Russell B. Muntifering

Cattle avoidance of leafy spurge: a case of conditioned aversion.

Leafy spurge (Euphorbia esula L.) represents a serious threat to the productivity and profitability of many cattle ranches in the midwestern U.S. Sheep and goats will graze the weed, but cattle generally do not. We hypothesized that cattle avoid leafy spurge because it contains 1 or more chemicals that elicit a conditioned flavor aversion when consumed. First, we tested cattle to determine if they reduced their intake of a novel feed on subsequent days if we modestly increased rumen fill by introducing additional feed or additional feed plus an aversive agent (lithium chloride, LiCl) after they had consumed the novel feed. We observed that cattle became averted (P = .0001) to the novel feed only when LiCl was administered with additional feed. Simply increasing rumen fill by a small amount did not cause cattle to reduce their intake of the novel feed the following day. Secondly, we tested cattle to determine if they reduced their intake of a novel feed on subsequent days if we introduced leafy spurge into their rumina following consumption of the novel feed. We also tested cattle to determine if a spurge-induced aversion to a novel feed was preventable by inoculation with rumen microbes from sheep with spurge in their diets. We found that introducing spurge into cattle after their intake of novel feed reduced (P .40) aversions to a novel feed paired with spurge introductions. Apparently, cattle avoid leafy spurge partly or wholly because they develop a conditioned aversion after first ingesting some threshold amount of it.

Yield and nutritive quality of sericea lespedeza (Lespedeza cuneata) and little bluestem (Schizachyrium scoparium) exposed to ground-level ozone

Sericea lespedeza (Lespedeza cuneata cv. Interstate 76) and little bluestem (Schizachyrium scoparium cv. Aldous) were raised from seed in a glasshouse, transplanted into 5.7-l pots and placed into open-top chambers (OTC) on 6 June 1999. Following a 7-day adjustment period, each of six OTCs (duplicate OTCs per treatment) was ventilated with either air that had been carbon-filtered (CF) to remove ambient ozone (O3); non-filtered (NF), representative of ambient air; or enriched to twice-ambient O3 concentration (2X). Primary-growth forage was harvested on days 7, 32, 46, 59 and 72 following the start of fumigation, and regrowth forage from the first primary-growth harvest was harvested on days 36, 54 and 72 following the start of fumigation. Dry matter (DM) yield of either forage species did not differ among treatments except in the final regrowth period when yield of sericea lespedeza was greater for the NF than 2X O3 treatment. In vitro DM digestibility (IVDMD) and concentrations of crude protein (CP), soluble phenolics (SP) and condensed tannins (CT) in primary-growth sericea lespedeza did not differ between treatments, but NF primary-growth forage had higher concentration of protein-precipitating tannins (PPT) than did 2X primary-growth forage. Concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were higher in NF and 2X than in CF primary-growth sericea lespedeza. Similarly, concentrations of NDF and ADL were higher, and IVDMD was lower for NF and 2X than for CF regrowth sericea lespedeza. Concentrations of ADF and ADL were lower, whereas IVDMD, in vitro NDF digestibility (IVNDFD) and concentrations of CP and SP were greater, in CF than in NF and 2X primary-growth little bluestem. Percentages IVDMD and IVNDFD and concentrations of CP and SP in NF primary-growth little bluestem were greater than those in forage exposed to 2X O3 treatment. No significant differences were observed among treatments in percentages IVDMD and IVNDFD, or concentrations of cell wall constituents or SP in little bluestem regrowth. Nutritive quality of little bluestem was decreased by < 2%, and that of sericea lespedeza by approximately 7% as a result of increased concentrations of cell wall constituents and decreased in vitro digestibility of NF and 2X compared with CF forages. Results indicate that existing and projected O3 levels can drive alterations in forage quality of select warm-season forages sufficient to have nutritional and economic implications for their utilization by ruminant herbivores.

Yield and quality characteristics of bahiagrass (Paspalum notatum) exposed to ground-level ozone

Early and late season-planted bahiagrass (Paspalum notatum Flugge, cultivar ‘Pensacola’) were grown in open-top chambers (OTC) to which added air had been carbon-filtered (CF), representative of that found at pristine air quality sites; non-filtered (NF), characteristic of ambient air in Auburn, AL and representative of that found in rural agricultural areas; or enriched with ozone (O3) to twice-ambient O3 concentration (2X), representative of that found in the vicinity of large metropolitan areas. Primary-growth and regrowth forages from each planting were harvested periodically throughout the experiment from each of six OTC (two OTC/air treatment). Mean daytime (09:00‐21:00 h) O3 concentrations over the entire 24-week experiment (7 May‐23 October 1997) were 22, 45 and 91 Z ll ˇ1 , respectively, for CF, NF and 2X treatments. Mean daytime ambient O3 concentrations peaked in mid-May and again in late August‐late September at 50‐ 60 Z ll ˇ1 , and highest individual ambient O3 concentrations were recorded in late June, late July, late August and mid-September at90 Z ll ˇ1 . Dry matter (DM) yield was greater for CF than for NF primary-growth forage, and concentrations of neutral detergent fiber (NDF) were higher in 2X than in NF primary-growth and regrowth forages from the early-season planting. Concentration of acid detergent fiber (ADF) tended to be higher in 2X than in NF primary-growth forage and was higher in 2X than in NF regrowth forage, whereas acid detergent lignin (ADL) concentration was higher in 2X than in NF primary-growth forage and tended to be higher in 2X than in NF regrowth forage from the early-season planting. Crude protein (CP) concentrations were lower in CF than in NF regrowth forage from the early-season planting and in CF than in NF primary-growth forage from the initial harvest of the late-season planting. No differences were observed among treatments in DM yield or concentrations of cell wall constituents in primary-growth or regrowth forages from the late-season planting, although concentrations of CP, NDF and ADF tended to be higher in 2X

Plant phenology, growth and nutritive quality of Briza maxima: responses induced by enhanced ozone atmospheric levels and nitrogen enrichment.

An assessment of the effects of tropospheric ozone (O(3)) levels and substrate nitrogen (N) supplementation, singly and in combination, on phenology, growth and nutritive quality of Briza maxima was carried out. Two serial experiments were developed in Open-Top Chambers (OTC) using three O(3) and three N levels. Increased O(3) exposure did not affect the biomass-related parameters, but enhanced senescence, increased fiber foliar content (especially lignin concentration) and reduced plant life span; these effects were related to senescence acceleration induced by the pollutant. Added N increased plant biomass production and improved nutritive quality by decreasing foliar fiber concentration. Interestingly, the effects of N supplementation depended on meteorological conditions and plant physiological activity. N supplementation counteracted the O(3)-induced senescence but did not modify the effects on nutritive quality. Nutritive quality and phenology should be considered in new definitions of the O(3) limits for the protection of herbaceous vegetation.

Cutleaf coneflower (Rudbeckia laciniata L.) response to ozone and ethylenediurea (EDU)

Cutleaf coneflower (Rudbeckia laciniata L.) seedlings were placed into open-top chambers in May, 2004 and fumigated for 12 wks. Nine chambers were fumigated with either carbon-filtered air (CF), non-filtered air (NF) or twice-ambient (2x) ozone (O(3)). Ethylenediurea (EDU) was applied as a foliar spray weekly at 0 (control), 200, 400 or 600 ppm. Foliar injury occurred at ambient (30%) and elevated O(3) (100%). Elevated O(3) resulted in significant decreases in biomass and nutritive quality. Ethylenediurea reduced percent of leaves injured, but decreased root and total biomass. Foliar concentrations of cell-wall constituents were not affected by EDU alone; however, EDUxO(3) interactions were observed for total cell-wall constituents and lignocellulose fraction. Our results demonstrated that O(3) altered the physiology and productivity of cutleaf coneflower, and although reducing visible injury EDU may be phytotoxic at higher concentrations.

Graze: A model of selective grazing by beef animals

Abstract A dynamic simulation model has been developed that relates beef animal performance to environment, management practices and selective grazing of pastures. Daily measures of pasture quality and availability are maintained. Measures of the animals physiological weight and age are computed at 15-min intervals or less, and body composition, efficiency of growth and feed utilization are determined. Rotational grazing may be evaluated with animal movement being based on time of grazing and/or availability of dry matter. During a simulated day, each pasture may be further divided into a variable number of subareas that reflect herbage quality and mass (kg ha −1 ) differences associated with selective grazing. The number and size of the subareas vary with environment and forage removal, and reflect conceptual, rather than distinct physical, boundaries within the pasture.

Digestive utilization of ozone-exposed forage by rabbits (Oryctolagus cuniculus)

A mixture of common Southern Piedmont (USA) grassland species (Lolium arundinacea, Paspalum dilatatum, Cynodon dactylon and Trifolium repens) was exposed to O(3) [ambient (non-filtered; NF) and twice-ambient (2X) concentrations] and fed to individually caged New Zealand white rabbits (Oryctolagus cuniculus) in a digestibility experiment. Forages and feed refusals were analyzed for concentrations of total cell wall constituents, lignin, crude protein, and soluble and hydrolyzable phenolic fractions. Neutral detergent fiber and acid detergent fiber digestibility by rabbits were significantly lower for 2X than NF forage. Decreased digestibility could not be attributed to lignin concentrations, but was associated with increased concentrations of acid-hydrolyzable and saponifiable phenolics. Exposure of forage to elevated O(3) resulted in decreased digestible dry matter intake by rabbits. Elevated O(3) concentrations could be expected to have a negative impact on forage quality, resulting in decreased nutrient utilization by mammalian herbivores in Southern Piedmont grasslands under projected future climate scenarios.

CASE STUDY: Productivity, quality characteristics, and beef cattle performance from cool-season annual forage mixtures

A grazing experiment was conducted to quantify productivity, quality characteristics, and beef cattle performance from mixtures of oat (Avena sativa L.) and ryegrass (Lolium multiflorum L.; O-RG), rye (Secale cereale L.) and ryegrass (R-RG), or oat and rye and ryegrass (O-R-RG) under continuous stocking. Six 1.42-ha paddocks were seeded with O-RG, R-RG, or O-R-RG mixtures (2 paddocks/treatment) in November 2008 and stocked initially with 3 yearling crossbred test steers (392 ± 31 kg initial BW) per paddock on January 8, 2009. Forage mass and nutritive quality were determined by clipping 0.25-m2 quadrats (8/paddock) before the beginning of grazing and every 2 wk during the experiment. Stocking densities were adjusted using put-and-take steers to maintain grasses in a vegetative state, and grazing was discontinued on May 28. Data were analyzed as a completely randomized design by the PROC GLM procedure of SAS. Steer ADG was greater (P < 0.10) for O-RG (1.39 kg/d) and O-R-RG (1.26 kg/d) than R-RG (1.13 kg/d). Number of steer-grazing-days was 547, 655, and 625 d for R-RG, O-RG, and O-R-RG, respectively, and mean forage allowance across all treatments was 1.06 kg DM/ kg steer BW over the 140-d grazing experiment. Results indicate that O-RG was superior to R-RG for supporting beef cattle performance under continuous stocking, and that inclusion of rye in a ternary mixture did not improve performance over that from O-RG.

Nutritive Quality of Big Bluestem (Andropogon gerardii) and Eastern Gamagrass (Tripsacum dactyloides) Exposed to Tropospheric Ozone

Abstract Tropospheric ozone (O3) is a phytotoxic air pollutant widespread in industrialized nations of the world. Ozone is produced by the photo-oxidation of hydrocarbons released into the atmosphere by combustion of fossil fuels. Studies demonstrate O3 can be transported from metropolitan areas to rural areas important to agricultural and forestry practices. Reports regarding O3 effects have focused on vegetation important to food production or agronomic crops of economic importance. However, relatively little is known about O3 effects on native plant species. The effects of tropospheric O3 on two warm-season grasses, eastern gamagrass (Tripsacum dactyloides L.) and big bluestem (Andropogon gerardii Vitman), were examined during June–September of 2003. Plants were fumigated with three levels of O3 in a randomized-block experiment with three replicates of each treatment. Grasses were grown in open-top chambers with introduced carbon-filtered (CF) air, characteristic of clean air quality; non-filtered (NF) air, representative of quality in Auburn, AL; and air with double (2×) the ambient concentration of O3. Because forage quality can be as important as quantity, we determined various effects on nutritive quality characteristics in addition to biomass yield. Big bluestem exhibited little response to O3 exposure. For eastern gamagrass, we generally found decreased nutritive quality with increasing O3 exposure as evidenced by increased concentrations of cell wall constituents and decreased concentrations of N. Regrowth of both species exhibited little treatment effect which emphasizes the importance of timing and duration of O3 exposures in relation to physiological stage of plant development. Decreased nutritive quality parameters observed for eastern gamagrass may have implications to diet selection and nutrient intake by ruminant herbivores. In addition, range managers can use species-specific information regarding O3 sensitivity to make decisions about mechanical harvesting and grazing regimes of these forages growing in areas exposed to elevated O3 concentrations.

Nutritive Quality of Highbush Blackberry (Rubus argutus) Exposed to Tropospheric Ozone

Abstract Numerous studies have examined the impacts of ground level O3 on plants that are important for human consumption, but native species that are important for wildlife have received less scrutiny. During May–August 2004 we examined the effects of O3 on biomass production and nutritive quality of highbush blackberry (Rubus argutus Link), an important forage for white-tailed deer (Odocoileus virginianus Zimmerman) and other herbivorous mammals. Plants were fumigated in open-top chambers with three levels of O3 in a randomized-block experiment with three replicates of each treatment. Our three experimental treatments were carbon-filtered air, characteristic of clean air quality; nonfiltered air, representative of air quality in Auburn, AL; and air with double (2×) the ambient concentration of O3. Although biomass production was not influenced by O3 exposure, nutritive quality of plants was associated negatively with O3 concentration. Specifically, neutral detergent fiber was greater and relative feed value was less in plants exposed to elevated levels of O3. Similarly, in vitro dry matter digestibility tended to be less in plants exposed to elevated O3. Nutritive quality of regrowth vegetation followed a similar pattern, where neutral detergent fiber was greater and relative feed value was less in plants exposed to elevated levels of O3. These data suggest that elevated levels of ground level O3 could have implications for diet selection of herbivorous mammals.