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Mule Genetics, Parasites and Vaccinations

Caring for Donkeys and Mules


Genetics and Breeding

Horses have 64 chromosomes, while donkeys have 62. When horses and donkeys are mated, the mule offspring have 63 chromosomes. The gestation period in donkeys is 12 months on average, but it may vary from 11 to 14 months. Despite being considered sterile, mare mules and mare hinnies will have estrus cycles. These cycles can be regular, or erratic and variable. Female hinnies and mules can be used as embryo transfer recipients but care must be given to compatibility of donor and recipient. There have been documented cases of fertility in the female mule but not the female hinny (7). A report from Morocco indicates that a mule mare produced a foal with 62 chromosomes. The cells of the mule mare were a mosaic, some carrying 63 chromosomes while others carried 62. The foal has 62 and is believed to be fathered by a donkey. This is the fourth female mule to be confirmed to be fertile (8).

Intact male donkeys and mules can be quite "stallion-like" or aggressive in behaviour. If they are not being used for breeding purposes or as a teaser, it is highly recommended that they be castrated. Castration must be performed by a veterinarian.


Donkeys and mules can also be infested by ectoparasites (skin parasites) such as flies, lice, ticks, mites and warbles. For further information on Lice on Horses refer to. www.omafra.gov.on.ca/english/livestock/horses/facts/info_lice.htm.

The internal parasites that affect donkeys and mules are typical for other equid species and, therefore, the recommendations for control and treatment are those that we use for horses. However, lungworms are reported to be more common in donkeys than horses. A comprehensive parasite control program should include pasture management and environmental sanitation, and regular anthelmintic wormer administration. Performing routine fecal egg counts will help to determine the efficacy of treatment and control programs. Anthelmintics should be chosen conscientiously and their use should be rotated slowly to decrease the occurrence of resistance. A slow rotation of wormers is recommended (the same wormer over the course of a year or more). Your veterinarian can help to determine the correct parasite control program for you.


The use of horse vaccines for donkeys and mules is necessary because there are no vaccines specifically developed for them. Protocols for a vaccination program are usually adapted from those recommended for horses. The chance of adverse reactions to vaccines are assumed to be the same as in horses. It is important that donkeys and mules are vaccinated to aid in controlling the spread of disease.


The above recommendations are intended to introduce basic concepts of management for your donkey or mule. For more information on donkey, mule and horse care and management, refer to http://www.omafra.gov.on.ca/english/livestock/index.html#horses.


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  • Burnham SL. Anatomical differences of the donkey and mule. Proceedings of the 48th Annual AAEP Convention 2002: 102-109.
  • Peregrine A. (2003) Personal communication.
  • The Donkey. Alberta Agriculture, Food and Rural Development http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex598
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  • Kay G. A foal from a mule in Morocco. Vet Record 2003;152 (3): 92.

Authors: Heather McClinchey MSx; Jeffrey Sankey , BSc, Ontario Veterinary College, Unversity of Guelph, Guelph, Ontario, Canada and Dr. Bob Wright, Ontario Ministry of Agriculture and Food, Fergus, Ontario, Canada

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