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.     

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.     

Pituitary responsiveness of mares challenged with GnRH at various stages of the transition into the breeding season

Four groups of mares, representing anestrus (AN; n = 8), early transition (ET; n = 7), late transition (LT; n = 8) and estrus (EST; n = 12) were used to examine release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) after a bolus injection of gonadotropin releasing hormone (GnRH) during the transition from anestrus into the breeding season. Estrous mares received GnRH on d 2 or 3 of estrus in the cycle immediately preceding slaughter. Anestrous, ET and LT mares received GnRH exactly 1 wk prior to slaughter. A single injection of GnRH (Sigma LHRH, L-0507, 2.0 micrograms/kg body weight in .9% saline, iv) was given to each mare. Blood samples were collected at -2, h, -1 h, directly prior to GnRH, then 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 300, 360, 420 and 480 min post-injection. Maximum release of LH and FSH was observed within 30 min after injection of GnRH. Except for the LH response in EST mares, concentrations of both hormones had returned to pre-injection baseline levels within 8 h. Group means for area under the curve (AUC) of concentrations of LH in serum, and the maximum amount (MAX) of LH quantified in serum, post-GnRH, increased (P less than .05) progressively from AN to the breeding season. The AUC and MAX responses for FSH showed a reverse pattern, decreasing (P less than .05) from AN to the breeding season.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased ovulation rate of adult ewes treated with anti-bovine LH antiserum during the normal breeding season

Adult Suffolk ewes (n = 14) were treated on d 10 of the estrous cycle with anti-bovine luteinizing hormone (LH) antiserum. Control ewes (n = 10) were treated with normal horse serum. Estrous behavior and the number of corpora lutea and ovarian follicles were examined at the subsequent estrous cycle. Daily plasma concentrations of progesterone (P4), follicle stimulating hormone (FSH) and estradiol were determined before and after treatment. Ewes treated with antiserum had a higher (P less than .05) ovulation rate (2.7 +/- .2) than did controls (2.1 +/- .1). No differences were found in the numbers of large (greater than 5 mm) or small (less than 5 mm) follicles between treatment groups. Estrus was delayed (P less than .025) approximately .6 d/in ewes treated with antisera. Immunoreactive FSH increased (P less than .05) within 1 d after treatment and remained higher than the controls for 5 d. Peak estradiol concentrations occurred on d 17 for treated ewes compared with peak concentrations on d 15 or 16 for control ewes. The P4 concentrations were generally less (P less than .025) in treated ewes throughout the luteal phase of the treatment cycle. These data demonstrate that ovulation rate is increased in ewes treated with LH antiserum. The marked increase in plasma FSH suggests a possible mechanism whereby ovulation rate is enhanced.     

Effects of induction of ovulation with GnRH or HCG on follicular and luteal blood flow in Holstein-Friesian heifers

The objective of this study was to compare the effects of gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) on follicular blood flow (FBF) during the pre-ovulatory period and on luteal blood flow (LBF) during dioestrus in Holstein-Friesian heifers. Twelve animals were randomly divided into two groups and treated with either intramuscular injection of 100 μg GnRH or intravenous (IV) injection of 5000 IU hCG on Day 0 (oestrus, 48 h after administration of PGF(2α) ) to induce ovulation. Follicular size (FS), FBF and time of ovulation were recorded with colour Doppler sonography at 0, 1, 3, 6, 12 and 24 h after GnRH and hCG treatment. Luteal size (LS) and LBF were investigated on Day 9 and 12 after ovulation. Plasma samples were taken to determine total oestrogens (E(tot) ) and progesterone (P(4) ) after each examination. Ovulation occurred between 24 and 48 h after treatment in all animals. No difference (p > 0.05) was observed in FS between the two treatment groups. Follicular blood flow was higher in the hCG group than that was in GnRH group at 1 h after treatment (p < 0.01). Total oestrogens were also higher (p < 0.01) in the hCG group than GnRH group; however, this difference was only obvious at 12 h after treatment. No difference (p > 0.05) was observed in LS, LBF or P(4) levels on Day 9 and 12 between treatment groups. In conclusion, the results suggest that induction of ovulation with hCG and GnRH has a temporary effect on FBF and oestrogen levels while no effect on the size of corpora lutea, LBF and P(4) levels was observed.     

Influence of dietary energy on follicular development, serum gonadotropins, and first postpartum ovulation in suckled beef cows

Twenty-eight Hereford x Angus cows (4 yr of age) were used to determine the effects of pre- and postpartum dietary energy on performance and reproductive function in suckled beef cows. The experiment was designed as a 2 x 2 factorial with cows receiving either 70 (L) or 150% (H) of NRC recommended level of dietary energy before and(or) after parturition, resulting in four treatment combinations (L-L, L-H, H-L, H-H). Prepartum diets were fed for approximately 110 d, and postpartum diets were fed until either 10 d after the second postpartum ovulation or 150 d postpartum for those cows that failed to ovulate. Cows receiving low compared with high levels of energy before calving lost more (P less than .01) weight, body condition, subcutaneous fat, and longissimus muscle area before parturition and had calves with lighter (P less than .01) birth weights. Cows receiving low compared with high levels of energy postpartum lost more (P less than .01) weight, body condition, and longissimus muscle area after parturition. Low levels of energy before and after parturition decreased (P less than .01) milk production and calf weight at 70 d of age. Rates of cervical and uterine involution were unaffected by dietary energy treatments. Cows receiving high levels of energy prepartum had increased (P less than .01) mean concentrations and pulse frequency of LH in serum after parturition, and cows receiving high levels of energy postpartum had increased (P less than .05) pulse frequency of LH. Low levels of energy postpartum decreased (P less than .01) appearance rate of small (5.0 to 7.9 mm) and large (greater than or equal to 10 mm) follicles, and low levels of energy prepartum decreased (P less than .02) appearance rate of large follicles based on transrectal ultrasonography. Cows receiving high levels of energy prepartum had shorter (P less than .02) intervals from parturition to ovulation, and a higher (P less than .01) percentage of the cows that received high levels of energy postpartum ovulated by 150 d postpartum. In summary, prepartum level of dietary energy influenced birth weight and weight gain of calves, milk production, concentrations and pulse frequency of LH in serum, appearance rate of large follicles, and the interval to first ovulation. Postpartum level of dietary energy influenced milk production, weight gain of calves, pulse frequency of LH, appearance rate of small and large follicles, and the percentage of cows that ovulated after parturition.     

Immunization of goats against inhibin increased follicular development and ovulation rate

In the present study, two experiments were conducted to induce superovulation in goats using passive and active immunization against inhibin. In the first experiment, two groups of goats were given an intravenous injection of either 10 ml normal goat serum (control; n=6) or inhibin antiserum developed against [Tyro30]-inhibin alpha (1-30) (passively immunized; n=6) 48 h before treatment with PGF2alpha. In the second experiment, two groups of goats were immunized with inhibin vaccine (actively immunized; n=5) or Freund's adjuvant (control; n=5) followed by three booster immunizations at 4 week intervals. Blood samples were collected for determination of FSH, LH, estradiol-17beta, and progesterone. Ultrasonography was used to determine ovarian activity at PGF2alpha injection and ovulation rate one week after estrus. In both experiments, there was a significant increase in plasma FSH concentration compared with the controls. However, the pattern of the FSH levels was different between the passively and actively immunized goats. The numbers of follicles in passively and actively immunized goats (22.4 +/- 2.3 and 18.6 +/- 2.1, respectively) were significantly greater than those in the controls (2.6 +/- 0.4 and 2.3 +/- 0.4, respectively). In addition, the ovulation rate was greater in the immunized animals compared with the controls. Therefore, either passive or active immunization against inhibin could be used to induce superovulation in goats.     

Effect of season and photoperiod on the time of first postpartum ovulation in Awassi ewes

Seasonal differences in the resumption of postpartum ovarian activity, milk production and periparturient metabolic status were investigated in lactating non-suckling dairy Awassi sheep in two consecutive experiments. In Experiment 1, autumn-lambing (AL, n = 27) and spring-lambing (SL, n = 37) ewes were investigated. Ovarian activity was monitored by means of individual progesterone (P4) profiles from day 5 to day 100 post partum. Most of the AL dams (89%) ovulated till day 35 after parturition and became cyclic thereafter. Incidence of persistent corpus luteum (CLP) and short luteal phases (sCL) was frequent (18% and 29%, respectively) among non-conceiving dams. In contrast, only 24% of the SL ewes ovulated before day 35. P4 levels during the luteal phase were lower in cyclic animals, and the cycle was longer in SL than in AL animals. No CLP or sCL was detected in the spring-lambing group, and 61% of SL ewes remained acyclic till the end of the trial. Lactation length was significantly longer in SL dams than in AL ewes (P = 0.008). According to the plasma metabolites (BHB, NEFA) and metabolic hormones (insulin, IGF-I, thyroxine) examined, negative energy balance did not appear in any of the animals. However, seasonal differences were seen in IGF-I and thyroxine levels, which were higher in the SL dams. In Experiment 2, influence of additional lighting was studied in autumn-lambing ewes. The long-day photoperiod (LD, n = 23) group was exposed to artificial light from sunset till midnight (approx. 16 h light/8 h dark) from some weeks before the expected date of delivery in mid-September until the end of December. The control group (n = 25) experienced only natural daylength. The first postpartum ovulation tended to occur later in the LD animals than in the controls (P = 0.047). The lactation of the LD group tended to be longer (P = 0.061). NEFA, BHB, insulin, IGF-I and thyroxine levels did not differ between the groups. Conclusions: (i) The ovarian function of the Awassi population is seasonal under temperate continental climate conditions. (ii) The first postpartum ovulation of non-suckling, autumn-lambing dams may occur very early, even before the completion of uterine involution. (iii) Additional artificial lighting may delay the time of first postpartum ovulation in AL ewes. (iv) Postpartum negative energy balance is unlikely to occur in dairy Awassi ewes even in high-producing intensive systems.     

Comparative efficiency of oestrus synchronization in sheep with progesterone/eCG and progesterone/GnRH during breeding and non-breeding season

The present study compared the occurrence of oestrus behaviour and ovulation in response to the insertion of CIDR devices plus a classical treatment with equine chorionic gonadotrophin (eCG; single dose at CIDR removal) or alternative treatments with gonadotrophin-releasing hormone (GnRH, either in a single dose at 56 hr after CIDR removal, or in one dose at CIDR insertion and another dose at 56 hr after CIDR removal). The appearance of oestrus behaviour during reproductive season ranged between 84% and 95% and all females showing oestrus signs had subsequent ovulations. The response, during seasonal anoestrus, was similar in the group treated with eCG, but less than half of the females in the groups treated with GnRH showed oestrus signs in response to the treatment, although more than 80% of them showed resumption of ovulatory activity after the treatment. In conclusion, protocols based on GnRH administration offer similar yields to eCG-based protocols during the reproductive season but occurrence of oestrus in response to GnRH-based treatments is highly compromised during seasonal anoestrus.     

非繁殖季节羊诱导发情排卵的研究进展

处于乏情状态的绵山羊,不管是泌乳性乏情还是季节性乏情,卵巢上都无发育成熟至可以排出的卵泡,也无功能黄体存在.这显然是由于垂体促性腺激素活动低下,FSH与LH的水平低,这种情况下,如果用外源的生殖激素(神经生殖激素、促性腺激素、性腺激素)或创造人工气候环境或公羊效应等其它方法引起内源促性腺激素分泌与释放,可使卵巢恢复活动,引起卵泡发育成熟至排卵.     

Effect of purified equine follicle-stimulating hormone on follicular development and ovulation in transitional mares

Horse owners want to have their mares bred as early as possible in the breeding season after February 1. Numerous medical treatments, such as progesterone, dopamine antagonists, and gonadotropin-releasing hormone have been administered to anestrous or transitional mares in an attempt to induce follicular development. Some of these treatments are ineffective or impractical, so there is a need in the horse industry to develop alternative techniques to stimulate follicular development and ovulation early in the breeding season. Twenty transitional mares were assigned to one of two treatment groups. Mares in group 1 (n = 10) served as untreated controls, and mares in group 2 (n = 10) were administered 12.5 mg of purified equine follicle-stimulating hormone (eFSH) (Bioniche Animal Health USA, Inc., Athens, Ga) intramuscularly twice daily for a maximum of 15 consecutive days. Mares were considered to be in transition when the diameter of the largest follicle was ≥25 mm. Once one or more follicles >35 mm were detected, eFSH treatment was discontinued and human chorionic gonadotropin was administered intravenously. The percentage of mares ovulating during the 15-day observation period was compared by means of chi-square analysis. The interval to ovulation and the number of ovulations per mare were compared between the two groups by Student t test. In 8 of 10 mares treated with eFSH follicles developed and ovulation occurred during the 15-day observation period, compared with 0 of 10 control mares. Interval from onset of treatment to ovulation was 7.6 ± 2.4 days for these eight mares. The eight mares were treated for an average of 5.2 ± 1.3 days with eFSH. Thus, the eFSH treatment was effective in advancing the first ovulation of the year in transitional mares.     

Reproductive performance and profitability of heifers fed to weigh 272 or 318 kg at the start of the first breeding season

Reproductive performance and weaning weight of the first calf was determined in 221 Brahman crossbred heifers fed to weigh either 272 (TW1) or 318 kg (TW2) at the start of their first breeding season (target weight). Heifers were divided into light- (below average) and heavyweight (above average) groups on the basis of initial weight. Within each target weight, heifers were fed in three lots. One lot contained lightweight heifers, the second contained heavy heifers and the third was composed of one-half heavy- and one-half lightweight heifers. Heifers were fed for 200 d before the start of the first breeding season. More heifers in TW2 showed estrus and became pregnant in the first 20 d of the breeding season and more were pregnant at the end of the first breeding season. These same differences in reproductive performance were also noted the second year. Each heifer exposed in TW2 weaned 43.4 kg more calf than those in TW1. An average heifer in TW2 was fed 220 kg more corn and 100 kg less hay than a corresponding heifer in TW1. Estrus and pregnancy rate for lightweight heifers in TW1 and TW2 were not improved by sorting and feeding them separately.     

Studies on the contractility of follicular wall with special reference to the mechanism of ovulation in hens

1. To investigate the mechanism of ovulation in the hen, histological and physiological investigations on the contractility of the follicular wall were carried out.

2. Smooth muscle bundles in the loose connective tissue coat from the stalk to the equator showed spontaneous rhythmic contractions with an alternation of contraction and pausing periods of about 4 min. The administration of prostaglandins F_2α (PGF_2α), E₂ (PGE₂), ovarian oviposition inducing factor (OOIF), oxytocin and acetylcholine increased the frequency and amplitude of the contractions.

3. The theca layer showed spontaneous contractions at a frequency of about 30 per 10 min. PGF_2α, OOIF, acetylcholine, adrenaline and noradren‐aline induced tonic contractions, whereas PGE₂, oxytocin and histamine induced relaxation.

4. It is suggested that the contraction of the follicular wall promotes the rupture of the stigma at ovulation and the neurotransmitters as well as prostaglandins and OOIF may be involved in this event.     

Studies of follicular vascularity associated with follicle selection and ovulation in cattle

We reviewed recent in vivo studies of the real-time changes in the vasculature of the follicle wall during selection of the dominant follicle as well as during ovulation in cows. Changes in follicle diameter and vascularity were determined by transrectal ultrasonography. Blood flow within the walls of the two largest follicles was detected at the time of wave emergence (largest follicle=5 mm in diameter). Before selection of a follicle (largest follicle <8.5 mm in diameter), the degrees of vascularity of the two largest follicles were not significantly different. After the largest follicle reached a diameter of 10 mm, the vascularity of the largest (dominant) follicle was higher than that of the second largest (subordinate) follicle. In the preovulatory follicle, follicular vascularity gradually increased, and as ovulation approached, the LH-surge induced an increase in blood flow within the follicle wall. The above results suggest that maintenance of follicular vasculature and appropriate blood supplies to follicles are essential for establishment of follicular dominance. Consequently, only a dominant follicle with high vascularity may have a chance to reach final maturation and acquire ovulatory capacity.     

Nutritional factors that regulate ovulation of the dominant follicle during the first follicular wave postpartum in high-producing dairy cows

During recent decades, milk production per cow has increased drastically due to improved management, nutrition, and genetic selection; however, the reproductive performance of high-producing dairy cows has been declining. One of the factors responsible for this low reproductive performance is negative energy balance (NEB). NEB affects the onset of first ovulation in early postpartum cows. It is generally accepted that early first ovulation positively relates to the resumption of normal ovarian function, first service, and conception rate in dairy cows. Hence, delayed first ovulation has a negative impact on subsequent fertility. The metabolic condition of cows in NEB shifts to catabolic metabolism, which in turn causes increased plasma growth hormone and non-esterified fatty acid concentrations and decreased plasma insulin-like growth factor-1, insulin, and glucose concentrations. On the other hand, plasma β-carotene concentrations decrease throughout the dry period and reach their nadir in about the first week postpartum, and this change reflects energy balance during the peripartum period. β-Carotene plays a role independently of vitamin A in the reproductive performance of dairy cows, and the positive relationship between supplemental β-carotene and reproductive function has been demonstrated in many studies during the past decades. However, β-carotene content in corn silage, which is a popular main feed in high-producing dairy cows, is very low. This review describes nutritional factors related to ovulation during the first follicular wave postpartum in dairy cows.