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a USDA-ARS and Dep. of Crop Science and Dep. of Animal Science, North Carolina State Univ., Raleigh, NC 27695
b USDA-ARS, Watkinsville, GA 30677
c Veterinary Medical Diagnostic Lab., Univ. of Missouri, Columbia, MO 65211
* Corresponding author (joe_burns{at}ncsu.edu)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: ADF, acid detergent fiber • CP, crude protein • DDM, digestible dry matter • D/PS, di-and polysaccharides • HEMI, hemicellulose • IVTD, in vitro true dry matter disappearance • MS, monosaccharides • NDF, neutral detergent fiber • NIRS, near-infrared reflectance spectroscopy • TNC, total nonstructural carbohydrates
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Animal responses from tall fescue, however, can be extremely variable because of the presence of an endophyte (Neotyphodium coenophialum Morgan-Jones and Gams.) that produces ergot alkaloids in the forage and can negatively influence the animal's physiological processes (Hill et al., 1994; Oliver, 1997). On the other hand, the presence of the endophyte has been associated with increased plant tolerance to environmental stress (Thompson et al., 2001) and pests (Funk et al., 1985; West et al., 1993). Loss of such plant attributes would reduce tall fescue's zone of adaptation.
Tall fescue is of particular value in ruminant production systems because autumn growth can be accumulated to provide a large quantity of pasture with high nutritive value for grazing throughout the late autumn and winter (Archer and Decker, 1977; Ocumpaugh and Matches, 1977; Fribourg and Bell, 1984; Burns and Chamblee, 2000). Recently, Jesup tall fescue has been released due to its greater tolerance to high summer temperatures and drought stress (Bouton et al., 1997). Presumably, this increases its adaptation and productivity farther south. Further, a novel (nontoxic) endophyte was incorporated into Jesup without the antiquality, ergot-alkaloid compounds (Bouton et al., 2002; Parish et al., 2003) and marketed under the trademark ‘MaxQ’ (Pennington Seed, Inc., Madison, GA). The objectives of this study were threefold. The first objective was to test the adaptation and production potential of Jesup tall fescue with the presence or absence of a novel (nontoxic) endophyte (MaxQ) for the mid-Atlantic region when subjected to two autumn managements of either repeated grazing or accumulated and grazed as an autumn stockpile. A second objective was to determine if the presence of a novel- or a wild-type endophyte would alter either the nutritive value of the forage or stand persistence when compared with the endophyte-free control. The final objective was to evaluate changes in grazed forage production and nutritive value of these forages during the autumn and winter when stockpiled for varying periods prior to grazing.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The experiment was conducted in a split-plot design with three replicates. Three wholeplots, randomized within each replicate, were established to one of three seed lots of Jesup tall fescue with each wholeplot 73 by 26 m. One lot was free of endophyte, a second lot contained a novel, nontoxic endophyte (free of ergot alkaloids) marketed as MaxQ, and the third lot contained a wild-type endophyte capable of producing ergot alkaloids.
Within each wholeplot, five subplots (micropastures) 9.2 by 9.2 m, were randomly assigned to one of five grazing defoliation treatments. Defoliation treatments consisted of; (i) grazing autumn growth to about 7 cm each time it accumulated approximately 10 to 15 cm of forage; and grazing stockpiled forage on (ii) 15 November; (iii) 15 December; (iv) 15 January; and (v) 15 February. Animals on stockpiled forage were removed when forage was defoliated to approximately 7 to 10 cm.
Forage Management
The experiment was initiated the summer following the previous autumn's seeding with an accumulation starting date of 15 August. The stockpiled treatments were evaluated for 3 yr with stand counts taken the summer after completion (4 yr after seeding). Immediately prior to 15 August, all forage was removed to an 8-cm stubble and the area uniformly top dressed with 78 kg N ha–1 as ammonium nitrate. The subsequent stubble of pseudostem and leaf tissue became reduced close to the soil surface (<5 cm) during summer drought and the onset of stand dormancy.
Following the final defoliation date (15 February) the residual forage from all plots was removed each year with a flail harvester set to leave an 8-cm stubble. The experimental area was uniformly top dressed in early March with 78 kg N ha–1 and the initial spring forage permitted to grow to the early-boot stage. Thereafter, it was cut and removed as hay (April), the area was again top dressed with 78 kg N ha–1 (total of 234 kg N ha–1 for the year) and a second hay crop removed in late June to mid-July.
Plant Sampling
Endophyte Level
Fifty pseudostems were selected from each field in June prior to initiating the defoliation treatments from each wholeplot within each land replicate according to standard procedures (Randall-Schadel, 1995). Samples were tested by the NC Department of Agriculture's Service Laboratory for the presence of an endophyte. The degree of endophyte infestation averaged 94% for the wild-type endophyte stand, 95.3% for MaxQ stand, and 5.3% for the endophyte-free stand.
Stand Counts
Within each defoliation treatment (subplot) six estimates of stand density were obtained at initiation of the experiment (September 2000) and at termination of the experiment (October 2003). This was achieved by locating two fixed transects 4.6 m in length 1.8 m from each side of the subplot and a third transect in the center of the subplot. At a randomly selected position along each transect, two 1-m sections were used to estimate fescue stands resulting in six scores per subplot. At each 1-m observational site the presence and absence of tall fescue in each 25-mm increment was recorded. The six 1-m readings were averaged for each subplot resulting in an index expressed as a percentage of the stand that contained tall fescue in each subplot. At the end of the study the process was repeated for each fixed transect and the percentage of stand loss was estimated from the difference between initial and final stand indices with the result expressed as a percentage of the initial score. This value gives a sensitive index to changes in plant stand but is not equivalent to ground cover since the 25-mm sections were simply scored for presence or absence of fescue.
Forage Mass
Forage mass was determined pregrazing the afternoon prior to each grazing and postgrazing the day after grazing. The potential 0.51-m-wide harvest strips (without overlap) running the length of the subplot were enumerated. To avoid border effects the 0.51-m strip from each side of the subplot was removed from consideration. Each harvest strip was initiated and terminated 1.2 m from the ends of the subplot resulting in a 6.8 by 0.51 m harvest strip. The particular strip to be harvested pregrazing was selected at random within each subplot for each defoliation event. The forage was harvested with a 0.51-m wide rotary mower fitted with a collection bag to a 5-cm stubble. The fresh forage was weighed and a subsample obtained and dried in a forced-air oven (75°C) for 48 h to estimate dry matter concentration. After grazing each treatment, postgrazing forage mass to a 5-cm stubble was obtained from a second harvest strip to the immediate right (0.1 m) of the pregrazing forage mass strip. The fresh forage weight was multiplied by the appropriate concentration of dry matter to estimate forage mass. Occasionally, prior to obtaining the postgrazing forage mass, a dung pad had to be removed. The forage mass utilized (kg ha–1) was determined by subtracting postgrazing forage mass from pregrazing forage mass.
Time and Handling
Forage samples were obtained for morphological separation and laboratory analyses the afternoon prior to defoliation. Four subsamples were cut by hand along each side of the pregrazing harvest strip (eight subsamples) to the same stubble height (5 cm). The subsamples were bulked into one for the subplot, placed in a plastic bag and preserved on ice until taken to the laboratory, refrigerated (4.4°C), and hand separations initiated. The samples were first separated into tall fescue and weeds (broad-leaved weeds and weedy grasses). The tall fescue was further separated morphologically into green leaf, green stem, and dead tissue. Samples that could not be separated within 24 h were frozen (–11°C) until separated. Once separated, the fractions were stored frozen (–26°C) until freeze dried. Following freeze drying, the sample fractions were weighed, and the samples ground through a Wiley mill to pass a 1-mm sieve and returned to the freezer (–26°C) until analyzed. The freeze-dried weights of the component fractions of the total sample were recorded and used to express the proportion of the forage mass that was "tall fescue" and "weeds" and the proportion of the tall fescue mass that was "green leaf," "green stem," and "dead tissue."
Animals
Angus steers were used to defoliate each subplot. In the first defoliation each year, steers purchased the previous spring were used and averaged 318, 283, and 298 kg in Years 1, 2, and 3, respectively. For all subsequent defoliations, a new set of steers was used each year and averaged, for the experiment, 244, 256, and 243 kg for Years 1, 2 and 3, respectively. Subplot paddocks (9.2 by 9.2 m) were bounded on each side with electric polywire and the morning following the pregrazing sampling (described above) steers were randomly allocated to the appropriate defoliation treatment. Generally, three steers were allocated to each subplot; however, on occasion up to five steers were used depending on steer sizes and forage mass. Animals were permitted to graze each subplot until the accumulated forage was defoliated to about 7 to 10 cm. Thereafter, the animals were removed and the subplot sampled for residual forage mass. Defoliation was generally achieved during a 2- to 7- h grazing period. If steers quit grazing prior to adequate herbage removal they were removed from the subplot and returned in the same afternoon or the following morning for another grazing period. The rate and degree of defoliation was dependent on individual steer behavior, weather conditions, and the condition of the forage relative to frost damage (green vs. dead), and its presentation to the animal (i.e., erect vs. bedded down). Defoliation took an average of 3.5 h in Year 1, 4.9 h in year 2, and 5.0 h in Year 3.
Laboratory Analyses
All samples were scanned in a near-infrared reflectance spectrophotometer (NIRS) and the H statistic (0.6) was used to identify samples with different spectra. These samples were selected for use in laboratory analyses for the development of prediction equations.
In Vitro True Dry Matter Disappearance, Crude Protein, and Fiber Fractions
Samples were analyzed for in vitro true dry matter disappearance (IVTD) using ruminal inoculum collected from a cannulated, mature Hereford steer fed pure alfalfa (Medicago sativa L.) hay. After 48-h incubation with ruminal inoculum (Burns and Cope, 1974) in a batch fermenter (ANKOM Technology Corp., Fairpoint, NY) samples were extracted with neutral detergent solution in a batch processor (ANKOM Technology Corp., Fairpoint, NY) to determine IVTD. Crude protein (CP) was estimated as 6.25 times the percentage of N determined by auto analyzer (AOAC, 1990).
Fiber fractions, consisting of neutral detergent fiber (NDF), acid detergent fiber (ADF), sulfuric acid lignin, and acid detergent insoluble ash, were sequentially estimated according to Van Soest and Robertson (1980) in a batch processor (ANKOM Technology Corp., Fairpoint, NY). Hemicellulose (HEMI) was determined by subtracting ADF from NDF and cellulose by subtracting lignin plus ash from ADF.
Soluble Carbohydrate Extraction and Determination
Total nonstructural carbohydrate (TNC) and constituent starch, monosaccharides (MS), and disaccharides plus polysaccharides (D/PS) were analyzed as follows. Two, 0.5-g samples of each unknown, one with the starch to be hydrolyzed to glucose by amyloglucosidase and the other unhydrolyzed, were weighed into 125-mL flasks. Each flask received 15 mL of water and was placed on a hot plate and brought to a boil for 3 min to gelatinize the starch. After cooling, each flask received 10 mL of a buffer solution (pH = 4.45) containing three parts of 0.2 M acetic acid and two parts 0.2 M sodium acetate. The samples to be enzymatically hydrolyzed received an additional 10 ml of a 0.5% solution of amyloglucosidase (EC 3.2.1.3, Rhizopus mold, Sigma-Aldrich, St. Louis, MO). All samples were then stoppered and incubated at 38 to 44°C for 44 h with occasional swirling. After incubation, samples were filtered through a Whatman no. 40 filter paper into a 100-mL volumetric flask and brought to volume with deionized water. This extract was used for TNC and constituent carbohydrate analyses. Enzyme blanks containing water, buffer, and enzyme were included in each run. In addition, a starch source was used to confirm the activity of the enzyme. All sample extracts were analyzed using the appropriate chemistry cartridge (below) in a Technicon Auto Analyzer (Technicon Industries Systems, Tarrytown, NY).
The TNC were determined on the extract from the hydrolyzed samples using the Total Sugar/Reducing Sugar cartridge according to Bran and Luebbe's colorimetric method G-227-99, Rev. 2 (Bran and Luebbe Auto Analyzer Methods, Roselle, IL). The extracts were first treated in-line with HCl at 90°C to chemically hydrolyze D/PS to reducing sugars. All reducing sugars were then reacted in-line with p-hydroxybenzoic acid hydrozide, which in alkaline medium at 85°C forms a yellow osazone, and the absorbance measured at 420 nm and the concentration of TNC determined. The extracts from the unhydrolyzed samples were analyzed for reducing sugars as noted for TNC, but without the addition of HCL, giving the concentrations of only the naturally occurring MS.
The extracts from both the hydrolyzed and unhydrolyzed samples were analyzed for glucose according to Bran and Luebbe's colorimetric method G-142-95, Rev. 1 (Bran and Luebbe Auto Analyzer Methos). The starch concentrations were calculated as [(mg glucose from the hydrolyzed extract – mg glucose from the enzyme blank) – mg glucose from the unhydrolyzed extract] (0.90 mg–1 dry sample) (0.90 is a factor used to convert milligrams of glucose to milligrams of starch; AOAC, 1990). The D/PS were determined by subtracting the concentrations of starch plus MS from the TNC concentrations.
Ergovaline Determination
Ergovaline analysis was conducted according to Hill et al. (1993) on a reduced set of samples. The set consisted of two replicates of the three canopy fractions from three (i.e., October grazed and December and February stockpiled) of the five defoliation treatments harvested in Years 1 and 3 for the endophyte-free and MaxQ samples (n = 72). Because the wild-type forage was expected to have ergovaline present, and ergovaline can be predicted using NIRS (Roberts et al., 1997), a subset of samples was selected including the categories noted above for the endophyte free and MaxQ but included samples from Year 2 and all five defoliation treatments (n = 90). This produced a data set based on laboratory determination of ergovaline for comparisons among endophyte status as well as permitting NIRS calibration and prediction for the entire set of samples from the wild-type forage.
Near Infrared Predictions
Laboratory values from the analyzed samples were used to develop NIRS calibration equations with acceptable standard errors of calibration and cross validation. These were subsequently used to predict individual observations for each constituent analyzed (Table 1).
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A second analysis of variance was conducted for the three endophyte treatments managed by only the grazing treatment. Unlike the stockpile management, this treatment was defoliated by grazing two times in the autumn each of the 3 yr. Forage from the autumn grazings was compared for endophyte status effects by using the same two contrast statements noted above and responses from the two defoliation dates were tested in the analyses of variance. Differences were tested at P 
0.05 unless otherwise stated.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Rotational stocking associated with the subplots could result in variable defoliation from subplot to subplot at any one defoliation date. This was tested by comparing total forage mass (tall fescue plus "other") pre- and postgrazing (Table 3). In general, the forage mass pregrazing and the residual forage mass postgrazing were similar among the three endophyte treatments indicating that the degree of defoliation was similar among the endophyte treatments. This was also reflected by similar mean compressed canopy heights among the endophyte treatments at the start (mean = 12 cm; P = 0.21) and at the end (mean = 6.7 cm; P = 0.22) of grazing. The percentages of reduction in compressed height among endophyte treatments were similar but approached significance (P = 0.07) and the contrasts of MaxQ with endophyte free showed the latter to be significantly less (P = 0.05). However, this difference was small and unlikely to have impacted other variables.
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The experimental plan included the opportunity to evaluate tall fescue regrowth after repeated defoliation following August for the grazing management and after initial defoliation for each of the stockpile treatments. However, only two defoliations occurred for the grazing management and no regrowth in any of the years approached 15 cm following defoliation of the initial stockpile. This lack of autumn regrowth was somewhat surprising, especially following the mid-November grazing based on previous experience with other tall fescue cultivars, namely ‘Kentucky 31’ and ‘Triumph,’ and may be a characteristic of Jesup.
Forage Mass and Nutritive Value
Neither the forage mass of tall fescue nor its nutritive value (ergovaline is an exception and will be addressed later) was altered by the presence or absence of the MaxQ or wild-type endophytes (Table 4). Grazing management resulted in a greater tall fescue mass (because it was the sum of two defoliations) and it had greater concentrations of IVTD and CP but decreased concentrations of HEMI compared with forage from the stockpile managements. When the period of autumn accumulation was extended by delaying grazing through mid-February, changes in tall fescue mass and the weedy fraction showed no trend while canopy height declined linearly.
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The degree of utilization in the stockpile treatments was influenced by the presence of dead tissue. Dead tissue averaged (over all treatments) 1190 kg ha–1 in Year 1, 2410 kg ha–1 in Year 2, and 850 kg ha–1 in Year 3. Steers were adept at selecting the green tissue as a moderately green pasture pregrazing became a totally brown pasture postgrazing. For example, in Year 2, when appreciable dead tissue was present, the dry matter concentration of the postgrazed forage from the February-stockpile was 720 g kg–1, indicating that the pasture was essentially dead plant tissue. Because animals were not retained on the pastures to accomplish maximum defoliation, a high proportion of the available forage pregrazing in Year 2 was left as residue. The apparent discrepancy between forage removed and compressed height is associated with the shifts in the proportion of green and dead tissue with the latter being more compressible.
Within the stockpile, the concentration of IVTD of the tall fescue forage declined linearly while NDF and other fiber fractions increased linearly as grazing was delayed until mid-February (Table 4). Crude protein did not vary significantly (P = 0.12). The changes noted for IVTD, CP, and NDF are consistent with the literature (Ross and Reynolds, 1979; Burns and Chamblee, 2000; Kallenbach et al., 2003). The TNC concentrations decreased linearly from mid-November to mid-February as noted in previous reports (Balasko, 1977; Rayburn et al., 1979; Collins and Balasko, 1981; Burns and Chamblee, 2000). The MS and starch concentrations declined similarly to TNC in response to the stockpiling treatments whereas the D/PS showed no significant trends. The general declining trend in TNC and increasing trends for NDF and its constituents are indicative of reduced nutritive value of the stockpile.
Tall Fescue Fractions
Green Leaf Tissue
Averaged over the endophyte treatments, the green leaf tissue of the tall fescue mass accounted for 45% of the whole plant dry matter giving a leaf mass of 1930 kg ha–1. Neither the leaf percentage of the tall fescue mass nor the leaf mass itself were altered by the presence or absence of the MaxQ or wild-type endophytes (Table 5). Grazing management resulted in greater tall fescue leaf mass compared with stockpile because it was the sum of two defoliations. Delaying grazing of the stockpile resulted in a linear decrease in leaf percentage with the proportion declining from 54% in mid-November to 31% by mid-February. These changes are consistent with those reported by Taylor and Templeton (1976), Archer and Decker (1977), and Burns and Chamblee (2000). The change in leaf mass was not significant (P = 0.15).
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Green Stem Tissue
The green stems contributed an average of 13% of the tall fescue dry matter giving a mean stem mass of 560 kg ha–1 and neither variable was altered by the presence of the endophytes (Table 6). Tall fescue mass had similar proportions of green stem from the grazed and stockpile treatments, but stem mass was greater from the grazed treatment because it was the sum of two defoliation periods (Table 3). The proportion of stem and stem mass in the stockpile decreased linearly as grazing was delayed until mid-February. Stem compositional changes associated with endophyte status were noted only for HEMI, but the differences were small (Table 6). MaxQ and the wild type had similar HEMI concentrations, but MaxQ was less compared with the endophyte free.
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Delaying the utilization of the stockpile to February showed a linear increase in stem CP and HEMI along with a decrease in lignin and TNC. The D/PS fractions of the TNC showed the largest change with concentrations declining from a high of 240 g kg–1 in December to 148 g kg–1 by February.
Dead Tissue
The proportion of the tall fescue mass composed of dead tissue averaged 42% resulting in a dead mass of 1780 kg ha–1 (Table 7). Neither the proportion, nor the dead mass, nor the nutritive value of the dead tissue, were altered by endophyte status. The proportion of the dead tissue mass and the dead tissue mass were greater in the stockpile compared with the grazed treatment and both increased linearly as utilization of the stockpile was delayed to February (dead proportion increased from 31 to 61% and mass from 1330 to 2220 kg ha–1).
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Ergovaline Concentrations and Relationships
Ergovaline concentrations of the reduced data set (Years 1 and 3 and October grazed and December and February stockpiles) showed endophyte status x defoliation treatment interactions (P < 0.01) for the whole canopy, and canopy leaf and stem fractions. These were simply nonparallel trends as grazing was delayed until February and therefore we averaged over these effects.
Ergovaline concentrations of the canopies were altered by endophyte status with MaxQ having a concentration that was less than the wild type (P = 0.05) but similar to the endophyte free (Table 8). The canopy of the October grazed treatment had greater ergovaline than the stockpile showing that stockpiling can be used as a method of reducing ergovaline concentrations (Kallenbach et al., 2003). Ergovaline concentrations of leaf and stem, but not dead tissue were altered by endophyte status. MaxQ had concentrations that were less than the wild-type, but similar to the endophyte free. Ergovaline changes in leaf, stem, and dead fractions as grazing of the stockpile was delayed from December to February, were not significant (Table 8).
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Wild-type Endophyte and Ergovaline
Because of the apparent relationship between the presence of ergovaline and fescue toxicosis, the greater ergovaline concentrations in Jesup with the wild-type endophyte, and the differences in both the proportion and ergovaline concentrations of the leaf, stem, and dead fractions of the canopy, further examination is warranted. Using the complete data set (i.e., all years, all defoliation treatments, and all replicates) for the wild-type endophyte, ergovaline concentrations of tall fescue declined linearly (P < 0.01) as did the concentrations in the leaf and stem fractions (P < 0.01) as grazing was delayed (Fig. 1A
). The dead tissue initially increased in ergovaline then declined as grazing was delayed resulting in a quadratic (P = 0.04) trend.
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Differences among years in ergovaline concentrations were evident in the tall fescue mass and could account, in part, for varying degrees of toxicosis when stockpiled forage is grazed by cattle. For example, ergovaline concentrations of tall fescue in Years 1 and 2 were similar averaging 168 and 185 µg kg–1, respectively, compared with 262 µg kg–1 for Year 3 (data not shown). Selecting data from Years 2 and 3 out of Fig. 1 as representative of the extremes, shows greater concentrations of ergovaline in tall fescue from the grazed treatment for Year 3 with concentrations declining and becoming similar in the stockpile in both years by February (Fig. 2A ).
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Quantity of Digestible Dry Matter, Crude Protein, and Total Nonstructural Carbohydrates
The quantities of digestible dry matter (DDM), CP, or TNC produced per hectare (concentrations in tall fescue x tall fescue mass) were not altered for the tall fescue mass, green leaf, stem, or dead fractions by endophyte status (Table 9). The grazed treatment with its two defoliations, compared to the stockpile, produced greatest DDM and CP per hectare from the tall fescue mass and from the green leaf and green stem fractions. The TNC produced was similar for the two defoliation treatments and attributed to the greater TNC concentrations in the stockpile but with less tall fescue mass. No difference was noted between defoliation treatments for the dead tissue.
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From both a nutritive value and utilization standpoint, the source of nutrients in stockpiled tall fescue present in either leaf or stem, or both, compared with that present in dead tissue is of major importance (Burns and Chamblee, 2000). The greatest proportion of the nutrients, and hence nutritive value of stockpiled tall fescue, occurred in the green leaf and green stem, however, the greatest concentration of ergovaline, an antiquality constituents, also occurred in the same tissue but with stem concentrations greatest. Delayed grazing of the stockpile resulted in a decrease of green leaf and green stem tissue which also reduces ergovaline concentration of the tall fescue mass as well as beneficial nutrients. Further, the concomitant increase in dead mass has a high potential, if consumed, to reduce animal performance. However, grazing animals selectively consume green tissue and avoid dead tissue when given the opportunity (Hodgson et al., 1994). This behavior permits grazing animals to consume a diet greater in nutritive value than represented by the available forage mass. However, the ergovaline concentration of the stockpile green leaf is only a fraction of that found in the green stem and the green stem proportion is only a fraction of the green leaf mass resulting in greatly reduced consumption of ergovaline. Dead plant tissue in the tall fescue canopy may simply represent dry matter lost for potential utilization. Also, dead tissue is rather quickly incorporated into the litter on the soil surface making it less available for grazing or harvest. Consequently, delaying tall fescue utilization beyond mid-December appreciably decreases ergovaline and nutritive value but increases the loss of DDM (137%), CP (133%), and TNC (142%) for animal production.
Autumn Grazing
Repeated grazing of autumn growth is a management alternative and a potential complement to accumulating and utilizing a stockpile within a production system. In this management strategy, represented by the grazed treatment in this study, all three endophyte treatments were grazed each time canopy height reached 10 to 15 cm. Pastures were grazed in late September to early October and again in mid-October to mid-November (depending on the year). A third grazing was anticipated for this treatment, but no regrowth attained 10 cm after the second (mid-October to mid-November) defoliation. Generally, the grazed treatment had greater quantities of forage mass and the forage was of more favorable nutritive value relative to the stockpile treatments discussed previously. In the analyses of the data, no endophyte x grazing interaction was present so only the main effects are presented in tabular form.
Forage Mass and Nutritive Value
When grazed twice during the autumn when forage attained 10 to 15 cm, the presence of the wild-type or MaxQ endophytes did not alter forage mass produced, the quantity grazed, or its nutritive value (IVTD, CP, NDF, and TNC) (Table 10). The forage mass at each grazing was similar but steers removed less mass at the second grazing and this effect was also evident in the compressed canopy heights.
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Tall Fescue Mass
Neither the proportion nor the nutritive value of the green leaf, green stem, or dead fractions of tall fescue was altered by the presence of the endophytes in the autumn-grazed forage (Table 11). The proportion of green leaf decreased in the forage at the second grazing with a concurrent increase in dead tissue. The proportion of green-stem tissue remained similar. On the other hand, the IVTD was greater in forage from the second grazing in all three plant fractions. The greater IVTD is attributed to the much greater TNC at the second grazing which averaged 2.3 times greater for green leaf, 1.8 times greater for green stem, and 1.5 times greater for the dead tissue. The large increase in TNC would have had a dilution effect on the concentration of the other constituents and is associated with the reduction in CP in all plant fractions and NDF in the leaf and stem fractions.
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The quantities of DDM produced from the tall fescue mass, green leaf, and green stem mass were similar at the two grazing periods. The greater proportion of DDM produced from the second grazing as dead tissue is attributed to the increase in the proportion of dead tissue (Table 11). Similar quantities of CP were produced at each defoliation from the green stem and dead tissue mass but less CP was produced from green leaf tissue at the second grazing (Table 12). The quantities of TNC produced were greater at the second grazing from the tall fescue mass as well as from its green leaf, green stem, and dead fractions with quantity increasing by 1.6 to 2.6 times (Table 12).
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As noted for the endophyte status, the stand indices were greatest for the grazed vs. the stockpile plots. After 3 yr of defoliation (4 yr after establishment) stand indices were similar between defoliation treatments as was stand reduction, but the weed percentage was greatest in the grazed treatment.
The reduction in the tall fescue–stand index during the 3-yr study was not altered by the length of the stockpile treatment. In year 3, delaying grazing of the stockpile reduced the percentage of weeds linearly (Table 13). The significant lack of fit term reflects the shifts from December to February. This decline was attributed mainly to repeated frost which killed the weedy grasses (mainly warm season annuals) and broad-leafed weeds causing them to collapse and fall below the sampling height.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication September 23, 2005.
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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