Each mammal's milk is different from every other mammal's milk. They vary in the amount and the composition of the fats, carbohydrates, and proteins they contain. That last is extremely important. It's not just that milk contains two main types of proteins, casein and whey, but that each are whole families of related proteins. Allergies, however, can be extremely specific. A reaction can occur to one type of casein but not another.
And that means that people who are allergic to the specific protein variations (technically known as protein fractions) in cow's milk may not be allergic to the different set of proteins in another mammal's milk.
In Italy, the researchers went to a showing of Shrek 3 and had an aha! moment. Maybe not, but they decided to investigate the allergenicity of donkey milk anyway.
And it worked.
"Adequacy and tolerance to ass's milk in an Italian cohort of children with cow's milk allergy," by Riccardina Tesse, Claudia Paglialunga, Serena Braccio and Lucio Armenio. Italian Journal of Pediatrics 2009, 35:19doi:10.1186/1824-7288-35-19
I found an article about it on Horsetalk.co.nz. (Horsetalk? Donkeys? Makes perfect sense to me.)
Thirty children with a suspected cow's milk allergy, aged six months to 11 years, were enrolled in the study.
They underwent skin-prick tests and a double-blind, placebo-controlled food challenge to confirm their cow's milk allergy.
Testing confirmed the existence of an allergic response in 25 of the children.
Each was then openly given fresh donkey's milk.
Specific biomarkers were checked to evaluate the health of the children before including donkey milk in their diet. The participants were checked again 4-6 months after going on to donkey's milk.
The researchers found that 24 out of 25 subjects (96%) tolerated donkey milk, with their blood biomarkers unchanged after incorporating it in their diet.
The children in the study had no more than moderate allergy. None of the test subjects with severe allergy agreed to take part in the study.
Where you would get donkey milk here is hard to say. I suppose you could talk to your local Democratic Party headquarters, but that's just a joke. I will hope that elephant milk will be tested next, for proper bipartisanship.