Pituitary responsiveness to GnRH in mares following deslorelin acetate implantation to hasten ovulation

The present experiment characterized the pituitary responsiveness to exogenous GnRH in the first 10 d after ovulation following commercially available deslorelin acetate implantation at the normal dosage for hastening ovulation in mares. Twelve mature, cyclic mares were assessed daily for estrus and three times weekly for ovarian activity starting May 1. Mares achieving a follicle at least 25 mm in diameter or showing signs of estrus were checked daily thereafter for ovarian characteristics. When a follicle >30 mm was detected, mares were administered either a single deslorelin acetate implant or a sham injection and then assessed daily for ovulation. On d 1, 4, 7, and 10 following ovulation, each mare was challenged i.v. with 50 microg GnRH, and blood samples were collected to characterize the LH and FSH responses. The size of the largest follicle on the day of treatment did not differ (P = 0.89) between groups. The number of days from treatment to ovulation was shorter (P < 0.001) by 2.0 d for the treated mares indicating a hastening of ovulation. The size of the largest follicle present on the days of GnRH challenge was larger in the treated mares on d 1 (P = 0.007) but smaller on d 10 (P = 0.02). In addition, the interovulatory interval was longer (P = 0.036) in the treated mares relative to controls by 4.4 d. Concentrations of FSH in plasma of the treated mares were lower (P < 0.05) than control concentrations from d 3 to 12; LH concentrations in the treated mares were lower (P < 0.05) relative to controls on d 0 to 5, d 7, and again on d 20 to 23. Progesterone values were the same (P = 0.99) for both groups from 2 d before ovulation though d 23. There was an interaction of treatment, day, and time of sampling (P < 0.001) for LH and FSH concentrations after injection of GnRH. Both the LH and FSH responses were suppressed (P < 0.009) in the treated mares relative to controls on d 1, 4, and 7; by d 10, the responses of the two groups were equivalent. In conclusion, deslorelin administration in this manner increased the interovulatory interval, consistently suppressed plasma LH and FSH concentrations, and resulted in a complete lack of responsiveness of LH and FSH to GnRH stimulation at the dose used during the first 7 d after the induced ovulation. Together, these results are consistent with a temporary down-regulation of the pituitary gland in response to deslorelin administered in this manner.     

Onset of luteal activity in non-foaling mares during the early breeding season in Finland.

The luteal activity in mares was studied in the Equine Research Station (ERS) and in trotting stables (TS) in South-Finland. The mares were Standardbreeds in the TS and mainly Finnhorses in the ERS. Between January and June blood was collected once a week for serum progesterone determinations. The mares in the ERS were distributed in 1 of 3 groups: three-years old not yet in training (N = 38), brood mares (N = 21) and mares in training (N = 47). A 4th group was the mares in training in the trotting stables (N = 73). Every 5th mare in the ERS and every 4th mare in the trotting stables were cycling already at the beginning of the year. Onset of luteal activity in anoestrous mares was most common in the middle of May. Over 95% of the mares were cycling at the beginning of June. In the ERS 40% of the Finnhorse mares in training were cycling through the winter. The three-years old and the brood mares were all anoestrous during winter. They started to cycle on average before the middle of May. Anoestrous training mares started before the middle of April. Anoestrous Finnhorse mares began to cycle later than warm blooded mares in all of the groups studied. Mares which had foaled the previous year were more often anoestrous during the winter than dry mares. The time of year when cycling began in a particular mare tended to be the same from year to year (p less than 0.01).     

Pituitary responsiveness to GnRH, hypothalamic content of GnRH and pituitary LH and FSH concentrations immediately preceding puberty in gilts

To determine whether pituitary concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) or hypothalamic content of gonadotropin releasing hormone (GnRH) change before puberty, 40 prepubertal gilts averaging 7 mo of age were slaughtered before or on the second, third or fourth day after relocation and boar exposure. Some gilts responded to relocation and boar exposure as indicated by swollen vulvae, turgid uteri and enlarged ovarian follicles at the time of slaughter. Pituitary concentrations of LH and FSH and hypothalamic content of GnRH were similar between gilts that responded to relocation and boar exposure and gilts that did not respond. In addition, boar exposure and relocation had no effect on pituitary concentrations of LH and FSH or on hypothalamic content of GnRH. To determine whether pituitary responsiveness to GnRH changes before puberty, a third experiment was conducted in which 72 gilts were injected with 400 micrograms of GnRH either before or on the second, third or fourth day after relocation and boar exposure. In gilts that subsequently responded (i.e., ovulated) as a result of relocation and boar exposure, pituitary responsiveness to GnRH was reduced as compared with gilts that failed to ovulate after relocation and boar exposure. Peak concentrations of serum LH after GnRH injection were 4.6 +/- 1.3 vs 9.8 +/- .8 ng/ml for responders vs nonresponders. Peak serum FSH after GnRH injection was also lower for responders than for nonresponders (29.5 +/- 4.2 vs 41.2 +/- 2.4 ng/ml). When compared with controls, relocation and boar exposure did not significantly affect GnRH-induced release of LH and FSH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effectiveness of a novel prostaglandin analog in postpartum mares and mares with early season anestrus

Contents Fifty thoroughbred mares, located at Central-Southern Brazil near Sao Paulo (13 anestrous maiden, 18 anestrous barren mares and 19 postpartum mares) were treated with one to three injections, 48 hrs apart, of 2 mg of the novel PGF analog K 11941*, during the early part of the breeding season. Early season anestrus in these problem mares was compounded by the adverse effects of a drought. Plasma progesterone determinations revealed unexpectedly elevated plasma progesterone levels in 61.5% of the maiden mares, in 77.8% of the barren mares and in 68.4% of the postpartum mares (20 to 25 days postpartum). Treatments with K 11941 initiated luteolysis, heat and ovulations in 91.4, 45.5 an 63.3% of these mares, respectively, but initiated also heat and ovulation in 13% and 33% of mares with baseline progesterone levels. Treatments initiated covert and overt cyclic functions in 17 and 12 of those animals which did not conceive immediately. Fifteen animals with recurrent anestrus received further treatment with K 11941. Ten mares cycling silently were force bred when palpations indicated ovulatory follicles, and 7 conceived. Of the 50 mares treated, 38 became pregnant (76%: maiden mares: 76.9%; barren mares: 77.8% and postpartum mares: 73.7%) with breeding indices of 1.9, 1.36 und 1.57, respectively; and 37 mares gave birth to a live foal (74%), At the same stud, 138 control mares had a foaling rate of 82.6%.     

繁殖季节蒙古母马垂体促性腺激素细胞分泌颗粒与血清FSH、LH浓度的相关性

研究证实，动物垂体FSH和LH呈脉冲式分泌，在接受适当刺激后开始释放，又能在接受另一些信息后调整分泌量或停止分泌，并且其血清FSH和LH含量随着年龄和生理状态的变化而变化上，而与垂体促性腺激素细胞数量的相关性极低；但是，在繁殖季节蒙古利亚矮种母马垂体促性腺激素细胞分泌颗粒的形态学特性是否与血清FSH和LH浓度变化存在相关性，目前尚未见有报道。为此，     

Assessment of the breeding prognosis of mares using paired endometrial biopsy techniques

Paired endometrial biopsy samples were taken from 530 subfertile mares, before and after treatment (where indicated) and a period of sexual rest. Prognoses were made after each biopsy (Categories 1A-4A before treatment and Categories 1B-4B after treatment), using histopathological criteria similar to those described by Kenney and Doig (1986). Eighty-seven per cent of the mares were assigned to first biopsy prognosis Category 3A. The second biopsy prognosis produced a more even population distribution (10, 47, 40 and 3 per cent respectively for Category 1B, 2B, 3B and 4B mares). First biopsy Category 3A and 4A mares produced mean foaling rates of 51 and 40 per cent respectively. None of the 14 second biopsy Category 4B mares delivered a live foal (12 were barren, one aborted and one suffered early foetal death). This study supports the hypothesis that a breeding prognosis assigned on the basis of two endometrial biopsy samples, taken before and after specific uterine treatment, where indicated, which takes into consideration the mare's ability to respond to treatment, is likely to be more accurate than one assigned after a single biopsy sample.     

Determinants of attenuated LH-release associated with the first ovulation of the equine breeding season

An attenuated ovulatory rise in circulating concentrations of LH is characteristically associated with the first seasonal reproductive cycle of horse mares. Unlike ovulations (OV) of subsequent estrous cycles, the first OV of the breeding season (OV1) is not preceded by elevated concentrations of progesterone (PROG). Hence, the ability of pretreatment with PROG to abolish attenuation of LH-secretion associated with OV1 was investigated. Ten nonpregnant anestrous mares were randomly divided into 2 groups; control (C) and treated (T). Per individual, when diameter of the largest follicle was consistently greater than or equal to 35 mm, C mares received 3 times daily injections of cottonseed oil (IM), for 15 d or until OV, while T mares received exogenous PROG (IM) for 15 d, in a manner designed to mimic a diestrous pattern of release. Jugular blood samples were collected daily from onset of treatment through 10 d following the third OV (OV3). Repeated measures analyses of area under the ovulatory LH-rise (AUC) and the maximum concentration of LH associated with OV (MAX) revealed a significant main effect of OV (P less than .005) but no main effect of group or OV by group interaction (P greater than or equal to .5). When groups were combined, a significant increase in mean AUC and MAX from OV1 to OV3 was observed (P less than .01). To evaluate the influence of hypothalamic-hypophyseal recrudescence on ovulatory LH-release at OV1, 16 mares were bred to foal, and subsequently initiate reproductive activity, early (E; mid April; n = 8) or late (L; mid July; n = 8) in the year. A significant OV (1, 2 or 3) by group (E or L) interaction was observed for AUC (P less than .06) and MAX (P less than .04). Mean AUC and MAX increased progressively from OV1 to OV3 in E mares (P less than .05). In L mares, neither AUC or MAX changed from OV1 to OV3 (P greater than .4). Based on these data, we suggest that attenuation of the LH-rise at OV1 in the mare, is a consequence of incomplete recrudescence of the hypothalamic-pituitary axis.     

Fertility at the first post partum estrous compared with fertility at the following estrous cycles in foaling mares and with fertility in nonfoaling mares

A retrospective study on the reproductive performance of 401 artificially inseminated trotter mares during six breeding seasons is presented. Mares, 279 post partum (PP) and 122 maiden and barren, or nonlactating (NL), were inseminated with fresh semen obtained from four fertile stallions of the same breed. Pregnancy rate (PR) of mares inseminated at the foal heat (182/253, 71.9%) was lower, but not significantly different, than the PR (22/26, 84.6%) of mares inseminated for the first time at the second post partum cycle and similar to the PR at the first and second cycle of NL mares (95/112, 77.8% and 25/33, 75.7%, respectively). PR of mares inseminated at the foal heat was higher, but nonsignificantly different, from PR of the post partum mares not pregnant after artificial insemination (AI) at foal heat and inseminated again at the following estrous cycle. The PR after AI at the foal heat was significantly higher than the PR when the AI was performed at the third or later cycle in NL mares (71.9% vs 22.2%, P<0.01). The estrus cycle/pregnancy ratio for the PP mares inseminated, for the first time at the foal heat or at the second heat and for NL mares was, respectively, 1.4, 1.2, 1.3 at first cycle and 1.4, 1.3 and 1.4 at the end of the season or when mares left the stud. The proportion of open mares at the end of the season or when leaving the stud was 7.1% (18/253), 3.8% (1/26) and 4.1% (5/122) for PP mares first inseminated at the first or second post partum cycle and for NL mares, respectively; the total rate of open mares was 6% (24/401). The foaling rate (FR) following conception at the foal heat (72.1%) was not statistically different from the FR following conception at any other cycle (50–100%). Based on the absence of significant differences in fertility at the first post partum estrus cycle versus any other estrus cycle, we conclude that breeding at the foal heat should be advisable.     

Use of oocyte transfer in a commercial breeding program for mares with reproductive abnormalities

In some mares with lesions of the reproductive tract, embryo collection and survival rates are low, or collection of embryos is not feasible. For these mares, oocyte transfer has been proposed as a method to induce pregnancies. In this report, a method for oocyte transfer in mares and results of oocyte transfer performed over 2 breeding seasons, using mares with long histories of subfertility and various reproductive lesions, are described. Human chorionic gonadotropin or an implant containing a gonadotropin-releasing hormone analog was used to initiate follicular and oocyte maturation. Oocytes were collected by means of transvaginal ultrasound-guided follicular aspiration. Following follicular aspiration, cumulus oocyte complexes were evaluated for cumulus expansion and signs of atresia; immature oocytes were cultured in vitro to allow maturation. The recipient's ovary and uterine tube (oviduct) were exposed through a flank laparotomy with the horse standing, and the oocyte was slowly deposited within the oviduct. Oocyte transfer was attempted in 38 mares between 9 and 30 years old during 2 successive breeding seasons. All mares had a history of reproductive failure while in breeding and embryo transfer programs. Twenty pregnancies were induced. Fourteen of the pregnant mares delivered live foals. Results suggest that oocyte transfer can be a successful method for inducing pregnancy in subfertile mares in a commercial setting.     

Human chorionic gonadotropin (hCG): the effect of dose on ovulation and pregnancy rate in Thoroughbred mares experiencing their first ovulation of the breeding season

AIM: To determine the effect of hCG dose on ovulation and pregnancy rate in Thoroughbred mares experiencing their first ovulation of the breeding season. METHODS: Over 3 successive breeding seasons, a total of 101 mares were randomly assigned to 1 of 4 treatment groups (intravenous injection of either saline, 1500, 3000, or 6000 IU hCG), as they approached their first ovulation of the breeding season. Mares were bred 1 day post-injection to 1 of 11 stallions, and every other day until ovulation occurred. Data were analysed using multivariable logistic regression with correction for over-dispersion due to clustering. RESULTS: Mares treated with hCG were more likely to ovulate within 72 h of treatment than mares treated with saline (p<0.001); there was no significant difference between doses of hCG on risk of ovulation (p>0.15). Farm also had a significant impact on the risk of ovulation (p=0.027). Mares treated with hCG were more likely to be diagnosed pregnant 14 days post ovulation than saline-treated mares (p=0.081, p=0.029 and p=0.026 for the 1500, 3000 and 6000 IU doses, respectively); there was no significant difference between doses of hCG on risk of pregnancy (p>0.45). CONCLUSIONS: A single injection of hCG (1500-6000 IU) is effective at inducing ovulation in late transitional mares and increases the likelihood of pregnancy at 14 days post ovulation. This paper supports the use of hCG as an integral part of optimal broodmare management.     

The effect of artificial photoperiod at the end of the breeding season on plasma testosterone concentrations in stallions

Testosterone concentrations in stallions showed a seasonal trend with peak concentrations in the spring (April and May in Britain) and lowest concentrations in the period from December to February. The effect on this pattern of changing the length of the photoperiod at the end of the normal breeding season (mid-summer's day) was studied in 2 experiments. In the first experiment artificial illumination was organised from 21 June to mimic the effect of transfer to a southern hemisphere spring and summer, that is short days becoming longer. The stallions had low concentrations of testosterone in February and high concentrations in April. Concentrations in July, August and September were extremely low with a return to high values in late November/early December. In the second experiment, illumination was maintained at the equivalent of a 16 1/2-hour day from 21 June to mid December. These stallions had high testosterone concentrations in April, after which they fell until August, later rising to a maximum in October. These results are discussed in relation to transfer of stallions between the northern and southern hemispheres.     

Synchronization of estrus in dairy goats treated with prostaglandin F at various stages of the estrous cycle.

Dairy goats were given IM injections of 125 micrograms of cloprostenol sodium on day 6 of the estrous cycle (prostaglandin F [PGF] 6, n = 22) or day 12 of the estrous cycle (PGF 12, n = 26). Mean +/- SE hours from injection to onset of behavioral estrus and proportion of goats responding were 46 +/- 4.2 (range, 12 to 88 hours) and 95% and 48 +/- 2.9 (range, 34 to 68 hours) and 100% for groups PGF 6 and PGF 12, respectively. There was no significant difference between the groups in mean time to onset of estrus, but variances about the means were different. Of the does in groups PGF 6 and PGF 12, 67 and 85%, respectively, had signs of onset of estrus between 36 and 60 hours after administration of PGF. Mean (+/- SE) hours from injection to time of peak concentrations of luteinizing hormone (LH) were 62 +/- 3.1 and 64 +/- 2.1 for groups PGF 6 and PGF 12, respectively. Of the does in groups PGF 6 and PGF 12, 86 and 100%, respectively, had LH peaks. Of the does in groups PGF 6 and PGF 12, 68 and 77%, respectively, had peak concentrations of LH between 48 and 72 hours after administration of PGF. All does in groups PGF 6 and PGF 12 had concentrations of progesterone greater than or equal to 1.0 ng/ml on the day of administration of PGF. Concentrations decreased to less than 1.0 ng/ml by 48 hours after injection in all does except 1 in group PGF 6.(ABSTRACT TRUNCATED AT 250 WORDS)     

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

Tropical Animal Health and Production - 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...     

Progesterone profiles of fat-tailed tuj ewes following tactile and visual separation of rams at the beginning of the breeding season

The aim of this study was to determine the level and duration of progesterone secretion during the sequential oestrous cycles in fat-tailed Tuj ewes following tactile and visual separation of rams during the breeding season. For these purposes, rams were separated from the main flock for 50 days starting from the beginning of the breeding season and 21 ewes were randomly selected for the current experiment. In order to assess luteal activity and the length of oestrous cycles, the ewes were blood-sampled thrice or twice weekly for the measurement of progesterone in plasma. The data showed that 3 +/- 0.2 oestrous cycles were observed in this time window, and the first oestrous cycle observed was shorter (P < 0.05) than the following cycles (mean +/- SEM, 14.6 +/- 0.82, 16.5 +/- 0.48 and 17.0 +/- 0.54 days, respectively, for cycles 1, 2 and 3). Progesterone production was significantly lower in the first oestrous cycle compared with the second and third cycles on days 9, 12 and 14 of the cycles. The follicular periods of ewes showed four accumulations (maximum values using a 3-day moving average technique) throughout the study and the percentages of ewes at each accumulation (peak day +/- 1 day) were 50, 35, 65 and 80% for the first, second, third and fourth accumulations, respectively (P < 0.05). It was concluded that progesterone production was lower and the oestrous cycles were shorter during the first oestrous cycle and that tactile and visual separation of rams at the beginning of the breeding season might enhance the synchronizing effect towards the end of the breeding season in the fat-tailed Tuj ewes.