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Sexual Behavior in Herds of Icelandic Horses Introduction The fertility in horses is considered low when compared to other species of domesticated animals. The horse is a domesticated animal species which was not bred in reference to signs of fertility by those raising it (Merkt, 1975; Stegen, 1934). Out in nature, feral horses have been observed as having a foaling rate in the range of 23-90% (Berger, 1983; Jezierski and Jaworski, 1995; Keiper and Houpt, 1984; Salter and Hudson, 1982; Tyler, 1972). Among freely ranging herds of Icelandic horses, fertility results were computed for 5,649 matings in 1978 and 1979, and the average fertility rate of 316 stallions was confirmed as 85.6% (Hugason et al, 1985). During recent years horse breeders in Iceland have observed decreasing fertility in their mares. In order to gain more knowledge of factors influencing the fertility of Icelandic horses on pasture, several aspects were monitored. Methods Three herds were closely monitored during one or two heat periods by observing them continuously for 24 hours per day (made possible by the sufficiently illuminated Icelandic summer nights). A camper was parked in the middle of the pasture and each horse marked unequivocally. Herd A comprised 29 fertile mares along with a 15-year-old stallion. Herd B was made up of 22 fertile, cycling mares, plus a 9-year-old stallion, while herd C consisted of 10 fertile mares and a 3-year-old stallion. These herds underwent continuous observation for 24, 41 and 28 days, respectively. Some of the mares received clinical, gynecological, and ultrasonic examinations, in order to determine precisely when they came into heat and their date of ovulation. In addition, the mating frequency and the reproductive behavior of the stallions and the mares were noted down. This approach made it possible to tell how often a stallion which had grown up in the herd covered the mares and what time relationship existed between matings and ovulation. The results regarding fertilization were corroborated by the foaling rate of the following year. The sexual behavior of a stallion was constantly recorded during activity, writing down the frequency of mating. Mating was considered successful if a stallion mounted the mare, inserted his penis in her vulva, performed friction movements, waved his tail like a flag, and jumped down with a slackened penis. At every whole hour, behavior was recorded for the entire herd. As observations progressed, mares in heat in Herd C were examined rectally and ultrasonically once daily. A mare was identified as in heat if she offered herself to the stallion, moved her tail to the side, winked her vulva, urinated, and stood still when he mounted her. Additional criteria evaluated included the condition of her uterus as well as the consistency and size of her follicles. The goal was to determine the relationship in time between matings and ovulation. Results When Stallion A is led to mares, he starts checking which of them are in heat. Next he drives them together into one group and keeps them that way during the mating season. Stallion B ranges together with his harem out in the pasture throughout the year. During the mating season, on the other hand, he keeps his mares together in a close group, although this strict order becomes relaxed after the mating season. Both of these stallions are experienced. Stallion C, by contrast, is inexperienced, and to begin with does not drive the mares together, but stays in their near vicinity. After some twelve hours he does chase the mares together; nevertheless, he does not keep the herd together under such strict order as the older stallions. For the greater part of the time, the stallions stay outside the herd. When the mares are grazing, the stallion is stationed either behind or beside the herd. From time to time, mares try to distance themselves from the herd. These mares are then driven back by Stallions A and B, which demonstrate a particular posture: they lay back their ears, drop their heads down to the ground with an outstretched neck, and circle the mares while maintaining this remarkable posture. The mares thereby become afraid of the stallions and run back. In fact, often it is enough for the stallion to call the mares and they will return right away. The inexperienced stallion, however, does not react so strongly; if his mares leave the group, he lets them have more free rein. When the herd moves, all three stallions stay behind it; in addition, they regularly drive their harem from place to place. As the harem moves, the stallions follow it, seeking out spots of feces and urine. The stallions then smell of them, often show the flehmen response (though not always), and deposit feces or urine on top. This behavior happens very often every day and seems important to the stallion. Both the stallion and mare are active during the mating period. A few days before the mare is covered by the stallion, she seeks out his presence. At that time, he often smells of her and perhaps makes an effort to mount her, though it may take up to two days for her to accept him. During this time, which might be called pre-estrus, the mare will not permit the stallion to mount her, but strikes him away. In contrast, when she comes in heat, she offers herself to him, lifts her tail to the side, pushes her back end in front of his head, everts her vulva, urinates, and stands still as he mounts. By this point in time, the mare is ready for conception and is covered by the stallion. Prior to commencing the act of mating, there is often some foreplay: nose-to-nose contact begins between the stallion and mare, who offers him her rear end and stands still. The stallion sniffs the mare from front to back - mostly however the vicinity of the mare’s genitals. She lifts her tail, winks her vulva, and urinates; this behavior seems important for the stallion. After sniffing her genital area for some time, he extends his penis from its sheath and it erects. After a short moment, the stallion mounts the mare and fulfills the act of mating. When he has ejaculated, he remains for a few seconds on the back of the mare before jumping down. Usually, the act of mating lasts less than one minute. A stallion and mare in heat often stay in the vicinity of each other. While they are grazing, it occurs that the stallion will abruptly mount and cover her without any further foreplay, after which they will continue grazing together. Moreover, it may happen that the stallion, standing outside the herd, will suddenly stop grazing, run neighing into the middle of the harem, mount one of the mares without foreplay, and service her. The older stallions, A and B, tried in exceptional instances to mate with mares that were out of heat or in the pre-estrus stage. Such mares defended themselves, trying to strike off the aggressive stallion with their back legs or to run away. In that case, the stallions chased the mares until they gave up, or the stallions stopped if the mares got their way. In stubborn cases, Stallion B chased mares systematically until they gave up; these pursuits could last 20-30 minutes, depending on how persevering the mare was. If the mare did not give up, the stallion treated her viciously and even injured her - a behavior he demonstrated three times. Two of the mares were pregnant and no other mare in heat at the time. The third mare was unbred, but not yet in heat. As for the inexperienced Stallion C, he never demonstrated this behavior. One mare was turned into his herd two days after the others. He refused to allow her to enter among the other mares until she came into heat. Not till then was she accepted into the herd and covered. In Herd I there were observations of Stallion A mounting pregnant mares. Pregnant mares were observed mounting mares in heat in his herd as well as in the herd of Stallion C; in fact, it once even happened that a mare mounted Stallion A, who tolerated it. The mares of this herd grew up together and have lived for years as one family. It was obvious that mares of this herd had built up strong ties of friendship with each other, of which the most common form was a two-party relationship between a couple of mares. In this case, when one of the mares in such a friendly relationship was in heat and the other had not yet foaled, there were frequent observations of the pregnant mare defending the one in heat, so that the stallion had great difficulty servicing it. Then the pregnant mare pushed in between the stallion and the mare in heat, raised her tail, winked her vulva and urinated as if she was also in heat. In addition, if the pregnant mare noticed the stallion marching up, she acted like a stallion herself. She then chased the mare in heat, bit her in the flanks, sniffed her genital area and performed flehmen. These mares also smelled the excretions of the mares in heat, showed the flehmen response, and urinated on these spots. This behavior of the mares obviously disturbed the stallion. Moreover, he often chased mares in heat away when they sought to be near him, even when they offered themselves, winked their vulvae and urinated; he simply did not want them. Discussion The reproductive behavior of the Icelandic horse is no different from that of other breeds, as described by other authors (Asa et al, 1979; Asa, 1986; Bristol, 1982; McDonnell, 1992; Tyler, 1972). Stallions and mares were both active during mating. When the mares came in heat, they sought to be near the stallion and offered themselves to him. Stallions drove the mares together in a tight group (Antonius, 1937; Ebhardt, 1957; McDonnell, 1986), which was perhaps to find out which mares were in heat. When the herd moved, the stallion remained beside it, and when the herd grazed, behind it. Stallions meticulously investigated a place where the mares had stayed, looking for feces and urine spots from the mares and sniffing them. Sometimes, though not always, the stallions would then urinate at these spots or deposit feces themselves and perform flehmen. It could be that the stallion in this manner sensed the proximity of ovulation in the mares, possibly through pheromones. The fact that Stallions A, B, and C only serviced the mares for respectively 3.8, 2.3 and 2.4 days during their estrus , although the average duration of estrus was 6.25, 4.4 and 4.7 days respectively, supports this surmise. The shorter period of time in heat during which the stallion covered a mare is subsequently referred to as the servicing period. Asa (1986) assumes that mares in heat attract the attention of a stallion toward themselves not only through winking and urinating, but also through pheromones. Houpt and Guida (1984) and Cromwell-Davis and Houpt (1985) feel that flehmen also plays an important role in recognizing heat. The stallions serviced the mares at all times of the day, with the frequency increasing between 00:00 hours and 06:00 hours. Perhaps this can be explained by the fact that the horses usually rested between sunset and sunrise. The stallions were extremely active in the morning hours. It was in the evening time that mating activity was lowest, i.e. from 18:00 hours to 24:00 hours for Stallions A and C, and between 06:00 hours and 12:00 hours for Stallion B. Stallion A covered mares successfully 37 times in ten days during the 24-day observation period, with a mating frequency of zero to nine times daily, which averaged to 3.7 times a day. He rejected mares with a foal by them and outside of a single exception serviced only unbred mares. He mounted 65 times without success. After that stallion had stayed with the mares for eight weeks, the next year’s foaling rate measured 31%. An andrological examination revealed severe hypospermia, while a palpatory examination showed a soft consistency and smaller size of the right testicle as compared to the left testicle. This explains the poor foaling rate and indicates how important a health and sexual examination is concerning the minimum demands for stallions (Klug, 1982; Kenney, 1983; Merkt and Klug, 1989). Stallion B was observed for 41 days. Six mares in his herd had foals during the period of observation, and five of the mares were successfully bred during foal heat, while the sixth did not go into heat during the period of observation. This stallion only needed to worry about one mare at a time, because no two mares foaled simultaneously and the other mares were already bred. During 13 days of breeding activity, these mares were serviced 30 times, or between zero and seven times per day for an average of 2.3 times daily. During. The following year, the foaling rate totaled 87%, counting the entire herd of mares. Stallion C was an inexperienced three-year-old stallion, observed for 28 days. During 19 days of breeding activity, he serviced ten mares 57 times, or from zero to eight times per day, for an average of 3.0 times a day. The foaling rate of the following year measured 90%. The mating outcomes for Stallions A, B and C brought out a similar mating frequency per day (0-9, 0-7, 0-8), as well as a similar average for mating frequency per day (3.7, 2.3, 3.0). The mating frequency per mare was most even for Stallion C, even though up to seven of his mares were in heat at once. Stallions A, B and C needed an average of 9.0, 6.0 and 5.7 mounts per mare while she was in heat. The average number of mounts/mare/estrus for Stallion A (9.0) can not be judged as normal, because, as mentioned above, he suffered from severe hypospermia and presented a hypoplasia and inadequate consistency of his right testicle. The mounts/mare/estrus for Stallions B and C (~6.0), on the other hand, can be viewed as in the range of normal. These stallions were 15, 9 and 3 years old, and their mean numbers of unsuccessful mounts were 8, 6 und 3. Mares offering themselves energetically to the stallion were serviced ahead of those acting shy. If many mares at once were in heat, it occurred that the stallion did not cover some of the mares over a certain period of time. Seven mares went into heat simultaneously for Stallion C. During a 24-hour period he only covered four of them; moreover, they were serviced with varying frequency. The other three mares were not serviced; however, they stayed in heat longer than the bred ones. This indicates that stallions have a performance limit, so that the danger exists of a stallion supplied with too many mares over a heat period leaving out some mares that are in heat. The average duration of estrus in the mares with Stallions A, B and C was 6.25, 4.4 and 4.7 days. While the mares of Stallions B and C were in heat for similar lengths of time, Stallion C had to worry about more mares than Stallion B, which perhaps explains why the average duration of estrus in his mares was a slight degree higher. On the other hand, the servicing period was shorter, although the mares were in heat and ready for conception. The servicing period averaged 3.8 days for Stallion A, 2.3 days for Stallion B and 2.4 days for Stallion C. Here, too, the figures for Stallions B and C are similar. This difference between the average duration of estrus and the average servicing period supports the theory that a stallion can find out the time of ovulation of the mares. According to mating figures for the harem of Stallion C, the servicing period for mares Nos. 1-10 lasted from 0.5 to 6.3 days, and these same mares were in heat for one to seven days. The mating frequency, in contrast, was more even, or from four to seven mounts/mare, for an average of 5.4 mounts/mare. This may mean that a high mating frequency over a short time could stimulate ovulation. Acknowledgement In memory of Professor Hans Merkt, Direktor des Instituts für Andrologie und Besamung der Haustiere, School of Veterinary Medicine, Hannover, Germany, who leant me insight into the world of equine reproductive medicine. References Antonius O (1937) Über Herdenbildung und Paarungseigentumlichkeiten der Einhufer. Z Tierpsychol 1: 259-267. Asa CS, Goldfoot DA, Ginther OJ (1979) Sociosexual behavior and the ovulatory cycle of ponies (Equus caballus) in harem groups. Horm Behav 13: 49-65. Asa CS (1986) Sexual behavior of mares. Veterinary Clinics of North America Equine Practice Vol 2 (3): 519-534. Berger J (1983) Induced abortion and social factors in wild horses. Nature 303: 59-61 Bristol F (1982) Breeding behavior of a stallion at pasture with 20 mares in synchronized oestrus. J Reprod Fert Suppl 32: 71-77. Crowell-Davis S, Houpt KA (1985) The ontogeny of flehmen in horses. Anim Behav 33: 739-745. Ebhardt H (1957) Drei unterschiedliche Verhaltensweisen von Islandpferden in norddeutschen Freigehegen. Säugetierkundl, Mitt, Stuttgart 5: 113-117. Houpt KA, Guida L (1984) Equine behavior. EqPract 6: 32-35. Hugason K, Árnason T, Jónmundsson JV (1985) A note on the fertility and some demographical parameters of Icelandic tölter horses. Livestock Prod Sci 12: 161 –167. Jezierski T, Jaworski Z (1995) Polnische Koniks aus Popielno Institut für Genitik und Tierzucht der Polnischen Akademie der Wissenschaften. Jastrzebiec, 05 – 551, Mroków Polen. Keiper R, Houpt K (1984) Reproduction in feral horses: An eight-year study. Am J Vet Res 45: 991-995. Kenney RM (1983) Clinical Fertility Evaluation of the Stallion. J Soc Theriogenology Vol IX, Part II: The Stallion. Hastings, Nebraska. Klug E (1982) Untersuchungen zur klinischen Andrologie des Pferdes Hannover. Tierärztl. Hochschule, Habil-Schrift. McDonnell SM (1986) Reproductive behavior of the stallion. Veterinary Clinics of North America Equine Practice Volume 2 (3): 535-555. Merkt H (1975) Massnahmen zur Fruchtbarkeitsförderung in der Pferdezucht am Beispiel der Vollblutzucht. Arch Tierärztl Fortbildung. Merkt H, Klug E (1989) Gesundheitliche und geschlechtliche Mindestanforderungen an Zuchthengste. Dtsch tierärztl Wschr 96: 433-472. Salter RE, Hudson RJ (1982) Social organization of feral horses in Western Canada. Applied Animal Ethology 8: 207-223. Stegen H (1934) Die Zucht des hannoverschen Pferdes – unter besonderer Berücksichtigung der Fruchtbarkeitsverhältnisse. Dt ges Züchtungskunde 66: 1-24. Schaper, Hannover. Tyler SJ (1972) The Behavior and Social Organization of the New Forest Ponies Anim Behav Mono 5: 175-188. |
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