Many animal species have developed social structures which favor the formation of harem-type social groupings. For these species, there is typically a single dominant male in the group along with multiple mature females and their respective offspring. Species with this type of social structure have presented some difficult problems for captive breeding programs in traditional zoos: although the ultimate structure of these groups is typically composed of more females than males, a similar number of both sexes are born. This gender ratio is further complicated by the fact that the majority of traditional zoo facilities cannot provide adequate space for the subordinate males to break away from the main group (as they would do in the wild) to escape physical harm from conflicts with the dominant male. The result is that captive populations often have numerous males that are difficult to maintain in a social group. The aim of this study was to assess the effectiveness of long-acting neuroleptics as an aid in the establishment of a bachelor herd comprised of mature male Mongolian wild horses.
The Mongolian wild horse (also known as Przewalski’s horse), which generally exhibits a single male, multi-female social structure, is extinct in the wild and has been one of the true success stories of organized captive breeding efforts around the world.2 Previous attempts to have more than one mature (older than 5 yr) stallion in a social grouping have resulted in extreme aggression between the males, often resulting in significant injury and on occasion, even death.5 As a result, the large number of males that is necessary for the genetic and demographic aspects of the captive population are maintained individually in zoos, thereby utilizing significant amounts of the limited space which is available for captive breeding programs. Working with the Mongolian wild horse Species Survival Plan (SSP), the Wilds identified eight mature (mean age 6.6 yr) males and established a fenced, 200-acre enclosure in which these animals could be maintained together as a bachelor group.
To facilitate the formation of this group, each animal was administered a long-acting neuroleptic (LAN), perphenazine enanthate (Trilafon® enanthate 100 mg/ml, Schering-Plough, 2000 Galloping Road, Kenilworth, NJ 07033 USA) in combination with a mid-duration neuroleptic, haloperidol (haloperidol tablets, USP, 10 mg, Par Pharmaceutical, Inc., Spring Valley, NY 10977 USA) prior to release into the pasture. Long-acting preparations of neuroleptic agents have been used in the medical field for many years to aid in the treatment of human psychoses, but have recently been used extensively in wildlife species in southern Africa to aid in the translocation and the adaptation of wild animals to new environments.3
Perphenazine is a member of the phenothiazine group of neuroleptic drugs. The effects of the long-acting formulation are generally not seen for 10–12 h after deep, intramuscular injection but tranquilization remains effective for approximately 7 days.4 The peak effect is usually reached after a period of 72 h, and for this reason, perphenazine enanthate is often combined with another, more rapidly acting neuroleptic such as haloperidol. Haloperidol is a neuroleptic drug that is a member of the butyrophenone group of compounds and may be injected or administered orally. The effects of this drug are seen within several hours of oral administration and last for approximately 10–12 h.1
In this study, weights of individual animals were estimated (325–375 kg) and perphenazine was given by intramuscular injection at a dose rate of 0.5 mg/kg and was administered 48 h prior to release of the animals into the pasture. The drug was delivered by projectile syringe (Pneu-Dart Inc., Williamsport, PA 17703 USA) and was injected into the muscles of the neck or shoulder. In addition, each animal was administered oral haloperidol at a dose rate of 0.3 mg/kg 2 h prior to release. All animals were individually identified and marked and all entered the new pasture area within a 1-h period. Observations of the release were performed and all animal interactions were recorded daily for a period of 10 days. Several phases of the introductory period were recorded on video tape.
Close observation revealed minimal interaction between animals upon release and there was significantly less aggression exhibited than expected. The animals formed a loosely structured group shortly after being placed together and the 7–8 day period of tranquilization was characterized by minimal aggression, excitement and anxiety without significant sedation. During this time, the animals became familiar with their surroundings, the boundaries of the pasture and with each other. The effect of tranquillization on herd formation was remarkable: by the end of the observation period, when the neuroleptic drugs were assumed to be no longer effective, it was evident that a level of dominance and social order had been effectively established within the group, with no significant injuries incurred as a result of fighting. The eight Mongolian wild horses involved in this study continue to thrive in this bachelor group and after 4 mo of daily observation, the initial social order appears to have remained intact and there has been no significant aggression observed between the animals.
1. Blumer, E. S. 1991. A review of the use of selected neuroleptic drugs in the management of nondomestic hoofstock. Proceedings American Association of Zoo Veterinarians. Pp. 333–339.
2. Boyd, L and K. A. Houpt. 1994. Introduction. In: Boyd, L and K. A. Houpt (eds). Przewalski’s Horse. The History and Biology of an Endangered Species. State University of New York Press, State University Plaza, Albany, N.Y., 12246. Pp. 1–4.
3. Ebedes, H. 1993. The use of long-acting tranquillizers in captive wild animals. In: McKenzie A. A. (ed). The Capture and Care Manual: Capture, Care, Accommodation and Transportation of Wild African Animals. Wildlife Decision Support Services CC and The South African Veterinary Foundation. Box 73528, Lynnwood Ridge, 0040 South Africa. Pp. 71–99.
4. Larsson, M., R. Axelsson and A. Forsman. 1984. On the pharmacokinetics of perphenazine: a clinical study of perphenazine enanthate and decanoate. Curr. Ther. Res. 36:1071–1088.
5. LaRue, M. D. 1994. Introduction. In: Boyd, L and K. A. Houpt (eds). Przewalski’s Horse. The History and Biology of an Endangered Species. State University of New York Press, State University Plaza, Albany, N.Y., 12246. Pp. 333–339.