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One or more of the preceding sentencesincorporates text from a publication now in the public domain:Chisholm, Hugh, ed. (1911). "Mule". Encyclopædia Britannica. Vol.18 (11thed.). Cambridge University Press. pp.959–960.
Camillo, Francesco; Rota, Alessandra; Biagini, Lorenzo; Tesi, Matteo; Fanelli, Diana; Panzani, Duccio (June 2018). "The Current Situation and Trend of Donkey Industry in Europe". Journal of Equine Veterinary Science. 65: 44–49. doi:10.1016/j.jevs.2017.11.008. hdl:11568/905165.
Wang, Xisheng; Bou, Gerelchimeg; Zhang, Xinzhuang; etal. (July 2021). "A Fast PCR Test for the Simultaneous Identification of Species and Gender in Horses, Donkeys, Mules and Hinnies". Journal of Equine Veterinary Science. 102 103458. doi:10.1016/j.jevs.2021.103458. PMID34119210.