Equine chorionic gonadotrophin administration to rams improves their effectiveness to stimulate anoestrous ewes (the “ram effect”)

Systematic review of hormonal strategies to improve fertility in rams

Reviewing the current state of knowledge on reproductive performance and productive traits in rams has many advantages. First, the compilation of this information will serve as a literature resource for scientists conducting research around the world and will contribute to the understanding of the data collected and interpreted by researchers on the different hormonal strategies used to improve reproductive performance in rams. Second, it will allow scientists to identify current knowledge gaps and set future research priorities in ram reproduction. Rams play an important role in the global flock economy, but their reproductive analysis has been limited in the use of hormonal technologies to increase the productivity of sheep flocks. In this review, we cite the most important works on six hormones that, in one way or another, modify the hypothalamus-pituitary-gonadal axis, at different doses, in and out of the reproductive season, breeds, application methods, among other factors. The overall aim is to increase the reproductive efficiency of rams in different scenarios and, in some cases, of other species due to the lack of limited information on rams.

A customized long acting formulation of the kisspeptin analog C6 triggers ovulation in anestrus ewe

The modulation of the kisspeptin system holds promise as a treatment for human reproductive disorders and for managing livestock breeding. The design of analogs has overcome some unfavorable properties of the endogenous ligands. However, for applications requiring a prolongation of drug activity, such as ovulation induction in the ewe during the non-breeding season, additional improvement is required. To this aim, we designed and tested three formulations containing the kisspeptin analog C6. Two were based on polymeric nanoparticles (NP1 and NP2) and the third was based on hydrogels composed of a mixture of cyclodextrin polymers and dextran grafted with alkyl side chains (MD/pCD). Only the MD/pCD formulation prolonged C6 activity, as shown by monitoring luteinizing hormone (LH) plasma concentration (elevation duration 23.4 ± 6.1, 13.7 ± 4.7 and 12.0 ± 2.4 h for MD/pCD, NP1 and NP2, respectively). When compared with the free C6 (15 nmol/ewe), the formulated (MD/pCD) doses of 10, 15 and 30 nmol/ewe, but not the 90 nmol/ewe dose, provided a more gradual release of C6 as shown by an attenuated LH release during the first 6 h post-treatment. When tested during the non-breeding season without progestogen priming, only, the formulated 30 nmol/ewe dose triggered ovulation (50% of ewes). Hence, we showed that a formulation with an adapted action time would improve the efficacy of C6 with respect to inducing ovulation during the non-breeding season. This result suggests that formulations containing a kisspeptin analog might find applications in the management of livestock reproduction but also point to the possibility of their use for the treatment of some human reproductive pathologies.

Semen quality, testosterone values, and testicular and accessory gland parameters in rams receiving sustained stimulation with low doses of buserelin

ContextThe use of buserelin, a gonadotropin-releasing hormone (GnRH) agonist, can improve semen quality. Nevertheless, the appropriate dosage, and frequency and time of application, remain to be established owing to the subsequent negative feedback on endogenous production of testosterone described so far.AimsThis study aimed to propose a new buserelin application protocol for sperm improvement in Santa Inês rams.MethodsFifteen Santa Inês rams were divided into two experimental groups: the first group (n=8) received 2.5μg buserelin acetate; and the second group (n=7) received saline solution. Treatments were applied for 21 days at intervals of 6h, totalling four hormonal or saline applications per day. In all animals, macroscopic and microscopic seminal characteristics and freezability, plasma testosterone, pixels of testicular parenchyma, and biometric analysis of testicular and accessory sex glands by ultrasound were evaluated throughout the period of hormonal application and for a further 7 days.Key resultsRams receiving buserelin showed a peak of testosterone after the first week (Day 7) of application, with a drop in values at Day 14, followed by negative feedback at Day 21 and return to basal concentrations at Day 28. They also showed improvement of kinetics parameters such as straight line velocity (μm/s: +buserelin 51.5±1.5 > control 46.6±1.6) and linearity coefficient (%: +buserelin 53.5±1.8 > control 47.5±1.9). Ultrasound parameters, pixels of testicular parenchyma, and freezability were not affected by treatment.ConclusionsThe administration of buserelin was able to improve some sperm kinetics parameters of Santa Inês rams.ImplicationsLow doses of this GnRH analogue can be used; however, further adjustments to the hormonal protocol are needed to obtain an effective improvement in sperm quality.

Daily variation of the cortisol and insulin concentration, glycemia, surface temperature, and behavior patterns due the administration of equine Chorionic Gonadotropin in rams

Sex steroids can modulate the circadian rhythmicity of some physiological and behavioral functions of sheep. During the non-breeding season, Corriedale rams have a low testosterone concentration, but the administration of equine Chorionic Gonadotropin (eCG) stimulates its secretion. Therefore, the daily variation of cortisol and insulin concentrations, glycemia, behavioral pattern (eating, ruminating, standing, lying, and sleeping), and rostral and eye surface temperatures were compared in rams treated or not treated with eCG during the non-breeding season [between August (late winter) and September (early spring)]. Twenty Corriedale adult rams (BW 63.4 ± 7.3 kg; BCS: 3.5 ± 0.5; mean ± SD; age: 2-3 years old) were randomly assigned to 1 of 2 treatments: a) Treated: administration of 1000 IU of eCG intramuscularly and b) Control: control, without application of eCG. All the rams were managed under the same feeding and environmental conditions (individual pens outdoors). All variables were measured each hour for 26 h, except testosterone and insulin that were measured at 09:00, 10:00, 12:00, 15:00, 18:00, 21:00, 22:00, 24:00, 03:00, 06:00, 09:00 and 11:00 h. Testosterone and cortisol concentration were greater in Treated than Control rams (testosterone: 32.7 ± 0.7 nmol/L vs 5.8 ± 0.7 nmol/L; P <0.0001; cortisol: 11.3 ± 0.6 nmol/L vs 9.9 ± 0.6 nmol/L; P =0.02). The eye surface temperature was 0.9°C lower in the Treated than in the Control rams (P =0.004). The characteristics of the daily variation pattern of cortisol, glycemia, glycemia:insulin ratio, and surface temperature were not affected by the treatment, the acrophases being at ∼06:00 h, ∼18:00 h, ∼08:00 h, and ∼11:00 h, respectively. The acrophase of insulin concentration was observed earlier in Treated than in Control rams (13:02 ± 0:56 vs 15:47 ± 0:53; P =0.04). Additionally, the acrophase of the time spent eating was advanced in Treated rams (09:48 ± 00:16 vs 10:20 ± 00:16; P =0.04) and sleeping (21:39 ± 00:57 vs 02:02 ± 01:06; P <0.0001). Treated rams slept less time than Control rams (P =0.04). In conclusion, the administration of eCG modulated the daily variation pattern of insulin concentration and the behavioral pattern (period in which rams were observed eating and sleeping). Nevertheless, although there was a greater cortisol concentration and reduced eye surface temperature, the administration of eCG did not modify their daily variation pattern, suggesting that this is robust, limiting the effect of testosterone on their basal pattern.

Approaches of estrous synchronization in sheep: developments during the last two decades: a review

The objective of the current review was to summarize the protocols used for estrous synchronization in ewes during the last two decades. Progesterone (P4) is a major hormone used in most protocols. P4 in the form of a controlled internal drug releasing (CIDR) device, medroxyprogesterone acetate (MAP), and fluorogestone acetates (FGA) has been used for estrous synchronization. Also, gonadotropins such as equine chorionic gonadotropin (eCG) and gonadotropin-releasing hormone (GnRH) are often administered at the end of P4-based protocols to improve fertility. Moreover, the administration of prostaglandins (PG) and ram effects have been used for estrus induction and synchronization of ewes. The findings of previous studies indicate that the outcome of administering various synthetics P4 analogues (CIDR, MAP, and FGA) in ewes is comparable in terms of estrous synchronization/induction. The supplementation of P4-based protocols with eCG, however, improves the estrus response and pregnancy rate during breeding and non-breeding season. On the other hand, PG is effective for successful estrous synchronization during the breeding season only. Often, two injections of PG are administered either 11 or 14 days apart along with P4-based protocols to lyse ovine corpus luteum (CL) when it is receptive to PG i.e., 3 days post-ovulation. Alternatively, the "ram effect" has been shown to improve the efficacy of P4-based protocols and can be used as an alternative to eCG in ewes. The current review describes the methods of synchronization and their outcomes during breeding and a non-breeding season in ewes.

Administration of a single dose of a PGF2α analogue (dinoprost) before sexual tests did not improve ram's sexual behaviour

The aim of this study was to determine if a single administration of dinoprost tromethamine before each test enhances sexual behaviour in inexperienced rams, and if the possible effect is maintained after the rams gain sexual experience. The study was conducted in northeaster Mexico during autumn (breeding season). The study was performed with 26 Saint Croix rams (16.1 ± 1.1 months old). Rams were allocated to two treatments, which were subjected to 15 tests with 2 restrained non-oestrous ewes. While rams from one group (group DIN) received a single dose of dinoprost (10 mg im, Lutalyse, Zoetis) immediately before the test, the other rams remained untreated (group CON). Sexual behaviours were recorded during 5 min. The data were analysed with a mixed model that included the treatment, number of test and their interaction as main effects, and the individual as a random effect. DIN rams displayed less ano-genital sniffings (6.6 ± 0.8 vs 9.7 ± 0.8, P = 0.007), matings (0.11 ± 0.05 vs 0.29 ± 0.05, P = 0.03), and had a lower mating/total mounts ratio (0.05 ± 0.03 vs 0.16 ± 0.03, P = 0.006) than CON rams. There were no other treatment effects, but there were significant effects of time and interactions between treatment and time in all the behaviours. Overall, administration of a single dose of dinoprost before testing did not have positive effects in the development of rams' sexual behaviour, and even, might have negative effects. However, it should be considered that in this study only one prostaglandin analogue, one dose of this analogue, administered immediately before the tests was used, so more studies involving other analogues, doses, and/or regimes of administration should be done.

Treatment of male goats with equine chorionic gonadotrophin during the non-breeding season does not affect their sperm characteristics during the subsequent breeding season

Equine chorionic gonadotrophin (eCG) is a hormone having FSH/LH effects. It can be used to enhance sperm quality in male goats (bucks) during the non-breeding season. In a previous study carried out during the non-breeding season, we treated ten bucks with eCG (leaving nine untreated animals as control). Over a 20-day period, the treated bucks received an initial dose of 800 IU of eCG, followed by four doses of 500 IU. We found eCG enhanced semen quality, however, as also happens in female goats (does), eCG also induced a high titer of anti-eCG antibodies. In does, this lowers fertility. The aim of the present study was to determine if the eCG treatment carried out on bucks during the non-breeding season had any negative effects on their reproductive status during the following breeding season. We measured serum concentration of testosterone and anti-eCG antibody, as well as key testicular and seminal characteristics. This study commenced 91 days after the final dose of eCG in the previous study. The anti-eCG titer was higher in the treatment bucks than in untreated ones (181.7 ± 61.3 ng/μL vs 31.1 ± 10.7 ng/μL; P < 0.05). However, there were no significant differences between treated and untreated bucks in testosterone concentration, scrotal circumference, testes pixel intensity, fresh and thawed semen characteristics, or sperm cryoresistance. So, although the eCG-treated bucks had greater titers of anti-eCG antibodies, their reproductive pattern was unaffected.

Treatments with eCG and courtship behaviour in rams during the breeding and the non-breeding seasons

Equine chorionic gonadotrophin (eCG or PMSG) is a hormone with FSH/LH effect that has been widely used in ewes and cows to induce follicle development. However, the possible positive effects of its administration to males have been rarely studied. ECG stimulates testosterone secretion and increases rams’ ability to stimulate ovulation in anoestrous ewes (the ‘ram effect’), but it is still not known if this effect is at least partially explained by an enhancement of a ram’s sexual behaviour. Thus, the aim was to determine if the administration of eCG induces an increase in testosterone concentration, and thus improves sexual behaviour of Saint Croix rams during both the breeding and the non-breeding seasons. Two doses of 1000 IU of eCG were administered separated by 4 days to 10 rams during the breeding and five rams during the non-breeding seasons, with the same number of animals as untreated controls. Administration of eCG increased testosterone concentration during the breeding (P = 0.008) and the non-breeding (P = 0.0009) seasons. The number of ano-genital sniffings, lateral approaches, as well as total courtship behaviours were greater in treated than untreated rams during the breeding season. Treated rams also tended to mount and mate more during the breeding season. During the non-breeding season, treated rams tended to display more ano-genital sniffs, lateral approaches and total courtship behaviours than untreated rams 6 days after the first dose. Overall, eCG increased testosterone concentrations the breeding and the non-breeding seasons, and was associated with a greater display of sexual behaviours during the former.