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Draft horses, mules, and donkeys

DG Pugh, DVM, MS, MAg, DACT, DACVN, DACVM; Sara Ziska, DVM, PhD; and Nicole Passler, DVM, MS

Draft horses, donkeys, and their hybrid crosses are discussed together in this chapter, as all three are traditionally thought of as working animals or "beasts of burden." Draft horses, mules, and donkeys still are used as working animals, but also as pets, for trail riding, cart pulling, showing, and other recreational uses. As all three are of the genus Equus, this chapter will review some of the differences between them and other horse breeds with respect to feeding.

2.1 Draft Horses

There are approximately 30 breeds of draft or draught horses found in the world today. These large horses (550-1180?kg or 1400-2600?lb) are utilized in farming and logging industries, blood or plasma donation, biological and pharmaceutical production, advertising campaigns, as carriage horses, show horses, and pets. The most popular breeds of draft horses in the United States, Belgians, Clydesdales, Percherons, and Shires, all originated in Western Europe. These breeds were selected for their tall stature, heavy bone and frame structure, muscular hindquarters, and patience to haul large loads.

Traditionally, these large working animals were thought to have a similar nutrient metabolism as pony breeds. Historically, draft breeds have been fed slightly less feed per kg of body weight than light breeds. The most recent National Research Council feeding guidelines for horses1 suggested that idle, mature, healthy draft horses could subsist on 30.3?kcal of digestible energy (DE)/kg of body weight daily. This energy requirement is slightly lower than 33.3?kcal/kg of body weight daily recommended for light horse breeds. Obviously, during work, growth, lactation, or other periods of increased energy expenditure, the energy requirements are greater. The total energy requirement is higher for draft horses (700?kg or greater) than light horse breeds (Thoroughbred, Quarter Horse, etc.), as these breeds may weigh substantially less (425-480?kg). Mature draft horses should be fed a minimum of 1.5% of their body weight in roughage daily, with a total dry matter intake between 1.5-3.0% of their body weight daily. Still, these breeds can be fed using many of the general guidelines applicable to light breeds.

Good quality grass-legume mixed pastures or hay will usually suffice for draft horses at maintenance (neither gaining nor losing weight). The caregiver should always be cognizant of carbohydrate concentrations in the forage and pastures, as with any breed of horse, to minimize the risk of colic and laminitis.

Feeding to maintain a body condition score (BCS) of 5-6/9 is optimal in most circumstances. The energy density of the diet and/or use of supplemental high energy feedstuffs (e.g., concentrates) should be adjusted to support growth, production, lactation, late gestation, work, and needs for increased energy use with the goal of maintaining a BCS between 5-6/9. Total dietary energy required will depend on the type of work, duration of work, weight of loads, or the amount of force exerted to perform work. Again, body condition should be used to adjust energy intake to meet demands and maintain BCS in the 5-6/9 range. Unfortunately, draft horses may be prone to Polysaccharide Storage Myopathy, Exertional Rhabdomyolysis, Equine Metabolic Syndrome, and other diet-related conditions.1-3 Thus, feeding diets high in carbohydrates should be done with extreme caution, and then only when necessary. Nutritional myopathies are discussed in Chapter 4.

Overall, these breeds seem less prone to developmental orthopedic disease.1,4,5 Of the draft horses, Clydesdales and Percherons appear to be the breeds most affected with metabolic bone diseases.5 The caregiver is cautioned to follow feeding practices that minimize developmental orthopedic disease in growing animals.

Unfortunately, the large size of draft horses presents other management issues that directly affect feeding. The authors have observed more catastrophic outcomes when draft breeds develop laminitis and increased heat stress with obesity, as compared to lighter breeds. The caregiver should strive to maintain a BCS of 5-6/9 and carefully monitor obese animals, particularly in times of warm weather or when laminitis is a concern.

Due to their impressive body weight, it is not uncommon for draft horses to require 24 gallons (91?L) of fresh, clean water daily. Dehydration may result if caregivers are unable to meet these extreme demands, which increases the risk of developing intestinal impactions and other potentially life-threatening conditions.

2.2 Donkeys

Donkeys or asses (Equus africanus asinus or Equus asinus) are traditionally thought of as working animals, and in many parts of the world are depended upon in this manner. In modern-day North America, donkeys or "burros" are used for work, show, cart and/or carriage pulling, competitive riding, drug smuggling, guard animals, training animals, and pets. There are 15-20 breeds of donkeys, including miniature, standard, large standard, and mammoth stock, which vary greatly in height (81-157?cm or 32-62 in). The female is commonly referred to as a jenny or jennet. Intact males are commonly called a jack or jackass. These animals characteristically have longer ears and make loud vocal noises ("bray"), as compared to horses. Their reproductive cycle has similarities to that of the horse and has been described.6

Donkeys are believed to have evolved in arid to semi-arid climates and show extraordinary tolerance for heat and dehydration. They seem able to continue eating for several days in the absence of drinkable water. This is in contrast to horses, which decrease forage and feed consumption in the face of dehydration. In modern agricultural husbandry practices, as with other equids, clean, fresh water should be offered to donkeys free choice, despite their relative hardiness.

Donkeys appear to readily adapt to new environments and feedstuffs, which is not common in other equids.1 It is an accepted husbandry practice to feed donkeys less than horses on a body weight basis, as they are not simply small horses.1 Donkeys have a narrow muzzle and mobile lips, which allow for greater feed selection in comparison to most horses. Therefore, they can selectively consume higher quality portions of available forages. Donkeys will subsist on more mature forages than are willingly consumed by most horses (e.g., bark on trees and shrubs), but can and will consume traditional feedstuffs.1,7,8 On poor quality forage diets, donkeys appear to have a lower dry matter intake requirement than ponies.9,10 Reported voluntary dry matter intake ranges for donkeys have been between 0.83-2.6% of body weight, depending on the type and quality of the feed stuff, along with physiologic requirements.11,12 However, dry matter intake between 1.75-2.25% of body weight of moderate to good quality forage will routinely meet maintenance requirements in mature donkeys.1 When offered moderate to good quality forages, donkeys will readily adapt to consume complete diets and employ their selective grazing habits only when offered mixed forage diets of differing quality.13

Traditional donkey feeding practices infer that donkeys are more efficient in digestion than horses. Donkeys appear to have higher apparent digestibility for dietary dry matter and fiber than ponies and horses, particularly when fed poor quality forages (e.g., oat straw).11,14 The higher digestibility ability of donkeys could be attributed to longer gut retention time or greater microbial cellulolytic activity in the cecum, compared to other equids.15,16

Some reports have shown that donkeys may require only 3.8-7.4% protein in their diet, due to efficient dietary protein utilization.17,18 Despite these findings, the authors recommend that dietary protein intake in donkey diets should be fed similar to recommendations for horses. Consequently, feeding as for horses should meet requirements for donkeys, with respect to protein intake.

In parts of the world where high quality feedstuffs are plentiful, obesity in donkeys is a major concern. Caregivers should be mindful to feed donkeys only to a desired body condition and avoiding over-conditioning. Energy-protein malnutrition, mineral deficiencies, and emaciation are of most concern in many tropical areas of the world where donkeys are used as work animals.

Donkeys fed to obesity will develop a fat roll over the neck (pones) and fat on the barrel and hips, which are quite unsightly. Donkeys, much like pony breeds, may be prone to hyperlipemia during stress and feed deprivation.1 Caregivers should closely monitor donkeys for feed intake in times of stress (e.g., changes in weather, illness, etc.). Because of the stoic disposition of donkeys, close attention to dietary intake and body condition is imperative. Body condition scoring systems for donkeys have been described.19,20 The Vall system assigns a score from 1 (emaciated) to 4 (good), with emphasis placed on the appearance of the flank and back.19

Diets appropriate and practical for horses can typically be fed to donkeys, with caregivers mindful to avoid obesity. Diets should include 6-10% protein intake for maintenance needs, free access to fresh clean water, and a good quality mineral mixture designed for horses.

2.3 Mules

Mules...