1. Water and Electrolyte Balance

2. Water 60% - 90% of BW in most life forms 2/3 intracellular fluid 1/3 extracellular fluid –plasma –lymph –interstitial fluid –gut

3. Dehydration Occurs when fluid loss exceeds intake –sweating vs time Fluid lost mostly from ECF –decreased circulating blood volume inadequate tissue perfusion, inefficient transport of substrates to muscle, and elevated HR

4. Dehydration Clinical Signs –persistent elevation of HR and RR –weak pulse –poor capillary refill –muscular weakness, tremors –depression –weak pulse, staggering –muscle cramps Treatment –IV or oral fluids and electrolytes

5. Estimates of Fluid Loss Weigh animal before and after exercise –1 kg = 1 L –loss of 3% of BW = reduce performance –loss of 10% of BW = serious, possibly life threatening

6. Estimates of Fluid Loss Blood analysis –PCV and total plasma proteins rise indicates dehydration –if PCV > 50% indicates hazardous fluid loss

7. Detecting Dehydration Skin pinch test –falls back instantly - normal –2 - 4 sec - moderate –4 -6 sec - severe Capillary refill –press finger on gums above an upper tooth if it takes longer than 2 seconds for blood to return - dehydration

8. Electrolytes Salt that dissociates in solution into electrically charged particles (ions) –cations - positive charge –anions - negative charge Function in fluid balance, transmission of nerve impulses, and muscular activity

9. Electrolytes Na, K, Cl –ICF predominate cation is K –ECF predominate cation is Na –determines water distribution between compartments

10. Electrolyte Replacement Sweat is hypertonic –100 mEq Na:30 mEq K: 130 mEq Cl –small amounts of Ca, Mg, and Zn also lost –Electrolyte loss is easily replaced by dietary means if sweat is sparse or infrequent

11. Electrolyte Replacement Electrolyte supplementation recommended if sweating is frequent –also in hot and humid weather Dietary electrolytes should replace ions lost in sweat in correct proportions –water or feed

12. Dietary Considerations Type of hay –legume vs grass DCAD - dietary cation anion balance –strong and weak cations vs anions

13. Strong Ions Cations –Na + –K + –Ca 2+ –Mg 2+ Anions –Cl - –SO 4 2- –lactic acid

14. Na/K ATPase Pump Lehninger, 1993

15. Stewart (1981) Concept of electrolytes as critical factors in acid/base balance Strong ion difference (SID) –sum of all strong cations minus sum of all strong anions (NA, K, CL, SO 4 2- ) –anions greater = negative SID = H + > OH - –cations greater = positive SID = OH - > H +

16. Stewart (1981) Balance of SID is maintained by the dissociation and reassociation of water

17. H + = Dependent Variable Three independent variables determine the value of H + : –SID –P co2 H increases as P co2 increases –CO 2 acts as an acid –Total concentration of weak acids (plasma proteins) H increases as weak acids increase

18. Regulation of pH Long Term –Kidney regulates electrolytes –primarily Na –GI tract absorption of cations and anions –dependent of needs Rapid –Lung releases CO 2 (HCO 3 -)

19. Altering Acid Base Balance DCAD diets Sodium bicarbonate administration –IV vs GI –effect of other sodium forms Furosemide