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© 2006 Plant Management Network.
Accepted for publication 30 November 2005. Published 13 January 2006.

Performance of Steers Fed Ammoniated Straw From Tall Fescue Seed Fields

Robert L. Kallenbach, Associate Professor, Craig A. Roberts, Professor, T. Ryan Lock, Senior Research Specialist, Division of Plant Sciences, Duane H. Keisler, Professor, Division of Animal Sciences, Mark R. Ellersieck, Research Associate Professor, Department of Statistics, and George E. Rottinghaus, Clinical Associate Professor, Veterinary Biomedical Services, University of Missouri, Columbia 65201

Corresponding author: Robert L. Kallenbach. KallenbachR@missouri.edu

Kallenbach, R. L., Roberts, C. A., Lock, T. R., Keisler, D. H., Ellersieck, M. R., and Rottinghaus, G. E. 2006. Performance of steers fed ammoniated straw from tall fescue seed fields. Online. Forage and Grazinglands doi:10.1094/FG-2006-0113-01-RS.

Abstract

Non-toxic endophytes are being inserted into cultivars of tall fescue (Festuca arundinacea Schreb.) to improve plant persistence and eliminate tall fescue toxicosis. Seed for these new cultivars could be produced in Missouri, which leads the nation in acreage of tall fescue harvested for seed. However, few studies have investigated the feeding value of straw baled after seed harvest from these cultivars. Our objectives were to evaluate (i) the nutritive value of straw from ‘Kentucky 31’ and ‘HiMag9’ tall fescue, and (ii) performance of steers fed ammoniated straw of Kentucky 31 and HiMag9. Cultivar had no effect on steer intake, gain, or rectal temperature. Ammoniation of straw improved steer performance. Averaged across cultivars, ammoniation of straw increased intake by 20% and improved average daily gain of steers from -0.15 lb/day to 0.46 lb/day when compared to untreated straw. Our results indicate that ammoniating straw improves its feeding value.

Introduction

‘Kentucky 31’ tall fescue (Festuca arundinacea Schreb.) grows on more than 29 million acres in the humid-temperate region of the U.S. (16) and is the predominant source of pasture for more than 10 million head of beef cattle, horses, and sheep. It is generally accepted that most of the Kentucky 31 tall fescue acres are infected with Neotyphodium coenophialum, a fungus known as endophyte, because it grows inside the plant (17). The endemic strains of this endophyte in tall fescue produce ergot alkaloids that cause several livestock disorders collectively known as fescue toxicosis. These disorders cost U.S. livestock producers at least 600 million dollars annually (7).

In the 1980s, endophyte-free cultivars of tall fescue were developed by removing the endophyte. Endophyte-free cultivars did not cause fescue toxicosis in livestock, but the plants lacked persistence, being susceptible to a wide range of biotic and abiotic stresses (14). Today, new cultivars are being developed with special endophytes reinserted into tall fescue (14). These special endophytes are strains of Neotyphodium that produce no or low concentrations of ergot alkaloids; they are called novel, beneficial, or introduced endophytes.

As new cultivars infected with novel endophytes increase in popularity, innovative producers in the lower Midwest are considering tall fescue as a seed crop. At present, Missouri accounts for over 50% of the tall fescue acreage harvested for seed in the United States. Missouri produced 65 million pounds of seed in 2002 (10). Rarely though is tall fescue seed production in this region a planned enterprise (Fig. 1). Rather, it is largely a byproduct of unutilized tall fescue pastures. Seed yields from these fields often average only 200 lb/acre (10) and the seed typically is sold as "common seed" for a relatively low price.

Fig. 1. A Southwest Missouri field of tall fescue drilled in 15-inch rows and managed for seed production. This type of enterprise is rare in Missouri.

Research in the mid-1970s showed that producers in the lower Midwest could achieve seed yields above 1000 lb/acre with proper management (8). This and subsequent research (22) shows that maximum tall fescue seed yields are possible only when (i) nitrogen fertilization is timely, (ii) weed control is adequate, and (iii) the residual dry matter or straw is removed. Of these key factors, managing the straw has proved most problematic.

One option for managing straw is to harvest it for hay and feed it to livestock. This option has application, because many farms suitable for tall fescue seed production also have, or are near, existing beef operations. However, before this option can be endorsed, the feeding value of non-toxic tall fescue straw and subsequent performance of beef animals needs to be evaluated.

Undoubtedly, the nutritive value of straw is low. Crude protein and neutral detergent fiber concentrations of 6.8 and 69.3%, respectively, have been documented in the straw of two turf-type varieties of tall fescue (18). This low nutritive value makes straw unsuitable for nearly all classes of beef animals (11). However, researchers have shown that ammoniating plant residues improves nutritive value (21) and in the case of toxic tall fescue, lowers ergot alkaloid concentrations (13). Thus, ammoniating and feeding tall fescue straw following seed harvest could offer a means to deal with this low quality material.

Our objectives were to evaluate (i) the nutritive value of untreated and ammoniated straw from Kentucky 31 and ‘HiMag9’ tall fescue, and (ii) the intake and performance of steers fed untreated and ammoniated straw of Kentucky 31 and HiMag9 tall fescue. HiMag9 is a tall fescue cultivar infected with a novel endophyte that does not produce ergot alkaloids. Evaluation included laboratory analyses of forage quality and ergovaline concentration as well as feeding trials to measure performance of beef steers.

Tall Fescue Straw

Field management. This experiment was conducted on a 26-acre field near Diamond, MO (37°0’N, 94°19W; elevation 1180 ft) on a Newtonia silt loam (fine-silty, mixed, superactive, thermic, Typic, Paleudoll). The 26-acre field was split into 10 equal areas; five of the areas were planted to Kentucky 31 and five into HiMag9 tall fescue. The field was planted in September 2000, and managed solely for seed production. Both cultivars were seeded in 15-inch rows at a rate of 6.5 lb/acre pure live seed. HiMag9 was provided by C. P. West at the University of Arkansas and determined to be infected at >80%; and Kentucky 31 was 65% infected with its endemic endophyte at planting. Given the cultivar × endophyte strain combinations available, we recognize the endophyte strain by cultivar combinations are confounded.

In the year following planting, a small seed crop was harvested in June 2001. After this initial seed harvest, the field was clipped to a 4-inch height on 4 August 2001 and again on 9 January 2002. Clipping was done to facilitate light penetration to the plant base which is known to increase seed yield the following year (16). Forty-six lb of nitrogen per acre were applied as urea on 20 September 2001, and 60 lb of nitrogen per acre as urea were applied 15 January 2002. Annual grasses and broadleaf weeds were controlled with the following chemicals: pendimethalin was applied at one qt/acre on 28 July and 1 October 2001; fenoxaprop-ethyl was applied on 5 October 2001 at 20 oz/acre; and one qt/acre of the 2-ethylhexyl ester of 2, 4-dichloroacetic acid was applied on 1 October 2001.

On 14 June 2002, the seed crop was windrowed with a Hesston 8100 self-propelled swather and allowed to dry in the field. The moisture of the seed at swathing was 34.5%. The seed was threshed using a John Deere 9400 combine equipped with a pick-up attachment when seed moisture was below 17%. On 20 and 21 June 2002, the straw was baled from windrows left after combining. Each cultivar was baled in separate operations to avoid contamination by hay equipment. In total, each cultivar produced approximately 15 tons of baled straw.

Straw management. The straw was transported to the University of Missouri’s South Farm near Columbia, MO. One-half of the bales of each cultivar were stacked in a barn and left untreated until feeding. The remaining bales were stacked onto wooden pallets outside and covered with 6-mil black plastic (Fig. 2). The perimeter of the plastic was sealed against the ground with crushed limestone. On 25 July 2002 these bales were treated with anhydrous ammonia at 3% (w/w) on a dry matter basis. After ammonia injection, the hay remained sealed for 42 days. After ammoniation of straw, there were four diet treatments, hereafter referred to as Kentucky 31, Kentucky 31 ammoniated, HiMag9, and HiMag9 ammoniated.

Fig. 2. Square bales of straw stacked on pallets, treated with anhydrous ammonia, and then stored under plastic and tarps during the feeding trial.

Steer Feeding Trials

Feeding facility. Two 56-day feeding trials were conducted at the University of Missouri’s South Farm feeding facilities in Columbia, MO. The cattle were housed in an open-faced barn with a concrete floor. Pen size was 12 ft by 52 ft. The feeding bunk and the 23 ft nearest the feeding bunk in each pen were covered while the remaining length of the pens was uncovered. The first trial began 1 October 2002 and the second began 11 February 2003. The average air temperature for the first trial was 47.2°F with a range of 18.2 to 89.4°F, and the average for the second trial was 40.6°F with a range of -0.6 to 81.4°F.

Straw sampling for chemical composition. The stacks of straw were sampled for fiber components, crude protein, and ergovaline concentration at the beginning and every 14 days thereafter throughout the feeding trials. At each sampling time, thirty bales of each type were cored with a Penn State hay sampling probe and then stored at -20°F until analyzed. Samples were freeze-dried to preserve alkaloids and then ground to pass a 0.04-inch (1-mm) screen. Neutral and acid detergent fiber were analyzed using an ANKOM 200 Fiber Analyzer (ANKOM Technology, Fairport, NY). Crude protein was measured by thermal conductivity of nitrogenous gases with a Leco Model FP-428 Nitrogen analyzer (Leco Corp., St. Paul, MN). Ergovaline was measured using the method of Hill et al. (6).

Beef steers. Forty-eight crossbred Angus steers were obtained from two University of Missouri Agricultural Experiment Station farms. Steers were born in February and March of 2002 and had been weaned and vaccinated for at least 21 days prior to the first trial. Steers weighed 453 (± 78) lbs per head at the start of the first trial and 485 (± 110) lbs per head at the start of the second trial. The steers were fed a common acclimation diet of hay for 6 days prior to the start of each trial. After the first 56-day feeding trial, steers grazed paddocks of stockpiled tall fescue, orchardgrass (Dactylis glomerata L.), and red clover (Trifolium pratense L.) for approximately 60 days. The ergovaline level of these paddocks was below detection limits and considered non-toxic. After this "flush-out" period, the same steers were stratified according to previous treatment and randomly reassigned to treatments for the second feeding trial. For each trial, the steers were sorted into four weight groups and one calf from each group was assigned at random to each of 12 pens. Treatments were then randomly assigned to pens, with each of the four treatments replicated three times. Initial and final body weights of steers were determined after withholding feed and water for 16 h prior to weighing. Steers were also weighed without fasting every 14 days during each trial to monitor performance. Jugular blood samples and rectal temperatures were taken at the beginning of each trial and at 14-day intervals thereafter.

All animals had ad libitum access to their treatment diet, water, and a trace mineral block (Fig. 3). No other feed was available to the animals. At feeding, the straw to be fed in each pen was weighed and recorded. Once each week, the orts were cleaned from the bunk, weighed, dried at 122°F for 96 h, and sampled for dry matter. In addition, the amount of straw wasted was estimated by sampling for three consecutive days at four times throughout each trial. Briefly, pens were cleaned on Monday and all wasted straw collected from the pen area on Tuesday, Wednesday, and Thursday. Much of the straw was trodden and soiled with manure so that all straw on the floor had to be washed over a 0.25-inch screen and then sampled for dry matter. Intake of the steers was estimated by subtracting the mass of refused and wasted straw from the mass of straw offered.

Fig. 3. Steers consuming straw of tall fescue during the feeding trial.

Statistical analysis. A completely randomized design was used with three replicates of four diet treatments. The four steers per pen were sub-samples for the parameters measured. For all variables except prolactin and rectal temperature of steers, the statistical model was a 2×2 factorial arrangement of treatments [2 tall fescue cultivars by 2 levels of ammonia (either treated with ammonia or not treated)] (19). For prolactin and rectal temperatures, a repeated ANOVA was conducted in which the main plot included the 2×2 described above and the sub-plot contained the effects of time (or day of experiment) and all possible interactions. No interactions were significant (P > 0.05) between the two 56-day feeding trials so data were pooled. The Proc GLM procedure of SAS (version 8) was used for statistical analyses (SAS Institute Inc., Cary, NC). Main effects and interactions were considered significant when P < 0.05. When the F-test was significant (P < 0.05), means were separated using Fisher’s protected LSD (alpha = 0.05) (19).

Chemical Composition of Straw

Fiber and crude protein. There was no cultivar effect on chemical composition, as Kentucky 31 and HiMag9 contained similar concentrations of neutral and acid detergent fiber and crude protein (Table 1). However, ammoniation decreased neutral detergent fiber by more than three percentage units and nearly doubled the crude protein concentration. Ammoniation did not change acid detergent fiber concentration. The changes in neutral detergent fiber and crude protein are similar to those reported by Buettner et al. (3) and Chestnut et al. (4).

Table 1. Nutritive value of straw and orts and ergovaline content of straw from two cultivars of tall fescue either treated or not treated with anhydrous ammonia and fed to steers. Data for straw and orts are means of eight and 16 samplings, respectively, during the two 56-day feeding trials.

 ^x NDF = neutral detergent fiber.

 ^y ADF = acid detergent fiber.

Ergovaline. Untreated Kentucky 31 contained 183 ppb ergovaline while HiMag9 contained none (Table 1). Ammoniation decreased the ergovaline concentration of Kentucky 31 by 33%. The reduction of ergovaline in our study is in agreement with Roberts et al. (13) who showed a 34% decrease in total ergot alkaloid concentration when fall-harvested tall fescue hay was ammoniated. This reduction in ergovaline also explains a previous report that showed lambs fed ammoniated, endophyte-infected tall fescue hay performed similar to those fed endophyte-free hay (5).

The low concentration of ergovaline in untreated Kentucky 31 straw was likely the cumulative result from several factors. First, straw contained no seedheads, the plant part in which ergovaline is most highly concentrated (15). Second, the endophyte infection level was 65%; while this level is considered toxic (17) it would produce less ergovaline than more highly infected fields. Finally, the straw was sun-cured and stored for over three months prior to feeding. Other research using fall-grown tall fescue showed that ergot alkaloid concentrations decreased 66% when the clipped forage was allowed to dry in the field, baled as hay, and stored for 60 days (13).

Steer Performance when Fed Straw

Dry matter intake. Cultivar did not affect dry matter intake (Table 2). This was not what we expected, as one cultivar contained ergovaline (Kentucky 31) and the other did not (HiMag9). However, it is understandable, because Kentucky 31 contained a relatively low concentration of ergovaline and the two cultivars contained similar fiber and crude protein concentrations (Table 1). Further, the air temperatures during the study were moderate and thus heat stress, which is known to intensify tall fescue toxicosis (1), was not a factor. Ammoniation did increase dry matter intake of straw. Steers fed ammoniated straw consumed 20% more feed each day than those fed untreated straw (Table 2). Our data show that the changes in forage characteristics due to ammoniation resulted in a 20% increase in dry matter intake of steers. The increased intake resulting from ammoniation is consistent with other work (5).

Table 2. Feed intake, daily gain, and amount of wasted feed for steers fed two cultivars of tall fescue straw that was treated or not treated with anhydrous ammonia at 3% of dry matter. Data are combined over two 56-day feeding trials.

 ^x ADG = average daily gain.

Steer gain. As with the intake data, there was no cultivar effect on gain, but there was an effect of ammoniation (Table 2). Averaged over the two cultivars, steers fed untreated straw lost an average of 0.15 lb/day, while those fed ammoniated straw gained 0.41 lb/day.

The high concentrations of acid and neutral detergent fiber along with low crude protein in the untreated straw likely affected animal performance more than did ergovaline concentration in this experiment. Ammoniation of either cultivar improved steer gain, but there was no interaction between cultivar and ammoniation treatment. We expected that ammoniation would improve the performance of steers fed Kentucky 31 more than those fed HiMag9. However, over the two 56-day feeding trials this was not the case.

Data from this feeding trial indicate that improvements in steer performance when straw is ammoniated were caused by an increase in nutritive value, not a decrease in toxicity. These results agree with other work that reported no difference in animal gain when cultivars of tall fescue straw fed to steers contained 0, 158, 317, or 475 ppb ergovaline (18). Results also agree with another report of 15% faster rate of gain for calves fed ammoniated tall fescue hay which was thought to be due primarily to increased dry matter intake (2).

Straw wasted and nutritive value of orts. The amount of straw wasted by the steers was equal for all four diet treatments (Table 2). It was our observation that straw wasted depended largely on animal behavior. We had hypothesized that cattle fed the Kentucky 31 straw would waste greater amounts of straw than the others. The steers did appear to sort through the straw that was fed to them, as crude protein of orts was lower than that of straw offered. (Table 1).

Prolactin. Stidham et al. (20) was an early reporter of the association between lowered blood serum prolactin and cattle consuming endophyte infected tall fescue. Since then, other work has shown this same hormonal effect on cattle (12). At the end of this experiment, serum prolactin concentration of steers fed untreated Kentucky 31 straw was 75% of the other three treatments (Fig. 4). Other experiments in the literature showed that prolactin decreases in the blood serum of cattle when they consume forage containing ergovaline ranging from 285 to 1300 ppb (1,18).

Although the ergovaline level in untreated Kentucky 31 straw was low, it was high enough to depress the prolactin levels of the steers. At the same time, it was not high enough to affect their feed intake and weight gain. Another experiment reported a decrease in serum prolactin concentration with little or no effect on steers when dosed with ergovaline near the threshold widely accepted to be toxic (18). Prolactin may be too sensitive as a marker for fescue toxicosis.

Rectal temperature. There were no cultivar effects on rectal temperatures of the steers. The low ergovaline concentration of the untreated Kentucky 31 straw may be one reason for lack of cultivar response. When averaged across cultivars, steers fed untreated straw had lower rectal temperatures than those fed ammoniated straw, although rectal temperatures for all steers were in the normal range for the entire experiment (Fig. 5). Mader et al. (9) found that steers limit-fed to 75% of their ad libitum intake had lower tympanic temperatures, due to lower metabolic rates, than steers feed ad libitum. In our study, steers fed untreated straw were fed a diet low in energy, and their lower rectal temperature could have been a result of lower metabolic activity.

Conclusions

Tall fescue straw can supply winter feed for beef cattle, even when the straw is Kentucky 31 infected with its endemic endophyte. Before such straw is fed, however, it should be ammoniated. Ammoniation improves the forage quality by reducing neutral detergent fiber and/or increasing crude protein. These changes increased dry matter intake and rate of gain in beef steers. In the case of straw, changes in chemical composition may be considered more critical to steer performance than the reduction in ergovaline. This is because straw contains no seedheads and is conserved as hay, which results in lower concentrations of ergovaline even in the absence of ammoniation.

In the Midwestern United States, ammoniated straw of tall fescue provides the seed producers with a valuable byproduct. Although ammoniated straw does not supply all the required nutrients to young, growing stock, it could supply feed to the region’s large spring-calving cow herd as a winter feedstuff (11). While our research provides baseline data for the use of this feed, additional studies should focus on its use in combination with supplemental feedstuffs.

Literature Cited

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