Donkey Milk Study: Ultrasound of the Teats in Donkeys (Accorroni 2025)

The teats of 28 lactating dairy donkeys were measured using ultrasound: the teat canal was on average 1.85 cm long and 0.41–0.46 cm wide. The width of the teat canal increased with the month of lactation (r = 0.32 and 0.54, respectively).

Study at a glance

• Original title: Ultrasonographic Assessment of Teat Structures in Healthy Lactating Jennies: A Pilot Study Establishing Reference Values for Clinical Application
• Authors: Accorroni L., Marchegiani A., Bazzano M. et al.
• Journal: Veterinary Sciences, 12(12), 1123 (2025)
• Country: Italy · Study type: Animal study

Study design

Observational cross-sectional pilot study of 28 clinically healthy, lactating dairy donkeys of mixed breeds (average age 7.4 ± 3.1 years, 2–13 years; 233.1 ± 58.7 kg) from a semi-intensive dairy farm in Italy. The animals were machine-milked twice daily; the foals were removed two hours before milking and otherwise remained with their mothers. The examination took place in the afternoon after the second milking, during the 1st to 8th month of lactation.

Key figures

• 28 – lactating dairy donkeys from one farm
• 7.4 ± 3.1 years – average age (range 2–13 years)
• 233.1 ± 58.7 kg – average body weight
• 1st–8th – month of lactation at the time of examination (11 animals in the 8th month, 1 animal in the 1st month)
• 13 MHz – frequency of the linear ultrasound probe
• 15–20 min – duration of examination per animal, without sedation

Results

The glandular tissue was clearly visible in all animals and showed a uniform, fine-grained, hypoechoic appearance. Each mammary complex consisted of two separate glandular units with their own cistern; milk ducts could be distinguished from blood vessels using color Doppler.

The teats appeared cone-shaped and trilayered in longitudinal section (skin, muscle layer, mucosa). Two separate duct systems were identified in all right and left teats.

According to Table 1, the average teat canal length on both sides was 1.85 cm, the teat canal diameter 0.41 cm (right) and 0.46 cm (left), the cranial wall thickness 0.73 and 0.58 cm, and the caudal wall thickness 0.82 and 0.75 cm.

Study limitations

• Small pilot sample: 28 animals from one farm were examined, with an uneven distribution of months of lactation (only one animal in the 1st month, eleven in the 8th month) and age groups. All measurements were performed by a single, unblinded person; the authors themselves identify this as a possible source of bias.
• Discrepancies between text and table: The main text states 0.38 cm for the right teat canal diameter, while Table 1 states 0.41 cm. The standard deviations also differ (e.g., cranial wall thickness on the right: 0.9 vs. 0.12 cm). The standard deviation of 0.73 cm for the left caudal wall thickness does not match the range of 0.39–0.91 cm.
• Implausible percentiles and confidence intervals: For the right teat, the mean wall thicknesses (0.73 and 0.82 cm) are above the respective 90th percentiles (0.70 and 0.72 cm). The stated 95% intervals are very narrow (e.g., 1.84–1.86 cm with an SD of 0.26 cm); based on the authors' own calculations, ±0.10 cm would be expected for n = 28.
• p-values and units: The p-values for the correlations cannot be consistently reproduced from r and n = 28 (for r = 0.317, a two-tailed p ≈ 0.10 is obtained; for r = 0.535, p ≈ 0.003). Table 2 uses millimeters, while Table 1 uses centimeters. The difference of approximately 6 mm between the 1st and 8th months of lactation mentioned in the text is derived from the minimum and maximum values of all animals, not from a comparison between months.
• No longitudinal measurements: Each animal was examined only once. The association with the month of lactation is based on a comparison of different animals and does not demonstrate a change in individual animals. Milk yield and composition were not measured.

Level of evidence: Animal study – describes measurements in the examined animals and their milk; no conclusions can be drawn about effects in humans.

Our assessment

The study provides anatomical measurements of the teats of dairy donkeys and concerns veterinary examination, not the milk itself. No conclusions about milk composition or the properties of commercial products can be drawn from it.

Source: Accorroni L., Marchegiani A., Bazzano M., Spaterna A., Laus F. (2025). Ultrasonographic Assessment of Teat Structures in Healthy Lactating Jennies: A Pilot Study Establishing Reference Values for Clinical Application. Veterinary Sciences. DOI: 10.3390/vetsci12121123 · Summarized by the DON DONKEY'S editorial team, as of October 2026.

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