Donkey Milk Study: Zamorano-Leonese Milk from Spain (Albertos 2022)

Milk from eight Zamorano-Leonese donkeys contained 1.68% protein, 0.56% fat and 6.6% lactose at 155 kJ/100 g. Polyunsaturated fatty acids made up 27.06% of the fatty acids, oleic acid 25.12%.

The study in brief

• Original title: Characterisation of Zamorano-Leonese Donkey Milk as an Alternative Sustainably Produced Protein Food
• Authors: Albertos I., López M., Jiménez J.-M. et al.
• Journal: Frontiers in Nutrition, 9, 872409 (2022)
• Country: Spain · Study type: Laboratory study

How it was investigated

Raw milk from eight healthy first- or multiparous donkeys of the endangered Spanish Zamorano-Leonese breed (4–8 years, 270 ± 30 kg) from a farm in Sieteiglesias de Tormes (Salamanca, Spain) was investigated. The animals were kept extensively with pasture, alfalfa as desired and an oat supplement. During the first six weeks, the foals received all the milk, after that about 2 L per day were hand-milked twice daily at intervals of around 4 hours.

Important figures

• 8 – Zamorano-Leonese donkeys, sampled on 4 dates (Day 60–120)
• 1.68 % – Protein content (Table 5)
• 0.56 % – Fat content (Table 5)
• 6.6 % – Lactose content
• 155 kJ/100 g – calculated energy content
• 7.16 – pH value of the milk

Results

The milk had a pH value of 7.16 and according to Table 5 contained 90.95% water, 0.36% ash, 1.68% protein, 0.56% fat and 6.6% lactose; the energy content was calculated at 155 kJ/100 g.

The most common fatty acids were oleic acid (25.12%), palmitic acid (21.56%), linoleic acid (14.31%) and α-linolenic acid (12.32%), followed by caproic (5.68%) and lauric acid (5.20%). Saturated fatty acids made up 43.91%, monounsaturated 29.03% and polyunsaturated 27.06%; the ratio of polyunsaturated to saturated was 0.62, the ω6/ω3 ratio was 1.16.

Among the amino acids, glutamic acid (0.35%), aspartic acid and proline (0.16% each) as well as leucine and valine (0.15% each) dominated. In the gel, β-Lactoglobulin, α-Lactalbumin, Casein and Lysozyme were the most abundant protein bands, immunoglobulins and Lactoferrin occurred in smaller proportions.

Limitations of the study

• Small sample, literature comparison: Eight animals from one farm were investigated over two months; the tables state n = 12 without explanation. Comparisons with other breeds and animal species are based exclusively on literature values with different methodology and without statistical testing.
• Swapped values and units: The results text states 0.56% protein and 1.68% fat, Table 5 the other way around. Linoleic acid and α-linolenic acid are assigned to the wrong ω-series respectively. B-vitamins are given in "µL/L", the acidity in the methods section in g/L, in the results per 100 g.
• Contradictory vitamin D data: According to the results section, vitamin D decreased by 10% upon heating, according to the discussion from 1.5 to 0.15 µg/100 mL (around −90%), while at the same time it is described as the most stable vitamin. The values for vitamin A are only available as a figure.
• Recalculated sums: After editorial recalculation, the essential amino acids in Table 2 result in around 44% of the total sum instead of the stated 54%. Monounsaturated and polyunsaturated fatty acids add up to 56.09%, stated are 55.09% unsaturated fatty acids.
• Health claims not investigated: Abstract and conclusion contain health-related statements that were not investigated in this study; only the composition was measured. The statement that copper and selenium were determined in donkey milk for the first time is not true according to the literature.

Level of evidence: Basic research (laboratory) – describes properties of the milk, no statement about effects in humans.

Our assessment

The study describes the composition of raw milk from a small group of Spanish donkeys and contains several numerical and unit errors. No conclusions about health effects or individual trade products can be derived from it.

Source: Albertos I., López M., Jiménez J.-M., Cao M.J., Corell A., Castro-Alija M.J. (2022). Characterisation of Zamorano-Leonese Donkey Milk as an Alternative Sustainably Produced Protein Food. Frontiers in Nutrition. DOI: 10.3389/fnut.2022.872409 · Summarized by the DON DONKEY'S editorial team, as of: October 2026.

End of the study summary. The study was conducted independently by DON DONKEY'S® and does not refer to our products. Our donkey milk is a food.