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a Plant Sci. Unit, Univ. of Missouri, Columbia, MO 65211
b Veterinary Diagnostic Lab., Univ. of Missouri, Columbia, MO 65211
c Southwest Missouri Res. and Education Center, Mt. Vernon, MO, 65712
d Dep. of Crop, Soil, and Environmental Sci., Univ. of Arkansas, Fayetteville, AR 72701
* Corresponding author (kallenbachr{at}missouri.edu)
| ABSTRACT |
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20% greater than HiMag E- or HiMag NTE. Herbage mass did not change from mid-December through mid-March for any entry. The nutritive value of all entries was equal on comparable dates with acid detergent fiber (ADF) ranging from 285 to 338 g kg-1 during the winter. Nutritive value was highest in mid-December of each year and then declined slowly after that. Neither HiMag E- nor HiMag NTE contained ergovaline, but K31 E+ had substantial concentrations of ergovaline in both years. The ergovaline concentration of K31 E+ was 454 µg kg-1 in December of Year 1 and 175 µg kg-1 in December of Year 2, but declined by
85% by March each year. The stable herbage mass, slowly declining nutritive value, and absence of ergovaline in HiMag E- and HiMag NTE suggest that livestock producers could eliminate toxicosis problems by stockpiling these forages for winter grazing.
Abbreviations: ADF, Acid detergent fiber CP, crude protein NDF, neutral detergent fiber NIRS, near infrared reflectance spectroscopy
| INTRODUCTION |
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While many cool-season grasses can be stockpiled, tall fescue is the species most often used (Matches, 1979; Sleper and West, 1996). Producers often choose tall fescue over other cool-season grasses for stockpiling because it: (i) produces more growth in autumn (Taylor and Templeton, 1976; Archer and Decker, 1977), (ii) retains its nutritive value longer into winter (Taylor and Templeton, 1976; Hitz and Russell, 1998), and (iii) growth the following season is affected little by winter defoliation (Collins and Balasko, 1981a; Gerrish et al., 1994; Riesterer et al., 2000). In addition, because tall fescue's regrowth in autumn is almost entirely leaf (Sleper and West, 1996), the nutritive value of well-managed stockpiled tall fescue is often better than much of the grass hay produced in the lower Midwest (Belyea and Ricketts, 1993; Hitz and Russell, 1998).
Despite the wide use of stockpiled pasture, many producers report animal health problems in winter that are consistent with the symptoms of tall fescue toxicosis. These symptoms include gangrenous or necrotic tissue on the tail, ears, nose, or hooves of animals (Sleper and West, 1996). Many producers call this condition fescue foot and the problem is especially troublesome when livestock are under cold stress (Tor-Agbidye et al., 2001).
The endophytic fungus [Neotyphodium coenophialum (Morgan-Jones & W. Gams) Glenn, Bacon, & Hanlin] infects >90% of the tall fescue pastures in the Midwestern USA (Sleper and West, 1996). This fungus, commonly found in Kentucky 31 tall fescue, produces ergot-like alkaloids that cause the health problems exhibited by livestock grazing stockpiled tall fescue. Infection of tall fescue with nontoxic endophytes (strains not producing ergot-like alkaloids) has the potential to improve plant persistence over endophyte-free tall fescue (Latch, 1998). We hypothesize that use of endophyte-free tall fescue or tall fescue infected with a nontoxic endophyte might reduce or eliminate the livestock health problems associated with grazing stockpiled tall fescue. However, there is a lack of data describing the stockpiling characteristics of endophyte-free tall fescue or tall fescue infected with a nontoxic endophyte. In addition, there is a lack of data describing the ergot-like alkaloid concentration of stockpiled tall fescue infected with a toxic endophyte during winter.
Our objective was to determine the herbage mass, nutritive value, and ergovaline (as a marker for ergot-like alkaloids) concentration of tall fescue infected with a toxic, native endophyte (K31 E+), a nontoxic endophyte (HiMag NTE), and no endophyte (HiMag E-) through winter.
| MATERIALS AND METHODS |
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From early April until early August each year, four 250-kg (± 20 kg) steers were continuously stocked on each pasture. On 5 Aug. 1999 and 15 Aug. 2000, livestock were excluded from a 10.6- by 13.7-m area within each pasture using electric fencing. Tall fescue growth from this excluded area was stockpiled and these were the main plots in this experiment. Just before erecting the electric fence, pastures were clipped to an 8-cm stubble height and received 56 kg ha-1 of N as ammonium nitrate. Plots were left unharvested until the first sampling in mid-December.
Herbage mass from the three tall fescue entries was measured monthly from mid-December through mid-March in 1999-2000 and 2000-2001. For simplicity, the 1999-2000 season will hereafter be referred to as Year 1 and 2000-2001 as Year 2. Herbage mass was taken from unharvested 0.8- by 10.6-m strips within main plots using a flail-type harvester. The fresh mass of each strip was recorded and a 350 g (± 50 g) subsample was dried at 50°C for 96 h to determine dry matter. Herbage mass measurements reflected net changes in growth and decomposition or tissue loss. Harvested forage consisted of both live and dead material.
An additional subsample was taken from
20 locations within each plot on each sampling date using battery-powered hand shears. Forage was clipped to a 6-cm stubble height and these samples were put into 3.8-L plastic bags, placed on ice in the field, and then transferred to a freezer held at -12°C. Frozen samples were lyophilized and then ground to pass a 1-mm screen. Hand-sheared samples were also collected at intermediate dates between herbage mass harvests (
14 d after each herbage mass harvest).
Acid detergent fiber, neutral detergent fiber (NDF), crude protein (CP), and ergovaline concentrations were determined from the hand-sheared samples. Ergovaline was measured using the procedure described by Hill et al. (1993). Acid detergent fiber, NDF, and CP were determined using near infrared reflectance spectroscopy (NIRS) using the scanning, calibration, and validation methods described by Marten et al. (1989) (Table 1). Crude protein for NIRS calibration samples was determined by measuring total N concentration using the micro-Kjeldahl technique outlined by Wall and Gerke (1975). Acid detergent fiber and NDF for calibration samples were determined using the methods described by Van Soest and Robertson (1980).
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| RESULTS AND DISCUSSION |
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Herbage mass was greatest for K31 E+ (2370 kg ha-1) while HiMag NTE and HiMag E- were equal to each other but
20% lower than K31 E+ (Fig. 1). Previous research has demonstrated that K31 often produces as much or more fall growth than other tall fescue cultivars (Joost and Mattas, 1996). While the addition of a nontoxic endophyte to endophyte-free cultivars of tall fescue may improve stand persistence (Latch, 1998), it did not alter fall growth of HiMag.
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Nutritive Value
For ADF, NDF, and CP, the main effect of entry and interactions including entry were not significant; however, years, sampling dates, and the year x sampling date interaction were significant. Thus, data are averaged across entries but presented separately by year and sampling date.
All entries had equal concentrations of ADF, NDF, and CP on comparable dates. Averaged across entries, in mid-December of Year 1, ADF was 296 g kg-1 and NDF 520 g kg-1, while in Year 2, ADF was 326 g kg-1 and NDF 578 g kg-1 (Fig. 2). Crude protein averaged 133 g kg-1 in mid-December both years. Generally, nutritive value declined slowly but steadily from mid-December through early March as ADF and NDF increased by 10 to 60 g kg-1 while CP decreased by 2 to 9 g kg-1. Other researchers have noted that the nutritive value of tall fescue declines slowly after early winter (Ocumpaugh and Matches, 1977; Collins and Balasko, 1981b; Fribourg and Bell, 1984). In Year 2 of our study, there was a notable drop in ADF and NDF and an increase in CP from early- to mid-January. This increase in nutritive value might be explained by an 11-d period of above-average temperatures in early January 2001 when the tall fescue initiated new growth. We hypothesize that brief warm periods in winter cause tall fescue to initiate small amounts of new growth, but that warm temperatures also accelerate the decay of older tissue. Other researchers have shown that tall fescue initiates new growth when ambient temperatures are as low as 1°C (Nelson, 1996). Thus, while herbage mass is static during the winter, nutritive value may be influenced to a greater degree by weather conditions.
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Ergovaline Concentration
HiMag E- and HiMag NTE contained no ergovaline, while K31 E+ had substantial concentrations of ergovaline (Fig. 3). Because only K31 E+ contained any ergovaline, HiMag E- and HiMag NTE were excluded from further analysis. For K31 E+, the effects of year, sampling date, and the year x sampling date interaction were significant, and thus the data for K31 E+ are presented by year and sampling date.
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85% by the end of winter (Fig. 3). The rapid loss of ergovaline after mid-December suggests that the forage becomes less toxic to livestock through winter. Stamm et al. (1994) suggested that ergovaline concentrations in excess of 150 µg kg-1 were associated with symptoms of tall fescue toxicosis in livestock during winter. Using this threshold, the forage in our study fell below toxic levels after early February in Year 1 and after early January in Year 2. This finding has important implications for winter-feeding systems that include stockpiled tall fescue. For instance, livestock producers might benefit by feeding nontoxic forages in early winter and then using stockpiled K31 E+ in mid- to late winter when ergovaline concentrations fall below threshold levels. Using this feeding strategy, livestock might not be subjected to ergovaline concentrations that are considered above threshold levels at any time in winter. In contrast, if the opposite feeding strategy were used (i.e., stockpiled K31 E+ fed in early winter followed by nontoxic forage), then livestock would be subjected to toxic concentrations of ergovaline in early winter. Further research involving animals is needed to see if this feeding strategy helps reduce or eliminate the symptoms of winter toxicosis.
Ergovaline concentrations were higher on comparable dates in Year 1 than in Year 2 (Fig. 3). Environmental conditions often impact ergovaline concentrations in tall fescue (Rottinghaus et al., 1991; Porter, 1995), and thus the differences between years may be the result of diverse weather conditions. In our study, precipitation from September through November of Year 1 was 48% below the 40-yr average in southwestern Missouri (Table 2). In addition, temperatures from November through March of Year 1 were above average, most notably in November when air temperatures were 4°C warmer than average. In Year 2, precipitation was closer to the long-term average while air temperatures were below average in November and December.
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| CONCLUSIONS |
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| NOTES |
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Received for publication March 18, 2002.
| REFERENCES |
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