Synvex@ H as a prenatal andrgenizing agent in beef cattle: Effects n the implanted pregnant heifer S. L. Aldrich, L. L. Bergerl, D. J. Kesler, D. B. Faulkner, and J. W. Castree Department f Animat Sciences, ljniversity f lltinis, ljrbana, tl IJSA 61801. Received 3 March 1995, accepted 19 Octber 1995. Aldrich, S. L., Berger, L. L., Kesler, D. J., Faulkner, D. B. and Castree, J. W. 1995. Synvex@ II as a prenatal andrgenizing agent in beef cattli: Effects n the implanted pregnant heifer. Can. J. Anim. Sci. 75: 543-548. A study was cnducted t evaluite the effectiveness f Synvex@ H as an agent fr prenatal andrgenizatin in beef cattle. Thirty Charlais-crss heifers, expsed t a fertile bull during a 55-d spring breeding seasn, were randmly assigned t a cntrl grup r implanted with three times the nrmal dse f Syn6vex@ tt Uet*""n daysl0 and 75 f gestatin. Serum cncentratins f teststerne, estradil, and prgesterne, calving rate, and grwth perfrmance were determined in the pregnant heifers. Teststerne levels were greater tf i O.OOtl in treated heifers than in cntrl heifers. Synvex@ H treatment had n affect n estradil levels. hgesterne levels were lwered (P < 0.05) in reated heifers. Synvex@ H treatment decreased (P < 0.05) calving rate and birth weight f calves bm t treated heifers. Calving ease scres were nt affected by Synvex@ H treatment. Weight was nt affected; hwever, average daily gain was imprvedlv by Synvex@ H treatment (0.88 vs. 0.82 t 0.04 kg d-1, treated and cntrl heifers, respectively). These."rulti." interprited t sugglstihat Synvex@ H is nt an apprpriate andrgenizing agent fr cattle due t adverse effects n prgesterne cncentratins during pregnancy and n calving rate. Key wrds: Cattle, prenatal andrgenizatin, Synvex@ H' pregnancy' hrmnes Aldrich, S.L, Berger, L. L., Kesler, D. J. Faulkner, D. B. et Casfree, J. W. 1995. Utilisatin de Synvex(-'dJ H cmme facteur andrg6n6isant pr6natal pur les bvins de bucherie: effets sur des g6nisses gravides munies d'un implant. Can. J. Anim. Sci. 75: 543-548. Le but de ns recherches 6tait d'dvaluer l'efficacit1 du Synvex H cmme agent andrg6n6isant pr6natal chez les bvins de bucherie. Trente g6nisses Charlais cris6es, exps6es d un taureau fertile durant 55 j pendant la saisn de mise d la reprductin de printemps, 6tiient r6parties au hasard entre un traitement t6min et un traitement par implantatin au Synvex H, au triple de la dse nrmale, entre lj20 etlel1e j de gestatin. Les cncentratins s6riques de testst6rne, d'eshadil et de prgest6rne ainsi que le taux de v6lage et les paramotres de crissance 6taient mesur6s chex les g6nisses gestantes. Les niveaux de testst6rne 6taient plus 6lev6s (P < 0,001) chez les g6nisses trait6es que chez les g6nisses t6mins, mais n n'bservait pas d'effet sur les cncentratins d'estradil. Les niveaux de prgest6rne 6taient plus faibles (P < 0,05) chez les g6nisses trait6es le Synvex H abaissait (P < 0,05) le taux de v6lage et le pidi d la naissance des veaux n6s des g6nisses trait6es, mais les i$tl d: facilit6 de v@lage ne subissaient aucune influence significative due au traitement. Le pids vifn'6tait pas tuch6, bien que le GMQ s'accrissait dj TV dansle traitement au Synvex, s;6tablissant i 0,88 cntre 0,82 + 0,04 kgj-l pur les g6nisses t6mins. Il ressrt de ces r6sultats que le Synvex H n'est pai un bn agent adrgdn6isant pur les bvins, en raisn de ses effets n6gatifs sur les cncentratins de prgest6rne durant la gestin ainsi que sur le taux de v6lage. Mts cl6s: Bvins, andrgdn6isatin pr6natale, Synvex H, gestatin, hrmnes In dmestic ruminants, males are heavier at birth and, whether intact r castrated, exhibit faster rates f grwth which are characterized by mre prtein and less fat accretin than females (Frd and Klindt 1989). This effect appears t be due, at least in part, t the expsure f males but nt females t andrgens in uter (Jst and Magre 1984). DeHaan et al. (1988, 1990b) reprted that mdifying the prenatal teststerne envirnment f heifers imprved their pstnatal rate and efficiency f grwth and cmpsitin f gain. Thus, efficiency f beef prductin culd be imprved if methds were develped whereby grwth rate, feed efficiency, and carcass cmpsitin f female cattle culd be enhanced t a level similar t thse f males. In ur research n prenatal andrgenizatin in cattle, silicne implants cntaining teststerne prpinate, which lt whm crrespndence shuld be addressed. Telephne: (217) 333-2006, FAX: (217) 244-3169 measure 0.953 cm (.d.) x 15 cm in length, have been used (DeHaan et al. 1988, 1990b). Fur f these implants, cntaining apprximately 2.25 g teststerne prpinate each, are required t elevate plasma cncentratins f teststerne in the implanted pregnant cw t the desired 2.0 ng ml--l level. This level f teststerne in the implanted pregnant cw is similar t that prduced by a develping bvine male fetus at 90 d gestatin (Mngknpunya et al. 1975) and has cnsistantly resulted in andrgenized female ffspring' These implants are impractical fr cmmercial beef prductin because f their large size, the amunt f teststerne they require, and the surgical methd by which they must be insirted and remved frm the pregnant cw. Synvex@ H is a cmmercially available grwth implant designed t Abbreviatins: BW, bdy weight; ELISA, enzymelinked immunsrbent assay; CV, cefficients f variatin; ADG, average daily gain il3'
5/U CANADIAN JOURNAL OF ANIMAL SCIENCE 0.6 :i 0.5 rs E 0.4 ; E.s E -" 6 P 0.., 0.0 0 7 1421283542 495563707784 Days pst-lmplantatin Fig, 1. Serum teststerne in 7 treated ( -.-) and 13 cntrl (-O-) pregnant be^ef heifers frm days 0 t 84 pst-implantatin with three Synvex@ H implants/heifer (200 mg testsrerne prpinate and 20 mg estradil benzate/implant; Syntex Animal Health, West Des Mines, IA). Serum cncentratins f teststerne (ng ml-1) were higher (P < 0.001) in treated heifers n days 3,7,14,21,28,42, and 56 f the bld cllectin Derid. Standard errr f the mean was 0.03 ns ml-1. increase rate f gain and imprve feed efficiency f female cattle in the feedlt. Synvex@ H cntains bth teststerne prpinate and estradil benzate. It was ur hypthesis that the teststerne prpinate in Synvex@ H culd be used as a prenatal andrgenizing agent in cattle. Thus, the primary purpse f the present study was t determine the effectiveness f Synvex@ H as an andrgenizing agent thrugh evaluatin f its effects n the circulating cncentratins f teststerne, estradil, and prgesterne in pregnant beef heifers. Grwth perfrmance and calving rates in respnse t treatment with Synvex@ H during gestatin were als evaluated. MATERIALS AND METHODS Experimental Design Thirty Charlais-crss yearling heifers with an average BW f 361 t 8 kg were alltted t treatment in a cmpletely randmized design experiment. Each treated heifer (n = 15) received three Synvex@ H implants (200 mg teststerne prpinate and 2O mg estradil benzate/implant; Syntex Animal Health, West Des Mines, IA) between days 20 and 75 f gestatin. Cntrl heifers (n = 15) received n implants. Animals Prcedures and justificatin fr the experiment were apprved by the Labratry Animal Care Advisry Cmmittee f the University f Illinis (Institutinal Animal Care and Use Cmmittee N. A1R0781234). Heifers were expsed t a fertile bull fr breeding by natural service ver a 55-d spring breeding seasn. Heifers were rtatinal- Table 1. Effect f Synvex@ H n mean serum cncentratins f teststerne, estradil, and prgesterne during pregnancy in beef heifersz Number f heifers Teststerne (ng ml-1) Estradil (pg ml--l) Prgesterne (ng ml--l) Cntrl TreatedY t37 0.245 0.401 0.0095 2t7.6 2t6.0 8.43 2.78 1.87 0.104 <0.001 0.93 0.03 Anean serum cncentratins fhrmnes in the 13 f 15 cntrl and 7 f 15 treated heifers that calved and thus cmpleted the study. veach treated heifer received three Synvex@ H implants (200 mg teststerne prpinate and 20 mg estradil benzate/implant; Syntex Animal Health, West Des Mines, IA). ly grazed n endphyte-infected fescue-red clver pastures and were given alfalfa-grass hay during the winter. Prir t the calving seasn, heifers were placed in drylt pens with pen frnt sheds and fed cracked cm (0.5Va f BW) and were allwed ad libitum access t alfalfa-grass hay and fresh water. Heifers were weighed n days 0,28,56, and 84 f Synvex@ H implantatin. At parturitin, calving rate, calving ease scres, sex and birth weight f the calves were recrded. Bld Cllectin Bld samples (10 ml) were cllected frm the heifers by cccygeal venipuncture n days 0, 3, 7, 14, 2I, 28, 42, 56, 10, and 84 f Synvex@ H implantatin. Bld samples were allwed t clt fr 2 h then centrifuged at 4"C and 1240 x g fr 20 min. Serum was cllected and divided int tw aliquts and stred at -20"C fr subsequent hrmne analyses. Hrmne Analyses Cncentratins f teststerne in serum were determined with the duble antibdy ELISA prcedure f Kesler et al. (1990) mdified such that anti-rabbit IgG was linked t 96- well plystyrene micrtiter plates (Falcn@ Micrtest IIIrM Tissue Culture Plate, Bectn Dickinsn, Franklin Lakes, NJ) in place f plystyrene tubes. Substrate was 3,3',5,5'- tetramethylbenzidine (300!L well-l; K-Blue Substrate@, ELISA Technlgies, Lexingtn, KY). Plates were spectrphtmetrically analyzed at an absrbance f 630 nm. Samples were analyzed in triplicate in 12 assays, with intraand inter-assay CV and sensitivity f the assay being3.34v, 7.887, and 0.05 ng ml-i, respectively. Intra-assay CV was calculated as the average CV fr all teststerne samples analyzed and inter-assay CV was calculated frm a single teststerne sera pl sample (bull) analyzed in every assay. Sensitivity f the teststerne assay was calculated as the teststerne cncentratin at B0-2 standard deviatins f B. Cncentratins f estradil in serum were determined with a duble antibdy ELISA. Anti-rabbit IgG was linked t 96-well plystyrene micrtiter plates (Falcn@ Micrtest IIIru Tissue Culture Plate, Bectn Dickinsn) by an enhanced linking prcedure (Kesler et al. 1990). Estradil in serum samples was exffacted with ethyl ether (anesthesia
ALDRICH ET AL. _ SYNOVHP H AS AN ANDROGENIZNG AGENT 545 3m E B 25{l. i z Er ut 100 g,?r 5 E;3 tr Sz Itt 0 7 142128 354249566:t70Tr8/ 7 1421 28354249 56637AT784 Days pst-l mplantatln Fig. 2. Serum estradil in 7 treated ( --) and 13 cntrl (-O-) pregnant beef heifers frm days 0 t 84 pst-implantatin with three Synvex@ H implants/heifer (200 mg teststerne prpinate and 20 mg estradil benzate/implant; Syntex Animal Health, West Des Mines, IA). Serum cncentratins f estradil (pg ml--l) were similar between treatments thrughut the bld.it".titr perid. Standard errr f the mean was 26'65 pgrnl--r. grade; Fisher Scientific, St. Luis, MO) at an ethyl ether t serum rati f 10:1. Blank tubes cnsistently cntained < 1 pg ml--l estradil and extractin efficiency fr estradil was 887.Ether extracted serum samples were recnstituted with 0.17 gelatin-phsphate buffered saline. At assay time, three cmpnents (100 pl each) were added t the plates in the fllwing rder: (1) standards r exffacted samples, (2) cnjugate, and (3) primary antisera. Standard cncentratins f estradil-17p were 0, 5, lo, 25,50, 100, 250, and 500 pg well-i. Cnjugate was 1 7 p-estradil 3-hemisuccinate linked with hrseradish perxidase. Estradil- 17B antisera (prvided by O. D. Sherwd, Department f Physilgy' University f Illinis, Urbana, IL) was used at a dilutin f 1:8000. Crssreactivity f estradil-17b antisera with estradil- 17p, andrstenedine, crticsterne, crtisl, estrne, teststerne, and prgesterne was loov, O.34V, <O.UlV, <0.0IV, 4.53V, 0.0'7V and <0.017, respectively. Fllwing an incubatin time f 1.5 h, the unbund free and cnjugated estradil-l78 were remved frm the plates by washing with distilled water. Substrate (300 pl well-'; 3,3',5,5i -tetrarnethylbenzidine; K-Blue Substrate@, ELISA Technlgies) was added t the plates fr a 30-min incubatin. Plates were then specrphtmetrically analyzed at an absrbance f 630 nm. Samples were analyzed in triplicate in 12 assays, with inha- and inter-assay CV and sensitivity f the assay being3.057, tl.94v, andl24 pg ml-', respectively. Intra-assay CV was calculated as the average CV fr all estradil samples analyzed and inter-assay CV was calculated frm a single estradil sera pl sample (estrus cw) aralyzed in every assay. Sensitivity f the estradil assay was calculated as the estradil cncentratin at B - 2 standard deviatins f B. DaYs Pst'lmPlantatln Fig. 3. Serum prgesterne in 7 treated ( and 13 cntrl --) t----l pregnant beef heifers frm days 0 t 84 pst-implantatin with three Svnvex@ H implants/heifer (200 mg teststerne prpinate and 20 mg estradil benzate/implant; Syntex Animal i{ealth, West Des Mines, IA). Serum cncentratins f prgesterne (ng ml--l) were lwer (P < 0.05) n all days except days 0 f the bld cllectin perid. Standard errr f the mean was 0'33 ng ml--l. Serum cncentratins f prgesterne were determined with the duble antibdy ELISA prcedure f Kesler et al' (1990) with the fllwing mdificatins: (1) anti-rabbit IgG was linked t 96-well plystyrene micrtiter plates (Falcn@ Micrtest IIIrM Tissue Culture Plate, Bectn Dickinsn) in place f plystyrene tubes; (2) prgesterne antisera (prvided by O. D. Sherwd, Department f Physilgy' University f Illinis, Urbana, IL) was used at a dilutin f 1:50 000; (3) substrate was 3,3',5,5'-tetramethylbenzidine (300 t[ well-l; K-Blue Substrate@, ELISA Technlgies); and (4) plates were spectphtmetrically analyzed ai an absrbanie f 630 nm. Crssreactivity f prgesterne antisera with prgesterne, andrstenedine, crticsterne, crtisl, estrne, estradil-17b, and teststerne was 100, 0.51, 1.82, 0.05, <0.01, <0.01, and 0.327a, respectively' Samples were analyzed in triplicate in 12 assays, with intraand inter-assay CV and sensitivity f the assay being3'857, li.44v, and 0.03 ng ml-l, respectively. Intra-assay CV was calculated as the average CV fr all prgesterne samples analyzed and inter-assay CV was calculated frm a single prgesterne sera pl sample (pregnant cw) analyzed in utsuy. Sensitivity f the prgesterne assay was calculated as the prgesterne cncentratin at B - 2 standard "u"ry deviatins f B. Statistical AnalYsis Perfrmance, hrmne cncentratin, and calf data were analyzedfr nly the heifers that calved and thus cmpleted the study t ensure that cmparisns were made n a hmgenus (all pregnant) ppulatin f animals' Bld cllectin was t infrequent t adequately determine when the heifers that did nt calve were n lnger pregnant'
546 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 2. Elfect f Synvex@ H during pregnancy in beef heifers Calvrng rate (V) Sex f calf (#) Male Female Calf birth weight ftg) Calving ease screj Treatedz SEM r3l15 (86.7) 7lrs (46.7) 0.4596 0.03 84 53 37.1 33.3 t;7t 2.11 l.t3 0.01 0.451 0.49 zeach treated heifer received three Synvex@ H implants (200 mg teststerne prpinate and 20 mg estradil benzate/implant; Syntex Animal Health, West Des Mines, IA). vl = n difficulty, 2 = minr difficulty, 3 = majr difficulty, 4 = caesiuean sectin, 5 = abnrmal presentatin. Statistical cmputatin was perfnned with the General Linear Mdel prcedure f SAS Institute, Inc. (1988). Data were analyzed as a cmpletely randmized design (Steel and Trrie 1980). Effect ftreatment (cntrl vs. Synvex@ H) n serum cncenffatins f teststerne, estradil, and prgesterne were determined with analysis f variance fr a split plt in time design with repeated measurements (Gill and Hafs 1971). The statistical mdel included heatment, day, and treatment x day. Animal within ffeatment was used as the errr term. Mean differences in ADG, serum cncentratins f teststerne, estradil, and prgesterne, calf birth weights and calving ease scres were separated with the F-test prtected Least Significant Difference methd (Carmer and Swansn 1973). Cmparisn f calving rates was made with chi-square analysis using the categrical data mdel (CATMOD) prcedures f SAS Instirute, Inc. (1988). RESULTS AND DISCUSSION Hrmne cncentratin, calf, and pedrmance data are presented fr the 7 treated and 13 cntrl heifers that calved and thus cmpleted the study as a hmgenus ppulatin f animals. Synvex@ H treatment increased (p < 0.001) mean serum cncentratins f teststerne in treated heifers as cmpared with cntrl heifers (Table l; 0.40 vs. 0.24 + 0.01 ng ml-i, respectively). Cncentratins f teststerne were similar between treatments n day 0, elevated in treated heifers n days 3, 7, 14, 21, 28, 42, and 56, and sirnilar n days 70 and 84 f Synvex@ H treatment (Fig. l). Results frm this study indicate that the pay-ut perid f the Synvex@ H implant was apprximately 60 d fr teststerne (Fig. 1). The dse f teststerne prpinate used in this study was 600 mg, which was much less than the 4.5 g and 9 g used in previus studies by DeHaan et al. (1988, 1990b; respectively). Cnsequently, serum cncentratins f teststerne in the treated heifers in this study were cnsiderably less, at 0.40 ng ml.-l, than the 2 ng.l-l "n."ntratin previusly reprted (DeHaan et al. 1987). A circulating teststerne cncentratin f 2 ng ml-l in the implanted pregnant cw is similar t teststerne levels prduced by a develping bvine male fetus at 90 d f gestatin (Mngknpunya et al. 1975). In additin t teststerne prpinate, Synvex@ H cntains estradil benzate. Althugh the dse f estradil benzate received by the treated heifers was 60 mg, mean serum cncentratins f estradil were Table 3. Effect f Synvex@ H n mean and average daily gain during pregnancy in beef heifersz Number f heifers On-test weight ftg) Off-test weight (kg) ADG (kg d-t) IJ 359.5 428.7 0.824 TreatedY SEM P= 7 360.7 434.8 0.882 1032 0.93 11.16 0.66 0.0365 0.21 zweight and ADG f the 13 f 15 cntrl and 7 f 15 rreated heifers that calved and thus cmpleted the study. veach treated heifer received 3 Synvex@ H implants (200 mg teststerne prpinate and 20 mg estradil benzate/implant; Syntex Animal Health, West Des Mines. IA). similar in treated and cntrl heifers (Table 1; 216.0 vs. 211.6 t 8.4 pg ml--r, respectively). In additin, esffadil cncentratins were similar at all times thrughut the 84-d bld cllectin perid (Fig. 2). Thus, at the initial evaluatin f hrmne cncentratins achieved by the triple dse f Synvex@ H, the presence f estradil in the Synvex@ H implant appeared t be irrelevant. Mean serum cncentratins f prgesterne were lwer in treated heifers (P < 0.05) than in cntrl heifers (Table 1; 1.87 vs.2.78 t 0.10 ng ml--l respectively). Cncentratins f prgesterne were similar between the treatment grups n day 0; hwever, by day 3 and thrughut the remainder f the 84-d bld cllectin perid serum prgesterne was lwer (P S 0.05) in the treated heifers than in cnffl heifers (Fig. 3). Synvex@ H cntains bth teststerne and estradil, and f the 15 treated heifers, nly 7 (46.7V) calved cmpared with 13 f 15 cntrl heifers (86.7Va). Althugh it cannt be stated that treatment with Synvex@ H during early gestatin caused abftin in the heated heifers that did nt calve, it appeared that Synvex@ H had a suppressive effect n prgesterne cncentratins and thus may have cntributed t calf mrtality in these heifers when prgesterne cncentratins in the treated heifers that did calve are cnsidered. Specifically, calving rate differed (P < 0.05) between freatments with 7 f 5 treated heifers (46.7 E) calving cmpared with l3 f 15 cntrl heifers (86.7V;Table2). Hamernik et al. (1987) reprted that 4 f 10 pregnant cws that received exgenus teststerne, 250 mg teststerne prpinate administered subcutaneusly every ther day in 1 ml safflwer il, during days 40-60 f gestatin abrted within 1 wk f cessatin f hrmne treatment. Furthermre, Faver et al. (1993) reprted that an injectin f estradil valerate and nrgestmet in additin t the administratin f a nrgestmet implant n day 12 after breeding has adverse effects n fertility; specifically, nly I f 21 heifers that received this treatment remained pregnant t that breeding. Likewise, Day et al. (1994) bserved that cnceptin rates were lwer in pstpartum cws receiving estradil supplementatin t melengesffl acetate esffus synchrnizatin; and Sanchez et al. (1993) reprted that greater estradil cncenfratins in cws treated with nrgestmet in the absence f a crpus luteum cntributed t the decreased cnceptin rate bserved in thse cws. Therefre, data frm this study and thers suggest that these cmbinatins f estradil, with teststerne r prgesterne in early gestatin caused mrtality, pssibly by mdifying luteal functin r interfering
ALDRICH ET AL. _ SYNOVE-)P H AS AN ANDROGENIZING AGENT 547 with maternal recgnitin f pregnancy. In additin, the heifers were grazing endphyte-infected fescue pastures in the summer during early gestatin. Reduced reprductive efficiency in cattle grazing endphyte-infected fescue has been reprted. Specifically, reduced calving rates have been attributed t endphyte-infected fescue pssibly thrugh effects n the crpus luteum, and subsequently prgesterne prductin (Prter and Thmpsn 1992). Thus, the endphyte-infected fescue pasture may have cntributed t the increased calf mrtality in the treated heifers as cmpared with the cntrl heifers because the treated heifers were already facing a cmprmised pregnancy as evaluated by their decreased serum prgesterne cncentratins; and therefre, may have been mre susceptible t the detrimental effects f endphyte-infected fescue n maintainence f pregnancy. Calves brn t treated heifers weighed 10.374 less (P < 0.05) than calves brn t cnffl heifers (Table 2;33.3 vs. 37.1 x.1.1 kg, respectively). Similarly, a decrease in birth weight was bserved in ewe lambs (Bremner and Cumming 1978; Jenkins et al. 1988; DeHaan et al. 1987,1990a) and heifer calves (DeHaan et al. 1988, 1990b) brn t andrgentreated ewes and cws, respectively. Cnversely, Hamernik et al. (1987) bserved n differences in birth weight between heifers expsed t teststerne during days 40-60 f gestatin when cmpared t cntrl heifers. It is unclear hw prenatal expsure t teststerne may decrease birth weight; it may adversely affect placental functin. The armatase enzyme system which mediates the cnversin f andrgens t estrgens is present in the placenta (Slmn 1988). In sheep, the fetplacental unit is capable f metablizing teststerne t estrgens (Findlay and Seamark 1971); and estrgens have been shwn t reduce fetal grwth in rats (Vannier and Raynaud 1975). Additinally, calving ease scres were similar between treated and cntrl heifers (Table 2; 2.1 vs. 1.7 + 0.45, respectively). Likewise, implantatin with teststerne did nt affect the incidence f dystcia in ewes (Clarke et al. 1976; DeHaan et al. 1987) r cws (DeHaan et al. 1988). Synvex@H is a sterid ear implant used t increase rate f gain and imprve feed efficiency in female cattle in the feedlt (Darling 1993). N differences were bserved in the weisht f heifers treated with three times the nrmal dse f Syn-vex@ H as cmpared with cnffl heifers (Table^ 3). Average weight f heifers n the day f Synvex@ H implantatin was 360.8 x.7.6kg. Weight f treated and cntrl heifers 84 d pst-implantatin f Synvex@ H was als similar (434.8 vs. 428.7 x. ll.2kg, respectively). Average daily gain was imprved 7V by Synvex@H treatment (Table 3; 0.88 vs. 0.82 t 0.04 kg d-1, treated and cntrl heifers, respectively). The imprvement in ADG bserved in this study was similar t that reprted fr use f Synvex@ H in feedlt heifers. CONCLUSIONS The primary bjectives f this study were t determine if elevated serum cncentratins f teststerne culd be achieved in the implanted pregnant heifer with an elevated dse f Synvex@ H and what effects the estradil prtin f the Synvex@ H implant wuld have n pregnancy' The data are interpreted t suggest that treafinent f pregnant beef heifers wlth Synvex@ H fr the purpse f prenatally andrgenizing the female ffspring will increase serum cncentratins f teststerne in the treated heifers, but have adverse effects n calving rates, pssibly thrugh the exgenus estradil in the Synvex@ H implant and decreased prgesterne cncentratins. Therefre, it is suggested that Synvex@ H is nt an apprpriate andrgenizing agent due t the adverse effects n prgesterne cncentratins during pregnancy and calving rate and is nt recmmended fr this purpse until further research has been cnducted. ACKNOWLEDGEMENTS The authrs wuld like t express their appreciatin t Syntex Animal Health fr prviding the Synvex@ H fr this study. Als, appreciatin is expressed t Dr. O. D. Sherwd, Department f Physilgy, University f Illinis, Urbana, fr prviding the antisera fr the prgesterne and estradil ELISA. Bremner, W. J. and Cumming, I' A. 1978. Inhibitin f fetal grwth and survival by teststerne adrninistratin t pregnant sheep. Metablism. 27 : 253-255. Carmer, S. G. and Swansn, M. R. 1973. An evaluatin f ten pair-wise multiple cmparisn prcedures by Mnte Carl methds. J. Am. Stat. Assc. lt:66-74. Clarke, I. J., Scaramuzzi, R. J. and Shrt, R. V. 1976. Effects f teststerne implants in pregnant ewes n their female ffspring. J. Embryl. Exp. Mrphl. 36:8'1-99' Darling, L. i993. Veterinary pharmaceuticals and bilgicals@. Veterinary Medicine Publishing C., Lenexa, KS. p. 1031. Day, M. L., Balthaser, E. C. and Andersn, L- H- 1994. 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This article has been cited by: 1. J.W Gill, B.J Hsking, A.R Egan. 1998. Prenatal prgramming f mammalian grwth a review f the rle f sterids. Livestck Prductin Science 54:3, 251-267. [Crssref]