Donkey Milk Study: Feed Oils and Lipid Profile (Ren 2025)

27 donkeys received soybean, linseed, or palm oil in their feed for four weeks. 725 lipids and 391 volatile compounds were identified in the milk; the fat content in the linseed oil group was 0.07%, compared to 0.25–0.26%.

The study in brief

• Original title: Dietary Oils Alter Lipid and Volatile Compound Profiles of Donkey Milk: A Comprehensive Analysis
• Authors: Ren W., Sun L., Du X. et al.
• Journal: Food Science & Nutrition, 13(5), e70291 (2025)
• Country: China · Study type: Animal study

How it was investigated

27 lactating four-year-old donkeys from a herd in Shandong Province, China, were selected based on uniform body weight, parity, and fertility, and randomly assigned to three groups of nine animals each. The ration consisted of 80% wheat straw plus corn, soybean, mineral and vitamin premix, and contained 1% soybean oil (SO), linseed oil (LO), or palm oil (PO). The animals were fed twice daily for four weeks in July and August (30 ± 5 °C).

Key figures

• 27 – lactating donkeys in three groups of 9 animals
• 1 % – proportion of soybean, linseed, or palm oil in the ration over 4 weeks
• 14.52 % – α-linolenic acid in the feed fat of the linseed oil group (soybean 2.47%, palm 2.55%)
• 0.07 % – milk fat in the linseed oil group (soybean 0.25%, palm 0.26%)
• 1.81 / 1.65 / 1.38 % – protein in the milk: soybean / linseed / palm
• 725 – identified lipids from 21 subclasses

Results

The milk composition differed depending on the feed oil: the fat content in the linseed oil group was 0.07%, thus lower than in the soybean (0.25%) and palm oil (0.26%) groups. Protein (1.81%), dry matter (9.43%), and lactoferrin were highest in the soybean group, lactose in the palm oil group (6.80%).

In the palm oil group, saturated (0.28%) and polyunsaturated fatty acids (0.24%) were higher, while saturated fatty acids were lowest in the linseed oil group (0.08%). Urea and freezing point depression were lower in the palm oil group.

In total, 725 lipids from 21 subclasses were identified, including 411 triglycerides, 84 diglycerides, 46 phosphatidylcholines, and 38 phosphatidylethanolamines. By relative amount, triglycerides made up around 91–92% in all groups. Diglycerides were higher in the soybean group (5.14% compared to 4.39–4.42%), sphingolipids (Sph) and AcHex in the palm oil group.

Limitations of the study

• Short trial under summer conditions: Nine animals from one herd in each group were sampled once after four weeks; baseline values and a group without oil addition are missing. The trial took place in July and August at 30 ± 5 °C, which may have additionally influenced milk production.
• Implausible units: Lactoferrin is stated in Table 2 as 9.34–9.78% and equated to "9.0–10.0%" in the discussion; this is orders of magnitude above usual values for donkey milk. The freezing point depression (443–458) is given in °C, presumably millidegrees are meant; the unit for urea is missing.
• Text contradicts tables: The text states the fat content of the palm oil group is higher than in the soybean and linseed oil groups; according to Table 2, palm (0.26%) and soybean (0.25%) are equal. The discussion describes Sph higher in the soybean and linseed oil group than in the palm oil group, Table 3 shows the opposite (0.2096 compared to 0.0839 and 0.1148).
• Counts are inconsistent: The broken-down classes of the 110 different lipids result in 108. The pairwise comparisons exceed the total number (soybean vs. palm: 128 lipids and 79 volatile compounds compared to 110 and 70 overall, respectively). The abstract and discussion mention 90% and 88.2% unsaturated lipids, respectively; the abstract and highlights mention 20 and eight metabolic pathways, respectively.
• Interpretations and study relevance: Statements in the discussion about the effects of diglycerides or unsaturated fatty acids come from the literature and were not investigated; odor assessments are completely missing. The same ethics approval number as in a parallel published soybean/linseed oil study by the group (28 three-year-old animals, four groups) is cited; the number of animals, age, and groups differ, and no data overlap is apparent.

Level of evidence: Animal study – describes measured values in the studied animals and their milk, no statement on effects in humans.

Our assessment

The study documents that even 1% oil in the ration leads to measurable differences in the lipid and aroma profile of the milk. Due to implausible unit specifications, several contradictions between the text and tables, and the short trial duration, the results should be read as indications; they cannot be extrapolated to taste, effect, or individual commercial products.

Source: Ren W., Sun L., Du X., Chen Y., Chen Y., Liang H., Kou X., Khan M.Z., Wang C., Li M. (2025). Dietary Oils Alter Lipid and Volatile Compound Profiles of Donkey Milk: A Comprehensive Analysis. Food Science & Nutrition. DOI: 10.1002/fsn3.70291 · 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.