Reproductive responses of cattle to GnRH agonists

Effect of a subcutaneous implant of deslorelin acetate on serum testosterone concentrations in male Hermann's (Testudo hermanni sp.) and Greek (Testudo graeca sp.) tortoises

Deslorelin acetate is a gonadotropin-releasing hormone agonist formulated in a controlled-release subcutaneous implant and designed for reversible suppression of testosterone production in dogs. It has also been demonstrated to be effective in other animal species, but no data on its effectiveness in male land tortoises are available. This study aimed to evaluate the effect of a 4.7-mg deslorelin acetate implant on serum testosterone concentrations in male Hermann's (Testudo hermanni sp.) and Greek (Testudo graeca sp.) tortoises. Twenty adult male tortoises housed under the same environmental conditions were enrolled for the study and randomly assigned to a treatment (D, n = 10) or a control (C, n = 10) group. Starting in May, males from the D group were implanted with a 4.7-mg deslorelin acetate device, whereas males from the C group did not receive any treatment. Blood samples were collected once immediately before implant application (S0-May) and at 15 days (S1-June), 2 (S2-July), and 5 (S3-October) months after application. Serum testosterone at each sampling time was measured through a solid-phase, enzyme-labeled, competitive chemiluminescent immunoassay. Median serum testosterone concentrations were not significantly different between the two groups in all sampling times, and no interaction between treatment and sampling time was observed. The present study, therefore, suggests that a single treatment with a 4.7-mg deslorelin acetate implant has no effect on testosterone circulation in male Hermann's and Greek tortoises during the following 5 months.

A role for GnRH in olfaction and cognition: Implications for veterinary medicine

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for the activation and maintenance of the function of the hypothalamic-pituitary-gonadal (HPG) axis, which controls the onset of puberty and fertility. Two provocative recent studies suggest that, in addition to control reproduction, the neurons in the brain that produce GnRH are also involved in the control postnatal brain maturation, odour discrimination and adult cognition. Long-acting GnRH antagonists and agonists are commonly used to control fertility and behaviour in veterinary medicine, primarily in males. This review puts into perspective the potential risks of these androgen deprivation therapies and immunization on olfactory and cognitive performances and well-aging in domestic animals, including pets. We will also discuss the results reporting beneficial effects of pharmacological interventions restoring physiological GnRH levels on olfactory and cognitive alterations in preclinical models of Alzheimer's disease, which shares many pathophysiological and behavioural hallmarks with canine cognitive dysfunction. These novel findings raise the intriguing possibility that pulsatile GnRH therapy holds therapeutic potential for the management of this behavioural syndrome affecting older dogs.

Iron deficiency and internalizing symptom severity in unmedicated adolescents: a pilot study

BACKGROUND

Iron plays a key role in a broad set of metabolic processes. Iron deficiency is the most common nutritional deficiency in the world, but its neuropsychiatric implications in adolescents have not been examined.

METHODS

Twelve- to 17-year-old unmedicated females with major depressive or anxiety disorders or with no psychopathology underwent a comprehensive psychiatric assessment for this pilot study. A T1-weighted magnetic resonance imaging scan was obtained, segmented using Freesurfer. Serum ferritin concentration (sF) was measured. Correlational analyses examined the association between body iron stores, psychiatric symptom severity, and basal ganglia volumes, accounting for confounding variables.

RESULTS

Forty females were enrolled, 73% having a major depressive and/or anxiety disorder, 35% with sF < 15 ng/mL, and 50% with sF < 20 ng/mL. Serum ferritin was inversely correlated with both anxiety and depressive symptom severity (r = -0.34, p < 0.04 and r = -0.30, p < 0.06, respectively). Participants with sF < 15 ng/mL exhibited more severe depressive and anxiety symptoms as did those with sF < 20 ng/mL. Moreover, after adjusting for age and total intracranial volume, sF was inversely associated with left caudate (Spearman's r = -0.46, p < 0.04), left putamen (r = -0.58, p < 0.005), and right putamen (r = -0.53, p < 0.01) volume.

CONCLUSIONS

Brain iron may become depleted at a sF concentration higher than the established threshold to diagnose iron deficiency (i.e. 15 ng/mL), potentially disrupting brain maturation and contributing to the emergence of internalizing disorders in adolescents.

DESLORELIN (SUPRELORIN®) USE IN NORTH AMERICAN AND EUROPEAN ZOOS AND AQUARIUMS: TAXONOMIC SCOPE, DOSING, AND EFFICACY

The Association of Zoos and Aquariums Reproductive Management Center (RMC) in the US and the European Association of Zoos and Aquaria Reproductive Management Group (RMG) in Europe monitor efficacy of contraceptive products in participating institutions and use those results to inform contraceptive recommendations. This study used the joint RMC-RMG Contraception Database to analyze efficacy of deslorelin implants (Suprelorin^®), a contraceptive used in a wide range of mammalian taxa. More recently its use has increased in birds and in some reptiles and fish. Deslorelin, a gonadotropin-releasing hormone (GnRH) agonist, stimulates the reproductive system before downregulating receptors on pituitary cells that produce hormones that stimulate gonadal steroids in both males (testosterone) and females (estradiol and progesterone), interrupting sperm production and ovulation, respectively. Nevertheless, it has been used mostly in females. Efficacy has been high in mammals, with failures resulting in offspring in only 1.3% of treated individuals and 0.5% of treatment bouts. The failure rate has been higher in birds, with 14.7% of individuals in 7.2% of bouts producing eggs, perhaps reflecting differences in avian GnRH molecules. Too few reptiles and fish have been treated for meaningful analysis. Although deslorelin appears very safe, a possible exception exists in carnivores, because the stimulatory phase can result in ovulation and subsequent sustained progesterone secretion that may cause endometrial pathology. However, the stimulatory phase can be prevented by treatment with megestrol acetate for 7 d before and 7 d after implant insertion. The two current formulations of Suprelorin are effective for minimums of 6 (4.7 mg) or 12 mo (9.4 mg). The data indicate that Suprelorin is an effective and safe contraceptive option for female mammals, although it may not be effective in males of some mammalian species. Further research is needed to ascertain its usefulness in nonmammalian taxa.

Transient suppression of ovulatory ovarian function in pony mares after treatment with slow-release deslorelin implants

Behavior during the estrous cycle of mares can affect their performance and therefore inhibition of cyclical ovarian activity is indicated. We hypothesized that implants containing the GnRH analog deslorelin downregulate GnRH receptors and inhibit ovulation in mares. The estrous cycles of Shetland mares were synchronized with 2 injections of a PGF_2α analog. One day after the second injection (day 0), mares received 9.4 (group D1, n = 6) and 4.7 mg deslorelin (D2, n = 5) as slow-release implants or 1.25 mg short-acting deslorelin as a control (C, n = 5). Ultrasonography of the reproductive tract and ovaries and observation of estrous behavior and collection of blood samples for analysis of progesterone and LH concentrations were performed every second day until day 10 and thereafter at 5-d intervals. Stimulation tests with the GnRH-agonist buserelin were performed on days 10 and 45. Until day 50, there were less spontaneous ovulations in group D1 (P < 0.01) and estrous behavior was reduced in groups D1 and D2 compared with group C (P < 0.05). The time until first ovulation (D1 62.0 ± 8.6, D2 44.2 ± 14.1, C 22.2 ± 3.1 d, P < 0.05) and the number of days with estrous behavior (P < 0.05) differed among groups. On day 10 after treatment, a GnRH stimulation test revealed interactions between group and time (P < 0.001) in plasma LH concentration that were no longer detectable on day 45 after treatment. In conclusion, long-acting deslorelin implants result in a transient downregulation of pituitary GnRH receptors that is associated with inhibition of ovulation and estrous behavior in Shetland mares.

Evaluation of alternative strategies to treat anoestrous dairy cows and implications for reproductive performance in pasture-based seasonal calving herds: A pilot study

The objective of the present study was to assess the effects on ovulation and reproductive performance of a single injection of either GnRH or hCG applied 9 days before the start of the seasonal breeding period in anovulatory anoestrus cows compared with a 7-day progesterone-Ovsynch protocol. The study was conducted on four grass-based seasonal calving dairy herds in Ireland. The total number of cows in the herds was 2112, of which 488 were diagnosed as anoestrus based on absence of behavioural oestrus during a 30 day period. Ovarian structures and the uterus were examined by transrectal ultrasound on all 488 presumptive anestrus cows 9 days before mating start date (MSD). The number of corpora lutea (CL), number of large follicles (≥10 mm) and uterine reproductive tract score were recorded. Only cows that had no CL, ultrasound reproductive tract score ≤2 and were ≥30 days in milk (DIM) were enrolled in the study (n = 214). Cows were blocked by parity, DIM and body condition score and randomly assigned to one of four treatments: i.m. injection of gonadotropin releasing hormone analogue [GnRH; (n = 57)], i.m. injection of human chorionic gonadotropin [hCG; (n = 48)], 7-day Progesterone-Ovsynch protocol [P4OV; (n = 60)] and Control (no hormonal intervention, n = 49). A second ultrasound examination was performed 7 days after treatment to determine ovulatory response. There was a treatment effect on ovulation rate (P < 0.0001), whereby Control cows had a lesser ovulation rate compared with GnRH-, hCG- and P4OV-treated cows. Submission rate during the first 21 days of the breeding period [SR21; (P = 0.74)], pregnant to first service [P/AI1; (P = 0.24)], pregnant within 42 days after the onset of breeding [P42; (P = 0.73)], and pregnant within 84 days after the onset of breeding were not affected by treatment. A tendency was observed (P = 0.07) for greater likelihood of pregnancy within 21 days after the onset of breeding (P21) for P4OV and Control cows compared with GnRH- and hCG-treated cows. GnRH- and hCG-treated cows tended (P = 0.10) to have greater P/AI1 when first service events occurred after day 21 of the breeding period compared with Control cows. P4OV cows had shorter MSD to first service interval (P = 0.0001) and shorter MSD to conception interval (P = 0.02) compared with Control, GnRH- and hCG-treated cows. In conclusion, treatment of anestrous cows with GnRH or hCG resulted in an increase in ovulation rate compared with untreated Control cows, but did not improve reproductive performance during the first 21 days of the breeding season. The best reproductive performance results were obtained with the P4OV treatment, but this treatment has the greatest cost, and has the greatest number of interventions. The observation of good P/AI1 in hCG- and GnRH- treated cows when the first insemination occurred later than day 21 after MSD warrants further investigation, and suggests that these interventions should be applied earlier than 9 days before the farm MSD.

A role for selective contraception of individuals in conservation

Contraception has an established role in managing overabundant populations and preventing undesirable breeding in zoos. We propose that it can also be used strategically and selectively in conservation to increase the genetic and behavioral quality of the animals. In captive breeding programs, it is becoming increasingly important to maximize the retention of genetic diversity by managing the reproductive contribution of each individual and preventing genetically suboptimal breeding through the use of selective contraception. Reproductive suppression of selected individuals in conservation programs has further benefits of allowing animals to be housed as a group in extensive enclosures without interfering with breeding recommendations, which reduces adaptation to captivity and facilitates the expression of wild behaviors and social structures. Before selective contraception can be incorporated into a breeding program, the most suitable method of fertility control must be selected, and this can be influenced by factors such as species life history, age, ease of treatment, potential for reversibility, and desired management outcome for the individual or population. Contraception should then be implemented in the population following a step-by-step process. In this way, it can provide crucial, flexible control over breeding to promote the physical and genetic health and sustainability of a conservation dependent species held in captivity. For Tasmanian devils (Sarcophilus harrisii), black-flanked rock wallabies (Petrogale lateralis), and burrowing bettongs (Bettongia lesueur), contraception can benefit their conservation by maximizing genetic diversity and behavioral integrity in the captive breeding program, or, in the case of the wallabies and bettongs, by reducing populations to a sustainable size when they become locally overabundant. In these examples, contraceptive duration relative to reproductive life, reversibility, and predictability of the contraceptive agent being used are important to ensure the potential for individuals to reproduce following cessation of contraception, as exemplified by the wallabies when their population crashed and needed females to resume breeding.

Gonadotrophin-Releasing Hormone Agonists and Other Contraceptive Medications in Exotic Companion Animals

The use of a gonadotrophin-releasing hormone agonist slow-release implant (GnRH A-SRI) has become increasingly popular as an alternative for surgical contraception in many species. Although these implants have proven to be very effective in some species (eg, ferrets, rats, chicken, psittacines, and iguanas), they have been found less effective in other species (eg, male guinea pigs and rabbits, veiled chameleons, slider turtles, and leopard geckos). This review provides an overview of the available literature on the effects of GnRH A-SRIs in companion exotic animals.

Administration of gonadotropin-releasing hormone agonist on Day 5 increases luteal blood flow and improves pregnancy prediction accuracy on Day 14 in recipient Holstein cows

This study assessed the effects of gonadotropin-releasing hormone (GnRH) treatment on Day 5 (Day 0 = estrus) on luteal blood flow and accuracy of pregnancy prediction in recipient cows. On Day 5, 120 lactating Holstein cows were randomly assigned to a control group (n = 63) or GnRH group treated with 100 μg of GnRH agonist (n = 57). On Days 3, 5, 7, and 14, each cow underwent ultrasound examination to measure the blood flow area (BFA) and time-averaged maximum velocity (TAMV) at the spiral arteries at the base of the corpus luteum using color Doppler ultrasonography. Cows with a corpus luteum diameter ≥ 20 mm (n = 120) received embryo transfers on Day 7. The BFA values in the GnRH group were significantly higher than those in the control group on Days 7 and 14. TAMV did not differ between these groups. According to receiver operating characteristic analyses to predict pregnancy, a BFA cutoff of 0.52 cm² yielded the highest sensitivity (83.3%) and specificity (90.5%) on Day 7, and BFA and TAMV values of 0.94 cm² and 44.93 cm/s, respectively, yielded the highest sensitivity (97.1%) and specificity (100%) on Day 14 in the GnRH group. The areas under the curve for the paired BFA and TAMV in the GnRH group were 0.058 higher than those in the control group (0.996 and 0.938, respectively; P < 0.05). In conclusion, GnRH treatment on Day 5 increased the luteal BFA in recipient cows on Days 7 and 14, and improved the accuracy of pregnancy prediction on Day 14.

Ovarian follicular growth suppression by long-term treatment with a GnRH agonist and impact on small follicle number, oocyte yield, and in vitro embryo production in Zebu beef cows

The aim of the present study was to evaluate small follicle number, oocyte yield, and in vitro embryo production (IVEP) in Zebu beef cows treated long term with a GnRH agonist to suppress ovarian follicular growth. Nelore (Bos indicus) cows (n = 20) showing regular estrous cycles were randomly assigned to one of two groups: control (n = 10, placebo ear implant without a GnRH agonist); GnRH agonist (n = 10, GnRH agonist ear implant containing 9.4-mg deslorelin). All cows underwent an ovum pick-up (OPU) session 14 days (Day 14) before the start of treatments (Day 0) followed by seven OPU-IVEP procedures at 30-day intervals (Days 0, 30, 60, 90, 120, 150, and 180). Semen from a single batch of a previously tested bull was used for all the IVEP. Cows treated with agonist reported a decrease over time in the proportion of animals with a (CL; P ≤ 0.05) and large follicles (>10 mm, P ≤ 0.05). These cows had a lesser number of medium + large follicles (>5 mm; 1.74 ± 0.5 vs. 4.13 ± 0.5; P ≤ 0.05), greater number of small follicles (2-5 mm; 44.3 ± 2.8 vs. 30.8 ± 1.8; P ≤ 0.05), greater yield of cumulus-oocyte complexes (COCs; 21.0 ± 2.3 vs. 15.6 ± 1.9; P ≤ 0.05), greater proportion of COCs cultured (79.2 vs. 73.9%; P ≤ 0.05), COCs cleaved (10.6 ± 1.5 vs. 6.8 ± 1.1, P ≤ 0.05), and cleaved rate (52.8 vs. 44.3%; P ≤ 0.05) compared with control cows. The number (3.4 ± 0.7 vs. 3.0 ± 0.6; P > 0.05) and proportion (16.5 vs. 19.1%; P > 0.05) of blastocysts produced were similar between agonist and control cows, respectively. The study has shown that Zebu beef cows treated long term with a GnRH agonist had follicular growth restricted to small follicles. This did not compromise the ability of oocytes to undergo IVF and embryonic development.

Recent advancements in the hormonal stimulation of ovulation in swine

Induction of ovulation for controlled breeding is available for use around the world, and conditions for practical application appear promising. Many of the hormones available, such as human chorionic gonadotropin (hCG), gonadotropin-releasing hormone (GnRH) and its analogs, as well as porcine luteinizing hormone (pLH), have been shown to be effective for advancing or synchronizing ovulation in gilts and weaned sows. Each of the hormones has unique attributes with respect to the physiology of its actions, how it is administered, its efficacy, and approval for use. The timing for induction of ovulation during the follicle phase is critical as follicle maturity changes over time, and the success of the response is determined by the stage of follicle development. Female fertility is also a primary factor affecting the success of ovulation induction and fixed time insemination protocols. Approximately 80%-90% of female pigs will develop mature follicles following weaning in sows and synchronization of estrus in gilts. However, those gilts and sows with follicles that are less developed and mature, or those that develop with abnormalities, will not respond to an ovulatory surge of LH. To address this problem, some protocols induce follicle development in all females, which can improve the overall reliability of the ovulation response. Control of ovulation is practical for use with fixed time artificial insemination and should prove highly advantageous for low-dose and single-service artificial insemination and for use with frozen-thawed and sex-sorted sperm.

Reproductive hormone monitoring of dugongs in captivity: detecting the onset of sexual maturity in a cryptic marine mammal

Determining the reproductive status of long-term captive animals is essential because the onset of sexual maturity and reproductive activity may necessitate changes in husbandry requirements. This study reports on the first multi-year reproductive hormone monitoring program for captive dugongs of both sexes using feces. Fecal samples were collected from one male (Pig) over 9 years (4-13.2y of age; n=288 samples, 0.8±0.1 samples per week from July 2007 to February 2012) and one female (Wuru) over 7 years (from neonate to 6.9 y; n=171 samples, 0.5±0.1 samples per week from July 2007 to February 2012), and from one solitary female dugong (Gracie) over 10 months (10.5-11.3y of age; n=54 samples, 1.1±0.2 sample per week from September 2008 to June 2009). Using enzyme-immunoassay, fecal progesterone (fP) and estradiol-17β (fE) concentrations were assayed in the two captive females, and testosterone (fT) concentration in the captive male, and compared these to concentrations in wild dugongs. Female Wuru exhibited increasing fP concentrations at 5+ y, indicating early onset of ovarian cycling typical of non-pregnant adult females. Female Gracie maintained basal fP concentrations consistent with wild immature dugongs, indicating that she had not reached puberty by 11y. Nutritional plane may account for differences in age at sexual maturity in these female dugongs. At age 3-4y, Wuru had fE concentrations 1.4 times greater than maximum concentrations recorded in all wild females, and these concentrations were coincident with a period of rapid weight gain. For the male Pig, increasing fT concentrations at 9y provided early indications of puberty. Pig's tusks erupted by 11y, and sexual maturity (indicated by spermatic semen) was confirmed by 12.8y. Identification of sexual maturation prompted two trials of a male contraceptive treatment using the GnRH agonist, deslorelin (9.4mg administered in 2010 and 15.6mg in 2011). Testosterone production was not significantly suppressed by these dosages, and treatment did not terminate sperm production at week 10-11 post-implantation, even at the larger dose tested. Routine analysis of fecal hormones was helpful for making reproductive management decisions regarding individual captives and in guiding the long-term captive management of this cryptic species.

Brushtail possums (Trichosurus vulpecula) in metropolitan Sydney: population biology and response to Suprelorin contraceptive implants

The cohabitation of the common brushtail possum (Trichosurus vulpecula) with people in urban areas often causes conflict. Basic biological parameters are needed to evaluate potential new management options such as fertility control. This study investigated the biology of an urban brushtail possum population and the effects of Suprelorin contraceptive implants on individual females within that population. Trapping success remained constant over time, with 2.8 ± 0.2 individuals trapped per residential property. Recapture rates for males declined rapidly over time, with only 30% of males recaptured on the same property 12 months after initial capture (n = 30) and no males recaptured after 18 months (compared with female recapture rates of 58% after 18 months, n = 33). These data, combined with the preponderance of males observed within the lower age classes, suggests that male possum turnover is high within urban areas. This may be partially compensated for by the male-bias (1.8 : 1) observed in pouch young. Breeding was seasonal with the main peak of births in autumn, and a secondary smaller peak in spring. Suprelorin contraceptive treatment effectively inhibited reproduction in adult females for a minimum duration of 519 ± 7 (n = 5) and ≥700 ± 20 (n = 5) days after administration of one or two 4.7-mg implants, respectively, with no negative side-effects obvious. The concurrent collection of data on contraceptive efficacy and population-specific life-history parameters provides a unique opportunity to highlight the importance of understanding local population dynamics when evaluating the likely efficacy and implementation of fertility control programs to manage problem wildlife.

The effect of buserelin injection 12 days after insemination on selected reproductive characteristics in cows

The aim of this study was to evaluate the effect of buserelin injection on day 12 postinsemination on fertility in lactating dairy cattle. A total of 57 cows were assigned to two groups and four subgroups. In the treatment group, the cows were synchronized with PGF2α-PGF2α (group A) or GnRH-PGF2α (group B) protocol, and buserelin was injected on day 12 postinsemination. Cows in the control group were synchronized with PGF2α-PGF2α (group C) or GnRH-PGF2α (group D) protocol, saline solution was injected on day 12, and served as controls. Pregnancy rates on day 21 and 45 and embryonic death rates were 85.7%, 71.4% and 16.7%, 85.7%, 85.7% and 0.0%, 73.3%, 62.1% and 27.3% and 85.7%, 71.4% and 16.7% in groups A, B, C and D, respectively. There was no significant difference between synchronization protocols for pregnancy rates, and among groups A, B, C and D for pregnancy rates and embryonic death rates. Mean progesterone concentrations in pregnant cows in groups A and B were higher than that in groups C and D, respectively, on day 18 and 21 (p < 0.05). In conclusion, GnRH injection on day 12 postinsemination increased the plasma progesterone concentrations on day 18 and 21 postinsemination. However, it did not alter the pregnancy rates and prevent embryonic deaths.

The effect of GnRH analogues for pituitary suppression on ovarian response in repeated ovarian stimulation cycles

INTRODUCTION

Ovarian stimulation is employed in assisted reproduction techniques in order to obtain as many oocytes as possible. The early rise in oestradiol levels may lead to the premature end of the respective cycle. In order to avoid such an effect, pituitary suppression has been employed. The aim of this study was to evaluate whether maintenance or replacement of the type of GnRH analogue (i.e., agonist or antagonist) employed for pituitary suppression in the consecutive intracytoplasmic sperm injection (ICSI) cycle would negatively influence oocyte quality and ICSI outcome.

MATERIAL AND METHODS

A retrospective observational study was conducted including 181 women with primary infertility. Patients were divided into four different groups according to the GnRH analogue used for pituitary suppression in the first and consecutive cycle.

RESULTS

When a GnRH agonist was employed for pituitary suppression in the first cycle, the consecutive cycle showed comparable outcomes when performed with either a GnRH agonist or a GnRH antagonist. When the first cycle was performed with a GnRH antagonist, the use of the GnRH agonist in the successive cycle led to an increased number of oocytes retrieved (7.5% vs. 10.3%, p = 0.032) and the production of a higher number of embryos (4.5% vs. 6.3%, p = 0.036).

CONCLUSIONS

When the first cycle is carried out with a GnRH antagonist, the use of a GnRH agonist in the successive cycle would lead to increased numbers of oocytes collected and embryos produced.

Deslorelin implants control fertility in urban brushtail possums (Trichosurus vulpecula) without negatively influencing their body-condition index

Wild brushtail possums (Trichosurus vulpecula) occur in large numbers in the grounds of Perth Zoo, Western Australia. These possums are a problem because they consume feed the zoo buys for its captive animals, damage seedlings and trees and many need to be treated for injuries sustained during fights with conspecifics. A contraceptive implant, which contains the gonadotrophin releasing hormone (GnRH) agonist deslorelin, could be a potential method of managing this population. We tested the efficacy of the implant and its impact on the body-condition index of treated possums with Kaplan–Meier analysis and a mixed model with residual maximum likelihood. We implanted 60 female possums with deslorelin and monitored reproductive success of treated and untreated possums for the following 18 months. At the conclusion of the study, 80% of 20 treated females recaptured had shown no evidence of breeding activity, giving an average minimum duration of effective contraception of 381 days. The implant did not have a negative impact on the body-condition index of treated possums during the course of the study. Our results suggest that deslorelin implants could be an effective management tool for brushtail possums at Perth Zoo and in other urban environments.

Morphofunctional alterations in testicular cells of deslorelin-treated boars: an immunohistochemical study

In this study we thoroughly scrutinized testes morphology and investigated whether treatment of recipient boars with gonadotropin-releasing hormone (GnRH)-agonist deslorelin could alter the expression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), luteinizing hormone receptors (LHRs), and androgen receptors (ARs) in testicular cells. An implant containing 4.7 mg of the GnRH-agonist deslorelin was subcutaneously inserted into crossbred male pigs at 91 and 147 days of age. Testicular traits, morphology of the testes, the proteins' expression, and testosterone concentration in blood plasma were analyzed in all boars after slaughter at 175 days of age. Histological analysis revealed significant alterations in both the interstitial tissue and seminiferous tubules of experimental animals after 28 and 84 days of deslorelin treatment. The intensity of the AR immunostaining within the testis appeared as a function of the severity of testicular dysgenesis. Time-dependent action of deslorelin on the expression of LHR and 3beta-HSD in Leydig cells was also detected. Staining for LHR and 3beta-HSD was very weak or the Leydig cells were immunonegative. Concomitantly, a significant decrease in plasma testosterone level was found in both groups of deslorelin-treated boars when compared with the control group. This is the first report showing the cellular distribution of AR, LHR, and 3beta-HSD in testicular cells of deslorelin-treated boars. It is concluded that morphological and immunohistochemical studies are important for the evaluation of testicular histoarchitecture and steroidogenic function. Subsequently, the endocrine control of reproduction in the GnRH-agonist deslorelin-treated males will be better understood.

Influence of a new slow-release GnRH analogue implant on reproduction in the Budgerigar (Melopsittacus undulatus, Shaw 1805)

The neuroendocrine conditioning of reproduction in birds could perform a very important role in captive breeding, especially in endangered species. Whereas in domestic and wild mammals pharmacological reproductive conditioning is well developed, in birds an effective method is not available. The aim of this study was to test the influence of a new slow-release GnRH analogue (buserelin acetate) implant on the reproductive activity of the Budgerigar (Melopsittacus undulatus), used as model species for captive-bred endangered birds. The effects were assessed by looking at reproductive parameters (egg-laying rate, egg fertility rate) and measuring excreted sex steroid metabolite concentrations in male and female birds. Modification of reproductive parameters and steroid metabolites excretion patterns were observed among birds administered with a GnRH analogue implant and maintained under artificial photoperiod (group I; 16L:8D). Implanted birds showed higher rates of egg-laying, potentially a higher proportion of fertile eggs and higher excreted steroid metabolite concentrations than birds maintained under natural photoperiod (group II; 10L:14D) and birds maintained under artificial photoperiod (group III; 16L:8D). Thus, it is concluded that the new slow-release GnRH analogue implant may represent an innovative and practicable treatment to rapidly induce reproductive activity in the Budgerigar, and that excreted sex hormone metabolites detection permits to monitor male and female gonadal activity.

Postpartum suppression of ovarian activity with a Deslorelin implant enhanced uterine involution in lactating dairy cows

Holstein cows received, subcutaneously a non-degradable implant containing 5mg of the GnRH agonist Deslorelin (DESL) or no implant (CON) at 2+/-1 days postpartum (dpp). All cows were injected with PGF(2alpha) at 9 dpp. Previous pregnant (PPH) and non-pregnant uterine horns (PNPH) were determined by palpation per rectum. In Experiment 1, cows [DESL implant (n=10) and CON (n=9)] were examined by ultrasonography to record ovarian structures (23, 30 and 37 dpp) and uterine horn and cervical diameters (16, 23, 30 and 37 dpp). Uterine tone was scored before ultrasonography. Vaginoscopy was conducted just after ultrasonography examination to assess cervical discharge and color of the external cervical os. Blood samples were collected on a weekly basis for hormonal analyses. In Experiment 2, cows [DESL implant (n=77) and CON (n=70)] were palpated per rectum and vaginoscopy at 30 dpp for scoring of uterine tone, uterine horns, cervical diameter, and discharge. Blood samples were collected only at 9 dpp. In Experiment 1, DESL-implant-treated cows had more Class 1 follicles (P<0.01), less Class 2 (P<0.01) and Class 3 follicles (P<0.01) and no corpus luteum (CL) formation (P<0.01). In CON cows, six of nine animals had visible CL at 25+/-7 dpp. At 9 dpp plasma concentration of E(2), P(4) (P<0.01) and PGFM (P<0.05) were less in the DESL-implant treatment group. Diameter of PPH (P<0.01), PNPH (P<0.01) and cervix (P=0.08) were less in the DESL-implant treatment associated with greater uterine tone (P=0.07). The DESL-implant cows had a greater frequency of clear cervical discharge (P=0.09) and pink cervical os (P=0.06). In Experiment 2, plasma concentrations of PGFM were less at 9 dpp in DESL-implant treatment (P<0.01). Diameters of the PPH (P<0.01) and PNPH (P<0.01) were less and more uterine tone (P<0.01) in the DESL-implant treatment. Diameter of cervix and frequency of a cervical discharge score did not differ between treatments. Treatment with non-degradable Deslorelin (5mg) implant during postpartum: (1) suppressed ovarian follicular development, (2) enhanced physical involution of the uterus and cervix, (3) increased tone of the uterine wall, (4) decreased frequency of purulent cervical discharges, and (5) reduced inflammatory processes of the reproductive tract.

Pituitary expression of LHbeta- and FSHbeta-subunit mRNA, cellular distribution of LHbeta-subunit mRNA and LH and FSH synthesis during and after treatment with a gonadotrophin-releasing hormone agonist in heifers

The aim was to examine transcriptional and post-transcriptional regulation of LH and FSH biosynthesis. Female cattle were allocated to three groups: (i) Group 1, control (n = 6), synchronized to be at around Day 11 of the oestrous cycle on Day 31; (ii) Group 2 (n = 6), treated with gonadotrophin-releasing hormone (GnRH) agonist (deslorelin) for 31 days; and (iii) Group 3 (n = 6), treated with deslorelin for 28 days. All animals were slaughtered on Day 31. For animals in Group 2, pituitary content of LHbeta-subunit mRNA was suppressed 60% (P < 0.001) and LH 95% (P < 0.001), whereas FSHbeta-subunit mRNA was suppressed 25% (P > 0.05) and FSH 90% (P < 0.001). Three days after treatment with deslorelin (Group 3) LHbeta-subunit mRNA and LH remained suppressed (50% and 95%, respectively; P < 0.001). At the same time, FSHbeta-subunit mRNA did not differ from controls (P > 0.05) whereas FSH remained reduced by 80% (P < 0.001). The ratio of LHbeta-subunit mRNA present in the nucleus versus cytoplasm of gonadotroph cells was reduced (P < 0.05) in heifers during treatment with deslorelin (0.59 +/- 0.05) compared with the ratio in control heifers (1.31 +/- 0.22) and heifers 3 days after discontinuation of treatment (1.01 +/- 0.05). The findings indicated that treatment with GnRH agonist can suppress LHbeta-subunit mRNA expression without any significant effect on FSHbeta-subunit mRNA. As LH and FSH contents were suppressed to a greater degree than their beta-subunit mRNAs, it would appear that treatment with a GnRH agonist might influence gonadotrophin biosynthesis by a post-transcriptional mechanism(s). For LHbeta-subunit mRNA, this would appear not to be reduced export of message from the nucleus.

Effects of a preovulatory administered depot gonadotrophin-releasing hormone agonist on reproductive hormone levels and pregnancy outcome in gilts

The present study aimed to explore the influence of a preovulatory administered depot gonadotrophin-releasing hormone (GnRH) agonist (GnRHa; Decapeptyl Depot) on the endocrine parameters and pregnancy outcome of gilts (n = 6). A GnRHa-supported preovulatory luteinising hormone (LH) surge was detected in all treated gilts. LH pulses were abolished completely by depot GnRHa on Day 7 and partly on Day 21 of pregnancy. In this treatment group (n = 6) four gilts were pregnant at slaughter on Day 28. In the control group receiving Gonavet, a non-formulated GnRHa (n = 6), all pigs showed LH pulses and were pregnant at slaughter on Day 28 of gestation. Mean progesterone concentrations were elevated in controls during the early luteal phase and were similar for both groups during the implantation period. Mean concentration of unoccupied progesterone receptor was significantly higher in uterine myometrium than in endometrium, but without treatment effects. Peripheral estrone sulfate concentrations showed a similar increase in all pregnant gilts on Days 17 and 18, and remained elevated. In summary, treatment with a depot GnRHa for synchronisation of ovulation alters pulsatile LH secretion during early pregnancy in pigs. In general, this alteration seems not to exert an injurious influence on luteal function and, therefore, on embryo and early fetal development.

Effects of deslorelin implants on reproduction in the common brushtail possum (Trichosurus vulpecula)

The present study investigated the effects of slow-release implants containing the gonadotrophin-releasing hormone (GnRH) agonist deslorelin on reproduction in the common brushtail possum (Trichosurus vulpecula). Captive female brushtail possums were assigned to control (placebo implant), low dose (4.7 mg deslorelin) or high dose (9.4 mg deslorelin) groups; males were assigned to control or high dose (9.4 mg deslorelin) groups. The acute effects of deslorelin treatment at the level of the pituitary gland were similar between the two sexes, where a transient rise in luteinising hormone concentration was induced over the first 24 h. In females, this was associated with the disruption of the normal oestrous cycle and mating within 2–10 days in some treated individuals, but no young were subsequently detected. By 3 weeks after treatment, treated females became anoestrus and remained infertile for at least one breeding season. The effects of treatment were reversible in a subset of females that had their implants removed, although the time taken to produce offspring was variable. Paradoxically, male brushtail possums remained fertile during chronic deslorelin exposure. Despite significant declines in basal follicle-stimulating hormone and testosterone concentrations, as well as an inability to respond to a GnRH challenge, treated males sired as many offspring as control males and there was no evidence of testicular regression. In conclusion, there is potential to control reproduction in female brushtail possums by using chronic GnRH agonist treatment.

Gonadotropin-releasing hormone (GnRH) and its natural analogues: a review

The pivotal role of gonadotropin-releasing hormone (GnRH) during the hormonal regulation of reproductive processes is indisputable. Likewise, many factors are known to affect reproductive function by influencing either GnRH release from hypothalamus or pituitary gland responsiveness to GnRH. In veterinary medicine, GnRH and its agonists (GnRHa) are widely used to overcome reduced fertility by ovarian dysfunction, to induce ovulation, and to improve conception rate. GnRHa are, moreover, integrative part of other pro-fertility treatments, e.g. for synchronization of the estrous cycle or stimulation for embryo transfer. Additionally, continuous GnRH which shows desensitizing effects of the pituitary-ovarian axis has been recommended for implementation in anti-fertility treatments like inhibition of ovulation or reversible blockade of the estrous cycle. Just as much, another group of GnRH analogues, antagonists, are now in principle disposable for use. For a few decades, GnRH was thought to be a unique structure with a primary role in regulation gonadotropins. However, it became apparent that other homologous ligands of the GnRH receptor (GnRHR) exist. In the meantime, more than 20 natural variants of the mammalian GnRH have been identified in different species which may compete for binding and/or have their own receptors. These GnRH forms (GnRHs) have apparently common and divergent functions. More studies on GnRHs should contribute to a better understanding of reproductive processes in mammals and interactions between reproduction and other physiological functions. Increased information on GnRHs might raise expectations in the application of these peptides in veterinary practice. It is the aim of this review to discuss latest results from evolutionarily based studies as well as first experimental tests and to answer the question how realistic might be the efforts to develop effective and animal friendly practical applications for endogenous GnRHs and synthetic analogues.

Endocrine, morphological, and cytological effects of a depot GnRH agonist in bovine

The present study was conducted to assess effects of the gonadotropin-releasing hormone agonist (GnRHa) triptorelin in dairy heifers. The peptide was released from a commercial 4-week depot formulation (Decapeptyl Depot) administered at animals' estrus (day 0). First experiment (EXP I, n=5), which was aimed to explore the availability of peptide, detected a maximum of triptorelin concentration between day 2 and 5 after depot injection, and the peptide remained detectable by RIA in peripheral blood for about 3 weeks. In further experiments, the peptide release was terminated on day 9 (EXP II, n=16) or day 21 (EXP III, n=47). Treatment effects were studied on follicular development, the characteristics of cumulus-oocyte complexes (COCs) (EXP II; EXP IIIa) and secretions of LH and progesterone (EXP IIIb). Results showed that the occurrence of the pre-ovulatory LH surge was more uniform in treated heifers than that in controls. The duration of ovulation periods was similar amongst the heifers of EXP II, but more compact amongst those of EXP III each compared with the respective controls. Post-ovulatory, the number of LH pulses was significantly reduced by treatment, whereas both basal LH and progesterone concentrations were elevated on a few days. Follicular growth was reduced only by the prolonged influence of the GnRHa. There were increased proportions of both degenerated COCs and immature oocytes from small follicles (<3mm in diameter), and meiotic configuration and quality of oocytes isolated from follicles 3-5mm were changed after the prolonged, 21-day treatment. These results indicate that a continuous influence of a GnRHa over more than 1 week may increasingly impair the development of bovine follicles and oocytes. This may have some significance for the development of novel GnRH-based techniques in regulating the reproductive function in cattle.

Fertility control in female eastern grey kangaroos using the GnRH agonist deslorelin. 2. Effects on behaviour

In recent years fertility control has been proposed as an ethically acceptable alternative to lethal control techniques when managing overabundant kangaroo populations. A promising non-steroidal, non-immunological approach to contraception in female kangaroos involves the use of slow-release implants containing the gonadotrophin-releasing hormone (GnRH) agonist deslorelin. The practicality of using deslorelin implants as a management option is dependant on its effective inhibition of reproduction without negative physical or behavioural side-effects. This study investigated the behavioural effects of deslorelin implants in female eastern grey kangaroos. Treatment had no detectable effects on crepuscular activity. Alterations in the frequency of sexual interactions were observed in deslorelin-treated females, with a behavioural oestrus induced ~3 days after combined removal of pouch young and deslorelin administration. Copulation was observed during this early oestrous period, but conception was not achieved and pouch young were not observed in any treated females. Control females gave birth within 69.6 ± 10.4 days (mean ± s.e.m., n = 9) of placebo implant administration. The first births observed in treated animals were on Days 510, 637 and 643 after treatment. The remaining seven treated animals had not bred by the end of the study, a period of 647 days.

Fertility control in female eastern grey kangaroos using the GnRH agonist deslorelin. 1. Effects on reproduction

Eastern grey kangaroos are widespread on the east coast of Australia and frequently reach high densities in reserves and parkland near urban areas. Management of these populations is highly contentious and non-lethal fertility-control technologies are sought as an alternative option to manage population size. This study evaluated the potential of slow-release gonadotrophin-releasing hormone agonist (deslorelin) implants to inhibit reproduction in female kangaroos. Deslorelin treatment effectively inhibited reproduction in adult females for periods of 559 ± 111 days (n = 6) and 651 ± 21 days (n = 5) after administration of one or two 10-mg implants respectively. Animals treated with the lower dosage tended to resume breeding earlier than those that received a total of 20 mg of deslorelin (minimum duration of 18 months). Deslorelin treatment had no effect on blastocyst reactivation in a single treated female and repeat treatment had no negative side-effects. This study has demonstrated that slow-release deslorelin implants can successfully inhibit reproduction for extended periods in the female eastern grey kangaroos. This approach may have potential application in reproductive management of problem kangaroo populations.

Application of pharmaceutical drug delivery for biological control of the common brushtail possum in New Zealand: a review

The common brushtail possum (Trichosurus vulpecula) is the most significant vertebrate pest in New Zealand, being a major ecological threat to the indigenous biodiversity and an economic threat as a vector for bovine tuberculosis. Novel and effective strategies to reduce the population of T. vulpecula are needed urgently. Several biocontrol agents are currently being assessed and from research to date it is likely that the biocontrol agents will be peptide or protein molecules. It is not possible to administer such biocontrol agents alone because they would be degraded rapidly in the animal, especially if delivered orally. Technologies used in the pharmaceutical industry to design efficacious drug-delivery systems for humans and animals can be applied to the design of delivery systems for biocontrol agents used in wildlife management, although there are some unique challenges that must be overcome.

GnRH in non-hypothalamic reproductive tissues

Gonadotropin releasing hormone (GnRH) is a hypothalamic neuronal secretory decapeptide that plays a pivotal role in mammalian reproduction. GnRH and its analogues are used extensively in the treatment of hormone dependent diseases and assisted reproductive technology. Fourteen structural variants and three different forms of GnRH, named as hypothalamic GnRH or GnRH-I, mid brain GnRH or GnRH-II and GnRH-III across various species of protochordates and vertebrates have been recognised. The hormone acts by binding to cell surface transmembrane G protein coupled receptors (GPCRs) and activates Gq/11 subfamily of G proteins. Although hypothalamus and pituitary are the principal source and target sites for GnRH, several reports have recently suggested extra-hypothalamic GnRH and GnRH receptors in various reproductive tissues such as ovaries, placenta, endometrium, oviducts, testes, prostrate, and mammary glands. GnRH-II appears to be predominantly expressed in extra pituitary reproductive tissues where it produces its effect by PLC, PKA2, PLD, and AC cell signalling pathways. In these tissues, GnRH is considered to act by autocrine or paracrine manner and regulate ovarian steroidogenesis by having stimulatory as well as inhibitory effect on the production of steroid hormones and apoptosis in ovarian follicle and corpus luteum. In male gonads, GnRH has been shown to cause a direct stimulatory effect on basal steroidogenesis and an inhibitory effect on gonadotropin-stimulated androgen biosynthesis. Recent studies have shown that GnRH is more abundantly present in ovarian, endometrial and prostrate carcinomas. The presence of type-II GnRH receptors in reproductive tissues (e.g. gonads, prostrate, endometrium, oviduct, placenta, and mammary glands) suggests existence of distinct role(s) for type-II GnRH molecule in these tissues. The existence of different GnRH forms indicates the presence of distinctive cognate receptors types in vertebrates and is a productive area of research and may contribute to the development of new generation of GnRH analogues with highly selective and controlled action on different reproductive tissues and the target-specific GnRH analogues could be developed.

Applications of GnRH in the control and management of fertility in female animals

Gonadotropin releasing hormone (GnRH) has long been recognized as a potential target for the control and management of fertility in female animals. Attempts to apply GnRH-based technology to manage fertility have focussed on the development of GnRH agonists, antagonists and vaccines. All of these methods have potential, but the widespread application of these technologies has been limited to date. The greatest advance in the use of GnRH-based technology for long-term fertility control in recent years has been the development and commercialization of depot formulations that release GnRH agonists for periods of up to 1 year. These products have a broad range of potential applications in production and domestic animal management. The further development and commercialization of GnRH vaccines has been hampered by the variability of response between individual animals. The need to use adjuvant and multiple boosters also make this a less attractive option than the current GnRH agonist technology. However, GnRH vaccines have the advantage that they do not induce the initial stimulatory response that follows GnRH agonist administration. GnRH antagonists and GnRH-toxin conjugates show promise but are in an earlier phase of development. To date, no depot or long-acting formulations of antagonists have been developed. GnRH-toxin conjugates have yet to achieve permanent sterilization, but further dose-response trials may advance this approach.

Using gonadotropin-releasing hormone (GnRH) and GnRH analogs to modulate testis function and enhance the productivity of domestic animals

Gonadotropin releasing hormone (GnRH) controls the activity of the gonadotrope cells of the pituitary gland and, as a consequence, is a critical component of the endocrine cascade that determines the growth, development, and functional activity of testicular tissue. The use of GnRH and GnRH analogs is common in domestic animal production systems. Although GnRH and GnRH analogs are most commonly used to control the fertility and reproductive events in female animals, GnRH agonists and antagonists are increasingly used to modulate the fertility, behavior, and productivity of male animals as well. This review will focus on recent advances in this use of GnRH agonists and antagonists.

Chronic cystic ovarian disease in a Holstein cow

Cystic ovarian follicles are commonly found during rectal examination of early postpartum dairy cows, usually presenting with anoestrus and occasionally nymphomania. Most cases self cure with time, or respond to exogenous hormonal treatment. This case report describes a refractory case in a Holstein cow in which a novel treatment approach was used. A gonadotrophin releasing hormone agonist implant was inserted for 180 d in an attempt to suppress pituitary gonadotrophin output, arrest abnormal ovarian follicle growth and prevent steroidogenesis. Frequent serial blood samples were collected before and after implant insertion to monitor changes in pulse release of luteinising hormone. Follow up ultrasound scans and blood samples were done to monitor ovarian structures; progesterone and oestradiol were collected at various times over the 180 d period. A normal, cycling herdmate was enrolled as a control. Prior to implant insertion, high frequency and low amplitude luteinising hormone pulses were detected in the cystic cow. Insertion was followed by a sustained surge in the release of luteinising hormone in both cows, but ovulation was not induced in the cystic cow. Plasma oestradiol levels remained consistently elevated and signs of oestrous behaviour were observed. Long term gonadotrophin releasing hormone agonist treatment failed to suppress either ovarian steroid production or cause regression of the cysts by 180 d.

Restoration patterns for luteinising hormone and ovarian function following treatment with GnRH agonist implants (deslorelin) for 7, 14 or 21 days in cycling dairy cows

Continuous GnRH agonist treatment of cows results in downregulation of GnRH responsiveness and a state of induced anoestrus. Inducing anoestrus in a precisely controlled manner could have several potential applications in dairy herd management. However, relatively little is known regarding the processes involved in restoring reproductive normality following an induced anoestrus. This study describes an experiment that was conducted to examine patterns of recovery of LH release and follicle growth in non-lactating Holstein cows immediately following cessation of treatment for 7, 14 or 21 days with a deslorelin implant. Oestrus cycles were synchronized at 7 days intervals and a deslorelin implant inserted in every cow 13 days after detected oestrus so that a group had implants for either 21 days (n = 9), 14 days (n = 10) or 7 days (n = 9). On the day of implant removal every ovarian follicle greater than 4 mm in diameter was ablated using ultrasound guided vacuum needle aspiration in an attempt to standardize follicle sizes. Daily ovarian ultrasound examinations were performed on each cow until 35 days after implant removal and again at 45, 59 and 74 days. A subgroup of four cows randomly selected from each treatment group had frequent serial blood samples collected over 8 h at 4 and 10 days after implant removal for LH profiling. There was no significant effect of treatment duration on any LH parameter and results were pooled. Mean LH pulse amplitude increased by 67% between 4 and 10 days after implant removal (0.34 ng/ml versus 0.57 ng/ml; 4 days versus 10 days post-implant, P < 0.001). Mean pulse frequency remained unchanged between the two samplings (5.9 pulses versus 6.9 pulses per 8 h; 4 days versus 10 days post-implant, P > 0.1). Smoothed mean LH concentrations were unaffected by treatment duration or time (0.36 ng/ml versus 0.41 ng/ml; 4 days versus 10 days post-implant, P > 0.1). The pattern of follicle growth and ovulation did not differ significantly between treatment durations and pooled means were used for comparative descriptions. The emergence of a new follicle wave could be detected beginning at 4 days after implant removal (mean 7.9 +/- 0.8 days). After emergence, a period of rapid follicle growth generally ensued with signs of oestrus occurring when the follicle reached 12.3 +/- 0.5 mm and ovulation when mean follicle diameter was 13.1 +/- 0.7 mm at 13.6 +/- 1.5 days after implant removal. Oestrus preceded ovulation in all cases where ovulation subsequently occurred. The mean interovulatory interval after implant removal was similar amongst groups (18.2 +/- 1.3 days). Follicle growth could be categorized into three groups based on the time to emergence and fate of the first wave DF. Spontaneous recovery was characterised by ovulation of the newly emerged DF. Failure to ovulate the first DF was associated with the formation of a persistent follicle by 35 days after implant removal with some 25% (7/28) of cows showing persistent follicles. Delayed emergence (>14 days after implant removal) was detected in 11% (3/28) of cows, but when a follicle did eventually emerge it was seen to ovulate normally. The correlation between number of days to first oestrus expression and LH pulse amplitude on 4 days post-implant removal was significant (R2 = 44%, P < 0.05). A model was then proposed for the restoration of reproductive function following GnRH agonist removal. In conclusion, duration of deslorelin treatment was associated with only small changes in LH and follicle parameters. The formation of persistent follicles delayed the recovery of more cows than delayed emergence of a new follicle wave after implant removal.

Effect of a deslorelin implant in a timed artificial insemination protocol on follicle development, luteal function and reproductive performance of lactating dairy cows

This study examined the influence of a GnRH agonist containing either 450 or 750 microg of deslorelin in an implant form or a gonadorelin injection (control) to induce ovulation in the Ovsynch protocol on pregnancy rates (PR), embryonic loss, and ovarian function in 593 lactating Holstein cows. Cows were given two injections of PGF2alpha 14 days apart, followed 14 days later by the Ovsynch protocol, and were timed artificially inseminated (TAI) at 68 +/- 3 days postpartum. Blood samples for determination of plasma progesterone concentrations were collected at 24 and 10 days prior to and 11 days after TAI. Pregnancy was diagnosed on Day 27 and reconfirmed on Day 41 after TAI. Non-pregnant, not re-inseminated cows at Day 27 had their ovaries examined by ultrasonography, and the number and size of follicles and presence of luteal tissue were determined. Simultaneously, these cows were re-synchronized with the Ovsynch protocol. Pregnancy during the re-synchronization period was determined between 35 and 41 days after insemination. On Day 27, PR were higher for control (39.0%) and deslorelin 450 microg (DESLORELIN 450) implant (41.3%) than for those receiving the deslorelin 750 microg (DESLORELIN 750) implant (27.5%; P<0.05). Pregnancy losses tended to decrease for DESLORELIN 450 compared with control (5.0% versus 12.7%; P<0.13). Plasma progesterone concentrations did not differ significantly among treatments. Deslorelin suppressed ovarian activity and decreased PR during the re-synchronization period compared with control. The percentage of non-pregnant animals that were re-inseminated by Day 27 was less for deslorelin compared with control. In conclusion, incorporation of an implant of the GnRH agonist deslorelin to induce ovulation in the Ovsynch protocol has the potential to reduce pregnancy losses, but the response was dependent upon implant concentration. Evaluation of lower doses to minimize the negative effects on subsequent fertility is warranted.

Use of GnRH agonist implants for long-term suppression of fertility in extensively managed heifers and cows

The ability of gonadotrophin releasing hormone (GnRH) agonist implants to suppress ovarian activity and prevent pregnancies, long-term, was examined in heifers and cows maintained under extensive management. At three cattle stations, heifers (2-year-old) and older cows (3- to 16-year-old) were assigned to a control group that received no treatment, or were treated with high-dose (12 mg, Station A) or low-dose (8 mg, Station B and Station C) GnRH agonist implants. The respective numbers of control and GnRH agonist-treated animals (heifers + cows) at each station were: Station A, 20 and 99; Station B, 19 and 89; Station C, 20 and 76. Animals were maintained with 4% bulls and monitored for pregnancy at 2-monthly intervals for approximately 12 months. Pregnancy rates for control heifers and control cows ranged from 60-90% and 80-100%, respectively, depending on the study site. The respective number of animals (heifers + cows) treated with GnRH agonist that conceived, and days to first conception, were: Station A, 9 (9%) and 336 +/- 3 days; Station B, 8 (10%) and 244 +/- 13 days; Station C, 20 (26%) and 231 +/- 3 days. Treatment with high-dose GnRH agonist prevented pregnancies for longer (approximately 300 days) than treatment with low-dose GnRH agonist (approximately 200 days). In the majority of heifers and cows treated with GnRH agonist, ovarian follicular growth was restricted to early antral follicles (2-4mm). The findings indicate that GnRH agonist implants have considerable potential as a practical technology to suppress ovarian activity and control reproduction in female cattle maintained in extensive rangelands environments. The technology also has broader applications in diverse cattle production systems.