impact of testosterone on the antler …5)/279_285.pdf280 this study was taken up to determine the...

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IMPACT OF TESTOSTERONE ON THE ANTLERSTAGES IN SAMBAR DEER (Rusa unicolor) STAGS

V. Vishnu Savanth1 and Saseendran. P.C2

ABSTRACT

This study was taken up to determine the impact of testosterone on the antlergrowth stages in sambar deer (Rusa unicolor) stags. Hierarchically higher six sambar deerstags at State Museum and Zoo, Thrissur, Kerala, India were selected for the study. Fecaltestosterone level was estimated using radioimmuno assay. The samples were collected ona weekly basis for a period of sixteen weeks from the selected six stags. The results revealedthat the stags in hard antler stage or rut season were found to have a significantly highertestosterone concentration in comparison to the velvet growth stage stags. The study alsoreveals that, it is the sudden dip in the testosterone concentration which causes the antlercasting. Velvet shedding was preceded by an increase in the testosterone level emphasizingits role.

Keywords: antler, Rusa unicolor, fecal testosterone, sambar deer, RIA

1PhD Scholar, 2Professor and Head, Department of Livestock Production Management, College of Veterinary and AnimalSciences, Mannuthy, Thrissur, Kerala;(Part of MVSc thesis work of the first author)

INTRODUCTION

Among the Indian ungulates none hasadapted itself to a wider variety of forest types andenvironmental conditions than the sambar (Schaller,1967). It is the largest Indian deer and bears thegrandest antlers. They belong to the family Cervidaeunder the order Artiodactyla. The habitats of thisdeer include mountains, coastal forests, swampylands and agricultural fields (Santra, 2008).

Antlers are appendages of the skull,composed of a solid bony core and are unique inthat they undergo an annual cycle of rapid growthin preparation for the breeding season (rut) and arecast after the rut, females generally do not growantlers, reindeer being the only exception (Morrowet al., 2009). Deer antlers are the only mammalianappendages capable of repeated rounds of

regeneration; every year they are shed and regrownfrom a blastema into large branched structures ofcartilage and bone that are used for fighting anddisplay (Price and Allen, 2004). In the case of somespecies they even represent the fastest rate of organgrowth in the animal kingdom.

Reproductive steroid hormone levelsprovide important information regarding thereproductive status of animals (Washburn et al.,2004). Monitoring hormone profiles by the use offecal steroid assays offers a noninvasive andpotentially long-term means of assessingadrenocortical, testicular and ovarian hormones inmany vertebrate taxa. In combination with behavioralobservations, it is now possible to investigate manyof the proximate physiological mechanisms thatunderlie animal behavior (Beehner and Whitten,2004).

Tamilnadu J. Veterinary & Animal Sciences 8 (5) 279-285, September - October, 2012

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This study was taken up to determine thenormal fecal testosterone level in sambar deer stagsand to correlate its relation with various stages ofthe antler cycle. The antler cycle in a deer is arepresentation of its breeding cycle. In most of theIndian zoos and other captive facilities, sambar deerare creating economic and space constraints due tohuge numbers (Savanth et al., 2010). Henceunderstanding the physiology behind the cycleespecially in a tropical region where the animals donot follow the same pattern of seasonality seen intheir temperate counterparts can help developstrategies for the control of the captive sambar deerpopulations wherever necessary.

MATERIALS AND METHODS

The study was carried out at the StateMuseum and Zoo, Thrissur, Kerala, India for a periodof four months. The zoo was chosen for theexecution of the study because of the large numberof sambar deer maintained there. There were a totalof 70 sambar deer in the enclosure, during thecommencement of the study, of which 22 were malesincluding 16 adult stags.

A preliminary observation was carried outto rank the stags in the herd on a dominance hierarchytable. In a population of captive sambar deer, malesare known to control the group led by alpha maleand it is identified by its good physical appearance,sharp and long antlers, positioning at vantage pointsto take the major share of feed and its mates(Saseendran et al. 2003).The characters that weretaken into account for this study were the body andantler size, ability of a stag to occupy vantagepositions during the feeding time, lead a largerharem, capacity to aggressively dictate othermembers of the herd and carry out most of thebreeding activities in the herd.

Based on the above mentionedcharacteristics, top three stags in the rut/ hard antlerstage, on a chronological order of dominance namelyH1, H2 and H3 were selected. Three more superior

stags in late stages of velvet growth, which wereexpected to come into rut/ hard antler stage duringthe observation period were also selected and werenamed V1, V2 and V3 as per descending order ofdominance. Thus, a total of six animals were selectedfor the study.

Fecal pellets were collected on a weeklybasis from all the six stags for a period of fourmonths. The samples were collected within half anhour of voidance and were labeled and kept inpolyethylene covers at -20 ºC until extraction forRIA. Frozen fecal samples were dried in aconventional oven. Each sample was powdered andmixed thoroughly. A sub sample weighing 0.2 g wasmixed with 5 ml of 90 per cent ethanol in a test tubeand vortexed briefly. The tubes were boiled in awater bath (90 ºC) for 20 minutes, adding ethylalcohol to avoid it from boiling dry. The extract wasbrought up to pre boil levels with 90 per cent ethanoland centrifuged at 1500 rpm for 20 minutes. Theextracts were poured off into another storage vial.To the remaining fecal powder 90 per cent ethanolwas added again and vortexed for 30 seconds andcentrifuged at 1500 rpm for 15 minutes. The firstand second extracts were combined and dried downand reconstituted in one ml of methanol andvortexed for a brief period. The methanol extractswere stored at -20 ºC until RIA analysis. The RIA kitused for the purpose was 125I labeled Testosterone(Direct) kit (M/s Immunotech, France).

The data were statistically analyzed usingSPSS software.

RESULTS AND DISCUSSION

The sambar deer herd selected for the study hadbeen observed to breed throughout the year andalso stags at various stages of the antler cycle couldbe seen at any point of the year. Brown et al., (1978)suggested that deer living near the equator, whereseasonal day length changes are slight, tend to beasynchronous in both their antler and sexual cycles.The findings of only little evidence of a clear


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seasonal synchrony in the antler cycle in a herd ofspotted deer by Loudon and Curlewis (1988) arealso supportive of the present findings. Thisobservation is also supported by Asher (2007) whoreported that equatorial region cervids arecompletely aseasonal.

Observation of the stags before, duringand after the four month study period revealed thatthe sambar deer antlers were in velvet growth for aduration of seven to eight months. Monfort et al.(1993) reported that antler length, body weight andchest girth were maximal during pre-rut in Eld's deerwhich was in complete agreement with the findingof the present study. The complete shedding ofvelvet took about 5-6 days. The hard antlersdecorated the stags for the whole rut season whichlasted for about four to five months. This wasfollowed by the antler casting stage wherein, thestags lost their antlers either in a fight or by hittingagainst tree or fencing (Savanth et al., 2011). Priceet al. (2005) stated that in each spring, deer shedantlers that were used for fighting and display duringthe previous mating season. Morrow et al. (2009)reported that antlers are cast after the rut. The stagsmost often lost both the antlers on the same daybut in some cases there was even a gap of 2-3 daysfor the second one to fall. This stage did not lastlong, as antler growth is a rapid continuous cycle,and the initiation of the next pair of antlers set inwithout much delay. The various stages of sambardeer antler cycle is shown in the plates 1 to 6 (allphotographs are not of the same stag).

In this study, good body condition wasmaintained at the initial phases of the rut seasonbut, during the later stages of rut/ hard antler phase,the stags were seen in a worn out conditionindicative of the hardships undergone during therut for maintenance of the harem as well as thedominance quotient. Asher et al. (1987) reported thatfallow deer bucks exhibited pronounced liveweightgains over spring and summer months, to reach apeak mean weight and rapid liveweight losses over

the rutting period with a minimum mean liveweight.The worst body condition was observed in thosestags whose antlers were freshly cast; the stagsappeared skinny, emaciated, lesser coat thicknessand some of them carried the gore wounds sustainedduring the tussles for territory, hinds and ration(Savanth et al., 2011). The sambar stags seemed tobe in peak size and maintained the best bodycondition during the later velvet stages. The wholeof antler regrowth stage was found to be arecuperating stage during which the stag prepareditself to face the next rut. McElligott et al. (2001)asserted that body mass was related to pre- rutdominance rank which was in turn strongly relatedto rut dominance rank, and thus there was an indirectrelationship between mating success and bodymass.

In most cervids, concentration of plasmatestosterone is associated with the phases of antlerdevelopment (Gomez et al. 2006, Ungerfeld et al.2009).The stag H1 maintained a testosterone levelof 14.66±2.30 ng g-1 of dry feces for the six weeksthat it remained in hard antler. A sudden decline inthe hormone level to 4.6 ng g-1 of dry feces duringthe seventh week triggered the antler fall. Thetestosterone level thereafter maintained a low profileof 7.85± 2.32 ng g-1 of dry feces for the remainingten weeks of observation. In roe deer thetestosterone showed the highest concentrationduring the rut (Roelants et al. 2002). In wapiti andred deer, preceding the rut, testosteroneconcentrations increased sharply, reaching a peakjust before the rut (Haigh, 2007).

The testosterone level of stag H2 was14.07±0.54 ng g-1 of dry feces during the hard antlerphase and its decline by the eighth week led to theantler casting. The testosterone level then was at alevel of 9.12± 2.40 ng g-1 of dry feces for nine weeks.Similar results were observed on male white taileddeer which revealed that mean levels of serumtestosterone increased during the breeding seasonuntil approximately 1- 2 weeks before the peak of


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the rut (Ditchkoff et al. 2001). Stag H3 hadtestosterone levels of 14.85±1.17 ng g-1 of dry fecesfor seven weeks before casting the antler. Thecasting was followed by testosterone levels of9.56±1.94 ng g-1 of dry feces for the rest of the studyperiod of nine weeks. Sempere et al. (1992), Blottneret al. (1996) and Roelants et al. (2002) found that inroe deer the testosterone showed the highestconcentration during the rut.

Significant correlation exists between fecaltestosterone and antler phases; antler casting andregrowth occurs under low testosteroneconcentrations, whereas velvet shedding isassociated with high concentrations of testosterone(Pereira et al. 2005). Stag V1, which was in the velvetstage initially, had testosterone levels of 13.52±1.82ng g-1 of dry feces, a sudden increase in the hormonelevels by the seventh week caused the velvet topeel off welcoming the stag to the rut season. Thestag, from thereon maintained a hormone level of18.65±1.20 ng g-1 of dry feces. V2 maintainedtestosterone levels of 12.45±0.91 ng g-1 of dry fecesfor seven weeks. This was followed by the velvetshedding and the testosterone level was thenmaintained at 18.77±1.03 ng g-1 of dry feces. Thestag V3 had the hormone levels at 12.32±1.18 ng g-1of dry feces before casting the velvet at the tenthweek. The testosterone level after the velvet castingwas higher at 18.72±0.79 ng g-1 of dry feces. Schamsand Barth (1982) emphasized that in roe deer stagsthe highest average levels of testosterone wereobserved before the start of the rutting season andsteadily declined thereafter which was completelysupportive of the results of the present study.

Antler growth cycles are closely related tosexual cycles in stags and can be directly attributedto variations in seasonal photoperiod influencinggonadal steroidogenic activity. Testosterone levelspeak immediately before rut and it is the rapid declinein its level that causes antler casting. Antler growthoccurs at a low testosterone concentration and isseen increasing when the antler growth nears

completion. Velvet shedding and antler hardeningis a consequence of high testosterone levels(Woodbury and Haigh 2007).

CONCLUSION

The fecal testosterone levels of the sixstags estimated by RIA revealed that testosteroneexerts a strong grip on the antler cycle. The stags inhard antler stage or rut season were found to havea significantly higher testosterone concentrationin comparison to the velvet growth stage stags.The results obtained in the present study on Indiansambar deer were completely in agreement withsimilar studies carried out in other species of deerwhich were mostly of temperate origin. Thefluctuations of testosterone level observed in thisstudy were in flow with the results of many otherauthors. This study also reveals that, it is the suddendip in the testosterone concentration which causesthe antler casting. Velvet shedding was precededby an increase in the testosterone level emphasizingits role.

ACKNOWLEDGEMENTS

The research was funded by KeralaAgricultural University. We are thankful to TheDirector, Directorate of Museums and Zoos,Thiruvananthapuram; Superintendent, curator andanimal keepers of State Museum and Zoo, Thrissurfor providing the facilities for the conduct of theresearch. The help by Dr. Sunil, Veterinary Surgeonat the State Museum and Zoo is also acknowledged.

REFERENCES

Asher, G.W., Haigh, J.C. and Wilson, P.R. (2007).Reproductive behavior of Red deer and Wapiti.In: R.S. Youngquist and W.R. Threlfall (Ed)Current Therapy in Large AnimalTheriogenology. 2nd edn. Saunders ElsevierInc., St. Louis, Missouri. 937-942.

Asher, G.W., Day, A.M. and Barrell, G.K. (1987).Annual cycle of live weight and reproductive


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changes of farmed male fallow deer (Dama dama)and the effect of daily oral administration ofmelatonin in summer on the attainment ofseasonal fertility. J. Reprod. Fertil. 79: 353-362.

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Brown, R.D., Cowan, R.L. and Kavanaugh, J.F. (1978).Effect of pinealectomy on seasonal androgentiters, antler growth and feed intake in white-tailed deer. J. Anim. Sci. 47:435-440.

Ditchkoff, S.S., Spicer, L.J., Masters, R.E. andLochmiller, R.L. (2001). Concentrations of insulin-like growth factor-I in adult male white-tailed deer(Odocoileus virginianus): associations withserum testosterone, morphometrics and ageduring and after the breeding season.Comparative Biochemistry and Physiology.129(A):887- 895.

Gomez, J.A., Garc?a, A.J., Castillejos, T.L. andGallego, L. (2006). Effect of advancing births ontestosterone until 2.5 years of age and pubertyin Iberian red deer (Cervus elaphus hispanicus).Animal Reproduction Science. 96: 79-88.

Haigh, J.C. (2007). Reproductive Anatomy andPhysiology of male Wapiti and Red deer. In: R.S.Youngquist and W.R. Threlfall (Ed) CurrentTherapy in Large Animal Theriogenology. 2ndedn. Saunders Elsevier Inc., St. Louis, Missouri.932-936 pp.

Loudon, A.S.I. and Curlewis, J.D. (1988). Cycles ofantler and testicular growth in an aseasonaltropical deer (Axis axis). J. Reprod. Fertil. 83: 729-738.

Mc Elligott, A.G., Gammell, M.P., Harty, H.C., Paini,D.R., Murphy, D.T., Walsh, J.T. and Hayden, T.J.(2001). Sexual size dimorphism in fallow deer(Dama dama): do larger, heavier males gaingreater mating success? Behav. Ecol. Sociobiol.49: 266-272.

Monfort, S.L., Brown, J.L., Bush, M., Wood, T.C.,Wemmer, C., Vargas, A., Williamson, L.R.,Montali, R.J. and Wildt, D.E. (1993). Circannualinter-relationships among reproductivehormones, gross morphometry, behaviour,ejaculate characteristics and testicular histologyin Eld's deer stags (Cervus eldi thamin). Journalof Reproduction and Fertility, 98: 471-480.

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Pereira, R.J.G., Duarte, J.M.B. and Negrao, J.A.(2005). Seasonal changes in fecal testosteroneconcentrations and their relationship to thereproductive behavior, antler cycle and groupingpatterns in free-ranging male pampas deer(Ozotoceros bezoarticus bezoarticus).Theriogenology. 63: 2113-2125.

Price, J. and Allen, S. (2004). Exploring themechanisms regulating regeneration of deerantlers. Phil. Trans. R. Soc. Lond. 359 (B): 809-822.

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Roelants, H., Schneider, F., Goritz, F., Streich, J. andBlottner, S. (2002). Seasonal changes ofspermatogonial proliferation in roe deer,demonstrated by flow cytometric analysis of c-kit receptor, in relation to follicle-stimulatinghormone, luteinizing hormone, and testosterone.Biology of Reproduction. 66: 305-312.



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Saseendran, P.C., Naser, A. and Sunilkumar, C. (2003).Dominance and activity pattern of captive alphastag of sambar deer population. Proceedings of28th conference of Ethological Society of India;Tamil Nadu Agricultural University. Coimbatore,pp.46-48.

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Plate 1. Antler cast stage Plate 2. Velvet growth -1

Plate 3. Velvet growth -2 Plate 4. Velvet shedding

Plate 5. Hard antler Plate 6. Both antlers cast



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