animals Review Comparing and Contrasting Knowledge on Mules and Hinnies as a Tool to Comprehend Their Behavior and Improve Their Welfare Amy McLean 1,*, Angela Varnum 2, Ahmed Ali 3,4, Camie Heleski 5 and Francisco Javier Navas González 6 1 Department of Animal Science, University of California-Davis, Davis, CA 95616, USA 2 College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA 3 Department of Animal Science, Michigan State University, East Lansing, MI 48824, USA 4 Department of Animal and Veterinary Sciences, Clemson University, Clemson, SC 29634, USA 5 Department of Animal and Food Science, University of Kentucky, Lexington, KY 40506, USA 6 Department of Genetics, Veterinary Sciences, University of Cordoba, 14071 Córdoba, Spain * Correspondence: [email protected]; Tel.: +1-706-296-8743 Received: 29 May 2019; Accepted: 20 July 2019; Published: 26 July 2019 Simple Summary: Mules and hinnies combine traits of their equid parents—the horse and donkey—but are less studied or understood. Still, their welfare varies greatly because of several factors. These hybrids have anatomy, health, nutritional, and behavioral particularities that are distinct from those of donkeys or horses. Their behavior can pose challenges to providing routine care and treatment during times of disease. Abusive treatment can result from those who have little understanding of learning theory or body language. Hence, an overview of studies and field observations can offer solutions for welfare enhancement. According to literature, participatory surveys and behavioral assessments across several countries, mule owners and handlers find it easier to interact with their animal as compared to allowing a stranger to do so. By contrast, unfamiliar persons had more success with mules handled at an early age. Gaining trust and proceeding with slow and methodical movements tend to work best for working with mules and hinnies. Early foal handling additionally creates success in training and behavior modification. Conclusively, the key to improving mule and hinny welfare is to shape human behavior, creating a training approach which will ultimately improve the animals’ welfare. Abstract: Mules and hinnies are the hybrids between donkeys (Equus asinus) and horses (Equus caballus). For centuries, mankind has used them for agrarian purposes, the military, or recreation. Contrasting literature with behavioral observations, we seek a better behavioral understanding andthus comprehensive solutions for their welfare enhancement. Over the past 6 years, we have assessed physical and behavioral welfare in over 900 mules by surveying owners from Egypt, Peru, Portugal, Spain, Mexico, and the U.S. These mules participated in shows, brick kiln work, cart-pulling, packing, tourism, and cattle herding. Observations are discussed alongside facts from the literature. Unfortunately, their behavior has been misunderstood by many, and harsh treatment and equipment has been used to control them. Few studies have attempted to define or use learning theory to understand how and why mules and hinnies behave as they do. Hence, understanding their health considerations, natural behavior, and training theory is crucial for those who work with them.Solutions to welfare improvement partially lie in an individual’s ability to handle mules and hinnies from birth, and to proceed slowly through training. Conclusively, this review sets forth a clearer understanding of these hybrids’ behaviors and promotes positive handling, allowing their access to more routine healthcare and ultimately, a higher welfare standard. Animals 2019, 9, 488; doi:10.3390/ani9080488 www.mdpi.com/journal/animals Animals 2019,, 9,, 488x FOR PEER REVIEW 2 of 16 Keywords: mules; hinnies; behavior; aggression; early foal handling; welfare Keywords: mules; hinnies; behavior; aggression; early foal handling; welfare 1. Introduction 1. Introduction The Equus family includes horses, donkeys, mules, and hinnies. Globally, there are 14 million mulesThe and Equus hinnies—the family includes smallest horses,sector of donkeys, the equid mules, population and hinnies. (112 million, Globally, 50 theremillion are horses, 14 million and mules54 million and donkeys) hinnies—the [1]. A smallest mule is sectorthe cross of thebetween equid a populationmale donkey, (112 a million,jack, and 50a female million horse, horses, a andmare. 54 The million reciprocal donkeys cross)[1]. produces A mule isa thehinny. cross They between serve aimportant male donkey, roles a as jack, working and a femaleequids horse,generating a mare. critical The income reciprocal and crosshave producesgrown in a hinny.popularity They amongst serve importanthorse owners roles looking as working for equidsrecreation generating and competition critical income mounts and worldwide have grown [2–4]. in popularityMules can amongstbe trained horse to compete owners in looking multiple for recreationdisciplines, and from competition dressage, jumping, mounts Western worldwide riding, [2–4 re].ining, Mules and can racing be trained [5] (Figure to compete 1). In the in multipleU.S., the disciplines,mule and donkey from dressage, population jumping, increased Western from riding,2007 to reining,2012 even and as racing the number [5] (Figure of U.S.1). Inhorses the U.S., and theponies mule declined and donkey [6]. population increased from 2007 to 2012 even as the number of U.S. horses and ponies declined [6]. Figure 1. Mules andand hinnieshinnies can can be be trained trained to to compete compete in multiplein multiple disciplines, disciplines, just just like like horses. horses. The The U.S. hasU.S. seenhas seen a growth a growth in mules, in mules, hinnies, hinnies, and donkeysand donkeys for recreation for recreation and competitionand competition mounts. mounts. Despite theirtheir prevalence,prevalence, mules mules and and hinnies hinnies are are some some of of the the least-studied least-studied equids equids alive. alive. Due Due to the to increasedthe increased number number of hybrid of hybrid equids equids (crosses (crosse betweens between different equinedifferent species) equine owned species) for recreationalowned for purposes,recreational the purposes, professional the professi communityonal community has seen an has increased seen an demand increased for demand information for information on mules and on hinniesmules and [7]. hinnies The donkey [7]. The is often donkey thought is often of as thought the least of researched as the least member researched of the member equids, but of the even equids, less is knownbut even about less mulesis known and hinniesabout mules [8]. Mules and andhinnies hinnies [8]. have Mules proven and tohinnies be more have challenging proven to to be research more basedchallenging on their to geneticresearch variation, based on especially their genetic from variat the horseion, especially side. Over from the pastthe horse ten years, side. thereOver hasthe beenpast antenincrease years, there in the has number been an of increase research in articles the number and information of research for articles donkeys. and Such information a growth for in donkeys. available informationSuch a growth has in yetavailable to be seeninformation for mules, has andyet to even be seen less for so mules, for hinnies, and even but less this so review for hinnies, compares but somethis review of the compares most relevant some contextual of the most and relevant global informationcontextual and available global from information multiple available countries from and behavioralmultiple countries assessments and behavioral [9,10]. assessments [9,10]. A new mule owner may first first wonder which parent the animal should be compared to, the horse or the donkey. A handler or owner of a mule or hinnyhinny in a working capacity may question why this animal is so difficult difficult to handle and train. Some of the greatest compromises in welfare for mules and donkeys are due to a lack of understanding of their behavior. There are many fallacies and opinions Animals 2019, 9, 488 3 of 16 Animals 2019, 9, x FOR PEER REVIEW 3 of 16 related toto working working with, with, treating, treating, training, training, and owningand owning mules andmules hinnies, and especiallyhinnies, especially when comparing when comparingthem to horses them (Figures to horses2 and (Figures3). 2 and 3). Figure 2. MulesMules and and hinnies hinnies are are often often worked worked or or ridde riddenn with harsh equipment to control their behavior such as this ring bit. This This can can result result in in lacerated lacerated tongues tongues and/or and/or paralysis paralysis to to the the tongue. tongue. Improved understanding aboutabout learninglearning theory could help reduce the use of such abusive equipment. Figure 3. Another example of harsh equipment being used to control a mule working in an Egyptian brick kiln. The The chain chain is is purposefully purposefully used to create lesions on the nose to sensitize the mule to further pressure. Improved understanding of mule behavior would decrease the need for abusive tools such as this. Animals 2019, 9, 488 4 of 16 Some experts will agree that mules are not for everyone [8,9]. The term “muleskinner” has been applied to a person who can understand the ways of a mule and work around the mule’s peculiarities without injury [8]. Mules have outperformed both parents, and even dogs, on cognition tests [11,12], showing that hybrid vigor may even enhance cognitive function [13]. Often, routine