Donkey milk in history: Galen

Around 175 AD, the physician Galen recommended that older people drink goat's milk and donkey's milk alternately: donkey's milk was thin and rich in whey, while goat's milk was of medium consistency.

The source in brief

• Author: Galen of Pergamon (Galen)
• Work: De sanitate tuenda (On the Preservation of Health)
• Location: Book V, Chapter 7; Kühn edition, Vol. VI, p. 346
• Time and place: around 175 AD · Roman Empire (Rome)
• Type of source: Ancient medical text

The original wording

Satiusque fuerit alterum capram, alterum asinam esse, earumque lacte alternis vicibus uti; quippe asinae lac tenue serosumque est, caprae mediocris substantiae est.

It would be better if one animal were a goat and the other a donkey, and their milk were used alternately; for donkey's milk is thin and rich in whey, while goat's milk is of medium consistency.

Latin, Kühn VI 346 (Latin translation of the edition)

τὸ δ᾽ ὄνειον ἀσφαλέστερον πάντη.

But donkey's milk is the safer choice in every respect.

Ancient Greek, Kühn VI 346

German translation: own, free translation by the DON DONKEY'S editorial team.

Background

Galen of Pergamon (129 – around 216 AD) was the personal physician to several Roman emperors and one of the influential physicians of antiquity. His writings shaped medicine in Europe and the Arab world until the early modern period.

"De sanitate tuenda" in six books is a treatise on healthy living. The fifth book deals with the lifestyle of older people. In it, Galen discusses foods according to their digestibility, including an extensive discussion of milk.

What the source reports

Galen begins with examples: A farmer had nourished himself mainly on milk until he was over a hundred years old; others, however, who imitated him, had tolerated the milk poorly and complained of pressure in the upper abdomen. Milk was therefore not suitable for everyone.

Anyone who wished to use milk should pay attention to the animal: It had to be in the best age and well nourished, and must not eat sharp or bitter fodder. Galen advised keeping a goat and a donkey and drinking their milk alternately.

To support this, Galen compares both types of milk: Donkey's milk was thinner and richer in whey, while goat's milk was of medium thickness. Goat's milk therefore nourished more, while donkey's milk was the safer choice in every respect: It passed more quickly through the body, caused hardly any flatulence, and did not curdle in the stomach, especially if some salt and honey were added.

Numbers and facts

• p. 346 – Page of the passage in Kühn's Galen edition, Vol. VI
• 2 – Types of milk Galen compared (goat, donkey)
• 6 – Books of De sanitate tuenda
• around 175 AD – approximate time of origin

Critical assessment

• Weighing up instead of generalizing: Galen does not recommend milk generally. He explicitly mentions cases in which it was poorly tolerated, and links his advice to the animal, the fodder, and the individual person.
• Agreement with Aristotle: Galen's description of donkey's milk as thin and rich in whey agrees with Aristotle. Today's analyses examine the composition of donkey's milk more closely (cf. archive studies 71 and 97).
• Medical framework: Galen's judgments are based on humoral theory and empirical knowledge. They have not been checked according to today's standards.
• Today's assessment: No health effects of donkey's milk can be derived from the passage. It documents how a leading ancient physician distinguished between types of milk according to their digestibility.

Our assessment

We like Galen because he is nuanced: He compares goat's milk and donkey's milk dispassionately and does not hide that milk does not suit everyone. We read this as medical history, not as dietary advice.

Proof: Greek text with Latin translation, edition C. G. Kühn, Vol. VI, p. 346 (Internet Archive) · Summarized by the DON DONKEY'S editorial team, as of November 2026.

End of the source summary. The source does not refer to DON DONKEY'S® or our products. Our donkey's milk is a food.