126. Electrolyte Supplementation for Gestating Beef Cows Under Heat Stress Conditions: Cow Performance and Physiological Responses

Abstract The objective of the study was to evaluate the effects of electrolyte supplementation for cows during late gestation under heat stress conditions on cow performance and physiological responses. Fifty-four fall-calving Angus-cross cows (6 ± 2 yrs of age, ∼ ⅞ Angus and ⅛ Brangus) were stratified by body weight [(BW) = 582 ± 8.43 kg] and body condition score [(BCS) = 5.9 ± 0.1] and allocated into 1 to 10 bermudagrass pastures ‘common and coastal’ (Cynodon dactylon; 3 to 5 ha pastures/4 or 6 cows per pasture) at approximately 90 days pre-partum (d 0). Treatments were randomly assigned to pastures as following: (1) Control: access to water only and (2) Electrolyte supplementation: water fortified with an electrolyte solution (Bovine GoldLyte®, BIOVet, Barneveld, WI), from day 0 to 90 (on average 90 ± 10 d prepartum). Electrolyte solution was diluted directly into the water tanks at a ratio of 25 g per total daily water intake per cow. The electrolyte supplement contained: 12.3% salt, 8.5% sodium, 0.44% magnesium, 26.5% potassium, 300 ppm Cu, 1,400 ppm Zn, 1,400 ppm Fe, 1,400 ppm Mn, and 40 ppm Co, 3,500,000 IU vitamin A, 700,000 IU vitamin D3, 5,000 IU vitamin E, 1,500 mg niacin, and 3,000 mg choline. Cow full BW and BCS were collected on d 0, 28, 56, 84 (near calving) and 168 (start of breeding season). Cow blood samples were collected on d 0, 14, 28, 58, 84, and 168 via jugular vein using commercial heparinized vacuum tubes for plasma harvest and tubes containing no additive for serum harvest (BD Vacutainer, 10 mL; Becton, Dickinson and Company, Franklin Lakes, NJ). Plasma samples were analyzed for measurement of pH, bicarbonate (HCO3⁻), base excess (BE) partial pressure of carbon dioxide (pCO2), partial pressure of oxygen (pO2), sodium (Na+), potassium (K+), ionized calcium (iCa), total concentration of CO2 (tCO2), hematocrit, and hemoglobin using an i-STAT blood analyzer (Zoetis Inc., Parsippany, NJ, USA) with CG8+ cartridges. No effects of treatment, or treatment and day were detected for cow BW, BCS, mineral intake or water intake (P ≥ 0.58). No effects of treatment, or treatment and day were detected for blood pH, pCO2, SO2, iCa, Na, K and hemoglobin (P ≥ 0.16). Cows supplemented with electrolyte tended to have lower hematocrit (P = 0.09), greater blood concentrations of HCO3 (P = 0.06) and greater BE (P = 0.04) compared to control. Electrolyte supplementation improved hydration status and acid-base balance but this did not translate into improvements in performance.