Edward D. Plotka

Hematologic and blood chemical characteristics of feral horses from three management areas.

Blood was collected from 486 feral horses of mixed sex and age classes captured from three wild horse management areas in Nevada and Oregon from December 1985 to February 1986. Males were significantly outnumbered by females in the Flanigan area, but both sexes were represented in approximately equal numbers in the Wassuk and Beatys Butte areas. Hematology and chemistry values averaged 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, 10.4 ± 0.14 and 23.4 ± 0.25 for hemoglobin (HGB), hematocrit (HCT), red blood cells (RBC), white blood cells (WBC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), Cortisol (F) and serum urea nitrogen (SUN), respectively. Statistically significant differences in HGB, HCT, RBC, WBC, MCV and MCH levels occurred with respect to age (P ≤ 0.001). Serum F levels were lower in immature animals than in either subadult or adults in all areas. Flanigan horses appeared in the poorest condition and had the lowest HGB, HCT and RBC counts while the values for Wassuk horses were significantly higher (P ≤ 0.001). Serum F levels were lowest in the Flanigan horses. A significantly lower (P ≤ 0.001) proportion of adult mares had progesterone levels consistent with pregnancy in the Flanigan horses versus those from the other two areas. These data are consistent with a subjective evaluation of the condition of the horses.

Effect of anosmia on reproduction in male and female wolves (Canis lupus)

Anosmia was produced in two female and three male wolves by transection of the olfactory peduncle and was confirmed by their inability to detect meat, urine, feces, anal-gland secretions, and fish emulsion. All operated animals continued to investigate the environment with their noses, to interact normally with other pack members, and to feed at levels which maintained presurgical body weights. No effect was found on reproductive physiology (females: estradiol or progesterone concentrations, ovulation, pregnancy or parturition; males: testosterone, testicular recrudescence or sperm numbers, motility or maturation). One anosmic female became dominant and although she urine-marked with a flexed leg, the rate was lower than typical for dominant females and perhaps contributed to her failure to pair-bond with the dominant male. One anosmic male raised-leg-urinated while competing for pack dominance and when kenneled away from other males. Precopulatory, copulatory, and maternal behavior were observed for one anosmic female and appeared normal. However, neither male that was sexually naive before surgery showed interest in proestrous or estrous females. The possibility that secondary degeneration of brain regions mediating sexual behavior was responsible for the failure of these males to respond was not supported. Not only was the lack of male sexual response the only serious deficit following transection, but the male which was sexually experienced prior to surgery did copulate successfully during his second postoperative breeding season despite continued anosmia. Chemosensory priming from female urine during the protracted proestrous phase, as well as urinary and vaginal odors during estrus, appear to be critical for induction of full sexual potency in sexually naive males. The importance of urine and vaginal secretions in the sexual response of experienced males is uncertain.

EFFECTS OF HORMONE IMPLANTS ON ESTRUS AND OVULATION IN FERAL MARES

Five groups of 30 captive feral mares each were implanted with silastic rods containing estradiol (E) and/or progesterone (P): E only with 8 g, P only with 24 g, P + HE with 8 g P + 8 g E, HP + E with 12 g P + 4 g E, HP + LE with 12 g P + 2 g E. Arbitrary group designations were differentiated by relative high (H) and low (L) amounts of steroid. Thirty mares received silastic rods containing no hormone (CI). Five mares from each group were bled every 2 wk for 4 mo and monthly for another 5 mo. All mares were tested for estrus by allowing them to stand in an alley between two pens of stallions and visually monitoring her response to the stallion. Serum P levels increased from 0.3 ± 0.1 to 1.8 ± 0.1 ng/ml in the P only group during the first 3 wk after implanting. Levels remained stable for the next 2 wk and then began a gradual decline. Serum P levels in the other groups were lower. Serum E levels were slightly increased in the groups receiving 8 g of E (E only and P + HE groups). Significantly fewer animals in the E only and P + HE groups exhibited estrus as compared with control animals (10 of 23 and 13 of 26 versus 22 of 25, respectively, P ≤ 0.003). However, animals receiving 24 g of P (P only) showed similar occurrences of estrus as controls. All animals detected in estrus ovulated as evidenced by elevations in serum P levels above 5 ng/ml collected 10 days after the mare was detected in heat. In spite of the significant effect of hormone implants on the occurrence of estrus, over 80% of mares bred and conceived when placed with a stallion. Our data suggest that these levels of implanted hormones can raise serum levels of P and E for at least 21 wk. These hormones, when implanted during early anestrus, can alter the occurrence of psychic estrus in captive feral mares without suppressing ovulation and conception.

Rapid reversible immobilization of feral stallions using etorphine hydrochloride, xylazine hydrochloride and atropine sulfate.

Forty-eight newly captured free-ranging feral stallions (Equus caballus) from two different locations and six captive stallions were immobilized using combinations of etorphine hydrochloride, xylazine hydrochloride and atropine sulfate with or without acepromazine. Six animals were immobilized twice, 1 mo apart. The drugs were administered either intramuscularly (n = 13) or intravenously (n = 44). Mean immobilization time (±SE) after intravenous (i.v.) injection of etorphine, xylazine and atropine was 55 ± 4 sec (range 20 to 185 sec) compared to 708 ± 131 sec (range 390 to 1,140 sec) for intramuscular (i.m.) injection. Immobilization was reversed with i.v. administration of 3 to 11 mg diprenorphine hydrochloride and 16 to 24 mg yohimbine hydrochloride. Average time from administration to standing and walking was 86 ± 7 sec (n = 55). Reversal of etorphine-induced immobilization with an amount of diprenorphine equal to the etorphine and administered i.v. was as effective as a 2:1 ratio of diprenorphine to etorphine. Acepromazine had no effect on induction time, but decreased relaxation after immobilization and prolonged ataxia after reversal of the etorphine and xylazine. Eight free-ranging horses were immobilized in 708 ± 132 sec by darting with 5.5 mg etorphine, 1,300 mg xylazine and 15 mg atropine from a helicopter. Three animals died during the study: one immediately after reversal of an i.v. administration, one from a broken neck during induction from darting, and one was found a week later at the site of darting. Comparisons of hematological values before and 15 min after drug immobilization demonstrated a small but significant decline in hemoglobin, red cells, and hematocrit with no significant effects on calculated red cell parameters. The horses captured in the Flanigan area had significantly lower values of hemoglobin, hematocrit and red cells (P < 0.001, 0.01, and 0.06, respectively) than stallions from Beatys Butte. This correlated with the poorer condition of the horses in the Flanigan area. The effectiveness of yohimbine as an antagonist for xylazine facilitated capture and immobilization of free-ranging feral horses and allowed their immediate release after handling with a minimum of postreversal depression.

HORMONAL CONTRACEPTION OF FERAL MARES WITH SILASTIC® RODS

Homogeneous Silastic® rods containing ethinylestradiol (EE) (1.5 or 4 g), estradiol-17β (E) (4 g) or progesterone (P) (6 g) were implanted into feral mares (Equus caballus) between 4-and 10-yr-old. Six treatment groups (≥10 mares/group) of non-pregnant mares received 36 g P and 12 g E (P + E), 36 g P and 8 g EE (P+HEE), 1.5 g EE (LEE), 3 g EE (MEE), 8 g EE (HEE) or control-implanted mares (CI). CI received implants containing no steroid. Two groups of pregnant mares received P + HEE or HEE. Stallions were placed with the mares 15 to 26 mo after implanting. Blood was collected biweekly for up to 28 mo after implanting and serum analyzed for P by radioimmunoassay. A single P value ≥2.5 ng/ml indicated ovulation and 2 consecutive values ≥2.5 ng/ml indicated pregnancy. Serum from blood collected before and at 4, 12, 24, 50, 64 and 89 wk after implanting was analyzed for EE concentrations. All animals pregnant at the time of contraceptive placement delivered normal foals. Contraceptive efficacy for groups LEE, MEE, HEE and P + HEE were 75, 75, 100, and 100%, respectively after two breeding seasons. Suppression of ovulation appeared to be inversely related to the concentration of EE used in the implant. The percent of animals ovulating after 2 yr of contraception in each group was 100, 100, 88, 62, 20, and 12 for groups CI, P+E, LEE, MEE, HEE and P+HEE, respectively. The pregnancy rate for the same groups was 100, 78, 25, 25, 0 and 0%, respectively. Contraceptive efficacy was followed for 3 yr in one group, P + HEE, and was 88%. Pregnancy rates for groups P+E and CI after 3 yr was 78 and 82%, respectively. Our data demonstrate effective contraception of feral mares for up to 36 mo without compromising a pregnancy in effect at the time of implanting. Calculating the decline in EE concentrations to 150% of pre-implantation concentrations, these data suggest an effective contraceptive life of approximately 16, 26, and 48 to 60 mo for LEE, MEE and HEE implants, respectively. Mechanisms that appear to be involved in contraceptive efficacy include preventing ovulation at higher concentrations of steroids and either suppressing ovulation or implantation at lower concentrations of steroid.

IMMOBILIZATION OF WHITE-TAILED DEER BY ETORPHINE AND XYLAZINE AND ITS ANTAGONISM BY NALMEFENE AND YOHIMBINE

White-tailed deer (Odocoileus virginianus) were immobilized with either 4.0 mg etorphine hydrochloride (ETOR) or 3.5 mg ETOR and 50.0 mg xylazine (XYL). Deer immobilized with ETOR only were given 4.0 mg nalmefene hydrochloride (NAL), a new opioid antagonist, 20 min after induction. Deer immobilized with ETOR and XYL received 3.5 mg NAL and 0.125 mg/kg yohimbine hydrochloride (YOH). The dose of 4.0 mg ETOR did not provide acceptable immobilization and was discontinued. A NAL:ETOR ratio of 1:1 was insufficient for complete and sustained antagonism of ETOR. Subsequently, deer were immobilized with ETOR and XYL as before which was then antagonized with 35.0 mg NAL and 0.125 mg/kg YOH. The 10:1 ratio of NAL:ETOR appeared to provide complete antagonism with no evidence of renarcotization. Although more study is required, NAL could become a useful antagonist for opioid-induced immobilizations.

Ovarian function in captive feral mares.

Ovarian function was monitored for 33 mo in captive feral mares (Equus caballus) by following serum progesterone (P) levels. A P level >2.0 ng/ml was considered indicative of ovulation. Feral mares were seasonally polyestrus with the majority of animals ovulating between May and October. During the first year after capture, none of the mares ovulated during the anestrous season. However, in subsequent years, approximately 10% of mares ovulated during the months of November, January and February. P levels during the luteal phase of the cycle ranged from 2.0 to 21.0 ng/ml which were similar to levels in domestic breeds of mares. The pattern of P concentrations during pregnancy was also similar to the pattern in domestic mares. These data confirmed the seasonality of ovulation in feral mares but indicated that this seasonality was not as rigid as previously believed. Captive feral mares were similar to domestic breeds in the percentage of mares ovulating all year and in the P levels achieved during the estrous cycle and pregnancy.

Contraception as a Tool for Managing Feral Horse Populations in the Western United States

Management of feral horse (Equus caballus) populations has been embroiled in controversy since the animals were protected by federal legislation in 1971. Populations are currently controlled by periodic capture, with over 100 000 horses removed from public lands over the past 17 years. Destruction of healthy animals is prohibited. Current programs place horses into private ownership or maintain unwanted animals in captivity for extended periods of time. These programs are expensive, and disposing of the large number of horses captured has been difficult. Numerous research initiatives over the last decade have focused on developing practical contraceptive tools. Male-oriented contraception has had limited success and may seriously disrupt normal seasonal reproductive cycles. Two contraceptive techniques have been developed for females, steroid implants which are effective for at least 3 years and an immunocontraceptive vaccine capable of blocking conception for 1 season. At present, the practicality of the vaccine is limited due to its short duration and the need for multiple injections per animal. The long duration of the steroid implants, coupled with the fact that horses can be easily and economically captured, suggests this technique may be practical for management applications.