Generally no. The caseins in sheep, goat and cow milk are structurally similar enough that the immune system frequently does not distinguish between them, and cross reactivity in cow milk protein allergy is documented as very high. Allergy guidance is consistent that sheep and goat dairy are not appropriate substitutes for a cow milk allergy. A small minority of people do tolerate them, but establishing that is a supervised clinical question, not something to test at home with a glass of milk.

No. It is graded at the maximum for lactose, the same grade cow milk carries. Measured as a percentage the two are close, but sheep milk is a much more concentrated milk overall, so a glass of it delivers at least as much lactose as the equivalent glass of cow milk. Changing which animal the milk came from does not address lactose intolerance. A lactase enzyme, a genuinely lactose free product or a plant milk are the routes that do.

Traditionally yes. Protected designation feta is made from sheep milk with a limited proportion of goat, pecorino means sheep cheese in Italian, manchego comes from Manchega sheep, and roquefort is a sheep milk blue. This is the practical reason sheep dairy matters even to people who never buy the milk. It also means the trigger picture changes completely once the milk is turned into cheese: ageing strips out most of the lactose but builds up histamine and tyramine, so an aged sheep cheese is close to the opposite trigger profile of the fresh milk.

Fresh sheep milk is, and it is graded low for both histamine and tyramine, alongside clean grades for salicylates, sulfites and free glutamate. Its problems are lactose and casein rather than amines. The caveat is that this only holds while it is fresh milk. Sheep yogurt, and especially the ripened sheep cheeses, gain histamine and tyramine through fermentation and ageing, and aged sheep cheese is graded high for histamine.