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Research on donkey milk · Study 109
Ultrasound of the teats: reference values in jennies
In 28 lactating dairy jennies, the teats were measured by 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).
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The key figures
Study design
How it was studied
Observational cross-sectional pilot study in 28 clinically unremarkable lactating dairy jennies of mixed breeds (on average 7.4 ± 3.1 years, 2–13 years; 233.1 ± 58.7 kg) on a semi-intensive farm in Italy. The animals were machine-milked twice a day; the foals were separated two hours before milking and otherwise stayed with their mothers. The examination took place in the afternoon after the second milking, in the 1st to 8th month of lactation. Using a 13 MHz linear probe, glandular tissue and teats (in a warm water bath) were imaged in longitudinal and cross sections. On both teats, teat canal length (TCL), teat canal diameter (TCD) and cranial and caudal teat wall thickness (CrTWT, CaTWT) were measured, each as the mean of three images by the same examiner. Descriptive statistics and Pearson correlations with age, body weight and month of lactation were evaluated.
Interactive chart · values from the study
Teat measurements, right and left compared
Means (n = 28) from Table 1 of the study; the main text gives a different value of 0.38 cm for the right teat canal diameter.
Second analysis
Jennies examined per month of lactation
Distribution according to section 2.1 (materials and methods); months 2 and 4 were not represented.
Results
What the study measured
The glandular tissue could be imaged well in all animals and showed a uniform, fine-grained, hypoechoic pattern. Each udder complex consisted of two separate glandular units, each with its own cistern; milk ducts could be distinguished from blood vessels by colour Doppler.
In longitudinal section, the teats appeared conical and three-layered (skin, muscle layer, mucosa). Two separate duct systems were found in all right and left teats.
According to Table 1, mean teat canal length was 1.85 cm on both sides, teat canal diameter 0.41 cm (right) and 0.46 cm (left), cranial wall thickness 0.73 and 0.58 cm and caudal wall thickness 0.82 and 0.75 cm.
According to the authors, right and left teats did not differ significantly; according to Bland–Altman analysis, the measurements were repeatable.
Teat canal diameter correlated positively with month of lactation (right r = 0.317, p = 0.040; left r = 0.535, p = 0.009; both sides combined p = 0.023). No significant relationships were found with age and body weight.
Under practical conditions, the examination could be carried out without sedation or restraint in 15–20 minutes per animal.
Authors’ conclusion: In the view of Accorroni et al. (2025), ultrasound examination of the teats in lactating jennies is possible in the stable quickly and without restraint; the measurements obtained were the same on both sides and could serve as preliminary reference values for veterinary udder checks. The authors interpreted the increase in teat canal diameter over the lactation as an adaptation to lactation. They themselves stressed that larger multicentre studies are needed for confirmation.
Critical assessment
Strengths and limitations
28 animals from one farm were examined, with unevenly distributed months of lactation (only one animal in the 1st month, eleven in the 8th) and age groups. All measurements were taken by a single, non-blinded person; the authors themselves name this as a possible bias.
The main text gives 0.38 cm for the right teat canal diameter, whereas Table 1 gives 0.41 cm. The standard deviations also differ (e.g. cranial wall thickness right 0.9 vs. 0.12 cm). The standard deviation of 0.73 cm for the left caudal wall thickness does not fit the range of 0.39–0.91 cm.
For the right teat, the mean wall thicknesses (0.73 and 0.82 cm) are above the respective 90th percentile (0.70 and 0.72 cm). The 95 % intervals given are very narrow (e.g. 1.84–1.86 cm with SD 0.26 cm); by our own recalculation, about ± 0.10 cm would be expected with n = 28.
The p-values of the correlations cannot be reproduced consistently from r and n = 28 (for r = 0.317, two-sided p ≈ 0.10; for r = 0.535, p ≈ 0.003). Table 2 gives millimetres, Table 1 centimetres. The difference of about 6 mm between the 1st and 8th month of lactation mentioned in the text results from the minimum and maximum of all animals, not from a comparison of months.
Each animal was examined only once. The relationship with month of lactation is based on a comparison of different animals and is not evidence of a change in the individual animal. Milk yield and composition were not recorded.
The authors describe the measuring points for length, diameter and wall thickness precisely, average three images per measurement and cover the 1st to 8th month of lactation. This makes future comparisons between studies easier.
Editorial assessment: The study provides anatomical measurements of the teats of dairy jennies and concerns veterinary examination, not the milk itself. No statements about milk composition or properties of commercial products can be derived from it. To the research archive.
Research question for DON DONKEY’S®
Do teat canal diameter and teat wall thickness actually change in the individual animal over the course of lactation, and are these measurements related to milking method, milking interval or milk flow?
Original publication
Ultrasonographic Assessment of Teat Structures in Healthy Lactating Jennies: A Pilot Study Establishing Reference Values for Clinical Application
Original title of the publication.
Accorroni L., Marchegiani A., Bazzano M., Spaterna A., Laus F.
Veterinary Sciences · 2025 · 12(12), 1123
School of Biosciences and Veterinary Medicine, University of Camerino, Matelica, Italy
10.3390/vetsci12121123: 10.3390/vetsci12121123
Transparency: no external funding. The authors declare no conflicts of interest. No product-related statement for DON DONKEY’S®.
Summarised and reviewed by the DON DONKEY’S editorial team on the basis of the original publication · as of October 2026
The study summarised above was carried out independently of DON DONKEY’S® and does not relate to our products. It serves solely to inform about the state of research.
DON DONKEY’S® donkey milk and donkey milk powder are foods. They are not intended to prevent, treat or cure any disease and do not replace medical advice.
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