According to the reasoning given for the Halachos involving the milk of a calf of Avodah Zarah and milk of a calf of an Olah, the milk in a calf of an Eglah Arufah should be Mutar. Actually, the milk is not part of the animal; the milk that was found in the stomach is milk that the animal drank. However, in the case of a calf of Avodah Zarah, it becomes part of the idolatrous sacrifice, because the Nochri is pleased that the sacrifice is fatter, so he includes even what is in the stomach. Obviously, this does not apply to Eglah Arufah.

D. Zupnik