It is impossible for cow to exhale oxygen. Every animal including cow breath in oxygen and breath out CO2 as respiration gaseous exchange. The CO2 is used by plants through what is known as photosynthesis in manufacturing their foods while the bye product of this process is been released by these plants as oxygen which animals use for their respiratory processes.
Yes cows really exhale oxygen, and so do all the mammals including human beings.
Cows do not produce oxygen - they are animals, not plants. Cows, like all other animals, use oxygen and exhale carbon dioxide. However, the lungs of any animal are not efficient at removing all oxygen from air, so some oxygen that was not absorbed is exhaled. This is why mouth-to-mouth resuscitation works.