The production of hay milk is strictly regulated
and all rules are summarised in an EU directive. For example: The proportion of roughage in the annual ration must amount to at least 75% of the dry weight. Roughage is dry, highly fibrous feed (e.g. hay, straw, chaff). There is absolutely no silage
(fermented feed) in the diet.
Compliance with the specification of production is monitored by independent and authorized inspection bodies.
The full set of regulations can be found on the European Union website: EU Implementing regulation 2016/304
The European Union has confirmed hay milk with the "TSG", or "traditional speciality guaranteed" seal of quality.