Long‐Term Effect of Deslorelin Implant on Ovarian Pre‐Antral Follicles and Uterine Histology in Female Rats

The objective of the present study was to investigate the inhibitory effects of long‐term deslorelin implant administration on the ovarian and uterine structures of female rats. A total of 16 non‐pregnant female rats were randomly assigned to two groups, each consisting of eight animals. Animals in the implant group (DESL) received subcutaneously (s.c.) a single deslorelin implant (4.7 mg), an analogue of GnRH, while no treatment was applied to the control group (CON). A single adult male rat was introduced into the cages of both the DESL and CON females after 6 weeks of implant administration. After 1 year of implant administration, all animals were killed and follicular structures and volumes of ovaries and uterus were examined using stereological methods. Stereological observations showed that the mean ovarian total volume of the DESL group (0.28 ± 0.07 cm3) was lower than that of the CON group (1.55 ± 0.23 cm3) (p < 0.001). On the other hand, the total number of pre‐antral follicles in the ovaries of DESL (555.32 ± 151.47) females were significantly lower than the control group (1162.96 ± 189.19) (p < 0.001). In the DESL group, the mean volumes of epithelium, endometrium, myometrium and total volume of the uterus were significantly (p < 0.001) lower than in the control groups. In conclusion, these findings indicate that the long‐term deslorelin implant (i) interferes with the normal cyclicity of female rats and (ii) affects the pre‐antral follicle population. Further studies will be required to determine the effects of long‐term deslorelin treatment on the pre‐antral follicle numbers and future fertility in other species.     

Morphological study of the effects of the GnRH superagonist deslorelin on the canine testis and prostate gland

The present study is part of a programme of research designed to evaluate the efficacy of the GnRH superagonist,deslorelin (D-Trp6-Pro9-des-Gly10-LHRH ethylamide), as a contraceptive for male dogs. Adult dogs were assigned to a completely randomized design comprising six groups of four animals. Each dog in the control group received a blank implant (placebo) and each dog in the other five groups received a 6 mg deslorelin implant. One group of deslorelin treated dogs was sacrificed on each of days 16, 26, 41, 101 and 620, and testicular and prostate tissues were collected for study by light and electron microscopy. On days 16 and 26 after implantation, we observed partial disruption of the seminiferous tubules, with early spermatids shed into the lumen. On days 41 and 101 after implantation, 90–100% of the seminiferous tubules were atrophic and aspermatogenic.On day 101 after implantation, 99% of all sections showed atrophy of the epithelium and shrinkage of epithelial height in the ductus epididymides. On days 41 and 101 after implantation, prostate tissue showed complete atrophy of the glandular epithelium (100% of sections) and an apparent increase in the relative proportion of connective tissue. At the electron microscopic level, in dogs treated with deslorelin for 41 and 101 days, the Sertoli cells were smaller and their nucleoli appeared smaller than in the control dogs. The nucleoli of the Leydig cells were atrophied and prostate glandular epithelium showed reduced epithelial height, a trophy of the nucleolus and an absence of secretory granules.Tissues collected during the recovery phase revealed a complete recovery of spermatogenesis. In conclusion, slow release implants containing deslorelin induce a striking a trophy of the testes and prostate gland by 26 days after implantation, explaining the previously reported loss of ejaculate and arrest of sperm output. At histological level,the entire process appears to be completely reversible, in accordance with data on endocrine variables and semen production.     

Effects of deslorelin acetate implants in horses: single implants in stallions and steroid-treated geldings and multiple implants in mares

Three experiments were performed to test the following hypotheses: 1) stallions and/or progesterone-estradiol-treated geldings could serve as models for the effects of a single implant of the GnRH analog, deslorelin acetate, on LH and FSH secretion by mares; and 2) multiple implants of deslorelin acetate could be used as a means of inducing ovarian atrophy in mares for future study of the mechanisms involved in the atrophy observed in some mares after a single implant. In Exp. 1, nine light horse stallions received either a single deslorelin implant (n = 5) or a sham injection (n = 4) on d 0. In Exp. 2, 12 geldings received daily injections of progesterone on d -20 through -4, followed by twice-daily injections of estradiol on d -2 to 0. On the morning of d 0, geldings received either a single deslorelin implant (n = 6) or a sham injection (n = 6). Daily injections of progesterone were resumed on d 2 through 15. In Exp. 1, plasma LH and FSH were elevated (P < 0.05) in the treatment group relative to controls at 4, 8, and 12 h after implant insertion. In the treated stallions, FSH was decreased (P < 0.05) on d 3 to 13, and LH was decreased on d 6 to 13. In Exp. 2, plasma LH and FSH were elevated (P < 0.05) at 4,8, and 12 h after deslorelin implant insertion. Plasma LH was suppressed (P < 0.05) below controls on d 2 to 7, 9, and 11 to 15; plasma FSH was suppressed (P < 0.05) on d 4 to 15. In Exp. 3, 21 mares were used to determine whether multiple doses of deslorelin would cause ovarian atrophy. Mares received one of three treatments: 1) sham injections; 2) three implants on the first day; or 3) one implant per day for 3 d (n = 7 per group). Treatment with multiple implants increased (P < 0.05) the interovulatory interval by 14.8 d and suppressed (P < 0.01) LH and FSH concentrations for approximately 25 d; no mare exhibited ovarian atrophy. In conclusion, after an initial short-term increase in LH and FSH secretion, deslorelin implants caused long-term suppression of both gonadotropins in stallions as well as in geldings treated with progesterone and estradiol to mimic the estrous cycle. It is likely that either of these models may be useful for further study of this suppression in horses. Although multiple implants in mares suppressed gonadotropin secretion longer than a single implant, the lack of ovarian atrophy indicates that the atrophy observed after a single implant in previous experiments was likely due to the susceptibility of individual mares.     

Restoration of reproductive potential following expiration or removal of melengestrol acetate contraceptive implants in golden lion tamarins (Leontopithecus rosalia).

Although reversible contraception is important to successful management of small populations, there are concerns about the reversibility of melengestrol acetate (MGA), the most commonly used implant in captive animals. Female golden lion tamarins (Leontopithecus rosalia) placed in potential breeding situations after surgical MGA implant removal showed a 75% return to reproduction within 2 yr, unlike golden-headed tamarins (Leontopithecus chrysomelas), which have had a 29% return to reproduction following implant removal. This rate was indistinguishable from the breeding probability for newly formed pairs involving nonimplanted females. Litter size, stillbirth rate, and infant survival rate were not significantly different between nonimplanted and implant-removed female golden lion tamarins. However, females with implants left in (and assumed to have expired) showed higher stillbirth and infant mortality rates than did females with implants removed. For seven female golden lion tamarins for which reproductive histories before and after MGA implantation were available, litter size was unaffected by MGA implantation and subsequent removal. Infant survival rate for these females appeared to be lower after removal but was indistinguishable from rates in the nonimplanted females. Prior reproductive experience, length of time with an implant, and age of the females did not affect the probability of breeding for females after removal of the implants. Overall, breeding probability of nonimplanted females declined with age. Although the results of this study confirm the reversibility of MGA implants in golden lion tamarins, there appear to be some effects on viability of offspring, particularly offspring born to females with implants left in and presumed expired.     

Effect of sex on lipogenic activity in swine adipose tissue

Adipose tissue was obtained from male, female and male pigs castrated either at birth, 2 or 4 mo of age. Pigs were biopsied at 11 and 20 wk of age to obtain adipose tissue samples. Lipogenic capacity was assessed by measurement of in vitro glucose incorporation into lipids of adipose tissue slices. At 20 wk of age, males were less fat than females or males castrated either at birth or 20 mo of age. Adipocyte volume at 20 wk of age was smaller in males, females and recently castrated males (4 mo) than males castrated at birth or 2 mo of age. Lipogenic rate at 20 wk of age was lower in males than in castrated pigs; females had intermediate lipogenic rates. The results provide a partial metabolic explanation for the difference in subcutaneous fat deposition in the sexually diverse groups. There was no effect of estradiol-17 beta or testosterone in vitro on adipose tissue lipogenesis, suggesting that sex hormone effects in vivo may not be involved in short-term regulation of lipogenesis.     

Long‐Term‐Release GnRH Agonists Postpone Puberty in Domestic Cats

The aim of this study was to assess the efficacy and safety of deslorelin acetate implants on domestic queen puberty postponement. Thirty, 114.4 ± 12.7 days old, 1.5 ± 0.1 kg prepubertal crossbred female cats were included in this study. The animals were kept under a positive photoperiod and randomly assigned to deslorelin acetate 4.7 mg SC implants (n = 15) or to a non‐treated control group (n = 15). The queens were followed up daily and weighed weekly until puberty. Vaginal cytology was also carried out three times a week. Puberty was diagnosed by the presence of the typical oestrous behaviour and vaginal cytology findings. At puberty, ovariectomy was performed and the gonads grossly described. Age (281.2 ± 21.6 vs 177.8 ± 10.8; p < 0.01) but not weight (2.6 ± 0.1 vs 2.5 ± 0.1; p > 0.1) at puberty differed between the deslorelin and control groups, respectively. One deslorelin‐treated female showed an oestrous response and another showed clinical signs of pyometra after the implants. Deslorelin‐treated ovaries appeared small, while control gonads were normal. It was concluded that long‐term‐release deslorelin, administered at approximately 50% adult body weight, postponed feline puberty without altering growing rate.     

Acceleration and Timing of Fertile Ovulation in Cyclic Mares with a Deslorelin Implant

In a blinded trial, the effectiveness and safety of 2.2 mg of the GnRH analog deslorelin acetate, administered in a short–term implant (STI) to normally cycling mares in estrus with a dominant ovarian follicle of 30 mm in diameter or larger, were evaluated, using a placebo implant as a negative control. A total of 39 mares received treatments at admittance with pre–randomized implants containing either 2.2 mg or 0 mg deslorelin. Mares were teased daily and examined rectally with ultrasound at 24 h intervals to determine time to Ovulation and duration of estrus. The number of breedings and the pregnancy rate at 18 (±3) and 38 (±3) days were recorded, as were systemic side effects and local reactions at the implantation sites. Pregnancies resulting from breedings during the treatment estrus and/or from breedings during the next estrus were followed and the early and late pregnancy loss rate, the number of pregnancies going to term and of live–born foals was recorded.Mean follicle diameter at treatment was not significantly different between the deslorelin and placebo treatment group with 41.6 mm and 40.8 mm, respectively. Treatment with deslorelin STI reduced the time interval to Ovulation significantly from 69.5±25.48 h to 42.7±12.35 h (p<0.001). The percentage of mares having ovulated within 48 h rose from 26.3% to 95.0%, respectively, for placebo and deslorelin STI (p<0.001). As a consequence, the duration of estrus in days and the percent of animals requiring more than 1 breeding were significantly reduced in deslorelin treated animals from 5.4 days to 4.6 days, and from 55.6% to 5.0%, respectively (p=0.009 and =0.001). The percent of mares pregnant from breedings at the treatment estrus (65.0% versus 44.4%) or the next estrus (83.3% versus 92.3%) was satisfactory and similar for deslorelin and placebo treated mares (p>0.005), and in 70.0% and 66.7% of these once or twice bred mares did pregnancies go to term and live foals were born. kw|Keywords|k]GnRH     

Fertility in Adult Bitches Previously Treated with a 4.7 mg Subcutaneous Deslorelin Implant

The absence of fertility problems in male dogs after a single treatment with deslorelin acetate (Suprelorin^®) is well acknowledged. However, reports on the application of deslorelin in the bitch and information concerning fertility after implant treatment are still limited. In this retrospective study, data concerning induced and spontaneous oestruses of 39 bitches from 17 breeds, treated with deslorelin acetate implants (4.7 mg Suprelorin^®, Virbac, France), were retrieved to assess post‐treatment fertility (ovulation rate, pregnancy rate and litter size). Animals were grouped according to treatment characteristics: group 1 (Gr1) – females submitted to oestrus induction, showing natural oestruses afterwards (n = 19); group 2 (Gr2) – females re‐implanted with 4.7 mg deslorelin acetate to re‐induce oestrus, showing subsequent spontaneous post‐implant oestruses (n = 7); and group 3 (Gr3) – females submitted to a 4.7 mg deslorelin acetate implant for oestrus suppression, evaluated at subsequent spontaneous post‐implant oestruses (n = 13). Comparison of fertility traits between induced and post‐treatment spontaneous oestruses in Gr1 and Gr2 (short treatments), or between spontaneous oestruses after long‐treatment schedules (Gr 3) revealed a slightly better performance in spontaneous cycles compared with induced cycles: ovulation rate post‐treatment was 97.1%, 94.1% and 94.4% and the pregnancy rate post‐treatment was 91.2%, 88.9% and 84.6% for groups 1, 2 and 3, respectively. Nevertheless, fertility in induced and post‐treatment oestruses was considered normal. Moreover, the individual litter size did not differ within groups between induced and spontaneous cycles. From these findings, we concluded that treatment with 4.7 mg deslorelin implants did not compromise the bitches' fertility in subsequent oestruses.     

Circulating concentrations and pattern of luteinizing hormone and follicle-stimulating hormone in circulation are changed by the circulating concentration of 17 beta-estradiol in the bovine male and female.

The objectives of the present study were 1) to determine whether 17 beta-estradiol (E2) regulation of tonic secretion of LH and FSH is sexually differentiated in the bovine and 2) to evaluate the effects of various physiological concentrations of E2 on the profiles and concentrations of gonadotropins in circulation. This was accomplished by administering different numbers of implants containing E2 to gonadectomized bovine males and females. Mean age at initiation of the study was 18.5 mo. Animals received 1, 2, 4, 8, or 16 implants of E2 or a sham implantation. Mean concentrations of LH in circulation and amplitude of LH pulses were similar between males and females after administration of E2. There was a cubic response for mean concentrations of LH and amplitudes of LH pulses across the dosages of E2 administered; lower concentrations of E2 had little effect, whereas higher concentrations of E2 suppressed both mean LH and amplitude of LH pulses. A linear decline in frequency of LH pulses occurred as concentrations of E2 in circulation increased. A treatment x sex interaction resulted for mean concentrations of FSH in circulation. Low doses of E2 resulted in a greater enhancement of circulating concentrations of FSH in males than in females. Tonic secretion of LH in bovine males and females responded in a similar manner to administration of various physiological concentrations of E2; however, a differential response between sexes was observed for FSH.     

Interovulatory intervals in mares receiving deslorelin implants in Ireland (2009 to 2010)

Deslorelin acetate implants, recently licensed in Ireland and the UK for ovulation induction in mares, have been associated with prolonged interovulatory intervals in USA studies, leading to the practice of removing implants postovulation. Trial data in Australia indicate a less pronounced effect on interovulatory intervals, suggesting possible geographical variation. Objectives of the current study were to assess the effect of deslorelin implants, with and without removal on oestrous cycle length in Irish- and UK-based Thoroughbred broodmares. Data were collected retrospectively from 88 oestrous cycles. A statistically significant difference (P=0.02) was found between interovulatory intervals in mares in which the deslorelin implant was not removed, compared with administration and removal of the implant or the use of human chorionic gonadotrophin. The results suggest that implant removal when possible is advisable. The delay in subsequent ovulations was less marked than that reported in some studies from the USA. This information is useful in deciding when to schedule subsequent breeding for mares which received a deslorelin implant during the previous oestrous period and provides evidence to counter-concerns that mares treated with deslorelin implants may experience a long delay in return to oestrus if the implant is not removed.     

The Treatment of Adrenal Cortical Disease in Ferrets with 4.7-mg Deslorelin Acetate Implants

Thirty pet ferrets with adrenocortical disease (ACD) of varying severity and duration were evaluated for response to a single administration of a slow release 4.7 mg deslorelin acetate implant. Clinical response to deslorelin was monitored via a physical examination performed every 3 to 4 months. Adrenal ultrasound measurements were taken every 3-4 months until clinical relapse. At clinical relapse, duration of symptom suppression and adrenal size and growth were determined. Administration of a single 4.7 mg implant of deslorelin acetate resulted in significant decreases in the clinical signs and hormonal concentrations associated with ACD. Within 14 days post-implant, vulvar swelling, pruritus, sexual behaviors and aggression decreased or disappeared. Hair re-growth was evident by 4-6 weeks post implant. Within two months post deslorelin implant, plasma concentrations of steroid hormones decreased: mean estradiol concentration decreased 28%; 17-hydroxyprogesterone levels decreased 89% and androstenedione levels decreased 88%. The response to a single 4.7 mg implant of deslorelin acetate was transitory. The mean ± SD time to recurrence of clinical signs was 17.6 ± 5.0 months (range, 8.0-30.0 months). Repeated ultrasound measurements revealed no statistical difference in size of the adrenals (right or left) before, during the months of deslorelin implant and at clinical relapse. Slow release 4.7 mg deslorelin implants can effectively be used to temporarily eliminate the clinical signs and reduce steroid hormone concentrations in ferrets with ACD. This dose of deslorelin does appear to influence adrenal tumor growth causing a decrease in adrenal size in some ferrets, and mild enlargement of adrenal glands in most ferrets with 2 of 30 implanted animals developing large tumors before clinical relapse. The long-term effect of treatment with deslorelin on adrenal tumor pathology requires additional investigation. At this time, surgical removal of the adrenal tumor remains the only curative treatment; however, 4.7 mg deslorelin implants are useful in the long-term management of ACD hormone-induced sequelae and may be as effective assurgical management.     

Clinical and endocrine responses to treatment with deslorelin acetate implants in ferrets with adrenocortical disease

OBJECTIVE: To evaluate the clinical and endocrine responses of ferrets with adrenocortical disease (ACD) to treatment with a slow-release implant of deslorelin acetate. ANIMALS: 15 ferrets with ACD. PROCEDURE: Ferrets were treated SC with a single slow-release, 3-mg implant of deslorelin acetate. Plasma estradiol, androstenedione, and 17-hydroxyprogesterone concentrations were measured before and after treatment and at relapse of clinical signs; at that time, the adrenal glands were grossly or ultrasonographically measured and affected glands that were surgically removed were examined histologically. RESULTS: Compared with findings before deslorelin treatment, vulvar swelling, pruritus, sexual behaviors, and aggression were significantly decreased or eliminated within 14 days of implantation; hair regrowth was evident 4 to 6 weeks after treatment. Within 1 month of treatment, plasma hormone concentrations significantly decreased and remained decreased until clinical relapse. Mean time to recurrence of clinical signs was 13.7 +/- 3.5 months (range, 8.5 to 20.5 months). In 5 ferrets, large palpable tumors developed within 2 months of clinical relapse; 3 of these ferrets were euthanatized because of adrenal gland tumor metastasis to the liver or tumor necrosis. CONCLUSIONS AND CLINICAL RELEVANCE: In ferrets with ACD, a slow-release deslorelin implant appears promising as a treatment to temporarily eliminate clinical signs and decrease plasma steroid hormone concentrations. Deslorelin may not decrease adrenal tumor growth in some treated ferrets. Deslorelin implants may be useful in the long-term management of hormone-induced sequelae in ferrets with ACD and in treatment of animals that are considered at surgical or anesthetic risk.     

Suppression of ovarian progesterone production in dairy cows using an implant of GnRH-agonist (deslorelin) for the purpose of evaluating progesterone metabolism

OBJECTIVE: To evaluate the potential of an implant of a GnRH-agonist (deslorelin) to create a progesterone free animal suitable for studying progesterone (P4) metabolism in intact cows by measuring blood P4 and faecal P4 metabolites. METHODS: Experiment 1: Eighteen non-lactating cycling Holstein-Friesian cows, 4 to 7 years old, were allocated to one of three groups to study plasma P4 concentrations preceding an intravaginal insert. These groups comprised: i) a deslorelin group (GnRH-agonist implanted); ii) a PGF group receiving two injections of prostaglandin (PGF2alpha) 12 days apart; and, iii) an ovariectomised (OVX) group. An intravaginal device (CIDR) was inserted into the vagina of each animal and left in place for 11 days. Plasma P4 concentrations were measured during the study period. Experiment 2: Twelve non-lactating cycling Holstein-Friesian cows, 4 to 7 years old, were allocated to two groups: i) a deslorelin group (GnRH-agonist implanted); and ii) an ovariectomised group. Plasma P4 and faecal P4 metabolites (20-oxo-pregnanes, 20alpha-OH and 20beta-OH) were monitored for a period of 5 weeks. RESULTS: Experiment 1: Average plasma P4 concentration did not differ between the three groups (1.28, 1.43 and 1.55 ng/mL for deslorelin, OVX and PGF cows, respectively, P = 0.8) during the period of supplementation. Experiment 2: There was no difference in plasma P4 (mean plasma P4 < 0.02 ng/mL, P = 0.9) and faecal P4 metabolites between deslorelin and OVX cows 2 weeks after the implantation (P = 0.7). CONCLUSIONS: These data showed that a GnRH-agonist (deslorelin) implant may be used as an alternative to ovariectomy to create a progesterone free animal suitable for studying the metabolism of administered P4.     

Reproductive performance of early postpartum Holstein cows where oestrus was synchronised following chronic GnRH agonist treatment

OBJECTIVE: The objectives of this study were: to compare the recovery of follicular development in early postpartum cows that had been treated for 7, 14 or 21 d with implants containing the GnRH agonist deslorelin; to evaluate the effectiveness of human chorionic gonadotrophin (hCG) for the induction of ovulation when a follicle was at least 10 mm in diameter following implant removal; and to compare final pregnancy rates for treated cows and untreated contemporaries. PROCEDURE: Within 3 d of calving Holstein cows were allocated to receive a single subcutaneous deslorelin implant to be left in place for either 7, 14 or 21 d, or to remain untreated as controls. Every deslorelin treated cow was monitored twice weekly for 35 d to determine the interval from implant removal to resumption of ovulation using serial transrectal ultrasonography and plasma progesterone assay. An injection of 1000 IU hCG was given to induce ovulation when a follicle of at least 10 mm diameter was first observed. Oestrous cycles of every cow were synchronised to facilitate artificial insemination (Al) at the start of the seasonally concentrated Al program and resynchronised for three rounds. Pregnancy testing was performed by ultrasonography 13 weeks after the first round of Al. RESULTS: Deslorelin implants inhibited ovulation for at least 10 d after they were removed. Ovarian follicles were smaller for the group that had implants for 21 d at the time of implant removal. Eighteen cows selected for treatment with hCG ovulated and formed multiple corpora lutea within 7 d. There was no effect of treatment duration on final pregnancy rates. After three rounds of AI the pooled final pregnancy rate for every cow that had received a deslorelin implant was similar to the rest of the herd (67% versus 63%; Deslorelin versus Herd, P > 0.1).The interval from start date of the AI program to conception was also unaffected by treatment (9.6 +/- 3.0 versus 14.8 +/- 1.7 d; Deslorelin versus Herd; P > 0.1). CONCLUSION: No significant effect was detected on the interval from implant removal to first ovulation by altering the duration of deslorelin treatment. Treatment with hCG when a follicle at least 10 mm in diameter was present induced ovulation in most cases. Although no significant improvement in fertility was found, a larger field trial using this model for induced anoestrous is necessary before any effect on fertility could confidently be stated.     

Induction of sexual activity in lactating anovulatory female goats using male goats treated only with artificially long days

Two experiments were conducted to determine the response of Creole male goats treated with long days and melatonin implants, and the response of the anovulatory does to male effect using males treated only with artificially long days. All animals were allocated to open sheds. In Exp. 1, one group of males was under natural photoperiod (CG; n = 7); the second group was submitted to 2.5 mo of long days followed by the insertion of two s.c. melatonin implants (LD+MEL; n = 7); the third group was subjected only to 2.5 mo of long days (LD; n = 7). Testicular weight was measured every 2 wk. Plasma testosterone concentrations were determined weekly. A treatment x time interaction was detected (P < 0.001) for testicular weight and plasma testosterone concentration. In the LD+MEL and LD groups, testicular size and plasma testosterone levels varied in a similar way, but differed from those observed in CG (P < 0.001). In this latter group, testicular weight displayed seasonal variations and peaked in June, whereas in treated groups this peak occurred in March. In CG, testosterone varied in a seasonal manner and plasma concentrations increased in June and remained elevated throughout the study. In experimental groups, testosterone increased in February and peaked in March. In Exp. 2, one group of males was left under natural photoperiod (CG, n = 5) and the other one was submitted to 2.5 mo of artificially long days (LD, n = 4). On March 16, two control and two treated males were put in contact with 20 and 19 females, respectively. Sexual behavior of the bucks was observed during the 5 d following male introduction. Progesterone assays and estrous behavior were used to determine ovarian and behavioral responses of the females to teasing. The anogenital sniffing, nudging, and mount instances registered in LD-treated males were greater than those observed in CG (P < 0.05). Of the does exposed to CG, none ovulated and only two of 20 females displayed estrous behavior. All does in contact with LD-treated males ovulated and showed at least one estrous behavior during the 15 d following joining (P < 0.001). These results indicate that the sexual activity of male goats from subtropical latitudes can be induced using only artificially long days. In addition, males treated in this way are capable of stimulating sexual activity in anovulatory females by the male effect.     

Short-term individual housing temporarily reduces the libido of bulls

The objective of the present study was to determine the effects of short-term (6 wk) individual housing on the sexual interest (libido) of sexually experienced bulls. Twenty-two Hereford bulls reared with both males and females (BMF) or in all-male groups (BM) and approximately 21 mo of age were given free access for 40 min to five restrained females in hormonally-induced estrus and restricted access for 30 min to a single enclosed estrous female on two separate occasions. Free-access tests were administered to bulls in groups of five or six individuals, whereas bulls were tested individually in restricted-access tests. After testing, half the animals were housed individually (physically isolated from conspecifics) and half remained in group housing for a 6-wk period. Libido tests were administered again at the end of the treatment period and 2 wk after reinstatement of group housing for the experimental subjects. Individually housed bulls exhibited fewer mounts (P less than .001) and spent less time with females (P less than .01) in tests administered during physical isolation than before or after treatment. Individual housing did not affect BMF and BM bulls differentially. In conclusion, short-term individual housing temporarily reduced libido of beef bulls.     

Immunocontraception in Eastern gray squirrels (Sciurus carolinensis): morphologic changes in reproductive organs

Eastern gray squirrels (EGS) (Sciurus carolinensis) damage trees through bark stripping or gnawing due to territorial marking or agonistic gnawing behavior in concert with higher densities. This study was conducted to determine the effects of a contraceptive vaccine on EGS and its reproductive organ histology. Free-ranging urban EGS were vaccinated with the immunocontraceptive GonaCon. All EGS were > or = 6 mo of age as determined by a combination of pelage characteristics and body weights. The vaccine was administered by injection at a dosage rate of 0.4 ml containing 400 microg of GnRH-mollusk protein conjugate i.m. in the thigh to 33 EGS (17 male [m], 16 female [f]) in trapping session 1 (TS1), 23 (14 m, 9 f) in trapping session 2 (TS2), and 11 (8 m, 3 f) in trapping session 3 (TS3). A sham injection containing 0.4 ml saline-AdjuVac was given as control to 22 EGS (16 m, 6 f) in TS1, 20 (12 m, 8 f) in TS2, and 8 (4 m, 4 f) in TS3. In the last trapping session (TS4), 35 EGS (16 treated, 19 control) were killed for necropsy to evaluate histologic changes in testes and ovaries. Treated EGS males had testicular, prostatic, and epididymal atrophy compared with control EGS males. The tubuli seminiferi and prostatic glandular lumen of treated EGS males were atrophic, and the epididymal lumen contained no sperm cells. No histologic changes were observed in treated EGS females; however, females likely were not collected when changes due to GonaCon would have been observed. There were no observable histologic differences in the pituitary gland of treated and control EGS. There were no statistically significant differences in either testosterone or progesterone concentrations between control and treated EGS. Although there were no serious side effects to the vaccine, six EGS developed injection site abscesses. GonaCon may be a potential tool for EGS population control.     

Trenbolone acetate in combination with 17 beta-estradiol: influence of implant supports and dose levels on animal performance and plasma metabolites

Twelve (Exp. 1) and 24 (Exp. 2) young growing bulls were used to compare the effects of long-acting, cholesterol-based implants with short-acting, lactose-based implants. Each implant contained 200 mg of trenbolone acetate and 40 mg of 17 beta-estradiol. The long-acting, cholesterol-based implants were applied once either 18 wk (early implantation) or 12 wk (late implantation) before slaughter. The lactose-based pellets were implanted once (6 wk before slaughter), twice (12 and 6 wk) or three times (18, 12 and 6 wk) before slaughter. Treated animals had higher live weight gains, a lower feed conversion ratio, a higher proportion of lean meat and a lower proportion of adipose tissue than control animals. In Exp. 1 live weight gain of bulls implanted early with a single cholesterol-based implant was similar to the gain of animals treated three times with a lactose-based implant, but in Exp. 2 the effects of the long-acting implants given early were not sustained. In Exp. 3, 24 young growing bulls were used in a 3 X 2 factorial design to compare the effects of three dose levels of trenbolone acetate (100, 200 and 300 mg) and two levels of 17 beta-estradiol (40 and 60 mg). There were no significant differences between treatment groups, but highest live weight gains were observed in animals implanted with 300 mg of trenbolone and 60 mg of estradiol. This group also yielded the highest proportion of lean meat and the lowest proportion of adipose tissue. There was a decrease in plasma urea concentration after each implantation. It appeared also that plasma trenbolone was higher with implants containing 60 mg of estradiol. There were no differences between groups in growth hormone response to arginine stimulation.     

Sexual behavior and serum testosterone concentration in stallions treated with slow-release implants of deslorelin acetate

The objective of this study was to determine the long-term effects of the administration of 4.7-mg slow-release deslorelin implant on stallions' plasma testosterone concentrations and sexual behavior. Five control animals received a subcutaneous dose of saline solution, whereas treated animals (n = 11) received a subcutaneous implant of 4.7-mg deslorelin acetate (Suprelorin; Virbac SA, Carros, France). Testosterone plasma concentrations were monitored from April to September every week for the first 30 days, then every 2 weeks until the end of the study (98 days in total). A stimulation test using human chorionic gonadotropin was performed before and 70 days after implant administration. Behavior was assessed by asking owners to fill out a questionnaire before treatment, weekly during the study, and then at 7 months after treatment. In treated stallions, an acute increase in testosterone concentration was evident within 7 days after treatment, which was followed by a gradual decline to below basal values over the next 42 days. Results of this study support that deslorelin is biologically active in the stallion. The answers to the questionnaires showed a significant decrease (P = 0.03) in the rearing up behavior at week 3 and 4 after treatment. At the end of the study, of 11 owners, 5 asked their stallions to be reimplanted. Lacking side effects, deslorelin could be considered, in some instances, in the treatment of some behavioral problems in stallions, although there are individual variations in response, which deserve further investigations.