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Effects of endophyte-infected tall fescue on indicators of thermal status and growth in Hereford and Senepol steers^1,2

Cooperative Agricultural Research Program, Tennessee State University, Nashville 37209-1561

Abstract

Poor growth often occurs in cattle consuming ergot alkaloids associated with endophyte-infected (EI) tall fescue. Hyperthermia may contribute significantly to poor growth resulting from fescue toxicosis. This study examined indicators of thermal status and growth in Hereford (n = 30; heat-sensitive Bos taurus; H) and Senepol (n = 28; heat-tolerant Bos taurus; S) steers fed EI tall fescue (TF) or orchardgrass (OG) in 2 x 2 factorial experiments. Respiration rates, daytime shade use, tail skin temperatures, and body weights were measured during the summer and fall of 2000 (Exp. 1) and 2001 (Exp. 2). Experimental diets consisted of hay and seed for 12 wk in 2000, hay for 6 wk during the summer of 2001, and hay plus seed for 6 wk during the fall of 2001. In Exp. 1, EI tall fescue increased (P < 0.01) respiration rates, shade use, and skin temperatures in both breeds. Breed x diet affected (P < 0.01) 12-wk ADG in Exp. 1. Growth rate was lower for H-TF (262 g/d) than for S-TF, S-OG, and H-OG (475, 497, and 524 g/d, respectively). In Exp. 2, Senepol had lower (P < 0.01) respiration rates, shade use, and skin temperatures compared with Hereford, but diet did not alter (P > 0.14) these indicator traits in either breed. Breed x diet affected (P < 0.01) summer growth rates. Growth rate was lower for H-TF (88 g/d) than for H-OG, S-TF, and S-OG (508, 555, and 566 g/d, respectively). Adding seed to the diets in Exp. 2 decreased (P < 0.01) ADG for both breeds on TF during the fall. Thermal status indicator traits in Senepol and Hereford steers were similarly altered by TF; however, only Hereford showed consistently poor growth. Senepol showed resilience in their capacity for growth under conditions of fescue toxicosis. Senepol influence may enhance cattle performance in production systems that use EI tall fescue as the base forage.

Key Words: Cattle Breeds • Festuca arundinacea • Growth Rate • Heat Adaptation • Heat Stress • Toxicosis

Introduction

Tall fescue (Festuca arundinacea) is a cool-season, perennial grass widely used in the United States to feed cattle. The endophyte Neotyphodium coenophialum infects most tall fescue pastures, producing ergot alkaloids that enhance tall fescue performance but induce fescue toxicosis in livestock (Bacon and Siegel, 1988; Porter, 1995). Fescue toxicosis reduces the growth and reproductive rates of cattle (Thompson et al., 1993; Paterson et al., 1995) and exacerbates hyperthermia under conditions conducive to heat stress (Osborn et al., 1992; Al-Haidary et al., 2001). Fescue toxicosis costs the U.S. beef cattle industry $500 million to $1 billion a year (Comis, 2000). A new pasture management option is tall fescue infected with "novel, nontoxic" endophytes (Parish et al., 2003). The time and expense of pasture renovation, the vast acreage of tall fescue infected with "common" endophyte, and the reluctance of some managers to eradicate long-established, robust tall fescue stands may limit the application of this alternative.

Heat stress is a general concern relative to climatic conditions (Finch, 1986; Silanikove, 2000). Brahman (Bos indicus)-influenced cattle, because of their heat tolerance, are common in areas where heat stress is a problem (Wyatt et al., 2002). Heat-tolerant germplasm might offset common negative effects (e.g., reduced ADG) of endophyte-infected (EI) tall fescue. Limited research indicates a tendency for Brahman influence to reduce the adverse effects of EI tall fescue on steer growth (Goetsch et al., 1988; McMurphy et al., 1990; Cole et al., 2001). Negative features of Brahman influence have led to the evaluation of other tropical breeds, such as Senepol (Browning et al., 1997; Chase et al., 1998). The Senepol is a Bos taurus breed developed in the Virgin Islands with heat tolerance similar to Brahman (Hammond and Olson, 1994; Hammond et al., 1996). This study assessed indicators of thermal status and growth in Senepol and Hereford cattle fed EI tall fescue.

Materials and Methods

Animals.
Purebred Hereford (n = 30) and Senepol (n = 28) steers were acquired in December 1999 and maintained together in pens on the Tennessee State University farm in Nashville, Tennessee (approximately 36°17'N, 86°81'W). All steers were born in the spring of 1999. Steers of each breed were represented by six sires and obtained from two established seedstock farms in eastern Tennessee and western Kentucky that use tall fescue as their base forage. The 58 steers were used on experiments conducted in the summer and fall of 2000 (Exp. 1) and 2001 (Exp. 2). Steers were kept as one group and provided orchardgrass hay, water, and mineral supplement for ad libitum consumption when not on study during the winter and spring of 2001. Senepol steers showed no fitness problems under the winter conditions of 1999 to 2000, 2000 to 2001, or 2001 to 2002 in Nashville. Steers in this project were managed in accordance with guidelines provided by the Consortium (1988) and with approval of the Tennessee State University Animal Care and Use Committee.

Diets.
In Exp. 1, yearling steers (Hereford = 280 ± 5 kg; Senepol = 261 ± 5 kg) within breed and farm of origin were paired by weight and randomly assigned to receive EI tall fescue or orchardgrass (Dactylis glomerata) in a 2 x 2 factorial arrangement. Each experimental diet was replicated in two drylot pens. Each of the four pens contained an even distribution of Hereford and Senepol steers. Steers in all pens were fed orchardgrass hay for ad libitum consumption, supplemented with 1.57 kg•animal^-1•d^-1 of a commercial concentrate from June 12 to July 13. The commercial concentrate contained 45 ppm of lasalocid. Each pen provided 9.75 m (linear) of bunk space. Steers were fed experimental diets from July 14 to October 14. Ambient temperatures for the months of study are presented in Table 1 as recorded at the Nashville climatological recording station (36°06'N, 86°42'W) of the National Weather Service, located 16 km east of the research farm. Experimental diets consisted of orchardgrass or EI tall fescue hay for ad libitum consumption, supplemented with 1.57 kg•animal^-1•d^-1 of the commercial concentrate plus 1.57 kg•animal^-1•d^-1 of orchardgrass or EI tall fescue seed (as-fed basis). Chemical composition of the pretreatment and experimental diets is presented in Table 2. Tall fescue hay came from a field that was 78% infected with N. coenophialum and had ergovaline concentrations of 80 ppb as determined by HPLC (Welty et al., 1994). Two lots of EI ‘Kentucky-31’ tall fescue seed were obtained from a commercial supplier and had ergovaline concentrations of 2,483 and 2,549 ppb with no ergotamine detected. Water and trace minerals were available for ad libitum consumption at all times.

Steers were maintained on their experimental diets for an additional 6 wk (September 18 to November 1) with the addition of tall fescue or orchardgrass seed (1.57 kg•animal^-1•d^-1) to the supplement (as-fed basis). The seed-augmented fall feeding period was intended to further assess Senepol responsiveness to an endophytic diet after an initial interpretation of the summer growth data. Tall fescue hay during the supplemental period was harvested from one field that was 60% endophyte infected and had a 29-ppb concentration of ergovaline. The EI tall fescue seed was obtained from a commercial source and had an ergovaline concentration of 2,353 ppb with no ergotamine detected.

Data Collection.
Body weights and skin temperatures were recorded at 2-wk intervals in each experiment. Steers were processed between 1100 and 1700 each day of measurement. One pen of each dietary treatment was worked through the chutes per day. From session to session, pens were processed so that both treatments were equally exposed to the first or second half of a work day to minimize variance in skin temperatures due to time of day. Approximately 5 to 10 min were allowed to pass from the time steers entered the working facility until the first steer was weighed and measured for skin temperature, which was taken with a digital Thermistor thermometer (Digi-Sense, Cole-Parmer Instrument, Niles, IL) with a detachable skin probe (YSI Inc., Yellow Springs Instrument, Yellow Springs, OH). Skin temperature was measured on the inner (left) side of the right fold of skin located beneath the tailhead. The cattle handling facility is located under an open-sided shed to avoid direct sunlight. Ambient temperature and relative humidity were measured at the covered cattle handling facility with a digital thermometer/hygrometer each time a pen of steers was processed for weights and skin temperatures (Table 3).

Daytime shade usage was recorded multiple times each day of observation between 0900 and 1600 by determining whether individual steers were standing or lying under the shade, standing or lying under the sun, or eating under the sun. Each pen had 60.39 m² of shade in the form of an open-sided shed covered with 80% shade cloth. Daytime shade use was determined 53 times over 18 d between 3 and 12 wk of dietary treatment in Exp. 1. Daytime shade use was determined 32 times across 8 d pretreatment and on 26 occasions across 8 d from 2 to 6 wk of summer treatments in Exp. 2. Shade use was not determined during pretreatment in Exp. 1 or during seed supplementation in the fall of Exp. 2. Shade use and eating activity were statistically analyzed after calculating the percentage of individual steers that were found under the shade or eating on each day of measurement. A minimum of 45 min was allowed to elapse between observations. Ambient temperature and relative humidity were measured at the pens during each observation period (Table 3) with a digital thermometer/hygrometer placed under the shade to avoid direct sunlight.

Statistical Analyses.
All data were analyzed by ANOVA using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) in a split-split-plot design. Diet was the whole-plot factor, breed was the subplot factor, and time was the sub-subplot factor. Data from each experiment were analyzed separately. Fixed effects in the models included diet, breed, time, and two- and three-way interactions among the three main effects. Time was represented by months on experimental diets in Exp. 1 and by overall period before or after the start of experimental diets in Exp. 2. Random terms specified in the mixed effects models included pen replicate within diet, animal within breed, and day or week within month or period. Data for the seed supplementation period of Exp. 2 were evaluated separately and without time as a source of variation. Similarly, time was not used in the analysis of ADG as each defined time interval was tested separately. Only the body weights recorded at the start and end of a specified time interval were used in determining ADG. The repeated measures technique was used for those models that included time as a source of variation with a compound symmetrical covariance structure. The Tukey-Kramer means separation test was used to compare least squares means for all analyses.

Results

Experiment 1
Breed x diet x time influenced (P < 0.01) respiration rates (Table 4). Hereford steers had higher (P < 0.01) respiration rates than Senepol steers during pretreatment. Within each breed, EI tall fescue increased (P < 0.01) respiration rates, whereas respiration rates were not altered by orchardgrass. The breed x diet interaction affected (P < 0.01) daytime shade use and eating activity (Table 4). Each breed had increased shade use and decreased eating activity on tall fescue. Because each breed responded to the fescue diet, the basis of significant interactions for respiratory rate, shade utilization, and eating behavior was likely a greater magnitude of responses to EI tall fescue in Senepol steers compared to Hereford steers.

Growth rates for each month are presented in Table 5. All steer groups had similar ADG during the 1-mo pretreatment period. Breed x diet affected (P < 0.05) steer ADG during the first and third months of treatment. Tall fescue consumption caused (P < 0.01) a lack of weight change in Senepol and weight loss in Hereford during the first month of experimental diets, whereas Senepol and Hereford on orchardgrass were gaining weight. Senepol on EI tall fescue tended to have higher ADG than Senepol on orchardgrass during the third month. Use of pretreatment ADG as a covariate did not significantly alter the relationships among treatment groups for monthly ADG during treatment. Overall weight gain during the 3-mo experimental diet period was influenced (P < 0.01) by a breed x diet interaction (Figure 1a). The 3-mo growth rate of Hereford steers on EI tall fescue steers was lower (P < 0.01) than that for Senepol steers on EI tall fescue or either breed on orchardgrass; the latter three groups did not differ.

View larger version (28K): [in this window] [in a new window]   Figure 1. Average daily weight gain (± SE) for Hereford (H) and Senepol (S) steers fed orchardgrass (OG; n = 15 H, n = 14 S) or endophyte-infected tall fescue (TF; n = 15 H, n = 14 S). Breed x diet influenced (P < 0.01) weight gain over (A) 12 wk in Exp. 1 and (B) 6 wk in summer of Exp. 2. a,bLSMeans with an experiment that do not have a common letter differ (P < 0.01).

Fall, Seed-Supplemented Diets.
When seed was added to the experimental diets, respiration rates and skin temperatures within breed did not vary (P > 0.50) by diet (Table 7). Senepol had lower (P < 0.01) respiration rates and skin temperatures than Hereford during the fall period (Table 7). Hereford and Senepol both experienced lower (P < 0.01) growth rates on the seed-supplemented fescue diet compared to contemporaries on orchardgrass (Table 7). The breed x diet interaction detected for growth rate on the seed-supplemented diets was likely based on the magnitude of difference in ADG between diets within the two breeds.

Endophyte-infected tall fescue and orchardgrass are both perennial cool-season bunch grasses. The quality of the two forages used here were comparable (Table 2), suggesting that they should support comparable steer growth rates. Peters et al. (1992) reported that endophyte-free tall fescue and orchardgrass resulted in similar cow-calf performance, whereas cow-calf performance was lower on EI tall fescue. The findings of Peters et al. (1992) and the nutritional analysis of orchardgrass and tall fescue diets on this study affirmed the use of orchardgrass as a suitable alternative forage for comparison. Ergovaline is a primary ergopeptine alkaloid produced by the endophyte and is considered the principal toxin responsible for fescue toxicosis (Welty et al., 1994; Porter, 1995). Ergovaline concentrations of the tall fescue hay lots were relatively low (<100 ppb) compared to other values cited for EI tall fescue grass or hay (Rottinghaus et al., 1991; Agee and Hill, 1994; Welty et al., 1994). Ergovaline, although a good indicator of the toxic potential of a tall fescue sample, probably acts as one of many ergot alkaloids and alkaloid metabolites that contribute to fescue toxicosis when ingested (Osborn et al., 1992; Hill et al., 2001; Gadberry et al., 2003).

Skin temperatures, respiration rates, and daytime shade use were traits considered to be physiological and/or behavioral indicators of thermal status and associated with thermoregulation in steers. Lower respiration rates, shade use, and skin temperatures of Senepol vs. Hereford steers on orchardgrass during the two experiments demonstrated the heat tolerance of Senepol. These results concur with studies on cows in which Senepol were superior to Hereford for heat tolerance (Hammond and Olson, 1994; Hammond et al., 1996). The lower skin temperatures for Senepol vs. Hereford steers agree with data from this location, showing lower skin temperatures and respiration rates for Brahman compared to Hereford steers (Browning, 2000).

In Exp. 1, respiration rates were elevated within both breeds when switched to tall fescue. Cattle on EI tall fescue typically experience increased respiration rates at high ambient temperatures (Osborn et al., 1992; Al-Haidary et al., 2001). Significantly higher respiration rates on tall fescue were indicative of hyperthermia. Open-mouth panting episodes were observed for many Hereford and a few Senepol on EI tall fescue. High respiration rates and panting represent heat-dissipating mechanisms activated primarily during extreme heat stress in cattle (Finch 1986; Silanikove, 2000). Increased daytime shade use by Hereford and Senepol on tall fescue also indicated that they experienced a greater magnitude of heat stress compared to contemporaries on orchardgrass. Increased shade use was coupled with decreased daytime eating activity for EI tall fescue steers of both breeds. These data agree with previous reports that cattle on EI tall fescue spend less time during the day grazing (Bond et al., 1984; Howard et al., 1992). Senepol cattle appear to be as susceptible as Hereford to the adverse affects of EI tall fescue on thermal balance. These results concur with those of Browning (2000) showing that physiological responses of Brahman and Hereford cattle were similarly responsive to ergot alkaloid exposure. Heat tolerance in the Senepol did not seem to minimize the negative effects of fescue-amplified heat stress on steer thermal status.

Increased skin temperature for tall fescue steers during Exp. 1 was unexpected. Others have found skin temperatures at various locations on the body to be reduced or unchanged in cattle fed EI tall fescue (Rhodes et al., 1991; Osborn et al., 1992; Al-Haidary et al., 2001). Reduced peripheral skin temperatures have been attributed to vasoconstrictive properties of ergot alkaloids (Dyer, 1993; Oliver et al., 1993). In previous work at this research station, skin temperatures at the tail tip and tailhead were reduced as a result of ergotamine treatment (Browning and Leite-Browning, 1997; Browning, 2000). The anatomical location used to measure skin temperature in the current forage study differed from the hairless, mid-ventral tailhead location used in the ergotamine experiments. Skin temperature in this study may have been influenced by rectal temperature more so than blood flow to the extremities. Rectal temperature, another indicator of thermal status in cattle, was increased by EI tall fescue in some studies (Rhodes et al., 1991; Osborn et al., 1992), but not affected in other studies (Stamm et al., 1994; Al-Haidary et al., 2001). Alternative to a rectal temperature association, increased skin temperatures in EI tall fescue-fed steers during Exp. 1 may reflect dissipation of an increased heat load generated by EI tall fescue. Increased skin blood flow to dissipate body heat via convective cooling cause skin temperatures in cattle to increase (Finch, 1986; Silanikove, 2000). Skin temperature responses to endophyte-infected fescue in this study further suggested a disrupted thermoregulatory ability in steers of both breeds.

In contrast to Exp. 1, thermal status indicator traits were not altered by EI tall fescue in Exp. 2. The seedless tall fescue diet fed during the summer of Exp. 2 had markedly lower ergot alkaloid content compared to the Exp. 1 tall fescue diet that consisted of hay and seed (Table 2). Climatic conditions were less conducive to heat stress when the ergovaline concentration of the EI tall fescue diet was increased by seed supplementation during the fall of Exp. 2. Responses of thermal status indicators to EI tall fescue generally did not differ between Senepol and Hereford in either experiment, indicating that both breeds were sensitive to the adverse effects of the tall fescue endophyte toxins on thermal balance. Various physiological indices and metabolic intermediates responded similarly to acute ergot alkaloid exposure in Brahman and Hereford steers (Browning, 2000; Browning and Thompson, 2002). However, ergotamine caused increased respiration rates in Hereford, but not Brahman (Browning and Thompson, 2002), suggesting a potential benefit of heat tolerance in cattle exposed to ergot alkaloids.

Endophyte-infected tall fescue affected growth differently in Hereford and Senepol steers during both experiments. Hereford steers in Exp. 1 lost weight during the first month on tall fescue and gained less weight across the 3-mo experimental period compared to Herefords on orchardgrass. This agrees with the general knowledge that EI tall fescue commonly reduces postweaning ADG (Paterson et al., 1995). Poor growth would also be expected considering the thermal strain exhibited by the Herefords. Senepol steers were similarly heat strained on tall fescue in Exp. 1, but they did not lose weight during the first month on tall fescue as did the Hereford steers. Moreover, ADG in the Senepol over the 3-mo experimental period was not adversely affected by tall fescue compared to Senepol steers on orchardgrass in Exp. 1. Tall fescue inhibited steer growth primarily during the first month. Hereford and Senepol steers apparently adapted to the fescue diet and gained weight during the last 2 mo at rates comparable to those of orchardgrass-fed steers. In some studies, growth rates of cattle were reduced within 1 mo after being placed on EI tall fescue but not during later intervals of fescue consumption (Goetsch et al., 1988; Emile et al., 2000). Others reported poor cattle growth on EI tall fescue to persist over extended periods (McMurphy et al., 1990; Davenport et al., 1993; Beconi et al., 1995). The former appears to have occurred in Exp. 1 of this series.

Although neither breed expressed clinical signs of hyperthermia on EI tall fescue in Exp. 2, ADG was reduced in Hereford but not Senepol steers on the seedless tall fescue summer diet. The reduction in growth for the Hereford steers on tall fescue may be explained by a procession of thermoregulatory mechanisms. Feed intake declines to reduce metabolic heat production and maintain body temperature under mild to moderate heat stress (Hahn et al., 1990; Silanikove, 2000). Mechanisms to dissipate excess body heat (e.g., increased respiratory rates and blood flow to the skin) occur at more extreme conditions of heat stress. This study was not designed to measure feed or water consumption. It is speculated that Hereford steers on EI tall fescue in Exp. 2 experienced mild to moderate levels of hyperthermia leading to lowered forage intake and poor growth. Senepol, with enhanced thermoregulatory ability at higher ambient temperatures as a tropically adapted breed, would not require lowered hay consumption to maintain thermal balance (Finch, 1986, Hammond and Olson, 1994; Hammond et al., 1996; Silanikove, 2000). Subsequently, summer growth in Senepol was not reduced by the EI tall fescue hay in Exp. 2.

Tall fescue seed supplementation during the fall of Exp. 2 inhibited growth in both breeds without clinical signs of hyperthermia. The 6-wk ADG by steers after inclusion of tall fescue seed mirrored the initial 4-wk ADG for both breeds to the introduction of endophytic fescue seed and hay in Exp. 1. Steer growth on the seed-supplemented tall fescue diet in Exp. 2 showed that Senepol were responsive to the toxic element(s) of the EI tall fescue endophyte at the higher concentration. The growth response to seed supplementation during the fall of Exp. 2 when ambient temperatures were not high also indicated that heat stress alone does not explain poor steer performance on EI tall fescue. Climatic conditions and dietary ergot alkaloid concentrations likely interact to elicit animal responses to EI tall fescue.

Results of the current research suggest that the sensitivity of an animal to heat stress is an important component to consider in the bovine fescue toxicosis model. Research into differences between heat-tolerant and heat-sensitive cattle for postweaning steer growth on EI tall fescue vs. endophyte-free tall fescue has been limited. Goetsch et al. (1988) compared the growth of B. taurus x B. taurus and Brahman x B. taurus steers, whereas McMurphy et al. (1990) and Cole et al. (2001) reported ADG for purebred Angus and crossbred Brahman x B. taurus steers grazing EI tall fescue. Although not always statistically significant, Brahman influence reduced the adverse effects of endophyte on steer growth by 10 to 65%. However, there was a consistent trend for EI tall fescue to lower growth rates in Brahman-cross steers. McMurphy et al. (1990) and Cole et al. (2001) also reported that Angus steers on EI tall fescue had elevated rectal temperatures at the end of the grazing periods in May and August, respectively, whereas rectal temperatures in Brahman-cross steers were unaffected by diet. Rectal temperatures in Cole et al. (2001) were recorded after 26-h transport. Rectal temperatures during cooler intermediate periods between December and April were not affected by EI tall fescue in either genotype, but weight gain of Brahman x Angus steers was less affected by EI tall fescue compared with Angus during most of those same winter and spring intervals (McMurphy et al., 1990). Periodic rectal temperature and growth responses to EI tall fescue in McMurphy et al. (1990) are comparable to results of the current study in not showing a clear relationship between clinical signs of thermal distress and inhibited weight gain, despite seasonal distinctions between the projects.

Contrary to the findings in Brahman-cross steers, growth rates in purebred Senepol steers were not reduced by EI tall fescue, with the exception of periods immediately after introduction of EI tall fescue seed to the diet. Senepol steers exhibited a resilience under the EI tall fescue challenge by gaining weight at a rate comparable to contemporaries fed orchardgrass. The underlying tropical adaptations responsible for the Senepol advantage on EI tall fescue are not evident. Tropical adaptations involving voluntary food intake and nutrient utilization are speculated as being important contributing factors (Frisch and Vercoe, 1977; Finch, 1986). It also remains to be determined the capacity for resilience and growth on EI tall fescue that would be exhibited by Senepol-crossbred steers.

Implications

Fescue toxicosis causes significant economic losses for cattle producers because of decreased growth and reproductive rates in cattle grazing endophyte-infected tall fescue. Hyperthermia is a manifestation of fescue toxicosis in cattle. It was proposed that heat tolerance in steers would minimize the adverse effects of endophyte-infected tall fescue on thermal balance and growth. Traits indicative of thermal status responded to endophyte-infected tall fescue in both Hereford and Senepol steers. However, weight gain by Senepol steers was not decreased on endophyte-infected tall fescue to the extent recorded in Hereford. Senepol cattle represent a genetic resource that has the potential to reduce problems of poor growth in cattle herds grazing endophyte-infected tall fescue.

Footnotes

¹ This work was supported by USDA-CSREES Grant No. 99-38814-8201.

² The author thanks C. Bradley, E. Bradley, D. Coleman, T. Payton, V. Sauve, N. Whittingham, and D. Young for their assistance in cattle management and data collection.

³ Correspondence: 3500 John A. Merritt Blvd. (phone: 615-963-5837; fax: 615-963-1557; e-mail: rbrowning{at}tnstate.edu).

Received for publication May 18, 2003. Accepted for publication September 22, 2003.

Literature Cited

Agee, C. S., and N. S. Hill. 1994. Ergovaline variability in Acremonium-infected tall fescue due to environment and plant genotype. Crop Sci. 34:221–226.

Al-Haidary, A., D. E. Spiers, G. E. Rottinghaus, G. B. Garner, and M. R. Ellersieck. 2001. Thermoregulatory ability of beef heifers following intake of endophyte-infected tall fescue during controlled heat challenge. J. Anim. Sci. 79:1780–1788.[Abstract/Free Full Text]

Bacon, C. W., and M. R. Siegel. 1988. Endophyte parasitism of tall fescue. J. Prod. Agric. 1:45–55.

Beconi, M. G., M. D. Howard, T. D. A. Forbes, R. B. Muntifering, N. W. Bradley, and M. J. Ford. 1995. Growth and subsequent feedlot performance of estradiol-implanted vs nonimplanted steers grazing fall-accumulated endophyte-infected or low-endophyte tall fescue. J. Anim. Sci. 73:1576–1584.[Abstract]

Bond, J., J. B. Powell, and B. T. Weinland. 1984. Behavior of steers grazing several varieties of tall fescue during summer conditions. Agron. J. 76:707–709.[Abstract/Free Full Text]

Browning, R., Jr. 2000. Physiological responses of Brahman and Hereford steers to an acute ergotamine challenge. J. Anim. Sci. 78:124–130.[Abstract/Free Full Text]

Browning, R., Jr., and M. L. Leite-Browning. 1997. Effect of ergotamine and ergonovine on thermal regulation and cardiovascular function in cattle. J. Anim. Sci. 75:176–181.[Abstract/Free Full Text]

Browning, R., Jr., and F. N. Thompson. 2002. Endocrine and respiratory responses to ergotamine in Brahman and Hereford steers. Vet. Hum. Toxicol. 44:149–154.[Medline]

Browning, R. Jr., B. G. Warrington, J. W. Holloway, and R. D. Randel. 1997. Testicular size at weaning in tropically-adapted beef bulls as influenced by breed of sire and dam. Theriogenology 48:257–265.

Chase, C. C., Jr., T. A. Olson, A. C. Hammond, M. A. Menchaca, R. L. West, D. D. Johnson, and W. T. Butts, Jr. 1998. Preweaning growth traits for Senepol, Hereford, and reciprocal crossbred calves and feedlot performance and carcass characteristics of steers. J. Anim. Sci. 76:2967–2975.[Abstract/Free Full Text]

Cole, N. A., J. A. Stuedemann, and F. N. Thompson. 2001. Influence of both endophyte infestation in fescue pastures and calf genotype on subsequent feedlot performance of steers. Prof. Anim. Sci. 17:174–182.

Comis, D. 2000. The grass farmers love to hate. Agric. Res. 48:4–7. ARS-USDA, Washington, DC.

Consortium. 1988. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Consortium for Developing a Guide for the Care and use of Agricultural Animals in Agricultural Research and Teaching, Champaign, IL.

Davenport, G. M., J. A. Holing, and C. H. Rahe. 1993. Growth and endocrine responses of cattle to implantation of estradiol-17ß during continuous or discontinuous grazing of high- and low-endophyte-infected tall fescue. J. Anim. Sci. 71:757–764.[Abstract]

Dyer, D. C. 1993. Evidence that ergovaline acts on serotonergic receptors. Life Sci. 53:223–228.

Emile, J. C., S. Bony, and M. Ghesquiere. 2000. Influence of consumption of endophyte-infected tall fescue hay on performance of heifers and lambs. J. Anim. Sci. 78:358–364.[Abstract/Free Full Text]

Finch, V. A. 1986. Body temperature in beef cattle: its control and relevance to production in the tropics. J. Anim. Sci. 62:531–542.[Abstract/Free Full Text]

Frisch, J. E., and J. E. Vercoe. 1977. Food intake, eating rate, weight gains, metabolic rate and efficiency of feed utilization in Bos taurus and Bos indicus crossbred cattle. Anim. Prod. 25:343–358.

Gadberry, M. S., T. M. Denard, D. E. Spiers, and E. L. Piper. 2003. Effects of feeding ergovaline on lamb performance in a heat stress environment. J. Anim. Sci. 81:1538–1545.[Abstract/Free Full Text]

Goetsch, A. L., K. L. Landis, G. E. Murphy, B. L. Morrison, Z. B. Johnson, E. L. Piper, A. C. Hardin, and K. L. Hall. 1988. Supplements, parasite treatments and growth implants for Brahman or English crossbred steers grazing endophyte-infected or noninfected fescue in the spring and fall. Prof. Anim. Sci. 4:32–38.

Hahn, G. L., R. A. Eigenberg, J. A. Nienaber, and E. T. Littledike. 1990. Measuring physiological responses of animals to environmental stressors using a microcomputer-based portable datalogger. J. Anim. Sci. 68:2658–2665.[Abstract]

Hammond, A. C., and T. A. Olson. 1994. Rectal temperature and grazing time in selected beef cattle breeds under tropical summer conditions in subtropical Florida. Trop. Agric. 71:128–134.

Hammond, A. C., T. A. Olson, C. C. Chase, Jr., E. J. Bowers, R. D. Randel, C. N. Murphy, D. W. Vogt, and A. Tewolde. 1996. Heat tolerance in two tropically adapted Bos taurus breeds, Senepol and Romosinuano, compared with Brahman, Angus, and Hereford cattle in Florida. J. Anim. Sci. 74:295–303.[Abstract/Free Full Text]

Hill, N. S., F. N. Thompson, J. A. Stuedemann, G. W. Rottinghaus, H. J. Hu, D. L. Dawe, and E. E. Hiatt, III. 2001. Ergot alkaloid transport across ruminant gastric tissues. J. Anim. Sci. 79:542–549.[Abstract/Free Full Text]

Howard, M. D., R. B. Muntifering, N. W. Bradley, G. E. Mitchell, Jr., and S. R. Lowry. 1992. Voluntary intake and ingestive behavior of steers grazing Johnston or endophyte-infected Kentucky-31 tall fescue. J. Anim. Sci. 70:1227–1237.[Abstract]

McMurphy, W. F., K. S. Lusby, S. C. Smith, S. H. Montz, and C. A. Strasia. 1990. Steer performance on tall fescue pasture. J. Prod. Agric. 3:100–102.

Oliver, J. W., L. K. Abney, J. R. Strickland, and R. D. Linnabary. 1993. Vasoconstriction in bovine vasculature induced by the tall fescue alkaloid lysergamide. J. Anim. Sci. 71:2708–2713.[Abstract]

Osborn, T. G., S. P. Schmidt, D. N. Marple, C. H. Rahe, and J. R. Steenstra. 1992. Effect of consuming fungus-infected and fungus-free tall fescue and ergotamine tartrate on selected physiological variables of cattle in environmentally controlled conditions. J. Anim. Sci. 70:2501–2509.[Abstract]

Parish, J. A., M. A. McCann, R. H. Watson, C. S. Hoveland, L. L. Hawkins, N. S. Hill, and J. H. Bouton. 2003. Use of nonergot alkaloid-producing endophytes for alleviating tall fescue toxicosis in sheep. J. Anim Sci. 81:1316–1322.[Abstract/Free Full Text]

Paterson, J., C. Forcherio, B. Larson, M. Samford, and M. Kerley. 1995. The effects of fescue toxicosis on beef cattle productivity. J. Anim. Sci. 73:889–898.[Abstract]

Peters, C. W., K. N. Grigsby, C. G. Aldrich, J. A. Paterson, R. J. Lipsey, M. S. Kerley, and G. B. Garner. 1992. Performance, forage utilization, and ergovaline consumption by beef cows grazing endophyte fungus-infected tall fescue, endophyte fungus-free tall fescue, or orchardgrass pastures. J. Anim. Sci. 70:1550–1561.[Abstract]

Porter, J. K. 1995. Analysis of endophyte toxins: Fescue and other grasses toxic to livestock. J. Anim. Sci. 73:871–880.[Abstract]

Rhodes, M. T., J. A. Paterson, M. S. Kerley, H. E. Garner, and M. H. Laughlin. 1991. Reduced blood flow to peripheral and core body tissues in sheep and cattle induced by endophyte-infected tall fescue. J. Anim. Sci. 69:2033–2043.[Abstract]

Rottinghaus, G. E., G. B. Garner, C. N. Cornell, and J. L. Ellis. 1991. HPLC method for quantitating ergovaline in endophyte-infected tall fescue: seasonal variation of ergovaline levels in stems with leaf sheaths, leaf blades, and seed heads. J. Agric. Food Chem. 39:112–115.

Silanikove, N. 2000. Effects of heat stress on the welfare of extensively managed domestic ruminants. Livest. Prod. Sci. 67:1–18.

Stamm, M. M., T. Del Curto, M. R. Homey, S. D. Brandyberry, and R. K. Barton. 1994. Influence of alkaloid concentration of tall fescue straw on the nutrition, physiology, and subsequent performance of beef steers. J. Anim. Sci. 72:1068–1075.[Abstract]

Thompson, R. W., H. A. Fribourg, J. C. Waller, W. L. Sanders, J. H. Reynolds, J. M. Phillips, S. P. Schmidt, R. J. Crawford, Jr., V. G. Allen, D. B. Faulkner, C. S. Hoveland, J. P. Fontenot, R. J. Carlisle, and P. P. Hunter. 1993. Combined analysis of tall fescue steer grazing studies in the eastern United States. J. Anim. Sci. 71:1940–1946.[Abstract]

Welty, R. E., A. M. Craig, and M. D. Azevedo. 1994. Viability of ergovaline in seeds among endophyte-infected genotypes of tall fescue. Plant Dis. 78:845–849.

Wyatt, W. E., T. D. Bidner, P. E. Humes, D. E. Franke, and D. C. Blouin. 2002. Cow-calf and feedlot performances of Brahman-derivative breeds. J. Anim. Sci. 80:3037–3045.[Abstract/Free Full Text]

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