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Does the protein content in donkey milk remain constant throughout lactation? A team from Liaocheng University in China examined milk from Dezhou donkeys at seven time points—from the first day up to 180 days after foaling. Using a proteomics analysis that simultaneously detects hundreds of proteins, the researchers identified 805 different proteins. Hundreds of these were more or less abundant in mature milk than in colostrum, the first milk after birth.
Laboratory study (proteomics)—it measures relative protein amounts and does not provide information about any effects in humans. Donkey milk is a food.
Study summary
| Feature | Information |
|---|---|
| Original title | Analysis of the Differentially Expressed Proteins in Donkey Milk in Different Lactation Stages |
| Authors | Zhou M., Huang F., Du X., Liu G., Wang C. |
| Journal | Foods, 12(24): 4466 |
| Year | 2023 |
| Country | China |
| Study type | Laboratory analysis of milk proteins (proteomics), cross-sectional study across seven lactation stages |
| Sample | 84 Dezhou donkeys (12 per stage), 4 pooled samples from 3 animals each per stage |
| DOI | 10.3390/foods12244466 |
What question did the researchers ask?
It is known that the composition of milk changes during lactation. However, how the entire protein profile of donkey milk shifts between colostrum and mature milk had hardly been investigated. The researchers wanted to know: Which proteins are in donkey milk, and which become more or less abundant over time?
How was the study conducted?
- Animals: 84 Dezhou donkeys at a farm in Dong’E, all fed the same diet (hay ad libitum plus 2 kg of concentrate per day).
- Samples: Machine-milked in the morning on days 1, 30, 60, 90, 120, 150, and 180 after foaling—12 animals at each time point. Three individual samples were pooled into one pooled sample.
- Measurement: Mass spectrometry using the DIA method, which detects protein fragments and assigns them to a donkey protein database.
- Analysis: A protein was considered "differentially abundant" if p < 0.05 and it showed at least a 1.5-fold change compared to day 1. Functions were assigned using databases (GO, KEGG).
The results
In total, the team identified 4,870 peptides (protein fragments) and 805 proteins. Compared to colostrum, the amount of several hundred proteins changed in each subsequent stage.
| Comparison with day 1 | More abundant | Less abundant |
|---|---|---|
| Day 30 | 161 | 166 |
| Day 60 | 178 | 201 |
| Day 90 | 176 | 188 |
| Day 120 | 177 | 185 |
| Day 150 | 176 | 191 |
| Day 180 | 157 | 216 |
| Days 30–180 combined | 226 | 219 |
According to the text, the main whey proteins—α-lactalbumin, β-lactoglobulin, albumin, and lysozyme—increased until day 60 and then remained roughly constant, while lactoferrin increased until day 180. All whey proteins and caseins were more abundant in mature milk than in colostrum. Among the proteins with the largest changes were an enzyme involved in lipid metabolism (ACSL1, more than 45-fold) and the vitamin B12 transport protein transcobalamin 1 (more than 26-fold). Parts of the complement system, among others, were more abundant in colostrum.
The protein profile of donkey milk differs significantly between colostrum and mature milk—measured as relative amounts, not concentrations.
Critical assessment
- Cross-sectional instead of longitudinal: Different donkeys were sampled for each stage. Differences between the time points could therefore also be differences between animals.
- Pooled samples: Three animals were pooled together, leaving four replicates per stage. The extent of variation among individual animals remains hidden.
- Relative amounts: The method compares signal intensities. A 45-fold change says nothing about how many grams of a protein are in the milk.
- Inconsistencies: For example, in Table 3, day 30 shows "620" in the "Number of DEPs" column, but 161 + 166 equals 327. The method is once incorrectly described as "data-dependent".
- Functions from databases: Entries such as "lupus" or "whooping cough" are database categories, not findings.
Funding, conflicts of interest, and level of evidence
The work was funded by the National Key R&D Program of China and two funding programs of Shandong Province. According to the paper, there are no conflicts of interest. The mass spectrometry was performed as a contract measurement by a laboratory service provider in Beijing.
Level of evidence: Basic research (laboratory analysis of milk proteins)—describes composition, not any effects.
What does this mean for donkey milk as a food?
The study shows that donkey milk is not a constant product: its protein profile depends on how long ago the foal was born. From the protein lists, the authors infer benefits for infants, the sick, older people, and cosmetics. This was not investigated. Donkey milk is not a substitute for breast milk or infant formula.
Our research question: How do we document the lactation stage of our milk so that it is understandable to you?
Frequently asked questions
What is proteomics?
A laboratory method that detects as many proteins as possible in a sample simultaneously. The proteins are broken into fragments, measured in a mass spectrometer, and assigned using a database.
What is the difference between colostrum and mature milk?
Colostrum is the first milk immediately after birth. In this study, it came from the first day; samples from day 30 onwards were considered mature milk.
Does "45-fold" mean that the milk contains 45 times more protein?
No. The number refers to a single protein and describes a ratio of the measured signals compared to colostrum, not an amount in grams.
You can find all the measured values, interactive graphics, and the complete critical assessment on our research page: Study 72: Protein profile across seven lactation stages. Further studies in the research archive.
Zhou M., Huang F., Du X., Liu G., Wang C. (2023). Analysis of the Differentially Expressed Proteins in Donkey Milk in Different Lactation Stages. Foods, 12(24), 4466. DOI: 10.3390/foods12244466
Summarized and reviewed by the DON DONKEY'S editorial team based on the original publication · As of October 2026. This summary does not replace the original work.
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.
