Bevendre

I actually really like this

Regular milking would nullify the magic as it would let the milk be exposed to air long enough for the effects to be negated.  If Raricow’s milk was extracted in a vacuum, like from it being gathered from a milking machine, then the magic would remain and those who drank it could experience changes.

Because there is only a little magic in the milk, it would take a lot for it to have a permanent effect on someone who drinks it, and if someone didn’t drink enough for it to be permanent, then they would go back to the way they were before, though they might be taller, or heavier in one manner or another than before.

That’s the plan at the moment.  Again, magic would only be present if the milk was bottled in certain ways and the magic hadn’t dissipated yet.

The idea, at the moment, is that the infections aspects are only present directly from the tap, so to speak, and that the magic dissipates after being exposed to air for a short time.  It would take a significant amount to fully turn a drinker into a cowpony, and an amount less than full transition would cause temporary changes.

Because the magic would only be present enough to cause changes while still in Rarity, a drinker would have to drink straight from her teats unless the milk was bottled in a near vacuum such as what could be done with a milking machine….

Repeated, or heavy drinking could lead to mild alterations in the drinker’s physique, even if they don’t change.  Kind of like how the use of certain chemicals and hormones in actual milk can cause maturation at ages earlier than were present before their use.

Again, mild.  Very mild.  A full transition to cowpony, and a permanent one, would have to be something not easy to accidentally do.

The milk would be mildly infectious, and take a large amount to fully change a drinker.  If not fully changed, the drinker would revert, more or less, to the way they were before.