HEMATOLOGIC AND BLOOD CHEMICAL CHARACTERISTICS OF FERAL HORSES FROM THREE MANAGEMENT AREAS

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1 HEMATOLOGI AND BLOOD HEMIAL HARATERISTIS OF FERAL HORSES FROM THREE MANAGEMENT AREAS Authors: E. D. Plotk, T.. Egle, S. J. Gulke, J. R. Tester, nd D. B. Siniff Source: Journl of Wildlife Diseses, 24(2) : Published By: Wildlife Disese Assocition URL: BioOne omplete (complete.bioone.org) is fulltext dtbse of 200 subscribed nd openccess titles in the biologicl, ecologicl, nd environmentl sciences published by nonprofit societies, ssocitions, museums, institutions, nd presses. Your use of this PDF, the BioOne omplete website, nd ll posted nd ssocited content indictes your cceptnce of BioOne s Terms of Use, vilble t Usge of BioOne omplete content is strictly limited to personl, eductionl, nd noncommercil use. ommercil inquiries or rights nd permissions requests should be directed to the individul publisher s copyright holder. BioOne sees sustinble scholrly publishing s n inherently collbortive enterprise connecting uthors, nonprofit publishers, cdemic institutions, reserch librries, nd reserch funders in the common gol of mximizing ccess to criticl reserch.

2 Journl of Wildlife Diseses, 24)2), PP 2:31 \Vikllife Disese Assocition 1988 HEMATOLOGI AND BLOOD HEMIAL HARATERISTIS OF FERAL HORSES FROM THREE MANAGEMENT AREAS E. D. Plotk, T.. Egle,2 S. J. Gulke, J. R. Tester,2 nd D. B. Siniff2 Mrshfield Medicl Reserch Foundtion, Inc., Mrshfield, Wisconsin 54449, USA 2 Deprtment of Ecology nd Behviorl Biology, University of Minnesot, Minnepolis, Minnesot 55455, USA ABSTRAT: Blood ws collected from 486 ferl horses of mixed sex nd ge clsses cptured from three svild horse mngement res in Nevd nd Oregon from December 1985 to Februry Mles were significntly outnumbered by femles in the Flnign re, but both sexes were represented in pproximtely equl numbers in the Wssuk nd Bety s Butte res. Hemtology nd chemistry vlues verged 16.4 ± 0.11, 46.3 ± 0.28, 9.9 ± 0.07, 6.9 ± 0.10, 47.1 ± 0.24, 16.6 ± 0.09, 35.2 ± 0.09, 10.! ± 0.14 rid 23.4 ± 0.25 for hemoglobin (HGB), hemtocrit (HT), red 1)100(1 cells (RB), white blood cells (WB), men corpusculr volume (MV), men corpusculr hemoglobin (NIGH), men corpusculr hemoglobin concentrtion (MH), cortisol (F) nd serum ure nitrogen (SUN), respectively. Sttisticlly significnt differences in HGB, HT, RB, WBG, NIGV nd NIGH levels occurred with respect to ge (P 0.001). Serum F levels were lower iii immture nimls thn in either subdult or dults in ll res. Flnign horses ppered in the poorest condition nd hd the lowest HGB, HT nd RB counts while the vlues for Wssuk horses were significntly higher (P 0.001). Serum F levels were lowest in the Flnign horses. A significntly lower (P 0.001) proportion of dult mres hd progesterone levels consistent with pregnncy in the Flnign horses versus those from the other two res. These dt re consistent with subjective evlution of the condition of the horses. Key words: Ferl horses, Equus cbllus, hemtology, serum chemistry, trpping nd hndling stress, field survey. INTRODUTION Enctment of the Wild FreeRoming Horse nd Burro Act in 1971 (PL 92195) b the ongress of the United Sttes hs resulted in incresed growth of mny popultions of ferl horses (Equns cbllus) in the western United Sttes. The Bureu of Lnd Mngement (BLM) estimted the popultion of ferl horses nd burros in western North Americ to exceed 50,000 nimls nd hs PrOposed pproprite mngement levels t 25,000 to 30,000 nimls (Boyles, 1986). The implied overstocking my result in depletion of forge in certin herd mngement res. Proper mngement of ferl horse popultions in western North Americ is dependent upon knowledge of popultion sizes, rtes of increse nd mortlity, nd other fctors ffecting herd helth. Reproduction nd mortlit re t lest prtilly dependent on the physicl condition of the nimls. Blood dt from wildcught nimls mx contribute to the pool of scientific informtion on its own merits but dt on blood chrcteristics nd composition from wildlife popultions could be helpful in compring helth nd disese sttus mong popultions of the sme species (Sel et l., 1978). This study ws undertken to compre the condition of three ferl horse herds by hemtologic nd metl)olic mesurements nd to estblish reference rnge of vlues in undrugged ferl horses. Dt re presented tht relte blood hemtologicl prmeters, serum tire nitrogen levels nd progesterone nd cortisol levels to subjective estimtion of body condition in popultions of ferl horses from three different mngement res. MATERIALS AND METHODS One hundred eighty ferl horses were cptured from the Flnign mngement unit (40#{176}0 to 40#{176}15 N, 1 19#{176}40 to 120#{176}O W) in northwestern Nevd during December 1985, 143 horses from the Wssuk Mountins (.38#{176}35 to 38#{176}55 N, 1 l8#{176}50 to 1 18#{176}55 W) of west centrl Nevd during Jnury 1986 nd 163 horses from the Bety s Butte mngement re (42#{176}0 to 42#{176}25 N, 1 19#{176}05 to 1 19#{176}25 W)in southern Oregon during Februry The cptured horses represent 231

3 232 JOURNAL OF WILDLIFE DISEASES, VOL 24, NO. 2, APRIL 1988 ed the mjority of horses in ech mngement re. Freernging bnds were herded into corrl trps on bnd by bnd bsis by professionl roundup service utilizing Bell Bi helicopter (Bell Helicopter Textron, Inc., P.O. Box 482, Fort Worth, Texs 76101, USA). As mny s seven bnds could be held t one time without mixing. Often one or two bnds would be held overnight for processing the next morning. These nimls were provided wter nd hy d libiturn. All nimls were visully nd subjectively grded ccording to condition. Animls were considered in excellent condition if they ppered ft nd the bckbone nd ribs were not visible. They were considered in good condition if they hd prominent withers but ribs nd bckbone were not visible. Animls in fir condition hd visible bckbone nd ribs tht were brely visible. Animls in poor condition hd visible ribs nd nimls in very poor condition exhibited prominent ribs nd hipbones. Bnd condition ws grded bsed on condition of the mjority of nimls in tht bnd. In lmost every cse ll nimls within bnd were considered to be in similr condition. Although condition of individul bnds within n re rnged from excellent to poor, ech re ws ssigned n overll condition bsed on the verge number of bnds fitting in tht rting. The nimls were plced in squeeze chute where they were ged nd bled. Ages were estimted ccording to tooth eruption nd wer (Ensminger, 1969) nd blood smple ws collected from the jugulr vein utilizing 35mi syringe nd 15g needle. A portion of the smple ws trnsferred to tube contining sodium EDTA nd mixed thoroughly. The reminder ws trnsferred to plin glss tubes nd llowed to clot for 212 hr. Blood ws kept in styrofom continers until processed. EDTA tubes for hemtology were shipped irmil in styrofom continers to the senior uthor s lbortory every other dy. lotted blood ws centrifuged in tbletop centrifuge every evening. The serum ws removed nd stored in cpped plstic tubes t 20 until ssyed. omplete blood counts were performed immeditely fter rrivl t the lbortory s described by Sel et l. (1977). Prmeters mesured included hemoglobin (HGB), hemtocrit (HT), red blood cell count (RB) nd white blood cell count (WB). Men corpusculr hemoglobin concentrtion (MH), men cell volume (MV) nd men corpusculr hemtocrit (MH) were clculted. Serum ure nitrogen (SUN) ws nlyzed colorimetriclly by the method of Fwcett nd Scott (1960) s modified by hney nd Mrbck (1962) utilizing regents nd procedure included in the Sigm Ure Nitrogen kit (Sigm hemicl ompny, St. Louis, Missouri 63160, USA). Serum progesterone (P4) nd cortisol (F) levels were estimted by rdioimmunossy nd competitive protein binding ssy, respectively, s previously described (Plotk et l., 1980; Sel et l., 1983). orpus luteum (L) function ws considered ctive when the serum P4 level ws 1.5 ng/ml or greter (Plotk et l., 1975). Sttistics in the text re mens (± stndrd errors). Blood nd chemistry comprisons were mde using ANOVA, correltions were mde using Lest Squres regression nlysis nd sex, ge nd P4 rtios were compred using hisqure nlysis. All nlyses were performed utilizing the Number runcher Sttisticl System version 4.21 for the IBM computer (J. L. Hintze, Kysville, Uth 84037, USA). This progrm follows the procedures outlined by Snedecor nd ochrn (1967) nd Ostle (1969). For two nd threewy ANOVA, nimls were divided into three ge groups: immture, <2 yr old; subdults, 23 yr old; dult, >3 yr old. Actul ges for the nimls were used in the correltion nlyses. RESULTS Popultion chrcteristics Horses cptured rnged in estimted ge from 0.5 to 20 yr (6.0 ± 0.3). The medin ge for horses from the Flnign nd Bety s Butte res ws 4 yr nd from the Wssuk re ws 6 yr. Overll mles nd femles were present in pproximtely equl numbers in the Wssuk (1:1.03) nd Bety s Butte (1:1.06) res. However, mles were outnumbered by femles (1:1.27) in the Flnign re. Femles outnumbered mles in the 0.5 nd 1.5 ge clss by 2.1:1 in Flnign nd 1.7:1 in Bety s Butte res. There were only seven subdult femles nd 20 subdult mles in Bety s Butte. Overll, the horses from the Flnign re were in the poorest condition nd horses from the Wssuk were in the best condition. Generlly, ll nimls within specific bnd were in similr condition. Hemtology Men HGB, HT, RB nd WB levels differed significntly (P < 0.001) mong res. For ll ge groups, Flnign horses

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7 236 JOURNAL OF WILDLIFE DISEASES, VOL 24, NO 2, APRIL 1988 hd the lowest HGB, HT nd RB levels nd Wssuk horses hd the highest (Tbles 13). Sttisticlly significnt differences in HGB, HT, RB, WB, MV nd MH occurred with respect to ge (P < 0.001). Sex by ge interctions were significnt for HGB, HT nd RB (P 0.001) but not for WB or erythrocyte prmeters. A significnt re by sex interction occurred for HGB only (P < 0.05) nd significnt re by ge interction ws pprent for RB nd WB (P 0.02 nd P 0.03, respectively). Hemoglobin nd HT levels hd low but significnt positive correltions with ge (r = 0.32 nd 0.31, respectively, P < 0.001). Since significnt sex by ge interctions were present, the dt were nlyzed by twowy ANOVA within ge groups. With this technique, significnt sex differences occurred for HGB, HT, nd RB levels mong immture nd dult horses, but not in subdults. In immture nimls, femles hd higher vlues thn mles (P 0.003, Tble 2). However, in dult nimls, mles hd higher vlues thn femles (P = 0.001, Tble 3). Significnt sex differences were not noted in MV, MH or MH. However, in immture nd dult nimls MV nd MH were significntly different mong res (P 0.004) nd in subdults MV, MH nd MH were different mong res (P 0.02). White blood cell counts were significntly lower in Wssuk horses thn in either Flnign or Bety s Butte horses in ll ge groups (P 0.004). Serum chemistry Serum ure nitrogen differed significntly mong res in dult (P 0.003) nd immture (P 0.04) horses but not in subdults (Tbles 13). Serum ure nitrogen levels were slightly but significntly (P < 0.04) higher in immture nimls from the Flnign re thn in the sme ged nimls from either the Wssuks or Bety s Butte. However, in dults SUN levels were significntly higher in the Bety s Butte nimls (P < 0.003). Serum cortisol levels rnged from 2 to 18 g/dl. Significnt differences occurred mong res nd mong ge groups within re (P < 0.001). The re by ge interction ws significnt lso (P < 0.03). However, there were no differences between cortisol levels in mles nd femles. ortisol levels were lower in immture nimls thn in either subdults or dults in ll res. Horses in ll ge groups in the Flnign re hd lower cortisol vlues thn horses in the other res (Tbles 1 3). However, the ge reltionship ws consistent with the other res. orpus luteum function A significntly higher (P < 0.001) proportion of dult mres 4 yr old hd P4 levels <1.5 ng/ml in the Flnign re (20/52) thn in the Wssuk re (4/38) nd Bety s Butte re (7/4 1). In ddition, only one of 15 subdults (23yrold) hd n ctive L in the Flnign re s compred with hlf or more in the Wssuk (8/16) nd Bety s Butte (4/7) res. Five of 27 yerlings showed L ctivity in Bety s Butte s compred with one of 30 in Flnign nd one of 12 in the Wssuk rnge. These results re reflected in the verge P4 levels (Tbles 13). DISUSSION Trpping nd hndling stress All the blood smples for this study were collected from undrugged horses hndled in squeeze chute. We ttempted to stndrdize procedures s much s possible; however, the nimls differed in terms of distnce herded, length of time in the trp, mbient tempertures, nd observed behvior. Most of these fctors should be rndomized both within nd between res becuse the roundups in ech re took severl dys nd herds within ech re were gthered ner the trp site s well s from severl kilometers wy. The mjor consequence would be to increse the vrince within n re nd thus reduce the significnce of differences mong res.

8 PLOTKA ET ALHEMATOLOGY AND HEMISTRY OF FERAL HORSES 237 However, interprettion of the results still must consider the probble effects of collection nd hndling procedures upon mesured blood prmeters (Frnzmnn, 1972; Sel et l., 1972; Schim et l., 1975). The results ffected my include HGB, HT, RB nd serum cortisol. Archer nd ibby (1965) observed tht pcked cell volume (PV) of the horse incresed promptly upon exertion, twitching nd hndling. An increse in circulting red cell mss s result of splenic contrction my occur with hndling; thus, resting horses from ny of the popultions might hve lower vlues thn those reported here. Totl erythrocyte count is incresed lso by stress nd exercise in horses (Hwkey, 1977). Although sesonl chnges in blood prmeters hve been reported, they should not be fctor in this study becuse ll collections were conducted during the v inter. Hemtology The hemtologic vlues reported here re within the rnge for hotblooded breeds (Thoroughbred, qurterhorse, Apploos, Stndrdbred, nd Arbin; Jm, 1986) nd re similr to vlues reported by Sel et l. (1985) for ferl horses cptured in the Ph Rh nd Pine Nut Herd mngement res of Nevd. These vlues re slightly higher thn vlues published for coldblooded horses (Jm, 1986). Pcked cell volume, RB nd HGB cn increse with excitement (Sercy, 1969; Swenson, 1970). Wild horses re likely to be more excited thn domestic nimls during blood smpling nd this could ccount for the higher hemtologicl levels observed in our study. In generl, vlues for immture nimls were lower thn in subdults or dults. This is consistent for published dt on MV in Equide (Hwkey, 1977) but contrsts with dt on erythrocyte counts. Hwkey (1977) reported tht in horses, the totl erythrocyte count is influenced by ge nd in wild Equide the erythrocyte count is higher nd MV lower in juveniles thn in dults. The opposite results seen in RB in the present study my be confounded by the effects of stress. Immture nimls did not pper s frightened s mture nimls in response to hndling. The lower cortisol vlues in immture nimls supported this conjecture. The lower hemtologicl vlues seen in the Flnign re s compred with vlues in the Wssuk nd Bety s Butte res re consistent with the concept tht hemtologicl vlues re n indictor of condition of these nimls. The Flnign horses ppered in much poorer condition thn either the Wssuk or Bety s Butte horses. Serum chemistry The lck of direct correltion of SUN with condition of the horses in the three res ws not surprising. Serum ure nitrogen is ffected by number of nutritionl nd physiologicl fctors mong which re ctbolism of body protein (Gud et l., 1976; Bhnk et l., 1979) nd qulity of nutrition, such s the mount of dietry protein nd/or energy (Preston et l., 1961, 1965; Kirkptrick et l., 1975). Further informtion bout the diet the nimls were on nd other environmentl fctors is needed before complete interprettion of the SUN levels cn be mde. Serum F levels vried with ge nd re. The lower levels of F in the Flnign horses re of interest since it might be suspected tht F levels would be incresed during periods of nutritionl stress (Sel et l., 1972). Possibly the bility of the horse pituitrydrenl xis to respond to the stress of hndling is diminished when nimls re lredy nutritionlly stressed. Sel et l. (1972b) observed similr effect in deer plced on different nutritionl diets. Since the horse is sesonlly polyestrous with nestrus occurring from November through Mrch (Kirkptrick nd Turner, 1983), P4 levels >1.5 ng/ml during the winter should indicte tht n niml is pregnnt. The mjority of studies indicte tht ferl horses re shrply sesonl with

9 238 JOURNAL OF WILDLIFE DISEASES, VOL 24, NO 2. APRIL 1988 respect to breeding nd foling (Kirkptrick nd Turner, 1986). Bseline P4 levels during nestrus or estrus prior to ovultion during cycle hve been reported to be <0.8 ng/ml in domestic horses (Plotk et l., 1975; Ginther, 1979). Sel nd Plotk (1983) used P4 level of 2.4 ng/ml in conjunction with n estrdiol level of 70 pg/ml in ferl horses from the hllis, Idho herd to determine tht 88 of 99 (88%) dult mres were pregnnt. Regrdless of the P4 level for discrimintion, it ws pprent from the number of nimls hving elevted P4 levels nd the verge P4 levels within ge clss (Tbles 13) tht there were fewer mres with L function in the Flnign herd thn in either the Wssuk herd or the Bety s Butte herd. Severl fctors my influence the fecundity of ferl horse herds including genetics, ecology of the rnges, popultion density, ge structure nd sex rtios. The higher proportion of nonpregnnt mres in the Flnign herd could be consequence of ny or ll of these fctors. Becuse the Flnign horses ppered to be in the poorest condition, it is possible tht indequte nutrition my hve been mjor contributing fctor in the lower number of nimls with elevted P4 levels in this herd. It is unlikely tht the ge structure could ccount for the differences in lutel function becuse the verge ge of dult mres in the Flnign re ws 8.3 ± 1.1 yr versus 6.7 ± 0.5 yr for the dult mres in the Bety s Butte re. The mres in the Wssuk re were slightly older thn the Bety s Butte mres (10.2 ± 0.8 yr versus 6.7 ± 0.5 yr) but the percentge of mres with khtel function in these two herds ws similr (90% versus 83%, respectively). Another contributing fctor for the lower reproduction in the Flnign mres could be the less stble bnd structure. Berger (1983) reported tht the foling rte of stble bnds (bnds in which there ws no chnge of the bnd stllion) ws 82% while the foling rte of unstble bnds (bnds in which stllions hd been replced by new mles) ws 38%. The Flnign unit hd been gthered by the BLM in September 1985, 3 mo before we collected our smples. A totl of 350 horses were removed from the re including 165 dult mres nd 129 stllions. This collection could hve disrupted the structure of mny bnds nd cused the loss of severl dominnt stllions nd the exchnge of dominnt stllions. AKNOWLEDGMENTS This reserch ws supported by Bureu of Lnd Mngement contrct AA852RP527 nd the Mrshfield Medicl Reserch Foundtion. We re grteful to BLM personnel of the rson ity, Nevd nd Lkeview, Oregon districts nd to the personnel of Helicopter Roundup Service who gthered nd provided help in hndung the horses. Our thnks lso go to the following for vluble technicl ssistnce: A. L. Koller processed blood, D. Veve nd F. Zrembk helped perform ssys, Doreen Luepke provided editoril ssistnce nd U. S. Sel gve vluble technicl dvice. LITERATURE ITED AIo:hIlh1, R. K., #{149}Nh) J. 1.,IshiY The effect of excittion nd exertion on the circulting blood of horses. Veterinry Record 77: B. R., J.. HoI.h.AND, L. J. VERSIE, AND J. J.OzocA Sesonl nd nutritionl effects on serum nitrogen constituents in whitetiled deer. The Journl of Wildlife Mngement 43: BEIIcEhS, J Induced bortion nd socil fctors in wild horses. Nture (London) 303: Bo i h.i S, J.S Mnging Americ s wild horses nd burros. Journl of Equine Veterinry Science 6: th.sni i, A. L., ANt) E. P Modified regents for determintion of ure nd mmoni. linicl hemistry 8: ENsIIN(;Fn, M. E Horses nd horsemnship, 4th ed. The Interstte, Dnville, Illinois, 546 pp. F,.w:h; rt, J. K., AND J. E. ScoTT A rpid nd precise method for the determintion of ure. Journl of linicl Pthology 13: FI1..\ L\IANN, A. W Environmentl sources of vrition of bighorn sheep physiologic vlues. The Journl of Wildlife Mngement 36: INTFIER, 0. J Reproductive biology of the mre. McNughton nd Gunn, Inc., Anti Arbor, Michign, 411 pp. G( AI)A, J. A., J. J. ROBINSON, ANI). FhsAsh.:R The effect of reduction in food intke during

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