Donkey Milk Study: Feed Energy and Milk Yield (Zhao 2026)

Among 24 Dezhou donkeys, the medium energy level (12.4 MJ/kg) yielded the highest amount of milk collected by hand at 0.93 kg/d (high: 0.86, low: 0.75 kg/d). Between the low and medium levels, 176 milk metabolites and 87 whey proteins differed.

The study in brief

• Original title: Integrating Metabolomic and Proteomic Profiles Reveals the Mechanism of Dietary Energy Levels Regulating Milk Performance and Antioxidative Capabilities of Lactating Donkeys
• Authors: Zhao Y., Yue Y., Zhao Z. et al.
• Journal: Antioxidants, 15(5), 528 (2026)
• Country: China · Study type: Animal study

How it was investigated

Feeding trial with 24 lactating Dezhou donkeys (average 29 days of lactation, 4.2 births, 256 ± 34 kg) and their foals at a farm in Inner Mongolia, China. The animals were randomly assigned to three total mixed rations with 13.1 (high, HED), 12.4 (medium, MED) and 11.7 MJ/kg of digestible energy (low, LED) (n = 8 each); the crude protein content was consistently around 14%. After 2 weeks of adaptation, 8 weeks of data collection followed.

Key figures

• 24 – Dezhou donkeys in three energy levels (8 animals each)
• 13.1 / 12.4 / 11.7 MJ/kg – digestible energy of the high, medium and low ration
• 0.93 kg/d – amount of milk collected by hand at medium energy (high 0.86, low 0.75 kg/d)
• 3.71 kg/d – extrapolated daily milk yield (EMY) at medium energy (high 3.43, low 2.99)
• 8.02 vs. 6.80 kg/d – dry matter intake at high vs. low energy
• 1.74 % – protein content of the milk at medium energy (high 1.66 %, low 1.70 %)

Results

The amount of milk collected by hand, extrapolated daily yield, energy- and dry matter-corrected milk, and milk yield per kg of feed intake were highest in the medium energy level (e.g., EMY 3.71 vs. 3.43 or 2.99 kg/d). No interaction between energy level and week of lactation occurred.

The milk composition changed only slightly: protein 1.66–1.74 %, lactose 6.50–6.57 %, dry matter 9.11–9.18 %; fat (0.28–0.32 %) and fat-free dry matter did not differ significantly. The daily amounts were more pronounced, with approximately 12.20 g of fat and 65.86 g of protein at medium energy.

With increasing energy, the dry matter intake increased from 6.80 to 8.02 kg/d, as did the digestibility of dry matter, fat and fiber (NDF). Serum β-hydroxybutyrate and free fatty acids decreased, which the authors interpret as reduced fat mobilization.

Limitations of the study

• Omics only for two groups: The metabolome and proteome were only evaluated for low vs. medium energy; why the high level yielded less milk remains unclear, as the authors themselves admit. For the proteome, a figure legend states n = 4, while the group size for the metabolomic analyses is not explicitly stated.
• Discrepancies between text and table: The results text describes an increase in feed intake followed by a decrease, but Table 2 shows a steady increase (6.80 – 7.20 – 8.02 kg/d). Contrary to the text, lactose was highest in the high level (6.57 %), and the fat content did not differ significantly (p = 0.102 or 0.108), although the abstract and text mention an increase in milk components.
• Rations differed in more than just energy: According to the methods section, the ratio of roughage to concentrate was 30:70; however, according to Table 1, the rations consist of around 70 % millet straw, alfalfa and corn silage. In addition, alfalfa (30.0 vs. 4.5 %), millet straw (26.9 vs. 54.8 %) and crude fat (4.46 vs. 2.82–2.96 %) vary considerably, so energy effects cannot be separated from the effects of the feed components.
• Unusual units and figures: Free fatty acids in the serum are stated as 191–403 mmol/L, which appears about 1000 times too high (probably µmol/L). The values for AST (4.2–5.0 U/L) and ALT (315–378 U/L) seem unusual. For OTU clustering, the methods section states 97 %, the results section 82.35 % similarity, and the number of jointly enriched metabolic pathways is stated once as 75 and once as 73.
• Amount collected by hand and interpretations: The amount collected by hand was measured after the foals were separated after 6 hours; the daily yield is extrapolated. The linking of metabolic pathways with milk yield is based on correlations and enrichment analyses and was not experimentally tested. Effects in humans were not the subject of the study.

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 provides data on the feeding of lactating donkeys and shows that the daily milk yield, above all, and less the percentage composition, changes with feed energy. It complements the already archived study by Hui et al. (2024) from the same research group, which investigated feed energy in late pregnancy and minerals in colostrum. No statements on effects in humans or on commercial products can be derived from this.

Source: Zhao Y., Yue Y., Zhao Z., Chen Y., Yan S., Shi B., Akonyani Z.P. (2026). Integrating Metabolomic and Proteomic Profiles Reveals the Mechanism of Dietary Energy Levels Regulating Milk Performance and Antioxidative Capabilities of Lactating Donkeys. Antioxidants. DOI: 10.3390/antiox15050528 · 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.