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Seasonal Changes in Body Condition of Przewalski's Horses in a Seminatural Habitat
Journal of Equine Veterinary Science 42 (2016) 73–76
Contents lists available at ScienceDirect
Journal of Equine Veterinary Science journal homepage: www.j-evs.com
Short Communication
Seasonal Changes in Body Condition of Przewalski’s Horses in a Seminatural Habitat Kristin Brabender a, *, Waltraut Zimmermann b, Brian Hampson c a
Hortobágy National Park Directorate, Hungary Cologne Zoo, Köln, Germany c Equine Consultancy, Sunshine Coast, Australia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 November 2015 Received in revised form 6 March 2016 Accepted 15 April 2016 Available online 29 April 2016
Identification of the normal fluctuations in body condition of equids is important for the monitoring and management of wild and feral equid populations. Knowledge of the causative factors and implications of body condition fluctuations may allow managers to better respond with interventions when body condition fluctuations are unseasonal or extreme. The body condition score (BCS) of 33 adult Przewalski’s horses (22 mares and 12 harem stallions) roaming freely in a population in excess of 300 in the Hortobágy Puszta in Hungary was assessed weekly for 12 months from January to December 2009. Mares had a higher mean BCS than stallions for each month of the year, and all horses maintained a moderate to fleshy condition score. There were two peaks and two troughs in BCS for both mares and stallions. It appears that an annual fluctuation of body condition of Przewalski’s horses is normal for horses living in a semiwild habitat. This can be explained by seasonal variation in pasture quality, an energy cost to mares in late gestation and early lactation, and a large energy cost to mares and stallions in protecting new born offspring from aggressive attacks by rival stallions and the work of band stallions protecting against challenging stallions. Although there was a seasonal fluctuation in body condition, semiwild horses living in a former wild horse habitat were never in poor condition. Managers of domestic, feral, and wild horses may tolerate a small reduction in body condition of horses during the annual seasonal cycle. Ó 2016 Elsevier Inc. All rights reserved.
Keywords: Przewalski’s horse Feral horse Body condition Population management Semireserve
1. Introduction The European wild horse, also known as Tarpan (Equus ferus gmelini), was hunted to extinction in the 19th century [1]. The Przewalski’s horse (Equus ferus przewalskii), also known as Mongolian wild horse or Takhi, is the only surviving wild relative of the domestic horse. It can be regarded as a representative of a group of related species, which were once widely distributed over Europe and Asia and from which the domestic horse derived [2]. The
* Corresponding author at: Kristin Brabender, Hortobágy National Park, PetTfi tér 13, 4071 Hortobágy, Hungary. E-mail address: [email protected] (K. Brabender). 0737-0806/$ – see front matter Ó 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2016.04.014
Przewalski’s horse became extinct in the Gobi desert in the late 1960s, but the species has returned to its natural habitat and other areas in the range of Mongolia and China due to breeding and reintroduction programs [3–7]. Przewalski’s horses have been roaming freely since 1997 in the Hortobágy Puszta in Hungary which is part of the largest Central European steppe area. In Hungary, preserving open grassland with large herbivore species is no longer possible with the wild Tarpan, so Przewalski’s horses were introduced for managing the landscape in the Pentezug area of the Hortobágy Puszta [8]. This herd size now exceeds 300 head and presents a good opportunity to study wild horses in a semiwild habitat. In recent decades, feral horses (Equus ferus caballus) have been introduced into European ecosystems for rewilding [9] to assist in keeping landscapes
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K. Brabender et al. / Journal of Equine Veterinary Science 42 (2016) 73–76
open as was their role in former times. However, large herds of wild horses have never been studied in European ecosystems so there is limited knowledge of wild horse ecology in these habitats. The large herd of semiwild Przewalski’s horses in the Hortobágy Puszta in Hungary represent the best opportunity available to study wild horse ecology. The goal of the present study was to investigate the body condition over a 12-month period of a large healthy group of adult mares and stallions living in a freeroaming European habitat. This data may then be used as a comparison to other feral and wild horse herds and to assist rangeland and wildlife managers to assess herd health throughout seasonal cycles. Identification of season patterns of body condition may also inform domestic horse (Equus ferus caballus) managers of important aspects of natural horse ecology.
from January to December 2009 using a standardized 9-point scoring system [10]. Values of 1 to 9 corresponded to the following descriptions for body condition: poor, very thin, thin, moderately thin, moderate, moderate to fleshy, fleshy, fat, and extremely fat. The body condition scoring system is based on the prominence of the bones and the thickness of muscle and fat layer of the horse. In this study, only visual assessments could be conducted, similar to the scoring system described in Rudman and Keiper [11]. Data for mares and stallions were managed separately as these groups of horses have quite different roles in the herd structure which was thought likely to affect body condition. The study was approved by Chief Veterinarian Dr Pál Póser of the Hajdú-Bihar County Agricultural Task OfficedDirectorate for Food chain Security and Animal Health Affairs according to Hungarian ethical restrictions.
2. Material and Methods 2.4. Statistical Analyses 2.1. Study Area The study was performed in the Pentezug, a steppe area which is now a biosphere reserve for wild horses. Its area is 2,388 ha (27 ha wood, 2,361 ha meadow) and is situated in the middle of the Hortobágy Puszta, Hungary. Pentezug is a former grass land that during summer is characterized by yellow meadow inula, and the blue thrift which is endemic for the Hungarian lowland plane. Like the rest of the Hortobágy steppe areas, Pentezug is characterized by a narrow mosaic of different plant communities. In addition to marsh plant communities which make about 10% of the area, at least three different grass communities occur in the drier areas. These can be roughly structurally divided into long grass and short grass steppe. The long grass or meadow covers about 15% of the area, 44% are covered with short grass steppe which is rich in Fescue species. About 30% is eroded area loosely covered with plants tolerant of salt. The climate is semiarid and is described as subcontinental wood and steppe climate [1]. The average temperature is 21 C (max 38 C) in July and 2.5 C (min 28 C) in January. The annual rainfall is 500 mm and snow falls on average 40–45 days per year (range, 2–10 cm). 2.2. Study Population
The significance of differences in body condition of mares and stallions over the whole study period, such as the differences of female body condition before and after foaling of the individuals, was tested with Mann–Whitney U-test, chi squared, with a P value <.01. 3. Results The mean (standard deviation [SD]) BCS for stallions for the 12-month period of the study was 7.3 (0.29) with a monthly mean range from 7.0 to 7.8. Stallions showed little variability among the group with the largest monthly SD of 0.3 scale points. The lowest BCS for stallions was 6 and the highest was 8. The mean (SD) BCS for mares for the 12month period was 7.9 (0.17) with a monthly mean range from 7.6 to 8.2. Mares showed similarly little variability among the group with the largest monthly SD of 0.4 scale points. The lowest BCS for mares was 7, and the highest was 9. The mean monthly BCS for stallions and mares is displayed in Fig. 1. The body condition of mares and stallions differed significantly over the whole year with the stallion values being slightly lower than the mare values (Mann–Whitney U-test, chi squared ¼ 349.3326; df ¼ 1; P value < .0001).
The study herd has a population of 310 horses and consists of approximately equal number of males and females, divided into approximately 25 of semistable social bands. The herd is relatively unmanaged, and breeding and social structures are natural processes. Thirty-three mature aged horses (21 mares and 12 harem stallions) were randomly selected for the study. Individual horses in this herd have been catalogued and can be identified by sex, color, and markings. All harem stallions belonged to separate harem bands, and all mares belonged to harem bands. 2.3. Body Condition Score The body condition score (BCS) of each horse was assessed weekly by the author (K.B.) for a 12-month period
Fig. 1. The mean monthly BCS of 33 adult Przewalski’s horses (22 mares and 12 stallions) roaming freely in a population in excess of 300 in the Hortobágy Puszta in Hungary assessed weekly for 12 months from January to December 2009 according to the Henneke BCS system.
K. Brabender et al. / Journal of Equine Veterinary Science 42 (2016) 73–76
There was no difference in female body conditions before and after foaling (Mann–Whitney U-test, chi squared ¼ 0.0007; df ¼ 1; P value ¼ .9982). 4. Discussion During the course of evolution, wild equids adapted to climatic and seasonal changes causing fluctuations in temperature, food abundance, and availability of water. In this landscape, seasonal fluctuations in body condition dynamics appear natural. Free-living equids have the possibility to avoid some negative factors causing a decline of body condition, such as food shortage and climatic extremes, by migrating great distances to habitats that offer more favorable conditions [3,5,6]. Equids living in captivity or confined reserves are forced to cope with the conditions presented in their surroundings. Therefore, it is important for animal and range managers to identify their needs and respond accordingly. The monitoring of the body condition can be a useful technique for the management of wild and feral horse populations and horses kept under seminatural conditions in reserves [3,12]. A decline of body condition can hint to food limitation due to too high density of grazers in the area, unsuitable vegetation, and health problems, such as parasite infestation, disease, tooth problems, or painful injuries [4,13]. A high abundance of biting insects in summer can also influence activity patterns, habitat use, and feeding behavior of free-roaming horses [5,6,11,14] and thus can also have an effect on the body condition of horses. The knowledge of normal annual fluctuations in body condition of horses living in a habitat may help managers to identify episodes when animals are stressed. This knowledge can assist managers in assessing optimal population density and timing of implementation of management interventions when required. Furthermore, when choosing individuals suitable for transports and reintroduction to the wild, consideration of body condition is an important factor impacting survival [6]. Numerous seasonal factors influence the body condition of horses and thus affect the health status, fitness, longevity, and reproductive success [4]. A fair-to-good body condition is considered optimal for horses irrespectively of their living conditions. Obesity is known to increase the risk of metabolic disease [15,16]. Low body condition reduces the fitness of horses, can have a negative effect on fertility [10,11,14], increases vulnerability to infectious diseases and parasites, and can be a symptom of serious disease or severe pain [16–21]. Free ranging Przewalski’s horses in Mongolia live in separated harem and bachelor groups with overlapping home ranges [5]. Since 2006, horses in the present study population have displayed unusual spatial organization. The majority of harem groups and bachelor stallions in Pentezug stay in close vicinity to each other. Visually, this population of horses appears to be one large herd, although closer observation identifies clear groupings within the larger herd structure [8]. This leads to a high frequency of agonistic interactions between the stallions, especially during the foaling and breeding season from late April till July [8]. Harem stallions suffer from high
75
stress, protecting their mares and foals against challenging bachelor stallions and competing harem stallions [22]. Stress is a possible factor influencing the body condition in this study as harem stallions show a lower BCS the whole year round than nursing and pregnant mares. The negative effect of stress on BCS has been reported in Kaimanawa feral horses in New Zealand, where mares in multistallion bands suffered more intraspecific aggression and showed significantly lower BCS than mares in singlestallion bands [15]. However, feral horses in Australia avoid unnecessary fighting and stress during the breeding season by maintaining a large physical separation between harem bands and avoidance of congestion at water holes [23]. Przewalski’s horses in the Pentezug population behave quite differently. The majority of the Pentezug population chose close contact and are subject to the inevitable consequences of stress from regular aggressive contact between challenging stallions. Although feral horses have been reported to be aggressive particularly during mating season, the main defense of harem bands appears to be avoidance of other horses [23]. The benefits of a social structure with single-stallion bands in contrast to multistallion bands are significantly higher fecundity of mares, better BCS, and lower parasitic loads in faecal samples due to decreased exposure of the individuals to stallion harassment [15]. The social structure of the Pentezug Przewalski’s horses population with a herd of several single-stallion bands in close vicinity appears to be reflected in the lower BCS of the stallions which have to invest much energy to protect their mares from the harassment of other stallions. Further investigations are needed to ascertain the reasons for the “herd” structure which does not appear in other free ranging Przewalski’s horse populations, but is reported from Camargue horses as well [14]. The majority of mares in the present study population foal in May and June, so that the main reproductive season lasts until July [8]. If food is not limited and forage quality is good, which is the case in the Pentezug, pregnancy and lactation apparently have no remarkable negative effect on the body condition of mares. This observation is in keeping with the reports of free-living Przewalski’s horses in Hustai National Park in Mongolia [6]. In habitats with food limitation or poor forage quality, lactating mares in feral horses showed significantly lower BCS than stallions and nonlactating females [11]. In the Pentezug, insect harassment in July and August is high and horses spend most of the day resting in dust bathes [22], using the cooler evening and morning hours to graze. Reduced grazing activity during daytime in summer is reported from free-living Przewalski’s horses in Mongolia as well [3–7]. This might be an explanation for the slightly reduced BCSs for both stallions and mares in that time of the year. In autumn, breeding season is over and insect harassment is reduced remarkably. Horses spend most of the day grazing in September and October [8], which results in a peak of BCS for both sexes in the middle of October. During the winter months, body condition decreases slightly, which can be explained by a reduced energy value of food in combination with low temperatures (up to 20 C) in the area.
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5. Conclusion This study highlights the advantage for wildlife managers of keeping historical records of population BCS. Significant reductions in BCS of a population compared to historical population data can signal food limitation or increased stress level of the horses and thus might indicate the need to reduce population size in the given area, the presence of predators, or abnormal social dynamics in the population. A decrease of BCS of individuals can be symptomatic of disease, injury, or unusual stress. Acknowledgments The authors are very grateful to Dr Zsolt Végvári, University of Debrecen, for the support with the statistical analyses.
[7]
[8]
[9] [10] [11] [12]
[13] [14] [15]
[16]
References [17] [1] Zimmermann W, Kolter L, Sandor I, Dukat Z. Przewalskipferde in der Hortobágy-Pusztadein Naturdund Artenschutzprojekt. Z Kölner Zoo 1998;41:37–55. [2] Nobis G. Vom Wildpferd zum Hauspferd. Köln: Böhlau Verl; 1971. [3] van Dierendonck MC, Bandi N, Batdorj D, Dügerlham S, Munkhtsog B. Behavioural observations of reintroduced Takhi or Przewalski’s horse (Equus ferus przewalskii) in Mongolia. Appl Anim Behav Sci 1996;50:95–114. [4] Bandi N, Usukhjargal D. Reproduction and mortality of reintroduced Przewalski’s wild horse Eqqus przewalskii in Hustai National Park, Mongolia, International Wild Equid Conference, Vienna. 2012 Contributed Presentation. [5] King SRB. Home range and habitat use of free-ranging Przewalski’s horses at Hustai National Park, Mongolia. Appl Anim Behav Sci 2012;78:103–13. [6] Souris A-C, Kaczensky P, Julliard R, Walzer C. Time budget-, behavioural synchrony- and body score development of a new released Przewalski’s horse group Equus ferus przewalskii, in the
[18] [19] [20]
[21]
[22]
[23]
Great Gobi B strictly protected area in SW Mongolia. Appl Anim Behav Sci 2007;107:307–21. Boyd L, Bandi N. Reintroduction of takhi, Equus ferus przewalskii, to Hustai National Park, Mongolia: time budget and synchrony of activity pre- and post-release. Appl Anim Behav Sci 2002;78:87–102. Zimmermann W, Brabender K, Kolter L. A Przewalski’s horse population in a unique European steppe reservedthe Hortobágy National park in Hungary. Praha: EQUUS, Zoo Praha; 2000. p. 257–84. Linnartz L, Meissner R. Rewilding horses in Europe. Nijmegen, The Netherlands: Rewilding Europe; 2014. Henneke DR. A condition score system for horses. Equine Pract 1985;7:13–5. Rudman R, Keiper RR. The body condition of feral ponies on Assateague island. Equine Vet J 1991;23:453–6. Scorolli AL. Feral horse body condition: a useful tool for population management? International Wild Equid Conference, Vienna, Contributed Poster. 2012. Zimmermann W, Sándor I, Brabender K. Naturschutzprojekt HortobágydJahresbericht 2008. Z des Kölner Zoo 2009;52:47–60. Duncan P. Horses and grasses. New York: Springer Verlag; 1992. Linklater WL, Cameron EZ, Minot EO, Stafford KJ. Stallion harassment and the mating system of horses. Anim Behav 1999;58: 295–306. Brown CM. The diagnostic value of the D-xylose absorption test in horses with unexplained chronic weight loss. Br Vet J 1992;148: 41–4. Frank N, Geor RJ, Bailey SR, Durham AE, Johnson PJ. Equine metabolic syndrome. J Vet Intern Med 2010;24:467–75. Parker JL, White KK. Lyme borreliosis in cattle and horses: a review of the literature. The Cornell Veterinarian 1992;82:253–74. Laverty S, Pascoe JR, Ling GV, Lavoie JP, Ruby AL. Urolithiasis in 68 horses. Vet Surg 1992;21:56–62. Sellon DC, Roberts MC, Blikslager AT, Ulibarri C, Papich MG. Effects of continuous rate intravenous infusion of butorphanol on physiologic and outcome variables in horses after celiotomy. J Vet Intern Med 2004;18:555–63. Adams AA, Katepalli MP, Kohler K, Reedy SE, Stilz JP, Fitzgerald BP, Lawrence LM, Horohov DW. Effect of body condition, body weight and adiposity on inflammatory cytokine responses in old horses. Vet Immun Immunopathol 2009;127:286–94. Zimmermann W, Kolter L, Sándor I, Kerekes V. Naturschutzprojekt HortobágydJahresbericht 2005 und 2006. Z des Kölner Zoo 2007;1: 35–48. Hampson BA, de Laat MA, Mills PC, Pollitt CC. Distances travelled by feral horses in ‘outback’ Australia. Equine Vet J 2010;42:582–6.
Contents lists available at ScienceDirect
Journal of Equine Veterinary Science journal homepage: www.j-evs.com
Short Communication
Seasonal Changes in Body Condition of Przewalski’s Horses in a Seminatural Habitat Kristin Brabender a, *, Waltraut Zimmermann b, Brian Hampson c a
Hortobágy National Park Directorate, Hungary Cologne Zoo, Köln, Germany c Equine Consultancy, Sunshine Coast, Australia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 November 2015 Received in revised form 6 March 2016 Accepted 15 April 2016 Available online 29 April 2016
Identification of the normal fluctuations in body condition of equids is important for the monitoring and management of wild and feral equid populations. Knowledge of the causative factors and implications of body condition fluctuations may allow managers to better respond with interventions when body condition fluctuations are unseasonal or extreme. The body condition score (BCS) of 33 adult Przewalski’s horses (22 mares and 12 harem stallions) roaming freely in a population in excess of 300 in the Hortobágy Puszta in Hungary was assessed weekly for 12 months from January to December 2009. Mares had a higher mean BCS than stallions for each month of the year, and all horses maintained a moderate to fleshy condition score. There were two peaks and two troughs in BCS for both mares and stallions. It appears that an annual fluctuation of body condition of Przewalski’s horses is normal for horses living in a semiwild habitat. This can be explained by seasonal variation in pasture quality, an energy cost to mares in late gestation and early lactation, and a large energy cost to mares and stallions in protecting new born offspring from aggressive attacks by rival stallions and the work of band stallions protecting against challenging stallions. Although there was a seasonal fluctuation in body condition, semiwild horses living in a former wild horse habitat were never in poor condition. Managers of domestic, feral, and wild horses may tolerate a small reduction in body condition of horses during the annual seasonal cycle. Ó 2016 Elsevier Inc. All rights reserved.
Keywords: Przewalski’s horse Feral horse Body condition Population management Semireserve
1. Introduction The European wild horse, also known as Tarpan (Equus ferus gmelini), was hunted to extinction in the 19th century [1]. The Przewalski’s horse (Equus ferus przewalskii), also known as Mongolian wild horse or Takhi, is the only surviving wild relative of the domestic horse. It can be regarded as a representative of a group of related species, which were once widely distributed over Europe and Asia and from which the domestic horse derived [2]. The
* Corresponding author at: Kristin Brabender, Hortobágy National Park, PetTfi tér 13, 4071 Hortobágy, Hungary. E-mail address: [email protected] (K. Brabender). 0737-0806/$ – see front matter Ó 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2016.04.014
Przewalski’s horse became extinct in the Gobi desert in the late 1960s, but the species has returned to its natural habitat and other areas in the range of Mongolia and China due to breeding and reintroduction programs [3–7]. Przewalski’s horses have been roaming freely since 1997 in the Hortobágy Puszta in Hungary which is part of the largest Central European steppe area. In Hungary, preserving open grassland with large herbivore species is no longer possible with the wild Tarpan, so Przewalski’s horses were introduced for managing the landscape in the Pentezug area of the Hortobágy Puszta [8]. This herd size now exceeds 300 head and presents a good opportunity to study wild horses in a semiwild habitat. In recent decades, feral horses (Equus ferus caballus) have been introduced into European ecosystems for rewilding [9] to assist in keeping landscapes
74
K. Brabender et al. / Journal of Equine Veterinary Science 42 (2016) 73–76
open as was their role in former times. However, large herds of wild horses have never been studied in European ecosystems so there is limited knowledge of wild horse ecology in these habitats. The large herd of semiwild Przewalski’s horses in the Hortobágy Puszta in Hungary represent the best opportunity available to study wild horse ecology. The goal of the present study was to investigate the body condition over a 12-month period of a large healthy group of adult mares and stallions living in a freeroaming European habitat. This data may then be used as a comparison to other feral and wild horse herds and to assist rangeland and wildlife managers to assess herd health throughout seasonal cycles. Identification of season patterns of body condition may also inform domestic horse (Equus ferus caballus) managers of important aspects of natural horse ecology.
from January to December 2009 using a standardized 9-point scoring system [10]. Values of 1 to 9 corresponded to the following descriptions for body condition: poor, very thin, thin, moderately thin, moderate, moderate to fleshy, fleshy, fat, and extremely fat. The body condition scoring system is based on the prominence of the bones and the thickness of muscle and fat layer of the horse. In this study, only visual assessments could be conducted, similar to the scoring system described in Rudman and Keiper [11]. Data for mares and stallions were managed separately as these groups of horses have quite different roles in the herd structure which was thought likely to affect body condition. The study was approved by Chief Veterinarian Dr Pál Póser of the Hajdú-Bihar County Agricultural Task OfficedDirectorate for Food chain Security and Animal Health Affairs according to Hungarian ethical restrictions.
2. Material and Methods 2.4. Statistical Analyses 2.1. Study Area The study was performed in the Pentezug, a steppe area which is now a biosphere reserve for wild horses. Its area is 2,388 ha (27 ha wood, 2,361 ha meadow) and is situated in the middle of the Hortobágy Puszta, Hungary. Pentezug is a former grass land that during summer is characterized by yellow meadow inula, and the blue thrift which is endemic for the Hungarian lowland plane. Like the rest of the Hortobágy steppe areas, Pentezug is characterized by a narrow mosaic of different plant communities. In addition to marsh plant communities which make about 10% of the area, at least three different grass communities occur in the drier areas. These can be roughly structurally divided into long grass and short grass steppe. The long grass or meadow covers about 15% of the area, 44% are covered with short grass steppe which is rich in Fescue species. About 30% is eroded area loosely covered with plants tolerant of salt. The climate is semiarid and is described as subcontinental wood and steppe climate [1]. The average temperature is 21 C (max 38 C) in July and 2.5 C (min 28 C) in January. The annual rainfall is 500 mm and snow falls on average 40–45 days per year (range, 2–10 cm). 2.2. Study Population
The significance of differences in body condition of mares and stallions over the whole study period, such as the differences of female body condition before and after foaling of the individuals, was tested with Mann–Whitney U-test, chi squared, with a P value <.01. 3. Results The mean (standard deviation [SD]) BCS for stallions for the 12-month period of the study was 7.3 (0.29) with a monthly mean range from 7.0 to 7.8. Stallions showed little variability among the group with the largest monthly SD of 0.3 scale points. The lowest BCS for stallions was 6 and the highest was 8. The mean (SD) BCS for mares for the 12month period was 7.9 (0.17) with a monthly mean range from 7.6 to 8.2. Mares showed similarly little variability among the group with the largest monthly SD of 0.4 scale points. The lowest BCS for mares was 7, and the highest was 9. The mean monthly BCS for stallions and mares is displayed in Fig. 1. The body condition of mares and stallions differed significantly over the whole year with the stallion values being slightly lower than the mare values (Mann–Whitney U-test, chi squared ¼ 349.3326; df ¼ 1; P value < .0001).
The study herd has a population of 310 horses and consists of approximately equal number of males and females, divided into approximately 25 of semistable social bands. The herd is relatively unmanaged, and breeding and social structures are natural processes. Thirty-three mature aged horses (21 mares and 12 harem stallions) were randomly selected for the study. Individual horses in this herd have been catalogued and can be identified by sex, color, and markings. All harem stallions belonged to separate harem bands, and all mares belonged to harem bands. 2.3. Body Condition Score The body condition score (BCS) of each horse was assessed weekly by the author (K.B.) for a 12-month period
Fig. 1. The mean monthly BCS of 33 adult Przewalski’s horses (22 mares and 12 stallions) roaming freely in a population in excess of 300 in the Hortobágy Puszta in Hungary assessed weekly for 12 months from January to December 2009 according to the Henneke BCS system.
K. Brabender et al. / Journal of Equine Veterinary Science 42 (2016) 73–76
There was no difference in female body conditions before and after foaling (Mann–Whitney U-test, chi squared ¼ 0.0007; df ¼ 1; P value ¼ .9982). 4. Discussion During the course of evolution, wild equids adapted to climatic and seasonal changes causing fluctuations in temperature, food abundance, and availability of water. In this landscape, seasonal fluctuations in body condition dynamics appear natural. Free-living equids have the possibility to avoid some negative factors causing a decline of body condition, such as food shortage and climatic extremes, by migrating great distances to habitats that offer more favorable conditions [3,5,6]. Equids living in captivity or confined reserves are forced to cope with the conditions presented in their surroundings. Therefore, it is important for animal and range managers to identify their needs and respond accordingly. The monitoring of the body condition can be a useful technique for the management of wild and feral horse populations and horses kept under seminatural conditions in reserves [3,12]. A decline of body condition can hint to food limitation due to too high density of grazers in the area, unsuitable vegetation, and health problems, such as parasite infestation, disease, tooth problems, or painful injuries [4,13]. A high abundance of biting insects in summer can also influence activity patterns, habitat use, and feeding behavior of free-roaming horses [5,6,11,14] and thus can also have an effect on the body condition of horses. The knowledge of normal annual fluctuations in body condition of horses living in a habitat may help managers to identify episodes when animals are stressed. This knowledge can assist managers in assessing optimal population density and timing of implementation of management interventions when required. Furthermore, when choosing individuals suitable for transports and reintroduction to the wild, consideration of body condition is an important factor impacting survival [6]. Numerous seasonal factors influence the body condition of horses and thus affect the health status, fitness, longevity, and reproductive success [4]. A fair-to-good body condition is considered optimal for horses irrespectively of their living conditions. Obesity is known to increase the risk of metabolic disease [15,16]. Low body condition reduces the fitness of horses, can have a negative effect on fertility [10,11,14], increases vulnerability to infectious diseases and parasites, and can be a symptom of serious disease or severe pain [16–21]. Free ranging Przewalski’s horses in Mongolia live in separated harem and bachelor groups with overlapping home ranges [5]. Since 2006, horses in the present study population have displayed unusual spatial organization. The majority of harem groups and bachelor stallions in Pentezug stay in close vicinity to each other. Visually, this population of horses appears to be one large herd, although closer observation identifies clear groupings within the larger herd structure [8]. This leads to a high frequency of agonistic interactions between the stallions, especially during the foaling and breeding season from late April till July [8]. Harem stallions suffer from high
75
stress, protecting their mares and foals against challenging bachelor stallions and competing harem stallions [22]. Stress is a possible factor influencing the body condition in this study as harem stallions show a lower BCS the whole year round than nursing and pregnant mares. The negative effect of stress on BCS has been reported in Kaimanawa feral horses in New Zealand, where mares in multistallion bands suffered more intraspecific aggression and showed significantly lower BCS than mares in singlestallion bands [15]. However, feral horses in Australia avoid unnecessary fighting and stress during the breeding season by maintaining a large physical separation between harem bands and avoidance of congestion at water holes [23]. Przewalski’s horses in the Pentezug population behave quite differently. The majority of the Pentezug population chose close contact and are subject to the inevitable consequences of stress from regular aggressive contact between challenging stallions. Although feral horses have been reported to be aggressive particularly during mating season, the main defense of harem bands appears to be avoidance of other horses [23]. The benefits of a social structure with single-stallion bands in contrast to multistallion bands are significantly higher fecundity of mares, better BCS, and lower parasitic loads in faecal samples due to decreased exposure of the individuals to stallion harassment [15]. The social structure of the Pentezug Przewalski’s horses population with a herd of several single-stallion bands in close vicinity appears to be reflected in the lower BCS of the stallions which have to invest much energy to protect their mares from the harassment of other stallions. Further investigations are needed to ascertain the reasons for the “herd” structure which does not appear in other free ranging Przewalski’s horse populations, but is reported from Camargue horses as well [14]. The majority of mares in the present study population foal in May and June, so that the main reproductive season lasts until July [8]. If food is not limited and forage quality is good, which is the case in the Pentezug, pregnancy and lactation apparently have no remarkable negative effect on the body condition of mares. This observation is in keeping with the reports of free-living Przewalski’s horses in Hustai National Park in Mongolia [6]. In habitats with food limitation or poor forage quality, lactating mares in feral horses showed significantly lower BCS than stallions and nonlactating females [11]. In the Pentezug, insect harassment in July and August is high and horses spend most of the day resting in dust bathes [22], using the cooler evening and morning hours to graze. Reduced grazing activity during daytime in summer is reported from free-living Przewalski’s horses in Mongolia as well [3–7]. This might be an explanation for the slightly reduced BCSs for both stallions and mares in that time of the year. In autumn, breeding season is over and insect harassment is reduced remarkably. Horses spend most of the day grazing in September and October [8], which results in a peak of BCS for both sexes in the middle of October. During the winter months, body condition decreases slightly, which can be explained by a reduced energy value of food in combination with low temperatures (up to 20 C) in the area.
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5. Conclusion This study highlights the advantage for wildlife managers of keeping historical records of population BCS. Significant reductions in BCS of a population compared to historical population data can signal food limitation or increased stress level of the horses and thus might indicate the need to reduce population size in the given area, the presence of predators, or abnormal social dynamics in the population. A decrease of BCS of individuals can be symptomatic of disease, injury, or unusual stress. Acknowledgments The authors are very grateful to Dr Zsolt Végvári, University of Debrecen, for the support with the statistical analyses.
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