An accurate determination of myoglobin (Mb) oxygen affinity (P-50) can be difficult due to hemoglobin (Hb) contamination and autoxidation of Mb to metMb which is incapable of binding oxygen. To reduce Mb autoxidation, P-50 is often measured at refrigerated temperatures. However, the temperature dependent shift in Mb oxygen affinity results in a greater oxygen affinity (lower P-50) at colder temperatures than occurs at physiological temperature (ca. 37-39 degrees C) for birds and mammals. Utilizing the temperature dependent pH shift of Tris buffer, we developed novel methods to extract Mb from vertebrate muscle samples and remove Hb contamination while minimizing globin autoxidation. Cow (Bos taurus) muscle tissue (n = 5) was homogenized in buffer to form a Mb solution, and Hb contamination was removed using anion exchange chromatography. A TCS Hemox Blood Analyzer was then used to quickly generate an oxygen dissociation curve for the extracted Mb. The oxygen affinity of extracted bovine Mb was compared to commercially available horse heart Mb. The oxygen affinity of extracted cow Mb (P-50 = 3.72 +/- 0.16 mmHg) was not statistically different from commercially prepared horse heart Mb (P-50 = 3.71 +/- 0.10 mmHg). With high yield Mb extraction and fast generation of an oxygen dissociation curve, it was possible to consistently determine Mb P-50 under physiologically relevant conditions for endothermic vertebrates. (C) 2014 Elsevier Inc. All rights reserved.