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Effects of dietary cation-anion balance on acid base balance and blood parameters in anaerobically exercised horses
Equine Nutrition and PhysiologySociety REFEREEDPAPERSFROMTHE 13THSYMPOSIUM
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
Equine Nutrition and PhysiologySociety REFEREED PAPERS FROM THE 13TH S Y M P O S I U M
DCAB. Horses consuming the most highly cationic diets had improved performance (p <.05) and quicker recovery of HR, even though blood LA concentrations were elevated. Results from this trial further demonstrate that horses ingesting highly anionic diets undergo a nutritionally induced metabolic acidosis. Moreover, when exercised within 4 hours of feeding, horses consuming highly cationic diets achieved greater work output and recovered more quickly due to the buffering effect of the diet. (Key Words: Horse, Exercise, Blood pH, Lactate)
INTRODUCTION
Dietary cation-anion balance (DCAB) has only recently begun to be investigated in the exercising horse. DCAB can be defined quantitatively as the meq [(Na+K)-(CI+S)]/kg dietary dry matter (DM). 1 While sodium, potassium and chloride are the major ions involved in the maintenance of acid-base balance and the regulation of osmotic pressure in body fluids, sulfur has been shown to have similar effects as chloride on acid-base status in lactating dairy cows, 1 and was included in the equation used in this experiment. The effects of DCAB on acid-base physiology has been researched in many species. Milk yields from Holsteins was increased by 8.6% as DCAB increased from -100 to +200 meq/kg DM. 2 Sodium bicarbonate, which increases DCAB, has been shown to significantly increase growth and feed intake when included in diets fed to swine, a Conversely, lowering DCAB in poultry and swine rations has been implicated as a predisposing factor to metabolic bone disorders,a,4 In addition, sedentary horses had significantly decreased blood pH, pC02 and HC03" as DCAB decreased,s Strenuously exercised horses have also been shown to experience a nutritionally induced metabolic acidosis when fed diets with a DCAB near zero. 6 Furthermore, these diets have been shown to significantly lower urine pH and increase calcium excretion in the urine, s,r,s The strong ions in extracellular fluid are the major factors in determining pH and buffering capacity. As sodium and potassium (strong cations) increase the hydrogen ion concentration decreases and pH increases. Conversely, as chloride and sulfate (strong anions) concentrations rise, so does the concentration of hydrogen ions, resultingin a decline in pH. 9 Hence, raising the level ofcations in the diet may increase the buffering capacity of extracellular fluid and prevent a drop in blood pH during strenuous exercise, thereby delaying the onset of fatigue. Therefore, it was the objective of this experiment to study the the effects of varying DCAB from near zero to highly positive on performance, HR during recovery, acid base status, LA concentrations and blood gases in horses doing anaerobic work.
MATERIALS
AND METHODS
Four mature geldings were used in a 4X4 Latin square exper-
Volume 13, Number 10, 1993
Table 1. Composition of treatment diets, as fed basis
Ingredient, % Corn Soybean Meal Cottonseed Hulls Dicalcium Phosphate Umestone, ground Trace Mineral Salt Calcium Chloride Ammonium Chloride Potassium Citrate Sodium Bicarbonate Native Grass Hay DCAB
L 37.1 6.3 14.9 .5 .5 .3 .4 40.0 10
Diet L 37.1 6.5 15.1 .5 .5 .3 40.0 95
MH 37.1 6.8 15.1 .5 .5 .5 40.0 165
I37.C 6.E 13.C .Zl .4 .~= 1.2 .7 40.C 295
iment designed to study the effects of varying DCAB on the aci( base status, work performance, LA concentration and recovery H in anaerobically exercised horses. Four diets providing a DCAI calculated as [(Na + + K +) - (CI" + S-)]/kg diet DM, of 10 (L 95(ML), 165(MH) or 295(1-1)were rotated among the four 15 d~ experimental periods. Diets consisted of a pelleted concentrate corn, soybean meal and cottonseed hulls fed in a 60:40 ratio wil native prairie grass hay (Table 1) at 12 hour intervals in amoun required to maintain constant body weight throughout the exper merit. The four treatments were formed by the addition of calciu] chloride and ammonium chloride to diet ~ calcium chloride to di( ML and potassium citrate and sodium bicarbonate to diet H. Diq MH received no supplementation and served as the control diet. Horses were aerobically conditioned 6d/wk for 4 weeks pri( to the beginning of the experiment using a Long Slow Distan( 0_.SD) training regimen which consisted of a 3.28 km gallop = target heart rates of 160 BPM. During the experimental period horses were exercised 6d/wk alternating LSD with sprint trainin 2d/wk. Sprint training consisted of one .8 km sprint at heart rate above 200 BPM. On the last day of each 15 day experimental perio~ horses performed the SET approximately two hours after tll morning feeding. The SET consisted of a 1.64 km sprint at speec sufficient to elicit heart rates between 200 and 210 BPM. Heart rate were recorded throughout exercise and recovery using a digit= onboard heart rate monitor, a Heart rate data were then downloade to a computer for statistical analysis. Arterial (A) and Venous (V) blood samples were taken vi indwelling catheters pre-exercise (P), immediately after exercis (0), and at 1, 2, 3, 4, 5, 10, 30, and 60 minutes of recovery (REC Samples for analysis of LAwere immediately deproteinized in 10 ~, w/v trichloroacetic acid, centrifuged and the supematant decante and stored. Lactic acid concentrations were determined using a: enzymatic assay.b Further, an additional sample was immediate! analyzed for pH, HC03, pC02, tC02 , t02, BEecf and BEb on a bloo, aUNIQ Computer Instruments Corp. Hempstead, NY bsigma Lactate Procedure No. 826-UV.
55
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Table 2. Effect of Dietary cation-anion balance on urine pH post feeding in anerobically exercised horses.
Time 11 3 7 11 3 7
am* pm pm pm* am am
L 5.88 a 6.03 a 5.89 a 5.97 a 6.01 a 6.14 a
Treatment ML 7.41 b 7.23 b 7.29 b 7.28 b 7.51 b 7.26 b
MH
H
Time
7.51 b 7.55 b 7,30 b 7.47 b 7,54 b 7,32 b
7.91 c 8.02 c 7.83 c 8,03 c 7.97 c 7.93 c
P 0 1 2 3 4 5 10 30 60
*1ndicates feeding time. abCMeans in rows with different superscripts differ (p<.05
gas analyzer, e Seventy two hours prior to the SET, total urine was collected every four hours, using a device suspended from a harness over each geldings back that allowed for normal urination into a collection apparatus. Urine pH was immediately determined on each sample. A 10% aliquot was composited and frozen for later analysis of mineral content, although those data are not presented in this paper. All data were analyzed using a general linear model for repeated measures, with horse, period and treatment as main effects and time as the repeated variable. Treatment least squares means over time were then calculated and tested for significance using the pdiff procedure. 1°
RESULTS AND DISCUSSION
Urine pH (Table 2) was lower (p<.001) for horses consuming diet L and higher (p<.01) for horses on diet H when compared to treatments ML and MH. The effect of treatment over time on urine pH is shown in Table 2. Least squ are means ranged from 5.88 to 6.14 on diet L, 7.23 to 7.51 on diet ML, 7.30 to 7.55 on diet MH and 7.83 to 8.03 on diet H. These data are consistentwith other work reported from horses and dairy cattle,2'5'8again demonstrating the systemic acid generating power of anions, and the systemic base generating power of cations. More specifically, as excess chloride is filtered from blood and excreted in urine, pH declines as the hydrogen ion concentrationincreases in an effort to maintainelectical neutrality.9 Conversely, as excess sodium and potassium are eliminated in the urine, pH increases as the hydoxyl ion concentration increases in response to strong cations in the solution. 9 Excess bicarbonate may also be eliminated via this route which would tend to further increase pH by buffering some of the hydrogen ions present. Differences between A and V blood for the measured parameters were largely insignificant except for P0a and pC02. Therefore, the data presented here are of venous origin. The effect of treatment on venous blood pH and HC0a- values pre- and postexercise are shown in Tables 3 and 4. The DCAB had a significant positive linear Clnstrumentation Laboratory Model 1304, Lexington, Ma.
554
Table 3. Effect of dietary cation-anion balance on venous blood pH pre and post-exercise in horses performing an aerobic exercise
L 7.35 a 7.32 a 7.31 a 7.31 a 7.32 a 7.31 a 7.32 a 7.34 a 7.38 a 7.37 a
ML
Treatment MH
H
7.37 a 7.29 a 7.30 a 7.30 a 7.29 a 7.30 a 7.30 a 7.34 a 7.38 a 7.40 b
7.39 b 7.32 a 7.32 a 7.33 a 7.33 a 7.33 a 7.34 a 7.36 a 7.40 b 7.41 c
7.44 c 7.29 a 7.31 a 7.29 a 7.28 a 7.30 a 7.28 a 7.35 a 7.39 b 7.43 d
a,b,CMeans in rows with different superscripts differ (p<.05).
Table 4. Effect of dietary cation-anion balance on venous blood HCO3 pre- and post-exercise in horses performing anaerobic exer-
cise
Time P 0
1 2 3 4 5 10 30 60
L
ML
26.25 a 19.53 a 19.91 a 20.69 a 20.81 a 21.20 a 21.11 a 22.82 a 24.89 a 24.19 a
27.58 b 19.83 a 19.59 a 19.76 a 19.88 a 20.75 a 20.75 a 23.09 a 26.01 b 27.39 b
Treatment MH 28.70 c 22.52 b 22.38 b 22.88 b 23.50 b 23.54 b 23.25 b 25.45 b 27.48 c 27.82 c
H 29.90 d 21.34 a 20.83 a 21.53 a 21.50 a 22.25 a 22.19 a 22.76 a 26.85 bc 29,26 ~
abCMeans in rows with different superscripts differ (p<.05).
Table 5. Effect of dietary cation-anion balance on SET times
SET Times (min:sec)
L
ML
2:55 a
2:37 ab
Treatment MH 2:31 b
H 2:26bc
abCMeans in rows with different superscripts differ (p<. 10).
effect on both pH and bicarbonate concentration. As the amount of strong cations in the diet increased, pH and bicarbonate concentration also increased. The pH and bicarbonate concentration preexercise and at 60 rain recovery are above normal values and indicate a slightly alkalotic state. Interestingly, the pH and bicarbonate concentrations at the end of exercise up through 10 min recovery
JOURNAL OF EQUINE VETERINARY SCIENCE
Equine Nutrition and PhysiologySociety REFEREEDPAPERSFROMTHE 13THSYMPOSIUM
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Time post-exercise Figure 1. Least squares mean blood lactic acid concentrations preand post-exercise in horses fed diets with varying cation-anion balances. tended to be similar across treatments. Taken alone, these data would seem to indicate that diet had no effect on buffeting capacity of the extracellular fluid. However, blood LA concentrations (Figure 1) were highest at all times for diet H and significantlylower for diet L at times P and 60 REC as compared to diets ML, MH and H. Additionally, horses consuming diet H had a significantly quicker recovery of HR (Figure 2) at 3,4,5,10 and 30 min post exercise even though least squares means for SET times were significantlyfaster (shorter time) for horses consuming diet H as compared to diet L (Table 5). During anaerobic glycolysis, lactate and hydrogen ions are released in stoichiometric equal amounts. When hydrogen ions leave the muscle and enter the blood they are sequestered by both bicarbonate and non-bicarbonate buffering systems. During the SET, mass over distance was held constant since all horses were worked the same distance with the same rider and at a constantheart rate between 200 and 210 BPM throughout the sprint in an effort to standardize work intensity. Therefore, horses consuming diet H may have had higher lactate clearance rates due to increased NaHC0 a concentrations in the blood, facilitating the flow of hydrogen ions out of the cells. 11 This could account for the higher lactate concentrations in the blood even though blood pH was unchanged between treatments. From these data we conclude that the ratio of cations to anions in the diet influencesacid-base balance, and that horses consuming diets with a low DCAB may experience a nutritionally induced metabolic acidosis. Moreover, there appeared to be a buffering effect of the highly cationic diet post exercise, which resulted in improved performance and faster recovery of heart rate even though there was an increase in blood lactate concentrations. These data demonstrate that anaerobic performance may be enhanced through the feeding of highly cationic diets when exercise is performed within 4 hours post feeding, while avoidingthe potential deleterious effects of sodium bicarbonate drenching.
Volume 13, Number 10, 1993
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Time post-exercise Figure 2. Least squares mean heart rates pre- and post-exercise in horses fed diets with varying cation-anion balances.
REFERENCES 1. Tucker WB, Hogue JF, Waterman DF, Swenson TS, Xin Z, Hemken RW, Jackson JA, Adams G D and Spicer LJ. Role of sulphur and chloride in the dietary cation-anion balance equation for lactating dairy cattle. J. Anim. Sci. 1991 ;69:1205. 2. Tucker WB, Harrison GA and Hemken RW. Influence of dietary cation-anion balance on milk, blood, urine and rumen fluid in lactating dairy cattle. J. Dairy Sci. 1988;71:346. 3. Patience JF, Austic RE and Boyd RD.. Effect of dietary electrolyte balance on growth and acid-base status in swine. J. Anim. Sci. 1987;64:457. 4. Austic RE. Excess dietary chloride depressed eggshell quality. Poultry Sci. 1984;63:1773. 5. Baker LA, Topliff DR, Freeman DW, Teeter RG and Breazile JE. Effect of dietary cation-anion balance on acid-base status in horses. J. Equine Vet. Sci. 1992;12:160. 6. Stutz WA, Topliff DR, Freeman DW, Tucker WB and Breazile JE.. Effects of dietary cation-anion balance on blood parameters in exercising horses. J. Equine Vet. Sci. 1992;12:160. 7. Topliff DR, Kennedy MA, Freeman DW, Teeter RG and Wagner DG. Changes in urinary and serum calcium and chloride concentrations in exercising horses fed varying cation-anion balances. Prec. Eleventh Equine Nutr. and Physio. Symp. Stillwater, OK. 1989;1. 8. Wall DL, Topliff DR, Freeman DW, Wagner DG and Breazile JE. Effects of dietary cation-anion balance on urinary mineral excretion in exercised horses. J. Equine Vet. Sci. 1992;12:168. 9. Stewart PA. How to understand acid-base. Elsevier. 1981 North Holland, Inc. New York, NY. 10. SAS Institute Inc. SAS User's Guide: Statistics, Version 5 Edition. 1985 Cary NC:SAS Institute Inc. 11. Beaver WL, Wasserman K and Whipp BJ. Bicarbonate buffering of lactic acid generated during exercise. J Appl Physiol 1986;60:472.
555
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
Equine Nutrition and PhysiologySociety REFEREED PAPERS FROM THE 13TH S Y M P O S I U M
DCAB. Horses consuming the most highly cationic diets had improved performance (p <.05) and quicker recovery of HR, even though blood LA concentrations were elevated. Results from this trial further demonstrate that horses ingesting highly anionic diets undergo a nutritionally induced metabolic acidosis. Moreover, when exercised within 4 hours of feeding, horses consuming highly cationic diets achieved greater work output and recovered more quickly due to the buffering effect of the diet. (Key Words: Horse, Exercise, Blood pH, Lactate)
INTRODUCTION
Dietary cation-anion balance (DCAB) has only recently begun to be investigated in the exercising horse. DCAB can be defined quantitatively as the meq [(Na+K)-(CI+S)]/kg dietary dry matter (DM). 1 While sodium, potassium and chloride are the major ions involved in the maintenance of acid-base balance and the regulation of osmotic pressure in body fluids, sulfur has been shown to have similar effects as chloride on acid-base status in lactating dairy cows, 1 and was included in the equation used in this experiment. The effects of DCAB on acid-base physiology has been researched in many species. Milk yields from Holsteins was increased by 8.6% as DCAB increased from -100 to +200 meq/kg DM. 2 Sodium bicarbonate, which increases DCAB, has been shown to significantly increase growth and feed intake when included in diets fed to swine, a Conversely, lowering DCAB in poultry and swine rations has been implicated as a predisposing factor to metabolic bone disorders,a,4 In addition, sedentary horses had significantly decreased blood pH, pC02 and HC03" as DCAB decreased,s Strenuously exercised horses have also been shown to experience a nutritionally induced metabolic acidosis when fed diets with a DCAB near zero. 6 Furthermore, these diets have been shown to significantly lower urine pH and increase calcium excretion in the urine, s,r,s The strong ions in extracellular fluid are the major factors in determining pH and buffering capacity. As sodium and potassium (strong cations) increase the hydrogen ion concentration decreases and pH increases. Conversely, as chloride and sulfate (strong anions) concentrations rise, so does the concentration of hydrogen ions, resultingin a decline in pH. 9 Hence, raising the level ofcations in the diet may increase the buffering capacity of extracellular fluid and prevent a drop in blood pH during strenuous exercise, thereby delaying the onset of fatigue. Therefore, it was the objective of this experiment to study the the effects of varying DCAB from near zero to highly positive on performance, HR during recovery, acid base status, LA concentrations and blood gases in horses doing anaerobic work.
MATERIALS
AND METHODS
Four mature geldings were used in a 4X4 Latin square exper-
Volume 13, Number 10, 1993
Table 1. Composition of treatment diets, as fed basis
Ingredient, % Corn Soybean Meal Cottonseed Hulls Dicalcium Phosphate Umestone, ground Trace Mineral Salt Calcium Chloride Ammonium Chloride Potassium Citrate Sodium Bicarbonate Native Grass Hay DCAB
L 37.1 6.3 14.9 .5 .5 .3 .4 40.0 10
Diet L 37.1 6.5 15.1 .5 .5 .3 40.0 95
MH 37.1 6.8 15.1 .5 .5 .5 40.0 165
I37.C 6.E 13.C .Zl .4 .~= 1.2 .7 40.C 295
iment designed to study the effects of varying DCAB on the aci( base status, work performance, LA concentration and recovery H in anaerobically exercised horses. Four diets providing a DCAI calculated as [(Na + + K +) - (CI" + S-)]/kg diet DM, of 10 (L 95(ML), 165(MH) or 295(1-1)were rotated among the four 15 d~ experimental periods. Diets consisted of a pelleted concentrate corn, soybean meal and cottonseed hulls fed in a 60:40 ratio wil native prairie grass hay (Table 1) at 12 hour intervals in amoun required to maintain constant body weight throughout the exper merit. The four treatments were formed by the addition of calciu] chloride and ammonium chloride to diet ~ calcium chloride to di( ML and potassium citrate and sodium bicarbonate to diet H. Diq MH received no supplementation and served as the control diet. Horses were aerobically conditioned 6d/wk for 4 weeks pri( to the beginning of the experiment using a Long Slow Distan( 0_.SD) training regimen which consisted of a 3.28 km gallop = target heart rates of 160 BPM. During the experimental period horses were exercised 6d/wk alternating LSD with sprint trainin 2d/wk. Sprint training consisted of one .8 km sprint at heart rate above 200 BPM. On the last day of each 15 day experimental perio~ horses performed the SET approximately two hours after tll morning feeding. The SET consisted of a 1.64 km sprint at speec sufficient to elicit heart rates between 200 and 210 BPM. Heart rate were recorded throughout exercise and recovery using a digit= onboard heart rate monitor, a Heart rate data were then downloade to a computer for statistical analysis. Arterial (A) and Venous (V) blood samples were taken vi indwelling catheters pre-exercise (P), immediately after exercis (0), and at 1, 2, 3, 4, 5, 10, 30, and 60 minutes of recovery (REC Samples for analysis of LAwere immediately deproteinized in 10 ~, w/v trichloroacetic acid, centrifuged and the supematant decante and stored. Lactic acid concentrations were determined using a: enzymatic assay.b Further, an additional sample was immediate! analyzed for pH, HC03, pC02, tC02 , t02, BEecf and BEb on a bloo, aUNIQ Computer Instruments Corp. Hempstead, NY bsigma Lactate Procedure No. 826-UV.
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Table 2. Effect of Dietary cation-anion balance on urine pH post feeding in anerobically exercised horses.
Time 11 3 7 11 3 7
am* pm pm pm* am am
L 5.88 a 6.03 a 5.89 a 5.97 a 6.01 a 6.14 a
Treatment ML 7.41 b 7.23 b 7.29 b 7.28 b 7.51 b 7.26 b
MH
H
Time
7.51 b 7.55 b 7,30 b 7.47 b 7,54 b 7,32 b
7.91 c 8.02 c 7.83 c 8,03 c 7.97 c 7.93 c
P 0 1 2 3 4 5 10 30 60
*1ndicates feeding time. abCMeans in rows with different superscripts differ (p<.05
gas analyzer, e Seventy two hours prior to the SET, total urine was collected every four hours, using a device suspended from a harness over each geldings back that allowed for normal urination into a collection apparatus. Urine pH was immediately determined on each sample. A 10% aliquot was composited and frozen for later analysis of mineral content, although those data are not presented in this paper. All data were analyzed using a general linear model for repeated measures, with horse, period and treatment as main effects and time as the repeated variable. Treatment least squares means over time were then calculated and tested for significance using the pdiff procedure. 1°
RESULTS AND DISCUSSION
Urine pH (Table 2) was lower (p<.001) for horses consuming diet L and higher (p<.01) for horses on diet H when compared to treatments ML and MH. The effect of treatment over time on urine pH is shown in Table 2. Least squ are means ranged from 5.88 to 6.14 on diet L, 7.23 to 7.51 on diet ML, 7.30 to 7.55 on diet MH and 7.83 to 8.03 on diet H. These data are consistentwith other work reported from horses and dairy cattle,2'5'8again demonstrating the systemic acid generating power of anions, and the systemic base generating power of cations. More specifically, as excess chloride is filtered from blood and excreted in urine, pH declines as the hydrogen ion concentrationincreases in an effort to maintainelectical neutrality.9 Conversely, as excess sodium and potassium are eliminated in the urine, pH increases as the hydoxyl ion concentration increases in response to strong cations in the solution. 9 Excess bicarbonate may also be eliminated via this route which would tend to further increase pH by buffering some of the hydrogen ions present. Differences between A and V blood for the measured parameters were largely insignificant except for P0a and pC02. Therefore, the data presented here are of venous origin. The effect of treatment on venous blood pH and HC0a- values pre- and postexercise are shown in Tables 3 and 4. The DCAB had a significant positive linear Clnstrumentation Laboratory Model 1304, Lexington, Ma.
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Table 3. Effect of dietary cation-anion balance on venous blood pH pre and post-exercise in horses performing an aerobic exercise
L 7.35 a 7.32 a 7.31 a 7.31 a 7.32 a 7.31 a 7.32 a 7.34 a 7.38 a 7.37 a
ML
Treatment MH
H
7.37 a 7.29 a 7.30 a 7.30 a 7.29 a 7.30 a 7.30 a 7.34 a 7.38 a 7.40 b
7.39 b 7.32 a 7.32 a 7.33 a 7.33 a 7.33 a 7.34 a 7.36 a 7.40 b 7.41 c
7.44 c 7.29 a 7.31 a 7.29 a 7.28 a 7.30 a 7.28 a 7.35 a 7.39 b 7.43 d
a,b,CMeans in rows with different superscripts differ (p<.05).
Table 4. Effect of dietary cation-anion balance on venous blood HCO3 pre- and post-exercise in horses performing anaerobic exer-
cise
Time P 0
1 2 3 4 5 10 30 60
L
ML
26.25 a 19.53 a 19.91 a 20.69 a 20.81 a 21.20 a 21.11 a 22.82 a 24.89 a 24.19 a
27.58 b 19.83 a 19.59 a 19.76 a 19.88 a 20.75 a 20.75 a 23.09 a 26.01 b 27.39 b
Treatment MH 28.70 c 22.52 b 22.38 b 22.88 b 23.50 b 23.54 b 23.25 b 25.45 b 27.48 c 27.82 c
H 29.90 d 21.34 a 20.83 a 21.53 a 21.50 a 22.25 a 22.19 a 22.76 a 26.85 bc 29,26 ~
abCMeans in rows with different superscripts differ (p<.05).
Table 5. Effect of dietary cation-anion balance on SET times
SET Times (min:sec)
L
ML
2:55 a
2:37 ab
Treatment MH 2:31 b
H 2:26bc
abCMeans in rows with different superscripts differ (p<. 10).
effect on both pH and bicarbonate concentration. As the amount of strong cations in the diet increased, pH and bicarbonate concentration also increased. The pH and bicarbonate concentration preexercise and at 60 rain recovery are above normal values and indicate a slightly alkalotic state. Interestingly, the pH and bicarbonate concentrations at the end of exercise up through 10 min recovery
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Time post-exercise Figure 1. Least squares mean blood lactic acid concentrations preand post-exercise in horses fed diets with varying cation-anion balances. tended to be similar across treatments. Taken alone, these data would seem to indicate that diet had no effect on buffeting capacity of the extracellular fluid. However, blood LA concentrations (Figure 1) were highest at all times for diet H and significantlylower for diet L at times P and 60 REC as compared to diets ML, MH and H. Additionally, horses consuming diet H had a significantly quicker recovery of HR (Figure 2) at 3,4,5,10 and 30 min post exercise even though least squares means for SET times were significantlyfaster (shorter time) for horses consuming diet H as compared to diet L (Table 5). During anaerobic glycolysis, lactate and hydrogen ions are released in stoichiometric equal amounts. When hydrogen ions leave the muscle and enter the blood they are sequestered by both bicarbonate and non-bicarbonate buffering systems. During the SET, mass over distance was held constant since all horses were worked the same distance with the same rider and at a constantheart rate between 200 and 210 BPM throughout the sprint in an effort to standardize work intensity. Therefore, horses consuming diet H may have had higher lactate clearance rates due to increased NaHC0 a concentrations in the blood, facilitating the flow of hydrogen ions out of the cells. 11 This could account for the higher lactate concentrations in the blood even though blood pH was unchanged between treatments. From these data we conclude that the ratio of cations to anions in the diet influencesacid-base balance, and that horses consuming diets with a low DCAB may experience a nutritionally induced metabolic acidosis. Moreover, there appeared to be a buffering effect of the highly cationic diet post exercise, which resulted in improved performance and faster recovery of heart rate even though there was an increase in blood lactate concentrations. These data demonstrate that anaerobic performance may be enhanced through the feeding of highly cationic diets when exercise is performed within 4 hours post feeding, while avoidingthe potential deleterious effects of sodium bicarbonate drenching.
Volume 13, Number 10, 1993
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REFERENCES 1. Tucker WB, Hogue JF, Waterman DF, Swenson TS, Xin Z, Hemken RW, Jackson JA, Adams G D and Spicer LJ. Role of sulphur and chloride in the dietary cation-anion balance equation for lactating dairy cattle. J. Anim. Sci. 1991 ;69:1205. 2. Tucker WB, Harrison GA and Hemken RW. Influence of dietary cation-anion balance on milk, blood, urine and rumen fluid in lactating dairy cattle. J. Dairy Sci. 1988;71:346. 3. Patience JF, Austic RE and Boyd RD.. Effect of dietary electrolyte balance on growth and acid-base status in swine. J. Anim. Sci. 1987;64:457. 4. Austic RE. Excess dietary chloride depressed eggshell quality. Poultry Sci. 1984;63:1773. 5. Baker LA, Topliff DR, Freeman DW, Teeter RG and Breazile JE. Effect of dietary cation-anion balance on acid-base status in horses. J. Equine Vet. Sci. 1992;12:160. 6. Stutz WA, Topliff DR, Freeman DW, Tucker WB and Breazile JE.. Effects of dietary cation-anion balance on blood parameters in exercising horses. J. Equine Vet. Sci. 1992;12:160. 7. Topliff DR, Kennedy MA, Freeman DW, Teeter RG and Wagner DG. Changes in urinary and serum calcium and chloride concentrations in exercising horses fed varying cation-anion balances. Prec. Eleventh Equine Nutr. and Physio. Symp. Stillwater, OK. 1989;1. 8. Wall DL, Topliff DR, Freeman DW, Wagner DG and Breazile JE. Effects of dietary cation-anion balance on urinary mineral excretion in exercised horses. J. Equine Vet. Sci. 1992;12:168. 9. Stewart PA. How to understand acid-base. Elsevier. 1981 North Holland, Inc. New York, NY. 10. SAS Institute Inc. SAS User's Guide: Statistics, Version 5 Edition. 1985 Cary NC:SAS Institute Inc. 11. Beaver WL, Wasserman K and Whipp BJ. Bicarbonate buffering of lactic acid generated during exercise. J Appl Physiol 1986;60:472.
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