Abstract

To assist the maintenance of normal hoof conformation in captive ungulates, a series of measurements were made from hooves of free-ranging animals. Differences in conformation between domestic animals and wild species were noted and several naturally occurring defects were seen. Factors affecting good hoof health are discussed.

Introduction

The word "hoofstock" is an appropriate alternate definition for ungulates. It emphasizes an important part of these animals. Hoof problems can quickly render an ungulate incapacitated. The external hoof is the foot's protection against injury and entry of pathogenic organisms.

Unfortunately captive individuals are frequently plagued by abnormal hoof growth and regular hoof trimming is necessary.^2,7 For trimming to take place the operator must have reference of a normal hoof.⁷ Frequently this is a mental image based on accumulated experience that blends normal domestic anatomy with wildlife anatomy. However, as species are different so are the parameters of their normal feet. It is necessary to know the normal parameters of animals within natural environments as a reference for captive counterparts.

Methods

Samples were derived from free-ranging animals that were immobilized, culled, or found dead. The species examined include: Burchell's zebra (Equus burcheli) (n = 59), Grevy's zebra (Equus grevyi) (n = 1), cape buffalo (Syncerus caffer) (n = 2), Grant's gazelle (Gazella granti) (n = 3), reticulated giraffe (Giraffa camelopardalis) (n = 5), common eland (Taurotragus oryx) (n = 4), gerenuk (Litocranius walleri) (n = 1), Jackson's hartebeest (Alcephalus bucelaphus) (n = 2), and impala (Aepyceros melampus) (n = 18). All animals had normal appearing hooves or the cause of death was not related to the feet. Several minor abnormalities were found, but if they did not seem to affect the animal they were included to give a normal range. For one giraffe, an abnormal foot was noted which may have contributed to the animal's death. This foot was not included in the analysis. In several instances not all feet of an animal were recovered. In these cases an investigation of circumstances of death was conducted to determine if the missing limb could have contributed to the animal's death.

Hoof angle was measured between the dorsal hoof wall and the plantar surface using a foot protractor (Horse Hoof Leveler, Nasco, Fort Atkinson, WI 53538-0901 USA). Toe length was measured from the distal edge of the coronary band to edge of the plantar surface. Heel lengths were measured from the distal edge of the coronary band to the most posterior point of the heel where weight bearing was noted. Mean averages, range, and standard deviation were calculated. Hooves were evaluated for shape and any defects were noted. In the event cracks or other opening in the hoof wall were noted, these were explored to determine if abnormal pathology was present.

Results

The results are summarized in Table 1.

The following abnormalities were noted in 17 of 233 feet of Burchell's Zebra: contracted heels (1), axial hoof bar larger than abaxial (3), rounded toes (3), broken toe (1), broken anterior hoof wall (1), overgrown frog (2), overgrown hoof walls (2), lateral wall cracks (2), and heel cracks (2).

Discussion

In cattle the transition from pasture management to confined management has greatly increased the incidence of hoof problems.⁴ The same has occurred in zoos by placing animal species that may normally move over many miles per day into confined areas. Factors that affect hoof health are environmental, genetic, and nutrition. All of these factors have been incriminated in the abnormal foot development of zoo animals. ⁵

Environmental factors include type of flooring (concrete, rock, gravel, or earth), abrasiveness of the floor (how the concrete was poured), or the amount of debris (rock, etc.) present. These factors must be related to the activity level of the animal throughout the seasons and management conditions.^3,5 Cold weather necessitates keeping some species indoors in limited enclosures, thus reducing exercise. Wet or humid conditions make softer hooves that are prone to injury and bacterial penetration. Dry environments cause brittle hooves that are prone to cracking. Enforcement of clean and dry areas for animal comfort must be maintained, particularly in high use areas near feed troughs, sleeping areas, and heavy traffic corridors. Distance between feeding areas and other favorite locations will increase exercise, maintaining good circulation in the feet and abrasion on the hooves. Daylight has an effect on hoof growth. Hoof growth increases during periods of increasing daylight, (i.e., the spring and early summer in the northern hemisphere).

Certain foot characteristics are known to have a degree of inheritance, such as heel depth, foot angle, and abnormally shaped toes.⁴ Breeding for good hoof health is frequently not a luxury that captive animal breeders may have. However, if genetics are considered a contributing cause to hoof problems then changes in the breeding group will be necessary.

Deficiencies or overfeeding of some nutrients are known to affect hoof health although the relationships are not always clear. Appropriate sulfur, zinc, copper, protein, and energy levels are necessary for healthy feet.^4,7 In addition, forage particle size and dietary fiber components should be examined to determine if they are a contributing factor for abnormal feet.

Cattle are generally considered to perform best with a hoof angle equal to or slightly greater than 45° and a dorsal toe length of approximately 7.5 cm.⁴ A similar species, the cape buffalo, has slightly different parameters with front and hind hoof angles of 53.5° and 50.3° respectively and a toe length of 8.09 and 8.47 cm respectively.

Hoof angles of horses are accepted to be 45-50° for the front foot and 50-55° for the hind foot.⁶ Surprisingly, zebras show an inverse relationship with the average front foot angle of 58°and 55°in the hind foot. The overall conformation of a zebra's hoof parallels that of a healthy domestic horse. Front hooves are wider and longer than hind hooves. The hoof bars are of equal length, appears to bear the body weight equally, and the foot is level with respect to the ground surface.^1,6 Uneven medial and lateral hoof wall lengths with no evidence of injury were noted in 3/233 zebra hooves examined. The zebra's sole is concave with a well-developed frog. Overgrown frogs were noted in 2/233 hooves. Other observed abnormalities appeared related to previous injuries of the hoof wall or coronary band. These included contracted heels (1), a broken anterior wall (1), and an overgrown hoof wall (2). Hoof wall cracks (sand cracks) were noted in the heels of two hooves and the lateral walls (2). No pathology was associated with these cracks.

The feet of impala, Grant's gazelle, Jackson's hartebeest, and gerenuk are similar in form to other small ruminants. Hoof walls are level with the sole and the peripheral edge of the sole is weight-bearing. The toes are pointed and the heels are rounded and soft. Impala and Grant's gazelle have steeper angles and larger hooves in the front feet. This could be compensation for the additional stresses placed on the front feet by a long jump style of ambulation.

Maintaining healthy animals in captivity requires attention to the details present in the animal's natural environment. Soft, hard, or a mixture of enclosure substrates which duplicate the animal's home range will encourage normal hoof growth, which in turn will maintain the normal biomechanical anatomy that empowers quadruped locomotion. When abnormalities develop intervention can be performed using a visual image of the normal anatomy as a guide.

Table 1. Hoof angles of selected African ungulates

References

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2.  Fowler ME. 1986. Hoof, nail and claw problems in mammals. In:Fowler, M.E. (ed.). Zoo and Wild Animal Medicine, 2nd ed. W.B. Saunders Co. Philadelphia, Pennsylvania. Pp. 550-556.

3.  Janssen DL, BA Rideout, MS Edwards. 1999. Tapir Medicine. In:Fowler ME, RE Miller (eds.). Zoo and Wild Animal Medicine, 4th ed. W.B. Saunders Co. Philadelphia, Pennsylvania. Pp. 562-568.

4.  Nocek JE. 1996. Hoof care for dairy cattle, 2nd ed. W.D. Hoard & Sons Co., Fort Atkinson, Wisconsin.

5.  Raphael BL. 1999. Okapi medicine and surgery. In: Fowler, M.E. and R.E. Miller (eds.). Zoo and Wild Animal Medicine, 4th ed. W.B. Saunders Co., Philadelphia, Pennsylvania. Pp. 646-650.

6.  Stashak TS. 1987. The relationship between conformation and lameness. In:Adams' Lameness in Horses, 4thed. Lea & Febinger, Philadelphia, Pennsylvania. Pp. 72-99.

7.  Wallach JD, WJ Boever. 1983. In: Wallach, J.D. and W.J. Boever, (ed.). Diseases of Exotic Animals: Medical and Surgical Management. W.B. Saunders Co., Philadelphia, Pennsylvania. Pp. 295.