The eliminative behavior seen in horses will nearly always involve either defecation or urination. Regurgitation is virtually non-existent; the closest being the feeble discharge of incompletely swallowed food or fluids caused, for example, by a blockage of the esophagus. In such instances, alteration of the horse’s behavior is usually minimal. Urination and defecation, how-ever, do occur with specific behavior patterns and are linked to social behavior as well. Thus the elimination of waste products is often more than a physiological discharge process; such activities frequently induce behav-iors in nearby animals and tell much about the social and reproductive sta-tus of the individuals involved. When one horse eliminates, others in the social unit, especially adult males, often appear induced to also eliminate.
The amount of elimination per day as feces and urine reflects the intake of the animal in food and drink, as well as factors such as ambient tem-perature. The daily fecal output per horse tends to be 14–23 kg (30–50 lb).
Normal daily urine volume can range from 3–18 ml/kg of body weight (Siegmund 1973). An adult Thoroughbred, for example, weighing 440 kg might have an average urine output of 183 ml/hr (about 1.2 gallons per day).
Of the total water consumed daily with food and drink, only about 22 per-cent will be eliminated as urine; most water loss occurs in respiration, feces, and sweat (Spector 1956).
Urination
A horse about to urinate stops locomotion and assumes a basic posture where the neck is slightly lowered, the tail is raised, and the hindlegs are spread apart and stretched posteriorly (Figure 10.1). Foals, even neonates, attain the basic posture for urination. When positioning the hindlegs, horses
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keep their hindlegs in place and step forward with the forelegs. In strong wind, horses often orient upwind. Females tend to spread their hindlegs more than males, and males tend to attain more posterior stretch of the hindlegs. In both sexes, a slight squatting motion is common during urine flow. A stallion when marking other excrement with his own urine often raises his tail well above the more horizontal position occurring in typical urination. The penis is commonly extended slightly for urination.
The urination sequence lasts approximately 10 seconds. After urination, the penis sometimes extends pendulously for a short time. In the female, urination concludes with a brief series of vulva contractions called wink-ing, where the clitoris is repeatedly everted. Non-estrous mares and males return to a normal stance soon after urine flow ceases, sometimes switch-ing the tail or shakswitch-ing the body. Estrous mares tend to retain the urination stance momentarily with tail raised and the winking sequence prolonged.
While in estrus, mares may urinate frequently and in small amounts (<0.5 liter). Stallions intent on marking excrement also may urinate in small amounts as well as repeatedly. A stallion’s discharge when marking is usu-ally one or two relatively forceful squirts of urine.
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Figure 10.1: Eliminative postures of female and male: (a) urination, (b) defecation.
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In foals, urination may begin during the third hour after birth and for several weeks recurs rather often. Jeffcott (1972) found colt foals first uri-nated at an average of 5.97 hours (range 2.75 to 8.0), whereas filly foals urinated at 10.77 hours (range 7.25 to 15 hours). During daylight, Tyler (1969) observed foals urinated hourly for the first two weeks before the interval gradually increased, stabilizing at one year at a frequency similar to adult mares. Adult mares were found to urinate an average of once every 3.8 hours in summer and every 4.5 hours in winter. In another population of horses under somewhat similar conditions, Kownacki et al. (1978) found mares urinated an average of 7.4 times in a 24-hour period, stallions 12.8 times, and foals 12.5 times.
During urination, grazing ceases in the majority of instances; yet no par-ticular site is sought. The animal in most cases seems merely to pause momen-tarily during other activity or as a transition occurs, such as after resting and just before grazing.
Stallions during the breeding season are often quick to investigate a mare after she urinates. Interest in the mare, however, is not prolonged if she is not in estrus. Stallions often direct their attention to the eliminated material. Feist and McCullough (1976) noted stallions responded to 50.6 percent of the 77 observed urinations of adult mares. The typical stallion response was to approach, smell the urine, step over it, urinate on it, and finally turn and smell again. Flehmen sometimes occurred during olfac-tory investigation. Although stallions in this feral population did not respond quite as often (39.5 percent, n = 76) to defecations of mares, the behavior of the stallions toward the material was similar. Approach, inves-tigation, and marking were done systematically as was the case with mare urine. Urination by a stallion rather than defecation occurred in 92.1 per-cent of the responses the males made toward the excrement of adult females as well as immatures of the herd. Young males, but no females, were occasionally seen to exhibit the response shown by adult males. Boyd (1980) witnessed young females in some instances also respond to excre-ment and add their own urine. In New Forest ponies (Tyler 1972), where comparatively few stallions were in the population, urination by adults onto feces was rare; the adult ponies were more inclined to add their own feces. Feist and McCullough (1976) noted that urination by feral stallions was uncommon (16.8 percent) on the communal stallion fecal piles. Dom-inant stallions otherwise showed a tendency to urinate on the excrement of subordinates.
Defecation
The process of defecation occurs without any specific posture except that the tail is raised and often held to one side (Figure 10.1). Many times horses do not cease locomotion or continue to graze while defecating. Yet if the animal does stop, it will typically first spread the hindlegs, then gradually raise its tail, protrude the anus, and finally commence elimination. The entire sequence seldom lasts more than 30 seconds, commonly less than 15. Some foals successfully defecate a few pellets before the end of the first hour after birth using a spread leg, tail-up posture. The neonatal foals Tyler (1969) observed seldom defecated, yet often strained, as if trying, when very young. The frequency of defecation increased with age (see Figure 4.8) and straining ceased after a few days.
After discharging feces, a horse steps forward and may switch its tail from side to side. If grazing or walking, it continues without interruption.
Occasionally, however, the horse turns and sniffs the fecal pile. Olfactory investigation is more often seen when the horse has added fecal material to an existing pile. As with urination, stallions move to fecal piles and inves-tigate them. Pawing of the material sometimes occurs before the animal steps over the pile and adds its own feces. A second bout of smelling con-cludes the marking routine.
The frequency of defecation can vary between sexes, age groups, and apparently with diet. Tyler (1969) found that during daylight hours New Forest ponies defecated on the average every 2.2 hours in summer and every 2.4 hours in winter. Kownacki et al. (1978) noticed eliminative behavior occurred somewhat uniformly throughout the 24-hour period in both sexes. In their study, defecation by stallions occurred an average of 12.8 times in a 24-hour period, in mares it was 6.5 times, and in foals 10.3 times in one day.
Horses in pastures not shared with other kinds of livestock commonly defecate more in certain poorly grazed areas than in areas heavily grazed.
Pastures thus become partitioned into zones of short grasses as well as rough areas of tall grasses and weeds. Ödberg and Francis-Smith (1976) found the adult horses they observed spent most of their time in the short grass zones, but prior to defecation the horses would proceed to a nearby rough area, sniff the ground, defecate, and then leave the rough. Foals were less inclined to restrict defecation to the rough areas and even grazed the roughs.
Free-roaming horses tend not to limit defecation to certain areas, except for the stallions. Adult males (harem stallions as well as bachelor males) 10 - Eliminative Behavior 147
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often become preoccupied with visits to established fecal mounds; these are thus called stud piles. Of the 186 defecations recorded by Feist and McCul-lough (1976), a total of 89.8 percent occurred at stud piles. Sometimes younger males also used the piles. Such mounds occurred periodically throughout the range and were added to by any stallion that encountered them. The largest piles were those along the routes of a number of social units, such as along a common path to water holes. Feist (1971) found the size of stud piles ranged from less than a square meter to a series of adja-cent piles of successive age as large as 1.8 by 7.6 meters. The piles were often used during encounters between stallions as part of their agonistic behavior pattern.
Stallions appear to limit the amount of fecal discharge when marking fecal piles or the dung of mares, thus repeated marking can occur in a short time. Tyler (1969), for example, saw one stallion defecate on three differ-ent piles and urinate on a fourth within a 10-minute period.
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