Broiler Water Balance and Thermobalance During Thermoneutral and High Ambient Temperature Exposure

Three experiments were conducted to evaluate the influence of heat distress (HD) on broiler water balance and thermobalance criteria including heat production, nonevaporative heat loss, evaporative heat loss (EHL), respiration rate, and apparent respiration efficiency (ARE). In the first experiment, 24 Cobb × Cobb chicks were precision fed feed and water at 3.5 and 8.5% of body weight, respectively, to determine HD effects on combined fecal and urinary water excretion. Exposing chicks to 35 C for 4 h increased water loss by 64% compared with birds housed at 24 C. In the second experiment, 10 precision-fed, colostomized birds were placed in individual respiratory chambers at 49 days of age and sequentially exposed to 24 and 35 C environments; water was consumed ad libitum. Water consumption and excretion increased (P < .05) by 78 and 133%, respectively, during HD. The increased water excretion was largely accounted for via hypo-osmotic urine with increased (P < .05) osmolar and free water clearance. Evaporative cooling (r = .73), ARE (r = .73), urine production (r = .72), and free water clearance (r = .74) were all correlated (P < .05) with water consumption. Plasma Na+ and K+ decreased (P < .05), whereas Cl− increased (P < .05) during HD. In the third experiment, supplementing the drinking water of chicks with .75% KCl increased (P < .05) water consumption by 91%, EHL by 20%, and ARE by 26.7%. The current studies suggest that broiler chicks adjust water consumption and renal handling of water during acute HD and that such handling impacts EHL.