Tall fescue utilization by exercised - yearling horses

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6. Erickson HH, Sexton WL, DeBowes RM, et al. Cardiopulmonary and metabolic responses to treadmill exercise and training in the Quarter Horse. In: East Lansing, MI: Proc 9th Equine Nutr Physiol Symp, 1985;194-199. 7. Erickson HH, Lundin CS, Erickson BK, et al. Indices of performance in the racing Quarter Horse. In: Persson SGB, Lindholm A, Jeffcott LB, eds. Equine exercise physiology IlL Davis, CA: ICEEP Pub, 1991;41-46. 8. Eisner R. Limits to exercise performance: Some ideas from comparative studies. Acta Physiol Scand 1986;128:Supl 556,4551. 9. Campbell ME, Potter GD, Webb SP. Cardiorespiratory response and blood chemistry in cutting horses subjected to two exercise regimens. In: East Lansing, MI: Proc 9th Equine Nutr Physiol Symp, 1985;188-193. 10. Beech J. 1991. Equine respiratory disorders. Philadelphia: Lea and Febiger, 1991;28. 11. Attenburrow DP. Time relationship between the respiratory cycle and limb cycle in the horse. Equine VetJ 1982;14(1):69-172. 12. Carlson GP. Thermoregulation and fluid balance in the exercising horse. In: Snow DH, ed. Equine Exercise Physiology. Cambridge: Granta Editions, 1983;291-309. 13. Judson GJ, Mooney GJ, Thornbury RS. Plasma biochemical

TALL FESCUE UTILIZATION BY EXERCISED - YEARLING HORSES J. Pendergraft, MS; 1 M.J. Arns, PhD; 1 F. K. Brazle, PhD 2

SUMMARY

Little information has been published concerning the effects of endophyte-infected tall fescue consumption on performance of young growing horses. Therefore, this study evaluated exercise performance and growth by yearlings fed endophyte-infected rescue. Twelve Quarter Horse yearlings (12-16 months of age) were blocked by age and sex and randomly assigned to one of three groups. Group I received native prairie hay (P), Group II received endophyte-free fescue hay (EF) and, Group III received endophyte infected fescue hay (El). Rectal temperatures were monitored daily Authors' addresses:1Departmentof AnimalSciencesand Industry,Kansas State University,Manhattan,66506. 2SoutheastArea ExtensionOffice, 20 South Highland,Chanute66720. Directcorrespondenceto Dr. Arns. ContributionNo. 93-346-Jfromthe KansasAgriculturalExperimentStation. Acknowledgments:Fundingprovidedby grants from KansasRacingCommissionand KansasAgriculturalExperimentStation.The authorsgratefully acknowledgethe assistanceof Dr. R. H. Rauband Dr. K. K. Bolsen,Kansas State University.

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values in Thoroughbred horses in training. In: Snow DH, ed. Equine Exercise Physiology. Cambridge: Granta Editions, 1983;354-361. 14. SnowDH. Biochemical changes in blood and muscle associated with exercise. In: Snow DH, ed. Equine Exercise Physiology. Cambridge: Granta Editions, 1983;427-444. 15. Carlson GP. Hematology and body fluids in the equine athlete: a review. In: Snow DH, ed. Equine Exercise Physiology. Cambridge: Granta Editions, 1983;393-425. 16. Odom TW, Ono Y. The time course in the development of hypocalcemia and plasma lactate accumulation in mature and immature hyperthermic domestic fowl (Gallus domesticus). Comp Biochem Physio11991;98A:2,207-210. 17. Harris P, Snow DH. The effects of high intensity exercise on the plasma concentration of lactate, potassium and other electrolytes. Equine Vet J 1988;20:2,109-113. 18. Garcia MC, Beech J. Equine intravenous glucose tolerance test: Glucose and insulin responses of healthy horses fed grain or hay and of horses with pituitary adenoma. Am J Vet Res 1988;47:3,570-572. 19. HawkeyCM. Comparative mammalian hematology. London: William Hernemann Medical Books Ltd, 1975. 20. Rose RJ, Allen JR. Hematologic responses to exercise and training. Vet Clin NAmer Equine Pract 1985;1:461-464.

and growth parameters (weight, hip and wither heights, and body fat) were measured at the start of the study (d 0) and every 2 weeks throughout the 106 d study. Additionally, blood samples were collected on d 0 and every 28 d for the duration of the study to monitor blood concentrations of calcium, phosphorus, prolactin (PRL), thyroxine (T4), and triiodothyronine (Ta). Horses were exercised twice a week for 10-30 min. Respiration, heart rate, and rectal temperature were measured at the start and 5, 30, and 60 min postexercise. Growth parameters and daily rectal temperatures were not different (P >.05) among grdups. No differences (P >.05) occurred among groups in concentrations of serum calcium, phosphorus, PRL, T a, and T 4. Respiration rates were lower (P <.05) at 30 and 60 rain postexercise for horses consuming fescue than for horses consuming prairie hay. Postexercise heart rates and rectal temperatures showed no difference (P <.05) among groups. These data suggest that young growing horses being exercised can utilize endophyte-infected fescue efficiently on a short-term basis.

INTRODUCTION

Tall fescue (Festuca arundinacea L. ) is considered to be the predominant cool-season grass species within the United States, covering approximately 35 million acres. It is estimated that over 8.5 million cattle and .69 million horses are maintained on tall fescue pastures. 1A majority of tall rescue pastures are infected with an endophyte fungus (Acremoniumcoenophialum)which enhances

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forage yields and grazing tolerance of tall fescue, but also may become associated with a number of problems when consumed by livestock.2 Specific syndromes associated with endophyte-infected tall fescue include rescue foot,a fat necrosis,4 fescue toxicosis,s and agalactia.6 These conditions result in poor growth performance and reduced reproductive efficiency in cattle,7 sheep,s and horses.9 A conservative estimate of $609 million is lost annually in cattle production1 from reduced conception rates and weaning weights, but the economic loss to the horse industry is unknown. Three groups of alkaloids, diaziphenanthrene, pyrrolizidine, and ergot, are present in plants infected with the endophyte.1° Although the exact toxin responsible for poor animal performance has not been fully elucidated, the ergot alkaloids produced by A. coedophialum 11 are considered to be the major toxic agent.2,12 Research concerning consumption of endophyte-infected tall rescue and the subsequent effect on the growth and development of the yearling horse is limited. The objective of this study was to determine if endophyte-infected fescue had an effect on growth and exercise performance of the yearling horse.

MATERIAL

AND METHODS

Twelve Quarter Horse yearlings were blocked initially by age (12-16 months) and sex (6 geldings and 6 fillies) and then randomly assigned to one of three groups (n = 4 per group). These groups received either a mixed native prairie (P), endophyte-free rescue (EF), or endophyte-infected fescue (El) hay. The ergovaline concentration detected in EI hay was 190 ppb; none was detected in P and EF hays. All hays were harvested 30-45 d prior to the onset of the study. Yearlings were fed a concentrate at 45% of the total diet with the respective hay treatments (Table 1) to meet the National Research Councils'st3 recommended nutrient requirements for rapid growth. The concentrate portion of the ration was fed in troughs that allowed 91.4 cm of bunk space per animal. Each group had free access to water and received their respective hay near ad libitum. Specifically, hay intakes were adjusted such that yearlings had a minimum of 8 h free access between feedings to their respective hay. Treatments were fed for 106 d starting on July 1, 1991. Table 1. Composition of the concentrate. Ingredients Corn, cracked Oats, rolled Supplement pellet1 Cane molasses

%, as fed basis 40 37 20 3

1Composition of the supplement (%, as fed basis): soybean meal, 55.5; dehydrated alfalfa, 33.4;dicalcium phosphate, 4.6; limestone, 2.4; trace mineral salt, 2.7; vitamin premix, 1.3; and copper sulfate, .03.

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Table 2. Nutrient composition and ergot alkaloid concentration of the concentrate and native prairie (P), endophyte-free (EF), and endophyte-infected (El) tall fescue hays fed to yearling horses. Item

Cone.

P

EF

El

Dry matter, % 92.13 Crude protein, % 14.62 Gross energy, kcal/g 4.03 Neutral detergent fiber, % 19.18 Acid detergent fiber% 6.00 Phosphorus, % .59 Calcium, % .58 Ergot alkaloid, ppb -

95.31 5.68 3.99 71.42 40.55 .08 .53 0

95.00 6.25 3.86 67.27 40.02 .17 .30 0

95.34 7.22 3.97 70.96 42.18 .24 .31 190

Yearlings were maintained in dry lots that averaged 24.4 m by 30.5 m, where they were fed the concentrate and hay twice daily. Initially and at 14-d intervals, yearlings were weighed and measured on 2 consecutive days for a single average value. Growth measurements included wither height, hip height, and body condition scores. 14 Blood was drawn at the start of the study and at 28-d intervals by jugular vena puncture. Samples were obtained at 0600 h and then cooled (5 C) for 24 h. Serum was harvested by centrifugation and stored at- 20 C until assayed for calcium, phosphorus, prolactin, thyroxine (T4), and triiodothyronine (T3). Serum calcium and phosphorus were analyzed by atomic absorption spectrophotometry. +s Serum PRL was determined by RIA. 16 A double antibody canine 12sI radioimmunoassay kita was used to measure the concentrations of thyroxine (T4) with a sensitivity level of 0.05 Ixg/dl. Triiodothyronine (T3) was measured using a solid-phase canine 125 I radioimmunoassay kit.a Yearlings were exercised biweekly at the trot on a mechanical walker at a speed of approximately3 m per sec. Duration of exercise was increased by 5 min every 4 wks and ranged from 10 min in the beginning of the study, to 30 min at the end of the study. Rectal temperatures, respiration, and heart rates were collected at the start and 5, 30, and 60 min postexercise to determine level of performance and the influence of endophyte consumption on postexercise recovery. Daily rectal temperatures were taken between 1530 and 1630 h. Digestibilitieswere evaluated using chromic oxide (Cr203) as a marker. The Cr20a (.3%) was added to the concentrate portion of the yearling diets 2 d after the final exercise period. Yearlings were individually fed the concentrate portion of the diet during the digestibilitystudy. Fecal grab samples were collected following an 8-d adjustment period for addition of the marker to the diets. Samples were taken for 3 d from each horse at 3-h intervals after the morning (0700 h) feeding to represent a 12-h collection period. Fecal samples we re composited for each horse for analysis. Concentrate, hay, and feces were analyzed for dry matter (DM), crude protein (CP), TM acid detergent fiber (ADF) and neutral detergent fiber (NDF). t7 Bomb calorimetry was used to determine gross aDiagnostic ProductsCorporation,Los Angeles,CA 90045.

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Table 3. Apparent digestibility of nutrients and dry matter intakes of diets containing concentrate and either native prairie (P), endophyte-free (EF), or endophyte-infected (El) tall fescue hays.

Table 5. Blood analysis of yearlings fed a concentrate and either native prairie (P), endophyte-free (EF), or endophyte-infected (El) tall fescue hay.

Item

P

EF

El

SE a

Item

Dry matter, % 57.58 Crude protein, % 58.55 Energy, % 57.56 Neutral detergent fiber, % 35.85 Calcium, % 46.59 Phosphorus, % 23.77

53.08 62.14 53.20 25.44 34.18 24.10

57.76 66.53 56.10 33.59 49.41 27.05

1.93 1.12 2.13 3.45 4.92 2.49

Calcium, mg/dl Phosphorus, mg]dl Prolactin, ng/ml Thyroxine, lag/dl Triiodothyronine, ixg/dl

2.90

2.94

.45

Dry matter intakes, %

2.94

aStandarderror of the mean.Treatmentswere not different(P<.05).

energy. Chromic oxide, Ca, and P were measured by atomic absorption spectrophotometry. Data were analyzed by analysis of variance procedures 18 as a split plot over time. Animals were considered random, and, thus, treatments were tested using the individual(treatment)mean square. When differenceswere detected by analysis of variance procedures, differences were identified using a Fisher's LSD.

RESULTS AND DISCUSSION

Yearlings receiving concentrate and either P, EF or EI hay had an average daily intake of 4.90, 4.90, and 4.95 kg concentrate and 6.0, 6.0, and 6.1 kg hay (P, EF, El, respectively). Ideally, horses would have been fed individually, however facility constraints did not allow this. The pen arrangement and size allowed for continued free access to the diets. Although, some social dominance and subsequent movement of horses existed, all horses had access to concentrate. The DM, NDF, ADF, and gross energy were similar between P, EF and E1 hay; however, the hays differed in CP, Ca, and P. Although the total diets were not similar in CP, Ca, and P; the yearlings consumed an average of 1060, 1090, and 1160 g CP; 60, 50, and 50 g Ca; and 35, 40, and 40 g P (P, EF, El, respectively), all of which are in slight to moderate excess of NRC requirements and Table 4. Growth performance of yearling horses fed a concentrate and either native prairie (P), endophyte-free (EF), or endophyteinfected (El) tall fescue hay. Item

P

Initial weight, kg 335.89 Final weight, kg 408.69 Growth in hip height, cm 5.56 Growth in wither height, cm 3.81 Average daily gain, kg .69

EF 335.43 418.55 4.45 4.78 .78

El 334.86 411.98 5.56 5.72 .73

SE a 4.64 4.64 .16 .18 .12

aStandarderror of the mean.Treatmentswere not different(P<.05).

550

P

EF

El

SE a

12.2 4.8 3.2 4.4 .50

11.7 4.8 2.8 4.2 .56

11.7 4.8 3.3 4.4 .46

.52 .15 .56 .46 .05

aStandarderrorof the mean,Treatmentswere not different(P<.05).

would not be expected to effect growth 13or the results of this study. Apparent digestibilityof nutrients and dry matter intakes were not affected (P=.2) negatively by the presence of the endophyte in the diet (Table 3). Palatability appeared to be lower for EI hay as compared to EF and P hays. Horses consumed the total amount of EI hay fed, but consistently required a longer time to consume the hay portion of the diet (data not shown). The results reported herein are in contrast to previous equine work, which showed that apparent digestibilities of DM, gross energy, and CP tended to be lower and fiber digestibilitywas lower for yearlings consuming EI hay as compared to yearlings receiving EF hay. 19 Redmond and coworkers2° also reported a tendency for lower nutrient digestibility in mature geldings consuming El hay. The differences reported may be due to variations in the experimental procedures, degree of supplementation, the quality of forage fed, the age of the horses utilized, the concentration of ergot alkaloids consumed, or the duration of E1 consumption in each of the respective studies. Growth performance, as measured by changes in wither and hip heights, was similar (P=.60) for all treatments (Table 4). Average dailygains (P=.49) and body condition scores (x=6, P =.91) were similar for yearlings consuming P, EF, and E1 hay. Average daily gains detected in this study were higher than those reported by McCann and coworkers, 19,21 but corresponded to previously reported gains ofyounghorses fed ad libitum.22 Moreover, our results are in agreement with those of McCann and coworkers', who indicated that consumption of 54% and 94% A.coenophialum infected fescue was not detrimental to growth performance of yearling horses. 19,21 This contradicts recent work by Aiken and coworkers,23 who reported lower weight gain for yearlings grazing endophyte-infected (75%) pastures. The infection level of the pastures in that study was similar to the infection level of the hay in our study but lower than the infection level of the hay in the recent study by McCann and coworkers.21 However, the concentration of toxin consumed by yearlings may have been higher in the Aiken trial because of the lack of grain supplementation or the use of fresh, mature forage. Quantification of the concentration of toxin consumed appears to be necessary and may clarify discrepancies in the literature.

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Table 6. Respiration (RSP), heart rate (HR), and rectal temperature (TEMP) before, and 5, 30, and 60 minutes postexercise of yearling horses fed a concentrate and either native prairie (P), endophytefree (EF) or endophyte-infected (El) tall fescue hay.

Item

P

EF

El

SE a

HR B, b/m HR 5, b/m HR 30, b/m HR 60, b/m

57.6 70.5 58.9 56.4

54.6 67.2 54.9 54.0

53.6 67.7 55.0 53.1

1.64 1.90 1.22 1.18

RSP. B, b/m RSP. 5, b/m RSP. 30, b/m RSP. 60, b/m

37.8 43.5 40.7 b 37.2 b

33.8 39.6 34.2 c 31.0 c

32.5 36.5 32.8c 30.3 c

2.43 3.46 2.09 1.54

TEMP. TEMP. TEMP. TEMP.

38.2 38.6 38.3 38.2

38.3 38.7 38.4 38.3

38.2 38.7 38.3 38.2

.07 .09 .08 .08

B, C 5, C 30, C 60, C

aStandarderrorof the mean. b,CMeanswith differentsuperscriptsdiffer (P<.05).

Serum calcium, phosphorus, thyroxine, and triiodothyronine concentrations did not differ (P>.05) between treatments (table 5). The lack of a dopaminergic effect on circulating thyroid hormone concentrations has previously been shown in sheep 24 and cattle.2s Prolactin concentrations were similar (P=.99) between treatments, and decreased (P<.001) over the course of the 106 d study. Seasonal fluctuations in PRL concentrations have been reported previously in nonpregnantmares, as The lack of a dopaminergic effect of El hay on serum PRL concentrationsin this study was unexpected. Mares consuming endophyte-infected tall fescue grass typically have lowered serum concentrationsof PRL. 2,s,27Serum PRL concentrations of mature geldings consuming El hay had a tendency to be lower than those of geldings consuming EF hay. Possibly, in the current study, insufficient concentrations of the toxin were consumed to cause dopaminergic effect. The El hay was cut from a pasture which tested at an infection level of 70%, and the concentration of ergot alkaloids in the hay at the start of the study was 190 ppb. Hay previously harvested from this field for use in cattle studies has caused manifestations typically associated with rescue toxicosis, b However, endophyte infection levels in pastures are not consistently correlated with signs offescue toxicosis 19"21.23. and previously reported equine studies have not measured the ergot alkaloid concentrations present; thus, direct comparisons are difficult. Postexercise heart rates, respiration rates, and rectal temperatures of yearlings fed P, EF, and EI hay are presented in Table 6. Respiration rates at 30 and 60 min postexercise were higher (P<.05;.02, respectively) for yearlings fed P. However, this differbCoffey, K. Personal communication.

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ence appears to be due to the location of those yearlings duringtheir recovery. They faced the dry lots that housed the EI- and EF-fed yearlings, which were returned before the final measurements for Pfed yearlings were taken. This situation resulted in increased activity of P-fed yearlings, which could explain their elevated respiration rates. The rectal temperatures were not different (P<.05) among groups at all periods of recovery. High rectal temperatures have been recorded in several studies with cattle consuminginfected tall rescue. 2a'29However, our results are similar to those of other equine studies, which indicated that consumptionof the endophyte does not elevate body temperature. 23

CONCLUSIONS

Fescue toxicity causes substantial losses each year to sheep, cattle, and horse producers. The losses may be attributed to an endophyte,Acremoniumcoenophialum, which inhabits the rescue plant. Our research indicates a safe and economical use for infected tall rescue in the horse industry. On a short-term basis, the endophyte-infected tall rescue supplemented with concentrate to meet NRC requirements, demonstrated no detrimental effects on growth or exercise performance in yearling horses. Further studies are necessary to substantiate these findings for horses consuming endophyte-infected rescue for longer durations.

REFERENCES 1. Hoveland, CS Survey reveals heavy losses from toxic tall fescue. Hay and Forage Grower 1991; 6:28. 2. Porter, JK and FN Thompson. The effect of feseue toxicosis on reproduction in livestock. JAnim Sci 1992; 70:1594. 3. Garner, GB and CN Cornell. Fescue foot in cattle. In: TD Wyllie and L G Morehouse (Ed.). Mycotoxic Fungi, Mycotoxins, Mycotoxicoses: An Encyclopedic Handbook, Marcel Dekker, New York 1978; 2:45. 4. Rumsey, TS, JA Stuedemann, SR Wilkinson, et al. Chemical composition of necrotic fat lesions in beef cows grazing fertilized Kentucky 31 tall fescue. JAnim Sci 1979; 48:673. 5. Henneke, DR, GD Potter, JL Kreider, et aL Relationship between condition score, physical measurement, and body fat percentage in mares. Eq VetJ 1983; 15:371. 6. Monroe, JL, DL Cross, LW Hudson, eta]. Effect of selenium and endophyte contaminated fescue on performance and reproduction in mares. J Equine Vet Sci 1988; 8:148. 7. Read, JC, and BJ Camp. The effect of the fungal endophyte Acremonium coenophialum in tall fescue on animal performance, toxicity, and stand maintenance. Argon J 1986; 78:848. 8. Hannah, SM, JA Paterson, JE Williams, et al. Effects of increasing dietary levels of endophyte-infected tall fescue seed on diet digestibility and ruminal kinetics in sheep. J Anim Sci 1990; 68:1693. 9. Putnam MR, DI Bransby, J Schumacher, et al. The effect of the fungal endophyte Acremonium coenophialum in fescue on

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pregnant mares and foal viability. Am J VetRes 1991; 52:2071. 10. Bush, LP and PB Burrus. Tall fescue forage quality and agronomic performance as affected bythe endophyte. JProdAgric 1988; 1:55. 11, Morgan-Jones, G and W Cams. Notes on Hyphomycetes. XLI. An endophyte of festuca arundinacea and the anomorph of Epichloe typhina, a new taxa in one of two new sections of Acremonium. Mycotaxon 1982; 15:311. 12. porter, JK, CW Bacon and JD Robbins. Ergosine, ergosinine and chanoclavine I from Epichloe tphina. JAgric FoodChem 1979; 27:595. 13. NRC. Nutrient requirements of domestic animals, No. 6, Nutrient requirements of horses. NationalResearch Council,Washington, DC 1989. 14. Hemken, RW, JAJackson, andJABoiling. Toxic factors intall fescue, JAnim Sci 1984; 58:1011. 15. A.O.A.C: Official Methods of Analysis (14th ed.): Assoc. of OfficialAnalytical Chemists, Arlington, VA 1984. 16. Colborn, DR, DL Thompson, Jr., TL Roth, et al. Responses of cortisol and prolactin to sexual excitement and stress in stallions and geldings. JAnim Sci 1991; 69:2558. 17. Goering, HKand PJ Van Soest. Foragefiber analysis. USDA ARSAgriculture Handbook, Washington, DC, Government Printing Office 1970; No. 379. 18. SAS: SAS User's Guide: Statistics. Can/, NC: Statistical Analysis System Institute 1985. 19. McCann, JS, GL Heusner, HE Amos et al. Growth rate, diet digestibility, and serum prolactin of yearling horses fed non-infected and infected tall fescue. J Eq Vet Sci 1992; 12:240. 20. Redmond, LM, DL Cross, TC Jenkins et al. The effect of Acremonium coenophialum on intake and digestibility of tall fescue hay in horses. Eq Vet Sci 1991; 4:215.

EFFECTS OF DIETARYCATION-ANIONBALANCE ON ACID BASE BALANCEAND BLOOD PARAMETERSIN ANAEROBICALLYEXERCISED HORSES J. C. Popplewell, BS; 1 D.R. Topliff, PhD; ~ D.W. Freeman, PhD; 1 J.E. Breazile, DVM, PhD2

SUMMARY

Four mature geldings were used in a 4X4 Latin square experAuthors'Addresses: 1Departmentof AnimalScience,Divisionof Agricultural Sciences and NaturalResourcesand 2Departmentof PhysiologicalSciences, College of VeterinaryMedicine, Oklahoma State University,Stillwater, OK 74078. Acknowledgement:This researchwas supported by the OklahomaAgricultural ExperimentStation, ProjectH- 1964.

21. McCann, JS, GL Heusner, HE Amos, et al. The effects of 94% endophyte infected tall fescue hay on growth, serum prolactin, and diet digestibility in early yearling horses. Proceedings 13th Equine Nutr Physiol Syrup 1993; p105. 22. Cymbaluk, NF, GI Christison and DH Leach. Nutrient utilization by limit and ad libitum, fed growing horses. JAnim Sci 1989; 67:414. 23. Aiken, GE, DI Bransby, and CA McCall. Growth of yearling horses compared to steers on high- and Iow-endophyte infected tall fescu e. J Eq Vet Sci 1993; 13:26. 24. Fiorito, IM, LD Bunting, GM Davenport et al. Metabolic and endocrine responses of lambs fed Acremonium coenophia/um. infected or noninfected tall fescue hay at equivalent nutrient intake. J Anim Sci 1991; 62:2108. 25. Hurley, WL, EM Convey, K Leung, et al. Bovine prolactin, TSH, 1"3 and T4 concentrations as affected by tall fescue summer toxicosis and temperature. J Anim Sci 1981; 51:374. 26. Johnson, AL, and BE Becker. Effect of physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare. J. Anita. Sci. 1981; 65:1292. 27. Kosanke, JL WE Loch, K Worthy et al. Effect of toxic tall fescue on plasma prolactin and progesterone in pregnant pony mares. Proceedings 1lth Equine Nutr Physiol Syrup 1989; p663. 28. Hoveland, CS, SP Schmidt, CC King, et al. Steer performance and association of Acremonium coenophia/umfungal endophyte on tall fescue pasture. Argon 1983; 6:28. 29. Osborn, TG, SP Schmidt, DN Marple et al. Effect of consuming fungus-infected and fungus-free tall fescue and ergotamine tartrate on selected physiological variables of cattle in environmentally controlled conditions. JAnim Sci 1992; 70:2501.

iment designed to study the effect of dietary cation-anion balance (DCAB), calculated as meq (Na +K)-(Cl+S)/kgof diet DM, on urine pH, arterial (A) and venous (V) blood pH, blood gases, blood lactic acid concentration (LA) and recove/y heart rates (HR) in horses performing anaerobic work. Diets consisted of a pelleted concentrate of corn, soybean meal and cottonseed hulls fed at a 60:40 ratio with native prairie grass hay. The four treatments were formed by supplementing the base concentrate with calcium chloride, ammonium chloride, sodium bicarbonate or potassium citrate to provide treatment cation-anion balances of 10(Low (L)) 95(Medium Low (ML)), 165(Medium High (MH)) and 295(High (H)). On the last day of each 15 day experimental period, horses performed a standard exercise test (SET) within 4 hrs of the morning feeding. The SET consisted of a 1.64 km sprint at speeds sufficient to elicit heart rates (HR) between 200 and 210 beats per minute (BPM). Seventy-two hours prior to the SET, total urine collections for determination ofpH were taken every four hours. Arterial (A) and Venous (V) blood samples were taken via indwelling catheters preexercise (P), immediately after exercise (0), and at 1, 2, 3, 4, 5, 10, 30, and 60 minutes of recovery. Urine and blood pH and blood bicarbonate concentrations increased significantly with increasing