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The effects of graded atmospheric O2 concentration (12, 14, 16, 18, and 20.6%) on chick performance and propensity to develop ascites were investigated using commercial male broilers. Chicks were housed in calorimetry chambers for 2 wk with incoming air diluted with N to provide the desired O2 concentration at thermoneutral (TN) ambient temperature. Day 14 body weight, weight gain, feed consumption, and gain-to-feed ratio increased (P < 0.01) as O2 concentration incrementally rose from 12 to 20.6%. Body weight was 138 g for the lowest atmospheric O2 level compared to 371 g for 20.6% O2. The greatest treatment difference occurred between the 12 and 14% O2 concentrations. Growth depression appeared related to feed consumption. Ascites heart ratio (AHR), ascites score (AS), right ventricular mass (RVM), and hematocrit (HCT) all increased (P < 0.01) as O2 concentration decreased. Blood HCT appeared to be a more sensitive indicator of physiological change attributable to atmospheric O2 than AHR, AS, or RVM. The data reported herein suggests that 19.6% atmospheric O2 is the minimal allowable level for housing birds within a relatively stress-free, TN environment to avoid cardiac and HCT changes related to ascites.

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Oxygen level, ambient temperature, and bronchodilator (metaproterenol) effects on performance, ascites incidence, and hematology were investigated using commercial broilers. In Experiment 1, two atmospheric oxygen concentrations (17.6, 20.6%) and two ambient temperatures (26.7, 32.2 C) were examined in a factorial arrangement. The low-oxygen (17.6%), ambient temperature combination (26.7 C) reduced (P < .01) weight gain whereas the high-oxygen ambient temperature combination enhanced (P < .05) such performance. Ascites incidence for chicks housed at 32.2 C was higher (P < .01) for birds maintained at 17.6% oxygen but oxygen concentration did not impact ascites incidence at 26.7 C. White blood cell counts were elevated in the low-oxygen (17.6%) group at both 26.7 and 32.2 C, and hematocrit was positively (R = .84; P < .05) correlated with ascites incidence. In Experiment 2, two oxygen levels (17.6, 20.6%) at constant 26.7 C were examined with and without metaproterenol, a bronchodilator. Metaproterenol reduced (P < .01) ascites incidence at 17.6% oxygen and completely prevented ascites at 20.6% oxygen. The data suggest that therapeutic development may be enhanced by using hematocrit as an indices of ascites and further that studies directed at bronchodilation have potential to alleviate ascites.