Equine Breathing is a variant of Buteyko Breathing.
Equine Breathing reduces the volume of air breathed which enables carbon dioxide levels to build back up. The more carbon dioxide is available the longer the cells can keep going on aerobic (oxygen based) respiration rather than having to switch to damaging and less efficient anaerobic respiration. Horses with better breathing (and therefore higher levels of carbon dioxide) will be able to maintain aerobic respiration for longer than horses with poor breathing (lower levels of carbon dioxide) during strenuous exercise and will therefore recover more quickly.
The fact that reducing the volume of air breathed also reduces the amount of oxygen intake is not addressed. Nonetheless, Equine Breathing is claimed to treat (seemingly on the basis of one case study):
arthritis, respiratory problems, sarcoids, mud fever or rain scald, behavioural problems such as wind sucking, anxiety or head shaking[,] receding gums, a hay allergy, difficulty keeping condition, high worm count[,] sarcoids, lameness, separation anxiety, attention deficit, phobias. It means that horse owners can heal their horses from even severe 'incurable' symptoms.
You can achieve all this with the "1N" method (that's technical talk for "one nostril"). Hold your hand over one of your horse's nostrils for five minutes, so he can only breath through the other nostril. Swap nostrils and block the second nostril for five minutes. Easy! Amazing! (A slightly longer, PDF, explanation is available here).
Equine Breathing has a direct and immediate physiological effect on the horse's body. Although gentle, 1N can have profound effects.
EoR wonders how this increases CO2 levels in relation to O2 levels, since the ratio of gases is not changed, only the volume of atmosphere.
This is, of course, just an attempt at hypoventilation:
Hypoventilation is breathing that is not adequate to meet the needs of the body (too shallow or too slow), or reduced lung function. Hypoventilation results in inadequate oxygenation of the blood due to a rise in the carbon dioxide level.
So, where are the studies that show blocking a horse's nostril increases CO2 concentration in the blood (let alone has all the miraculous curative properties claimed for it)? How is this "better" breathing maintained when the nostril is not blocked? At what level is inadequate oxygenation a concern?
EoR would like answers to these questions before he even considers the effectiveness of this in treating sarcoids, mud fever (a bacterial skin infection), levels of worm infestations, attention deficit (EoR wasn't even aware there was an equine variant of ADHD) or phobias.
EoR also wonders why it's not called Equine Buteyko? Were there copyright reasons? "Equine Breathing" is too twee. All equines breathe. The promoter of this woo needs something catchy to sell it under. Something like "Enhanced Equine Breathing" or "Equine Quantum Breathing". EoR himself is developing a variant (and therefore much stronger, much gentler and much more effective since all renamed woo therapies are automatically better) called Quantum Enhanced Equine Respiration. So, if you want to QUEER your horse's breathing, give EoR a call (it's okay, the special enhanced woo waves can be sent without EoR attending). The magic healing breath of life will be sent as soon as EoR receives your credit card number.