Donkey Milk Study: Methionine and Milk Yield (Huang 2024)

With 5 g of methionine per day, the yield of milk collected was 1.72 kg compared to 1.15 kg without supplementation; 15 g/d showed no dose effect (1.14 kg). 568 metabolites were identified in the milk, 41 of which differed between the groups.

The study in brief

• Original title: Effects of Methionine on Milk Performance and Milk Constituents of Lactating Donkeys
• Authors: Huang F., Du X., Ma Z. et al.
• Journal: Animals, 14(20), 3027 (2024)
• Country: China · Study type: Animal study

How the study was conducted

Feeding trial with 18 healthy, multiparous Dezhou donkeys (average 71 days of lactation, 273 ± 30 kg) and their foals on a farm in Liaocheng (Shandong, China). Six mare-foal pairs each received 0 g (control), 5 g (M1), or 15 g of methionine per day in addition to 6 kg of grass hay and 2.5 kg of concentrate per animal. The trial lasted 5 weeks, including 1 week of pre-feeding.

Key figures

• 18 – multiparous Dezhou donkeys in three groups (6 each)
• 0 / 5 / 15 g/d – methionine supplementation per animal per day
• 1.72 kg – yield of milk collected with 5 g of methionine (control 1.15 kg, 15 g: 1.14 kg)
• 25.18 vs. 16.62 g – milk protein quantity with 5 g of methionine vs. control
• 110.26 vs. 73.10 g – lactose quantity with 5 g of methionine vs. control
• 1.71 vs. 1.51 % – milk protein content with 15 g of methionine vs. control

Results

With 5 g of methionine per day, the yield of milk collected was 1.72 kg, significantly higher than the control (1.15 kg) and the 15-g group (1.14 kg). The foals in the 15-g group gained 19.6 kg more than the control (15.1 kg); the 5-g group was in between (19.4 kg).

Only minor differences were observed in the contents: dry matter (9.27 and 9.32 vs. 9.04 %), lactoferrin (0.097 vs. 0.094 g/L), and polyunsaturated fatty acids were higher in both methionine groups, while the protein content was only higher in the 15-g group (1.71 vs. 1.51 %). There were no significant differences in fat, lactose, and urea content.

Due to the higher milk yield, the daily amounts of protein (25.18 vs. 16.62 g), lactose (110.26 vs. 73.10 g), fat, dry matter, and fat-free dry matter in the 5-g group were also higher than those of the control.

Limitations of the study

• Small pilot study: Six animals per group were examined for only 5 weeks, and milk and blood were sampled only once at the end of the trial without baseline values. The authors themselves refer to the work as a pilot study in the discussion.
• Abstract goes beyond the tables: According to the abstract, 5 g of methionine increased the protein and fat contents; according to Table 3, the protein content at 5 g does not differ from the control (1.55 vs. 1.51 %), and the fat content does not differ in any group (p = 0.08). The abstract and conclusion state that L-ascorbate is increased, while Table 7 shows it as lower at 15 g (factor 0.43); D-glutamine and L-lysine do not appear in any table.
• Units of component quantities: The lactoferrin quantity (10.35 mg with 1.15 kg of milk and 0.094 g/L) is calculated to be about 10 times too low, and the quantity of polyunsaturated fatty acids is given in mg instead of g. The fat quantity of the control (1.88 g) does not match 1.15 kg × 0.40 % (around 4.6 g); the milk yield has no time reference.
• Dosage and information in the methods section: Table 1 lists the methionine addition as 0.002 % or 0.006 % of the concentrate, which would correspond to only 0.05 or 0.15 g with 2.5 kg instead of 5 or 15 g. The animal trial approval carries the same number as another study by the working group (Zhou et al. 2025).
• Metabolite assignment and interpretations: Among the metabolites listed as different are several compounds that appear synthetic, whose assignment to milk or serum is not plausible; the annotation of untargeted LC-MS data should be read with caution here. The authors' interpretations regarding suitability for infant food were not investigated; effects in humans were not the subject of the study.

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

Our assessment

The study shows above all an effect on the yield of milk collected with 5 g of methionine, while the percentage composition of the milk changed only slightly. Due to the small groups and several inconsistencies between the text and tables, the results should be considered preliminary.

Source: Huang F., Du X., Ma Z., Liu G., Wang C., Zhou M. (2024). Effects of Methionine on Milk Performance and Milk Constituents of Lactating Donkeys. Animals. DOI: 10.3390/ani14203027 · Summarized by the DON DONKEY'S editorial team, as of October 2026.

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