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 x 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 CI" increased (P < .05) during HD. In the third experiment, supplementing the drinking water of chicks with .75% KC1 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. (

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1. Two experiments were conducted on control (intact) and colostomised 4 to 7 week old broilers to evaluate the influence of 24 degrees C, diurnally cycling 24 to 35 degrees C and chronic 35 degrees C ambient temperatures on broiler mineral balance, urinary and faecal mineral excretion and urinary osmolar characteristics. 2. In the first experiment, colostomy had no significant effect on mineral balance. However, broilers exposed to high cycling ambient temperature reduced their retention of phosphorus, potassium, sodium, magnesium, sulphur, manganese, copper and zinc compared with birds housed at 24 degrees C. 3. Despite the minimal effect of high ambient temperature on urine production, minerals excreted disproportionately excreted in urine included potassium, magnesium, phosphorus and sulphur while copper and magnesium were lost primarily via the faeces. 4. In the second experiment, exposure to 35 degrees C increased urine output from 50.7 ml/12 h per kg of body weight at 24 degrees C to 101.3 ml/12 h per kg of body weight and was associated with an increased urine:water ratio and reduced urine osmolality. 5. Reduced urinary chloride and higher potassium, phosphorus, sulphur, sodium, magnesium, calcium and manganese excretion was observed for broilers housed in under high ambient temperatures compared to 24 degrees C. 6. These studies suggest that high ambient temperatures adversely influence mineral metabolism and, furthermore, that the route of excretion varies with the specific mineral and the environmental temperature exposure.

Two experiments were conducted utilizing 4- to 7-wk posthatching Vantress x Arbor Acres male broilers to evaluate heat distress effects on mineral balance partitioned into urinary and fecal loss. In the first study, 8 colostomized and 14 intact birds were allotted to two environmental chambers maintained at either a thermoneutral temperature (24 C) or a cycling temperature heat distress (24 to 35 C) in a switch-back design. Birds were precision-fed 2% of body weight thrice daily to equalize consumption prior to and over each 48-h experimental period. Feces and urine for colostomized birds and total excrement for intact birds were collected and analyzed for mineral content. Averaging across surgical classification, heat distress increased (P less than .05) excretion of K, P, S, Mg, Cu, Mo, and Zn. Despite little heat distress effect on urine production, minerals disproportionately excreted in urine included K, Mg, P, and S; Cu and Mg were lost primarily in feces. In the second study 42 colostomized birds were used to expand the urinary excretion data with the period of heat distress held at 35 C for 36 h. Heat distress increased (P less than .05) urine output from 52.3 +/- 5.3 to 109.9 +/- 4.5 mL/12 h and also increased total urinary K, P, S, Na, Mg, Ca, and Mn excretion. The present data provide evidence that heat distress adversely impacts bird mineral balance and that the excretion route for this effect varies with the specific mineral and possibly, heat distress severity.

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