short (S) (10―16 cm), Medium (M) (20―26 cm), and Tall (T) (35―41 cm) canopy heights. From April to mid-July (Period 1) FM for S, M, and T average 818, 2164, and 3294 kg ha ―1 , respectively. Canopies had similar in vitro organic matter disappearance (IVOMD) (626 g kg ―1 ), but increased in neutral detergent fiber (NDF) from S (645 g kg ―1 ) to T (665 g kg ―1 ). Diets decreased in IVOMD from S (744 g kg ―1 ) to T (706 g kg ―1 ). Digesta kinetics data were not altered and average daily gain was similar among FM (1.11 kg d ―1 ). From mid-July to late September (Period 2), FM averaged 465, 1282, and 2388 kg ha ―1 , respectively, for S, M, and T. Whole canopy IVOMD increased from S (484 g kg ―1 ) to T (538 g kg ―1 ), whereas NDF was not altered (696 g kg ―1 ). Steers selected a diet similar in IVOMD (685 g kg ―1 ) and NDF (667 g kg ―1 ) among FM. Estimates of dry matter intake (kg 100 ―1 kg body weight) increased from S (1.75) to T (2.54). Tiller density decreased from T to S. Continuously stocked switchgrass at 20 to 40 cm remained vegetative with 1279 tillers m ―2 after 3 yr of grazing.

Improved cool-season grass cultivars may add production potential to ruminant enterprises across the North–South transition zone. Quality among hays of ‘MaxQ’ (‘Jesup’ with novel endophyte), HM4 (‘HiMag’ with novel endophyte No. 4) and ‘Cajun’ (without endophyte) tall fescues [Lolium arundinaceum (Schreb.) Darbysh.] and ‘Persist’ orchardgrass (Dactylis glomerata L.) was evaluated. Forage was harvested in the fl ag-leaf stage in three of 4 yr and a regrowth (late fl ag-leaf to heads-emerging stage) in 1 yr. Goats (four trials) consumed MaxQ, HM4, and Persist similarly (P = 0.12; mean = 2.49 kg 100 –1 kg body weight [BW]) and Cajun least (P

Eastern gamagrass [Tripsacum dactyloides (L.) L.] (EG), a native warm-season perennial grass, lacks evaluation for use in grazing systems. Our objective was to test EG in a 4-yr experiment to estimate forage mass (FM) that maximizes steer (Bos taurus) performance and pasture productivity. Pasture canopy characteristics, diet selection by grazing steers, and stand persistence from EG continuously grazed at Short, Medium, and Tall heights and two rotationally stocked treatments were compared with continuously stocked ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] (BG). The EG had proportionally more green leaf (78.2 vs. 24.5%), less stem (4.4 vs. 45.2%), less heads (0.4 vs. 5.6%), and similar dead tissue (17.0 vs. 24.8%). Plant fractions were similar in proportion among EG treatments. Digestible leaf mass was greater in EG than in BG (P < 0.01; 713 vs. 292 kg ha–1) and dominated the EG canopies with a linear (P < 0.01) increase in leaf mass with increasing FM (194–922 kg ha–1). Diets were similar in IVTOD (738 g kg–1), CP (151 g kg–1), and NDF (654 g kg–1) when continuously stocked but greater (P < 0.01) in IVTOD (791 g kg–1), and least in NDF (624 g kg–1) from the rotation. Stand declined linearly (P = 0.09) with decreasing FM (Tall = 34.5 and Short = 11.7% basal cover) but was similar between the two rotational systems (35.5%). Continuously stocking EG at about 38 cm gave greatest steer daily gain but rotations may prevent declines in stands with some sacrifice in gains.

Waste handling systems for confined swine production in the upper South (approximately 32-37 degrees N and 79-93 degrees W) depend mainly on anaerobic lagoons and application of the waste effluent to cropland. The main objective of this study was to evaluate the quality of 'Coastal' bermudagrass [Cynodon dactylon (L.) Pers.] hay receiving effluent generated from a raw swine waste treatment system designed to reduce P and K concentrations and delivered by subsurface drip irrigation (SDI) compared with hay produced from commercial N fertilizer. Eight treatments, consisting of commercial N fertilizer or effluent, each irrigated at two irrigation rates (75 and 100% of estimated evapotranspiration) and two lateral spacings (0.6 and 1.2 m), were compared with a control treatment of commercial N fertilizer without irrigation. Three harvests were taken in each of 2 yr and five of the six evaluated using wether sheep (30-45 kg). Greatest dry matter intake (DMI) per unit body weight occurred for the control vs. all irrigated treatments (1.94 vs. 1.77 kg 100(-1) kg; P = 0.02; SEM = 0.11). Among irrigated treatments, DMI was greatest from commercial N vs. effluent (1.81 vs. 1.71 kg 100(-1) kg; P = 0.05; SEM = 0.11). Dry matter intake was similar for the 75% rate treatments and the non-irrigated treatment (mean, 1.87 kg 100(-1) kg) but was reduced for the 100% rate (1.94 vs. 1.72 kg 100(-1) kg; P = 0.03; SEM = 0.11). Hay from the 75% rate was more digestible than hay from the 100% rate (527 vs. 508 g kg(-1); P = 0.03; SEM = 21). The SDI system functioned well, and lateral spacing did not alter hay quality. Treated waste from a raw waste treatment system was readily delivered by SDI at the recommended rate to produce bermudagrass hay of adequate quality for ruminant production systems.

'Coastal' and 'Tifton 44' (T44) Bermudagrass [Cynodon dactylon (L.) Pers.] are well adapted across the lower southern United States, but the grazing response of (T44) to N application in the Piedmont of the upper South warrants further evaluation. This 3-yr experiment compared animal and pasture productivity of Coastal and T44 with three annual N rates of 101, 202, and 303 kg of N ha -1 on a Cecil clay loam (fine, kaolinitic thermic Typic Kanhapludult) soil typical of the Piedmont. Herbage mass differed for Coastal and T44 (3.5 and 3.0 Mg ha -1 respectively, P < 0.01), but not among N rates. The canopy of T44 was leafier (20.6 vs. 14.5% of dry matter) than Coastal and greater for in vitro true organic matter disappearance (IVTOD) (522 vs. 498 g kg -1 ) and CP (107 vs. 84 g kg -1 ) and lesser in NDF (596 vs. 605 g kg -1 ). The diet selected from T44 was greater in IVTOD (764 vs. 743 g kg -1 ) and lesser in NDF (596 vs. 605 g kg -1 ) giving greater steer average daily gain (0.63 kg vs. 0.57 kg; P < 0.01) which increased (P = 0.05) with N rate. Weight gain ha -1 (884 kg) and effective feed units (EFU) (4735 kg ha -1 ) were similar, and N rate linearly increased gain from 723 to 1073 kg ha -1 and EFU from 3978 to 5523 kg ha -1 . Soil inorganic N was similar between cultivars but differed among soil depths. Tifton 44 pasture was greater in nutritive value, hence steer performance, and as productive as Coastal in the Piedmont.

Tall fescue [ Schedonorus phoenix (Scop.) Holub.] is an important source of forage but often con-tains a fungal endophyte [ Neotyphodium coeno-phialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin] that can produce alkaloids and decrease anmi al perf ormance. Removing the endophyte can reduce agronomic performance and persistence. An improved cultivar (‘Jesup’) with a novel (nontoxic) endophyte (trademark “MaxQ”) has improved agronomic performance. Persistence may be related to agronomic traits and animal feeding preferences. We tested for variation in animal preference among two har-vests by testing each of three hays made from Jesup tall fescue that varied in endophyte sta-tus (no endophyte, containing the novel endo-phyte, or containing a wild-type endophyte that produces alkaloids associated with toxicosis). We tested for preference using goats ( Capra hir-cus ), sheep ( Ovis aries ), and cattle ( Bos taurus ). All possible pairs were tested using traditional analysis of variance as well as multidimensional scaling. Multidimensional scaling of the animal preferences indicated that two dimensions were being used to rank the hays. The fi rst dimension for all three animal species was related to varia-tion in forage nutritive value. The second dimen-sion was not correlated with any of the measured variables. Endophyte status was not a factor in the preferences expressed by the three animal species. It appears that no effective feedback mechanism exists related to endophyte status.D.S. Fisher, USDA-ARS, 1420 Experiment Station Rd., Watkinsville, GA 30677; J.C. Burns, USDA-ARS and Dep. Crop Science and Dep. Animal Science, North Carolina State Univ., Raleigh, NC 27695. Cooperative investigation of the USDA-ARS and the North Carolina ARS, Raleigh, NC 27695-7643. The use of trade names does not imply endorsements by USDA-ARS or by the North Carolina ARS of the products named or criticism of similar ones not mentioned. Received 3 Oct. 2007. *Corresponding author (Dwight.Fisher@ars.usda.gov).

Hybrid cultivars of bermudagrass [Cynodon dactylon (L.) Pers.] are a major feed source for ruminants across the southeastern United States. This 4-yr experiment compared animal and pasture performance of 'Coastal' and 'Tifton 44' bermudagrasses over three canopy heights designated as short (5.6 cm), medium (10.1 cm), and tall (13.1 cm). The relationship of canopy height to ingestive mastication and canopy characteristics was also studied. Soil was a Cecil clay loam (clayey, Kaolinitic thermic Typic Hapludult). Pastures were continuously stocked using variable stocking to maintain the targeted canopy heights. Herbage mass (to soil surface) was similar between Coastal and Tifton 44 (T44) within each canopy height averaging 2.36, 4.08, and 5.25 Mg ha -1 . Steer average daily gain (ADG) was greater (P = 0.09) from T44 than Coastal (0.58 vs. 0.51 kg) but no differences were noted in pasture productivity. Increasing herbage mass linearly increased (P < 0.01) ADG (0.40-0.59 kg) but reduced (P < 0.01) stocking rate (16.1-11.2 steers ha -1 ), which influenced animal days (1810-1079 d ha -1 ), weight gain (1057-786 kg ha -1 ), and effective feed units (6392-4452 kg ha -1 ). Steer ADG increased (P = 0.01) from short to medium canopy height (0.40-0.64 kg) with little change between medium and tall canopy height (0.64-0.59kg). Tifton 44 pasture is ofgreater quality than Coastal giving greater ADG but both were productive producing about 1100 kg of gain ha -1 when effectively managed and utilized.

Forages accumulate nonstructural carbohydrates during the day, with animals showing preference and improved daily responses from afternoon compared with morning cut hays. This study evaluated alfalfa (Medicago sativa L.) hay harvested at 0700, 1000, 1300, 1600, and 1900 h to determine how nutritive value changes during the day and to assess the impact of these changes on animal preference using cattle (Bos taurus L.), sheep (Ovis aries L.), and goat (Capra hircus L.) responses. Total nonstructural carbohydrates were altered by time of cut (cubic contrast, P < 0.01) ranging from 85 g kg −1 at 0700 h to 83 g kg −1 at 1000 h, then increasing to 97 g kg −1 by 1600 h with little change at 1900 h (96 g kg −1 ). Fiber fractions also varied diurnally, with a quadratic decrease from 418 g kg −1 at 0700 h to

Understanding cover crop and tillage system interactions within specific environments can help maximize productivity and economic returns of cotton (Gossypium hirsutum L.) produced on sandy coastal plain soils of the southeastern USA. A strip-plot design with three replications was used to evaluate the cover crops Austrian winter pea [Pisum sativum L. ssp. arvense (L.)], balansa clover (Trifolium michelianum Savi), crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth subsp. villosa), oil seed radish (Raphanus sativus L.), black oat (Avena strigosa Schreb.), and rye (Secale cereale L.) and tillage (strip and none) influences on cotton grown on a Bonifay fine sand (loamy, siliceous, subactive, thermic Grossarenic PlinthicPaleudults)nearWaynesboro,GAfrom1999to2003.Drought influenced production 3 of 4 yr. Cover crop biomass was greatest from rye, intermediate from black oat, oilseed radish, hairy vetch, and Austrian winter pea. Hairy vetch and Austrian winter pea contained more than 80 kg N ha 21 while other cover crops averaged ,40 kg N ha 21 . Cotton yields following black oat and rye had returns above variable costs ha 21 $461 and $406, respectively. Strip-tillage increased yields by 192 kg ha 21 and annual returns by $112 ha 21 over no-tillage, most likely due to improved available water. Combining strip-tillage with black oat was the best combination for maximizing profit. Using black oat with strip-tillage could increase cotton profit by $50 to $75 ha 21 compared to systems using rye on the 1.45 million ha of cotton where conservation systems have been adopted.

Introducing novel endophytes into tall fescue (Festuca arundinacea Schreb.) that produce no ergot alkaloids could prevent negative impacts on animal performance while improving plant persistence. This 3-yr study evaluated ‘Jesup’ tall fescue (TF) for forage mass, nutritivevalue, and stand persistence when containing no endophyte, a novel endophyte (no ergot alkaloids), or a wild-type endophyte (ergot alkaloids). Forage was accumulated from mid-August and treatments consisted of (i) a grazed control (grazed when growth approximated 10 to 15 cm), or forage accumulated and grazed in (ii) mid-November, (iii) mid-December, (iv) mid-January, and (v) mid-February. Endophyte status had no influence on total forage mass; forage removed by grazing; proportion of leaf, stem, and dead fractions; or on nutritive value (except ergovaline which was greatest in the wild type). Delaying defoliation linearly reduced forage mass, ergovaline concentration, and nutritive value. All stands of TF declined with losses similar (P 5 0.37) for wild-type and novel stands (29 vs. 42%) but were greatest for the TF without an endophyte (29 vs. 75%; P 5 0.01 and 42 vs. 75%; P 5 0.04). These data support the use of novel endophytes in TF for animal production and caution against the use of endophyte-free TF because of decreased stand longevity. The presence of ergovaline can be minimized by stockpiling TF with utilization after late autumn but occurs with a sacrifice in forage mass and nutritive value.

Few studies have reported runoff from small agricultural watersheds over sufficiently long period so that the effect of different cover types on runoff can be examined. We analyzed 45-yrs of monthly and annual rainfall-runoff characteristics of a small (7.8 ha) zero-order typical Southern Piedmont watershed in southeastern United States. Agricultural land use varied as follows: 1. Row cropping (5-yrs); 2. Kudzu (Pueraria lobata; 5-yrs); 3. Grazed kudzu and rescuegrass (Bromus catharticus; 7-yrs); and 4. Grazed bermudagrass and winter annuals (Cynodon dactylon; 28-yrs). Land use and rainfall variability influenced runoff characteristics. Row cropping produced the largest runoff amount, percentage of the rainfall partitioned into runoff, and peak flow rates. Kudzu reduced spring runoff and almost eliminated summer runoff, as did a mixture of kudzu and rescuegrass (KR) compared to row cropping. Peak flow rates were also reduced during the kudzu and KR. Peak flow rates increased under bermudagrass but were lower than during row cropping. A simple process-based ‘tanh’ model modified to take the previous month's rainfall into account produced monthly rainfall and runoff correlations with coefficient of determination (R2) of 0.74. The model was tested on independent data collected during drought. Mean monthly runoff was 1.65 times the observed runoff. Sustained hydrologic monitoring is essential to understanding long-term rainfall-runoff relationships in agricultural watersheds.

test of the ruminant's ability to learn that the nutritive value or taste of one feed varies slightly from another As a result of photosynthesis, plants typically have greater concen- at two levels of nitrogen fertility in 1999 to produce eight hays; and three times in 2000 to produce six Alamo hays. The hays were field- Alamo was produced at two levels of nitrogen fertility. dried, baled, and passed through a hydraulic bale processor. Hays Thisselectionofhaysproducedoverthreeyearsallowed from each year were tested with cattle (Bos taurus L.), goats (Capra forawiderangeofsignificantvariationinforagecompo- hircus L.), and sheep (Ovis aries L.). During an adaptation phase, sition (or nutritive value) and environmental conditions hays were offered individually. In the experimental phase, all possible within which to test for the impact of PM and AM hay pairsofhayswerepresented.Datawereanalyzedbymultidimensional mowing in the humid southeastern USA. scalingand bytraditional analyses.Multidimensional scalingindicated that selection was based on multiple criteria. The suite of improve- ments associated with PM-harvested hays in fiber content, digestibil- MATERIALS AND METHODS ity, and nonstructural carbohydrate observed for alfalfa and fescue Field Procedures hays in the western USA was difficult to reproduce with switchgrass hay in the southeastern USA. This difficulty is likely related to the All hays for the experiments reported were harvested from less favorable environment for haymaking as well as the physiology, well established stands of switchgrass grown on a Cecil clay anatomy, and morphology of this C4 grass. loam (fine, kaolinitic, thermic Typic Kanhapludults) soil near Raleigh, NC. The hay cuts were paired at each harvest so that each cut in the evening (PM) was followed by another cut the next morning (AM) at sunup. P

Forage yields are influenced by plant response to defoliation. We examined the photosynthesis and nutritive value of first (first leaves) and third (third leaves) fully expanded leaves (numbered from the apex) in three warm-season (C4) grasses. Net photosynthetic rates at uniform temperature and light both before and after a 2-wk exposure to full sunlight and the effect of leaf position on nutritive value were determined on vegetative tillers in well-established swards of bermudagrass [Cynodon dactylon L. (Per.) cv. Tifton 44], Caucasian bluestem [Bothriochloa caucasica (Trin.) C.E. Hubb.], and Atlantic coastal panicgrass [Panicum amarum var. amarulum (Hitchcock and Chase) P.G. Palmer] growing on a Cedl clay loam (clayey, kaolinitic, thermic Typic Hapludults). Bermudagrass had the greatest level of crude protein (CP), followed by panicgrass and bluestem. Fiber was greater in the first leaves than in the third leaves for bermudagrass and panicgrass but not for bluestem. Photosynthetic rates of panicgrass and bluestem third leaves estimated 2 wk after defoliation of the surrounding canopy were less than estimates made before defoliation in the first leaves but were similar to the third leaves before canopy defoliation. The third leaves of bermudagrass 2 wk after defoliation had lesser photosynthetic rates per unit chlorophyll than the first or third leaves before defoliation. Photosynthetic rates were correlated with hemicellulose across leaf classes and species (r 2 = 0.93). The photosynthetic decline observed in third leaves of bermudagrass compared with panicgrass and bluestem is evidence of variation in leaf response after defoliation among warm-season grasses.

The objective of this research was to examine the effect of high concentrations of nonprotein nitrogen (NPN) on the voluntary food intake of sheep fed high-quality grasses. Wether lambs (n = 6 per treatment) were fed dried switchgrass (Panicum uirgatum L.; Exp. 1) or dried tall fescue (Festuca arundinacea Schreb.; Exp. 2). In both experiments, urea was added to the dried forage at 0 (control), 12, or 24 g of N/kg of DM to increase the NPN concentration. Acid detergent fiber concentrations were 305 g/kg of DM in both experiments, although DM digestibility was 663 and 618 g/ kg of DM in Exp. 1 and Exp. 2, respectively. Voluntary feed intake of the control forage was 28.2 and 19.1 g/ kg of BW in Exp. 1 and Exp. 2, respectively, and decreased for the high-urea treatments to 25.2 and 16.2 g/kg of BW in Exp. 1 (P = 0.07) and Exp 2 (P = 0.03), respectively. Total feed N concentrations increased from 29.5 g to 45.7 g of N/kg of DM in Exp. 1 (P < 0.01) and from 28.4 to 55.9 g of N/kg of DM in Exp. 2 (P < 0.01). Nonprotein N concentrations increased from 28. 3 to 53.8% of the total N in switchgrass diets (Exp. 1; P < 0.01), and from 26.4 to 64.0% in tall fescue diets (Exp. 2; P < 0.01). Plasma urea concentrations of the lambs increased from 3.1 to 6.6 mM (Exp. 1; P < 0.01) and from 2.9 to 5.8 mM (Exp. 2; P < 0.01) as the amount of urea added to the diets increased. These changes resulted in an increase in plasma osmolality from 298 to 307 mOsm/kg (Exp. 1; P = 0.04), and from 299 to 307 mOsm/kg (Exp. 2; P = 0.06). Increasing feed N and NPN concentrations through the addition of urea caused a significant decrease in the voluntary feed intake of sheep fed tall fescue and switchgrass. These responses showed no significant cause-and-effect relationship between voluntary feed intake, plasma urea concentrations, and plasma osmolality.

Plant growth and yield responses to carbon dioxide (CO2) enrichment are well es- tablished. Much less is known of the response of arthropod pests to CO2 enrichment. Reproductive response of twospotted spider mites (Tetranychus urticae Koch) on white clover (Trifolium repens L.) to a range of CO2 concentrations was measured. The CO2 treatments were applied for 24 h d 1 at395, 484, 570, 657, and 748 LL 1 on the 14 d before and 26 Ð27 d after infestation with mites. Eggs, larvae, nymphs, and adult mites were removed from leaves and counted 27Ð29 d after infestation. Leaf area and weight were measured, and leaves were analyzed to measure structural and nonstructural carbohydrates, N, amino acids and digestibility. Carbon dioxide enrichment caused linear increases in plant growth and foliar nonstructural carbohydrates, but caused linear decreases in foliar N. Carbon dioxide enrichment signiÞcantly increased the rate of mite reproduction on both clover clones. Correlations between mite population increase were signiÞcantly positive for foliar nonstructural carbohydrates and signiÞcantly negative for foliar N. Concentrations of ambient CO2 expected in the 21st century may increase the risk of mite population damage on some plant species.

Diurnal variation in the concentration of total nonstructural carbohydrates (TNC) occurs in plants as a result of photosynthesis. Ruminants have been shown to prefer tall fescue (Festuca arundinacea Schreber) hays cut in the afternoon but the effect of morning vs. evening cutting had not been tested in legumes. To test for diurnal variation in preference for alfalfa (Medicago sativa L.), we harvested six times in the midbud stage. Harvests were paired so that each time a cutting of alfalfa was made at sundown (PM) another was made the next morning at sunup (AM). We harvested in this manner three times resulting in six hays. The hays were field dried, baled, and chopped prior to their use 3 to 6 mo after harvest. Three experiments were conducted [Exp. 1, sheep (Ovis aries); Exp. 2, goats (Capra hircus hircus); and Exp. 3, cattle (Bos taurus)] utilizing six animals in each case. During an adaptation phase, hays were offered alone as meals. In the experimental phase, every possible pair of hays (15 pairs) was presented for a meal. Data were analyzed by multidimensional scaling as well as by traditional analyses. Multidimensional scaling indicated that the animals were basing selection on at least two criteria. Variables associated with preference through multiple regression varied across experiments but significant coefficients were found between preference and nitrate, protein, carbohydrate fractions, lignin, and cellulose. Coefficients varied depending on which other variables were in the model; however, carbohydrates were associated with positive coefficients. Shifting hay mowing from early in the day to late in the day was effective in increasing forage preference as expressed by short-term dry matter intake.

Calliandra calothyrsus, Paraserianthes falcataria and Gliricidia sepium leaves were supplemented at both 25 and 50% of dietary crude protein to a basal concentrate and fed to growing ram lambs. A control diet consisted of concentrate and the forage grass Brachiaria brizantha. Dry matter intakes and ADG of tree legume supplemented treatments were lower (P < 0.05) than control lambs, but increasing the amount of tree leaves fed did not result in further decreases in either dry matter intake or ADG. Dry matter digestibility was lower (P < 0.05) in both 25 and 50% dietary treatments compared with the control, while NDF digestibility was lower (P < 0.001) only in the 50% dietary treatments. Increasing the amount of leaves fed from all three tree species, led to decreased NDF digestibility. Fecal NDF-N was higher in tree-supplemented groups (P < 0.01) compared with control and increased (P < 0.05) with increasing amounts of tree leaves fed. Both apparent and true N digestibility were lower (P < 0.05) in C. calothyrsus, than in the other tree legume treatments. True N digestibility of 91% for the control was higher (P < 0.01) than the tree legume treatments supplemented at both 25 (range, 83‐86%) and 50% dietary CP (range, 74‐79%). Increasing the amount of tree leaves fed, regardless of tree species, decreased N digestibility in the diets. Higher fecal NDF-N and lower N digestibility in tree leaf supplemented lambs indicated that condensed tannins present in these tree species were binding protein and rendering it less available for digestion. Supplementation with C. calothyrsus, which had the highest levels of SPHE and

Eastern gamagrass [ Tripsacum dactyloides (L.) L.] (GG) hays were harvested May 23 when vegetative (GG-V) and 28 days later (June) when reproductive culms were developing (GG-R) and were compared. The GG-V hay was further compared with a vegetative switchgrass ( Panicum virgatum L.) (SG) hay harvested May 29. The GG-R hay was also compared with a late-early-boot flaccidgrass ( Pennisetum flaccidum Griseb.) (FG) hay harvested on the same day. Forages were direct-cut with a flail chopper, artificially dried (24 h) in a forced-air bulk dryer (82 °C), baled after drying, stored, and without further processing fed to Suffolk wethers ( Ovis aries ) in a 4 × 4 latin square design. The GG-V and GG-R hays had similar apparent dry matter digestion coefficients averaging 0.64 and were also similar to SG and FG averaging 0.64 and 0.61, respectively. All hays had similar concentrations of crude protein (100 g kg −1 ), neutral detergent fiber (715 g kg −1 ), acid detergent fiber (373 g kg −1 ), hemicellulose (342 g kg −1 ), cellulose (305 g kg −1 ) and acid detergent lignin (58 g kg −1 ). Dry matter intake (kg/100 kg body weight) was similar for GG-V (2.42) and GG-R (2.19) and for GG-V and SG (2.27), but wethers fed GG-R had higher intake compared with FG (1.27). Nitrogen (N) retention, as a percent of total N intake, was higher for wethers fed GG (23% for GG-V and 33% for GG-R) than for either SG (15%) or FG (14%). Differences in N retention were reflected in N excreted in the urine. Eastern GG shows potential as a useful perennial C 4 grass for ruminant production systems.

Masticated forage provides information related to the quality and fractionation characteristics of a ruminant's diet. This study reports the use of near infrared reflectance spectroscopy (NIRS) to predict the in vitro dry matter disappearance (IVDMD), in vitro organic matter disappearance (IVOMD), and cell-wall concentrations of particle size fractions and the whole masticate of temperate forages. Esophageal extrusa samples, with saliva retained, were obtained from fistulated steers (Bos taurus) that were intermittently grazing tall fescue (Festuca arundinacea Schreb.), orchardgrass (Dactylis glomerata L.), and ryegrass (Lolium perenne L.) [...]

The daily forage intake of ruminants is made up of a series of meals. These meals are especially pronounced in animals fed in stalls and coincide with the distribution of food. A relatively simple model of ruminant digestion was developed and used to test equations designed to predict rate of forage intake during meals. An equation that had been published previously as a means of controlling daily dry matter intake was combined with a Michaelis equation to control intake rate as the integrated hunger signal from chemostatic and distension feedbacks varied. The termination of the meal was based on experimental observation and the status of the model was examined for indications of the satiety mechanism at the end of the meal. The predicted level of hunger at the end of the meal varied. It is proposed that the end of the meal is triggered by an integrated hunger and palatability signal and two simple products are suggested by the data; however, the problem is likely to require a more complex function.

Switchgrass ( Panicum virgatum L.) harvested at several maturities was readily ensiled when either directly cut and stored at a dry matter (DM) concentration of about 250 g kg −1 or wilted and stored at a DM concentration of about 350 g kg −1 . Silage pH ranged from 4.6 to 5.1 for all treatments with acetic and lactic acids predominating. Acetic acid concentrations in the direct cut silage was double the concentrations in the wilted silage while lactic acid concentrations were similar. Forage at ensiling was high in cell walls (694 to 743 g kg −1 ) and low in crude protein (53 to 63 g kg −1 ). Silage was stable when either direct cut or wilted and well preserved when air was excluded. Forage artificially-dried (hay) or when ensiled (direct cut or wilted) did not alter DM intake (kg 100 −1 kg body weight) which averaged 1.48 for the late boot stage and 1.41 when fully mature. Apparent digestion coefficients for DM and cell wall constituents of fully headed switchgrass showed no difference when preserved as hay or silage. Digestion coefficients from wilted silage were lower, however, than from direct cut silage for DM, crude protein, neutral detergent fiber, acid detergent fiber and cellulose. These results indicate that switchgrass can be preserved through fermentation with best results from immediate ensiling and subsequently utilized as silage in animal production systems.

Three grazing experiments were conducted to compare actual fecal output (FO) by sheep, determined with fecal collection bags, to fecal output predicted using Captec chromic oxide (CrzO3) controlled-release capsules. In Exp. 1, 14 crossbred wethers dosed with controlled-release Cr2O3 capsules rotationally grazed four paddocks of alfalfa (Medicago sativa L.) for 18 d. Total fecal collection and grab samples were taken daily from each animal; feces were dried and assayed for Cr. From d 5 to 12 after dosing, mean actual FO (429 f 9.6 g of DM/d) differed (P < .001) from FO predicted by the capsule (463 f 12.8 g of DM/d). The correlation between actual and predicted FO was r = .59. When data were averaged by day, the correlation increased to .82. In Exp. 2, Tifton 44 bermudagrass (Cynodon dactylon IL.1 Pers.) was strip-grazed for 30 d by the same 14 wethers used in Exp. 1. Mean actual FO (369 k 5.1 g of DM/dl differed (P < .0001) from predicted FO (415 k 9.3 g of DM/d), with a correlation of .60. In Exp. 3, 72 crossbred lambs were blocked by weight (light and heavy) and assigned to six groups of eight wethers ffour with fecal bags) and four ewes, allotted randomly to three stocking rates (74, 99, and 148 sheep/ha). Sampling occurred from d 6 to 10 after dosing (Period 1) and d 20 to 24 after dosing (Period 2). The correlation between actual and predicted FO in Period 1 was better (r = .63) than that in Period 2 (r = .461; using means improved the results only for Period 1 (r = .77). Although correlations were significant between predicted and actual FO, the controlled-release Cr capsule did not adequately predict total FO by wether lambs.

Eastern gamagrass (Tripsacum dactyloides [L.] L.) has attracted attention as a forage crop, but information on its use is lacking. This 2-yr study compared diet quality, ingestive mastication, and ADG by steers grazing eastern gamagrass (GG), flaccidgrass (Pennisetum flaccidum Griseb.), and Tifton 44 bermudagrass (Cynodon dactylon [L.] Pers.). The design was a randomized complete block with two agronomic replicates. The diet selected by steers from GG in May did not differ from the diet selected by steers from flaccidgrass (FG) for IVDMD (77.3%), NDF (44.0%), CP (19.5%), and mean and median particle sizes of the ingesta (1.8 and 1.4 mm). In July, GG diets had three percentage units less IVDMD (P less than .05), 8.4 percentage units more NDF (P less than .05), and 4.5 percentage units less CP (P = .07) than the mean of FG and bermudagrass (BG). The canopy (July) of GG had the greatest proportion of its DM as leaf (59 vs 26% for FG and 22% for BG) and the least proportion as stem (25 vs 40% for FG and 59% for BG). Mean particle size (millimeters) of masticates differed (P = .05) among forages with GG greatest (2.2), followed by FG (1.6), and BG particles were smallest (1.2). Proportion of large (greater than or equal to 2.8 mm), medium (less than 2.8 greater than or equal to .5 mm), and small (less than .5 mm) particles of the masticate DM, and their IVDMD and NDF concentration, interacted with species (P less than .05). Gamagrass masticate had the greatest proportion (28%) of large particles and BG the greatest proportion (23%) of small particles. The least IVDMD occurred for large particles of BG (62.5%) and small particles of GG (63.8%). Digesta kinetics did not differ among species. Characteristics of GG yielded steer ADG of .82 vs .67 kg for FG and .30 kg for BG (P = .05).

Grazing ruminants use both visual cues and taste in selecting their diet. Preference during grazing may not be the same when forage is dried for hay and cut into lengths prior to feeding in confinement. Eight cultivars of tall fescue (Festuca arundinacea Schreb.), previously evaluated for preference while grazed, were harvested three times over a period of 2 yr. The hays were air-dried, baled, and passed through a hydraulic bale processor prior to feeding. Five experiments were conducted. All three harvests were evaluated with sheep and the last two also with goats, using six animals each time. During an adaptation phase, hays were offered alone as meals. In the experimental phase, every possible pair of hays (28 pairs) was presented for a meal. Data were analyzed by multidimensional scaling and by traditional analyses. Preference was significant among cultivars in all experiments. Multidimensional scaling showed that selection was based on two criteria with two dimensions being significant. Sheep preferred KENHY followed by KENTUCKY 31 and STARGRAZER but preferenced against BARCEL. HIMAG, MO-96, and C1 were intermediate and MOZARK was variable. Goats were similar to sheep in preferring KENHY followed by STARGRAZER and selected against MOZARK and BARCEL. KENTUCKY 31, HIMAG, MO-96, and C1 were intermediate. In all five experiments, the general association was positive for available carbohydrate fractions and negative for fiber fractions that contribute to cell wall rigidity.

Plants vary diurnally in concentrations of nonstructural carbohydrates. If ruminants prefer forages with higher total nonstructural carbohydrates (TNC), then the preference for hays harvested within the same 24-h period may vary. An established field of tall fescue (Festuca arundinacea Schreb.) was harvested six times in the vegetative stage. Harvests were paired such that each cutting at sundown (PM) was followed by a cutting the next morning at sunup (AM). We harvested in this manner three times, resulting in six hays. The hays were field-dried, baled, and passed through a hydraulic bale processor prior to feeding. Experiments were conducted with sheep, goats, and cattle, using six animals in each case. During an adaptation phase, hays were offered alone as meals. In the experimental phase, every possible pair of hays (15 pairs) was presented for a meal. Data were analyzed by multidimensional scaling and by traditional analyses. Multidimensional scaling indicated that selection was based on a single criterion. Preference for PM hays was greater than for AM hays (P < .01) in all experiments. Increased preference was associated with increased TNC (P < .01) and in vitro true DM disappearance (P < .01) and decreased fiber concentration (P < .01; NDF, ADF, cellulose, and ADL). Mowing hay late in the day was effective in increasing forage preference.

Little progress has been made in modeling intake regulation in spite of the many mechanisms identified as important. A model with relatively simple inputs was developed that included compartments for protein, soluble carbohydrate, digestible fiber, and very slowly digesting fiber. Distention and chemostatic feedbacks were combined using a previously published equation. The ratio of current ruminal fill to a modulating parameter for ruminal fill represented distention feedback. The ratio of the current flow of available energy to a modulating parameter for chemostatic demand represented chemostatic feedback. The modulating parameter for ruminal fill was based on literature reports of ruminal contents. Intake was adjusted based on current fill and energy flow relative to modulating parameters for fill and chemostatic feedback. The effect of the digestible organic matter (DOM) to CP ratio on DOM intake was modeled to adjust rates of digestion, rates of passage, and the chemostatic feedback. The model tested an integrated concept of intake regulation with only CP, IVDMD, and NDF as inputs. In spite of relatively simple inputs, the model behavior in response to variation in protein, digestibility, and fiber was similar to observations of animal responses.

Animal responses to treatments in grazing experiments frequently remain unexplained because of inadequate pasture and(or) animal measurements. This 2-yr study examined DMI, gastrointestinal tract fill of undigested DM (FILL), rate of digesta passage (ROP), and digesta mean retention time (MRT) for steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.). A randomized complete block design was used with two agronomic replicates. Comparisons in June (yr 1) among continuously grazed switchgrass (SG), flaccidgrass (FG), and bermudagrass (BG) or in May (yr 2) among tall fescue (TF), SG, and FG showed similar digesta kinetics, but different DMI (kg.d-1.100 kg BW-1), among these forages within each sampling. In the June evaluation, the DMI of SG and FG were similar (means = 3.09), DMI of bermudagrass (BG) was lowest (2.23), and fecal DM output (FO) was similar among forages. In the May evaluation, DMI by steers grazing SG (3.90) was higher than that by steers grazing FG (2.97); DMI of tall fescue (TF) was intermediate (3.41) but similar to DMI of FG. Differences in DMI were due to differences in diet in vitro DM disappearance (IVDMD) rather than to differences in digesta kinetics. In July (yr 2), the MRT was highest for BG (84 h) and similar for SG and FG (57 h). Steers grazing different forages exhibited similar ROP and FILL, but FO (kg.d-1.100 kg BW-1) among steers varied (.37 for steers fed BG; .74 for steers fed SG and FG).(ABSTRACT TRUNCATED AT 250 WORDS)

In traditional grazing trials, per animal and per hectare productivity are determined, but pasture and animal measurements are generally inadequate to address reasons for different treatment responses. This 2-yr study examined the diet and diet characteristics of steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.) pastures. A randomized complete block design was used with two agronomic replicates. In vitro DM disappearance (IVDMD) of masticates from tall fescue (TF), switchgrass (SG), and flaccidgrass (FG) generally were similar; all exceeded 70% (70.3 to 79.9%), except for bermudagrass (BG), which was lowest (63.5 to 65.0%). Sieving the masticate DM showed BG to contain the highest proportion (20 to 29%) of particles passing a .5-mm sieve and the lowest proportion (6 to 8%) of particles retained on a 2.8-mm sieve. This resulted in BG having the smallest mean (1.29 mm) and median (1.08 mm) particle sizes in yr 1 and a mean (1.10 mm) and median (.91 mm) particle size smaller than SG in yr 2. Except for BG, the IVDMD of the masticate DM was lowest for small particles. Canopies showed BG and SG to have the highest proportion of stem (47 and 52%, respectively); the BG canopy was composed of fractions that were consistently lowest in IVDMD. In general, BG offered the grazing animal a canopy inferior in IVDMD concentration and had canopy characteristics that limited the animals' selection of a diet with quality as high as that of TF, SG, or FG.

Ruminant intake and digestion of dry matter was simulated using the proportions of masticated dry matter in three particle-size classes as well as the concentration of neutral detergent fiber and in vitro dry matter disappearance. This approach permitted the simulation of digesta flow through the rumen and intestines, intake, in vivo digestion, and fecal output. Distension and chemostatic feedback controls allowed simulation of the interaction of energy demand and rumen capacity in regulating ad libitum intake. Results indicated that a linear relationship between digestibility and animal intake does not necessarily imply an absence of chemostatic effects. In addition, the similar fecal outputs of animals fed forages of varying digestibilities were viewed as an effect of limited rates of ruminal digestion and passage rather than a cause of lower animal intake rates. Simulations of particle-size reductions such as might occur due to increased mastication or from mechanical grinding or pelleting resulted in declines in percent digestibility and increased rates of digestion due to an increased rate of passage.

Experiments were conducted to investigate the use of an esophageal plug and the influence of a 16-h fast, prior to collection, on the particle size distribution and quality of masticated forage. Extrusa was freeze-dried and sieved into seven size-classes, and the weight of masticate in each class was determined. The proportions of large (>1.7 mm), medium (0.5-1.7 mm), and small (