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15 Nordestino donkey mares: After 4 h of udder filling, an average of 312.38 g of milk was milked, after 2 h 188.76 g. Milking three times resulted in 724 g per day (median), compared to 131 g with milking once.
Animal study on animals and their milk – no statement about an effect in humans. Donkey milk is a food.
Study summary
| Feature | Information |
|---|---|
| Original title | Milking frequency and the effect of fill time on the production and conformation in Nordestino ecotype donkeys |
| Authors | Santana K. C., Lucena J. E. C., Pinheiro A. K. S. et al. |
| Journal | Veterinary and Animal Science, Volume 33, Article 100717 |
| Year | 2026 |
| Country | Brazil |
| Study type | Animal study |
| DOI | 10.1016/j.vas.2026.100717 |
How the study was conducted
15 mares of the Brazilian Nordestino ecotype (3–7 years, 185 ± 30 kg) received a controlled ration of 60% Tifton-85 hay and 40% concentrate. In Trial 1 (lactation days 15–75, block design), the foals were separated from the mares 2, 3, or 4 hours before hand milking, for 20 days per interval; milk yield and ten udder and teat measurements were recorded.
In Trial 2 (lactation days 76–135), 5 mares each were milked once, twice, or three times daily; milk yield and somatic cell count (flow cytometry, at the beginning and end) were recorded.
The most important figures
| Value | Meaning |
|---|---|
| 15 mares | Nordestino donkey mares, 3–7 years, average weight 185 ± 30 kg |
| 188.76 g | average milk yield per milking after 2 h of udder filling |
| 249.34 g | average milk yield per milking after 3 h of udder filling |
| 312.38 g | average milk yield per milking after 4 h of udder filling (rounded to 313 g in the abstract) |
| 25.80 → 27.01 cm | Udder length at 2 h vs. 4 h filling time |
| 6.44 → 7.19 cm | Diameter of the right teat at 2 h vs. 4 h filling time |
| r = 0.6425 | highest correlation coefficient: length of the left teat and milk yield (2 h) |
| 131 g | Median of the daily milk yield with milking once |
The results
With a longer udder filling time, the milked milk yield increased: 188.76 g after 2 h, 249.34 g after 3 h, and 312.38 g after 4 h (all significantly different). The authors describe this as an increase of 40%; mathematically, the 4-h value is about 65% higher than the 2-h value.
The udder and teats also changed: the udder length increased from 25.80 to 27.01 cm, the diameter of the right teat from 6.44 to 7.19 cm, and the left from 6.41 to 7.04 cm. Only the udder height above the ground decreased slightly (from 66.65 to 66.25 cm).
Most udder and teat measurements correlated positively with milk yield. The highest coefficients were shown by the teat length (left up to r = 0.6425) and the udder length (up to r = 0.5317); the udder width did not correlate significantly at any filling time.
In Trial 2, the median of the daily milk yield was 131 g (once daily), 250 g (twice), and 724 g (three times); the authors state the increase as 457%.
The somatic cell count was between 3.50 and 7.33 × 10³ cells/mL and did not differ between the beginning and end of the 60-day trial (P = 0.6657).
Based on 100 kg body weight, the result was 169.19 g per milking at 4 h filling time. The authors compare this with literature values of other breeds (126.03 to 242.19 g per 100 kg).
The authors conclude that an udder filling time of 4 hours and milking three times daily increase the milk yield in Nordestino donkeys. They see the moderate to strong correlations between udder or teat measurements and milk yield as possible criteria for breeding programs.
Critical assessment
- Note – Calculation errors in percentage figures: The stated "40% more" milk does not correspond to the table values (312.38 vs. 188.76 g ≈ +65%). Likewise, the 9.7% increase in teat diameter (mathematically approx. 10.7%) and 457% (mathematically approx. 453%) deviate; also the statement "62.4% higher" in comparison with another study is phrased inversely.
- Note – Units and group sizes: Table 4 is headed with "g" but apparently contains kg values; in Tables 4 and 5, n = 15 is stated, although only 5 animals were milked per group.
- Note – Cell count only before-after: The cell count was compared between the beginning and end, not directly between the milking groups. In addition, the Narsi and North African donkeys in Table 6 (242.19 g/100 kg) are above the Nordestino value, although the text states a higher yield than this breed.
- Limitation – Small groups: Only 15 mares at one location, in Trial 2 5 animals each; hand milking without foals, although according to the authors, residual milk remained in the udder. Longer filling times than 4 h were deliberately not tested.
- Limitation – No milk composition: Only milk yield, udder and teat measurements, and cell count were recorded; milk ingredients were not analyzed.
- Strength – Systematic study design: Controlled ration, randomized order of filling times in the block design, standardized milking procedure, ten udder and teat measurements, and ethics approval.
Funding, conflicts of interest, and level of evidence
Supported by the Universidade Federal Rural de Pernambuco (UFRPE), the PPGCAP graduate program of the UFAPE, and the Brazilian funding agency CAPES (Call No. 4/2021).
The authors state that there are no competing financial interests or personal relationships that could have influenced the work.
Level of evidence: Animal study – describes measured values in the studied animals and their milk, no statement about effects in humans.
Our assessment
The study concerns the milk yield and milking management of a Brazilian donkey population; it makes no statement about the composition of the milk.
Open research question: Does the composition of donkey milk change if udder filling time or milking frequency is adjusted?
You can find all measured values, interactive graphics, and the complete critical assessment on our research page: Study 96: Milking frequency and udder filling time in donkey mares. Further studies in the research archive.
Santana K. C., Lucena J. E. C., Pinheiro A. K. S., Pinto D. S. A., Farias I. M., Silva A. H., Maia V. N., Diniz W. J. S., Santiago J. M. (2026). Milking frequency and the effect of fill time on the production and conformation in Nordestino ecotype donkeys. Veterinary and Animal Science, Volume 33, Article 100717. DOI: 10.1016/j.vas.2026.100717
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.
