Effect of the increase of steroid binding plasma levels after passive immunization against testosterone on the control of luteinizing hormone (LH) secretion in ovariectomized underfed dairy heifers.

The ability of passive immunization against testosterone to increase sex steroid binding levels in plasma and thus to overcome the negative feedback of oestradiol-17 beta (E2) on LH secretion in underfed heifers was investigated. Dairy heifers were ovariectomized and divided in 3 groups: high energy diet (H group, n = 4), low energy diet (L group, n = 3) and low energy diet + E2 implants (LE2 group, n = 4). Twenty-four h before injection of bovine immunoglobulins, the mean concentrations of LH were not different between H and L groups. LH baseline was lower (0.8 vs 1.1 ng/ml, P less than 0.03) and the median number of LH pulses was higher (10 vs 5, P less than 0.03) in H than in L group. E2 markedly decreased (P less than 0.01) the mean and basal concentrations of LH (0.27 ng/ml), and number of LH pulses (0) in the LE2 group (P less than 0.05). After injection of anti-testosterone immunoglobulins in the L group, mean and basal LH concentrations tended to decrease. The median number of LH pulses in the L group rose 8 days after immunization (5 vs 7 on day -1 and day +8, P less than or equal to 0.05). Amplitude of pulses tended to decrease after injection (P = 0.08). In the LE2 group, the mean concentration and baseline of LH were not affected by passive immunization against testosterone, while pulses of LH appeared at day +1 and rose (P = 0.07) at day +8 after immunization with 3.5 pulses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gonadotrophin secretion and ovarian responses in prepubertal heifers actively immunized against androstenedione and oestradiol-17 beta

Groups of heifer calves received a primary immunization against androstenedione (Group A; N = 11) or oestradiol-17 beta (Group E; N = 10) at 3 months of age and booster injections on 5 occasions at 2- to 3-month intervals. Controls (Group C, N = 11) were immunized against human serum albumin alone using the same protocol. Immunity was achieved against both steroids as judged by the secondary antisteroid antibody titres in Group A (1126 +/- 261; reciprocal of titre) and Group E (10,357 +/- 4067) heifers. In Groups A and E there was a general decline in the respective peak antibody titres after successive booster injections. From 3 to 9 months of age mean plasma concentrations of LH were higher (P less than 0.05) in Group E heifers (0.89 +/- 0.08 ng/ml) than in Group C (0.46 +/- 0.03 ng/ml) and Group A (0.59 +/- 0.05 ng/ml) heifers which did not differ from one another. There were no differences between groups in plasma FSH concentrations. At 10 months of age the LH response to exogenous LHRH was of higher (P less than 0.05) amplitude for heifers in Group E (2.59 +/- 0.56 ng/ml) than for those in Groups C (0.61 +/- 0.07 ng/ml) and A (1.04 +/- 0.22 ng/ml). Elevated plasma progesterone concentrations at 5 months of age were shown by 2 heifers in Group C, 10 in Group A, and 6 in Group E. From 8 to 14 months of age a consistently higher proportion of Group A heifers exhibited elevated progesterone compared with Group C and Group E heifers. After ovarian synchronization and booster injection at 15 months of age a corpus luteum was present in 2 heifers in Group C, 7 in Group A and none in Group E. The ovaries of Group A heifers were different from those of Groups C and E and were characterized by greater numbers of 2-4 mm follicles. It is concluded that active immunization against gonadal steroids influences both LH secretion and ovarian function in prepubertal heifers. Early increases in ovarian activity in androstenedione-immunized heifers are maintained after puberty and may therefore confer some lifetime reproductive advantages.     

Use of a GnRH agonist to prevent the endogenous LH surge and injection of exogenous LH to induce ovulation in heifers superstimulated with FSH: a new model for superovulation

A new protocol for superovulating cattle which allows for control of the timing of ovulation after superstimulation with FSH was developed. The preovulatory LH surge was blocked with the GnRH agonist deslorelin, and ovulation was induced by injection of LH. In Experiment 1, heifers (3-yr-old) were assigned to a control group (Group 1A, n = 4) or a group with deslorelin implants (Group 1B, n = 5). On Day -7, heifers in Group 1A received a progestagen CIDR-B((R))device, while heifers in Group 1B received a CIDR-B((R))device + deslorelin implants. Both groups were superstimulated with twice daily injections of FSH (Folltropin((R))-V): Day 0, 40 mg (80 mg total dose on Day 0); Day 1, 30 mg; Day 2, 20 mg; Day 3, 10 mg. On Day 2, heifers were given PGF (a.m.) and CIDR-B((R)) devices were removed (p.m.). Three heifers in Group 1A had a LH surge and ovulated, whereas neither of these events occurred in Group 1B (with deslorelin implants) heifers. In Experiment 2, heifers (3-yr-old) were assigned to 1 of 4 equal groups (n = 6). On Day -7, heifers in Group 2A received a norgestomet implant, while heifers in Groups 2B, 2C and 2D received norgestomet + deslorelin implants. Heifers were superstimulated with FSH starting on Day 0 as in Experiment 1. On Day 2, heifers were given PGF (a.m.) and norgestomet implants were removed (p.m.). Heifers in Groups 2B to 2D were given 25 mg LH (Lutropin((R))): Group 2B, Day 4 (a.m.); Group 2C, Day 4 (p.m.); Group 2D, Day 5 (a.m.). Heifers in Group 2A were inseminated at estrus and 12 and 24 h later, while heifers in Groups 2B to 2D were inseminated at the time of respective LH injection and 12 and 24 h later. Injection of LH induced ovulation in heifers in Groups 2B to 2D. Heifers in Group 2C had similar total ova and embryos (15.2 +/- 1.4) as heifers in Group 2A (11.0 +/- 2.8) but greater (P < 0.05) numbers than heifers in Group 2B (7.0 +/- 2.3) and Group 2D (6.3 +/- 2.0). The number of transferable embryos was similar for heifers in Group 2A (5.8 +/- 1.8) and Group 2C (7.3 +/- 2.1) but lower (P < 0.05) for heifers in Group 2B (1.2 +/- 0.8) and Group 2D (1.3 +/- 1.0). The new GnRH agonist-LH protocol does not require observation of estrus, and induces ovulation in superstimulated heifers that would not have an endogenous LH surge.     

Failure of the LH-releasing hormone agonist, deslorelin, to prevent development of a persistent follicle in heifers synchronized with norgestomet

The use of exogenous progestagens for estrus synchronization in cattle can result in a persistent dominant follicle which is associated with reduced fertility. We examined whether the LHRH agonist, deslorelin, would prevent the formation of a persistent follicle in heifers synchronized with norgestomet. The estrous cycles of heifers were synchronized with cloprostenol, and on Day 7 of the ensuing cycle the heifers received one of the following treatments for 10 d: Group C (n = 5), untreated control; Group N (n = 6), injection of a luteolytic dose of cloprostenol on Days 7 and 8 and implant of norgestomet from Day 7 to Day 17 (i.e. typical 10-day norgestomet implant period); Group D (n = 6), injection of cloprostenol on Days 7 and 8 and implants of deslorelin from Day 7 to Day 17; Group ND (n = 6), injections of cloprostenol and both norgestomet and deslorelin implants as above. Follicle growth was monitored using ultrasonography. Group-N heifers showed continued follicle growth and had larger follicles on Day 17 of the cycle than Group-C heifers (16.8 +/- 1.6 and 10.4 +/- 1.6 mm). Follicle growth for Group-D and ND heifers was similar and variable, and seemed to depend on follicle status at the initiation of treatment. Heifers with follicles of 5 to 10 mm (n = 9) in diameter either showed no follicle growth (2 9 ) or developed large follicles (7 9 ), while heifers with follicles approximately 12 mm (n = 3) in diameter showed follicle atresia with no further significant growth. On Day 17, size of the largest follicle was similar for Group-ND (14.3 +/- 2.9) and Group-D (16.8 +/- 1.6) heifers. Heifers in Group N showed estrous behavior 1.8 +/- 0.2 d after treatment, whereas heifers in Groups D and ND did not show estrus for 2 to 4 wk. The results show that combined treatment with progestagen and an LHRH agonist does not consistently prevent the development of a persistent dominant follicle and that return to estrus can be delayed after treatment with an LHRH agonist.     

Effect of dietary energy and protein density on body composition,attainment of puberty,and ovarian follicular dynamics in dairy heifers

The objectives were to examine the effects of dietary energy and protein density on age and body composition at puberty, and on ovarian follicular dynamics during the pre- and peripubertal periods in Holstein heifers. In Phase 1, heifers were randomly allotted (n=10 per diet) at 100 kg body weight (BW) to diets with either low (P1L), medium (P1M) or high (P1H) energy and protein formulated for an average daily gain (ADG) of 0.5, 0.8 or 1.1 kg per day, respectively. During Phase 2 (P2), all heifers were fed ad libitum a common diet formulated for an ADG of 0.8 kg per day. Half the animals within the high (n=5) and low groups (n=5) entered P2 either at 12 months of age (P2H-12; P2L-12) or at 330 kg BW (P2H-330; P2L-330). Heifers fed P1H, P1M, P1L, and P2L-12 diets attained puberty at approximately 9, 11, 16, and 14 months of age, respectively (P<0.01). Urea space estimates of body fat and protein percent, and back-fat thickness, were lower in P1L heifers compared to P1H or P1M heifers at similar chronological ages (P<0.05) but did not differ at puberty (P>0.10). Compared to P1L heifers, P1H heifers had high amplitude LH pulses at 8 months, and high frequency low amplitude LH pulses at 10 months of age (P<0.05). The mean diameter (mm) of the dominant follicle was smaller (P<0.05) in P1L heifers (10.6) compared to P1H (12.8) or P1M (12.2) heifers at 8 months. Maximum size and growth rate of the nonovulatory dominant follicle increased with age (P<0.05) but did not differ between P1H and P1M heifers at puberty. The diameter (mm) of the nonovulatory dominant follicle, and the first and second ovulatory follicles were larger in P2L-12 heifers (14.0, 14.7, and 14.9) compared to P1M heifers (13.1, 12.5, and 11.9), while the peak progesterone levels and CL growth were lower (P<0.05) in the first cycle. In conclusion, dairy heifers attained puberty at a constant body weight and body composition independent of dietary manipulation, the size of dominant follicles increased with age in association with increased LH support, and heifers realimented from a low energy diet developed larger first ovulatory follicles and smaller CL with lower peak progesterone concentrations in the first cycle.     

Close synchrony of ovulation in superstimulated heifers that have a downregulated anterior pituitary gland and are induced to ovulate with exogenous LH

The synchrony of ovulation was examined in superstimulated heifers that had a downregulated pituitary gland and which were induced to ovulate by injection of exogenous LH. The pituitary was downregulated and desensitized to GnRH by treatment with the GnRH agonist deslorelin. Nulliparous heifers (3.5 yr old) at random stages of the estrous cycle were assigned to 1 of 3 groups, and on Day -7 received the following treatments: Group 1 (control, n = 8), 1 norgestomet ear implant; Group 2 (GnRH agonist, n = 8); Group 3 (GnRH agonist-LH protocol, n = 8), 2 deslorelin ear implants. Ovarian follicle growth in all heifers was superstimulated with twice-daily intramuscular injections of FSH (Folltropin-V): Day O, 40 mg (80 mg total dose); Day 1, 30 mg; Day 2; 20 mg; Day 3, 10 mg. On Day 2, all heifers were given a luteolytic dose of PGF (7 A.M.), Norgestomet implants were removed from heifers in Group 1 (6 P.M.). Heifers in Group 3 were given an injection of 25 mg, i.m. porcine LH (Lutropin) on Day 4 (4 P.M.). Ovarian follicle status was monitored at 8-h intervals from Day 3 (8 A.M.) to Day 6 (4 P.M.) using an Aloka Echo Camera and 7.5 MHz transducer. Heifers in Groups 2 and 3 exhibited estrus earlier (P < 0.05) than heifers in Group 1. Heifers in Group 2 did not have a preovulatory LH surge and they did not ovulate. Individual control heifers in Group 1 ovulated between 12 A.M. on Day 5 and 8 A.M. on Day 6. Heifers with deslorelin implants and injected with LH in Group 3 ovulated between 4 P.M. on Day 5 and 8 A.M. on Day 6. It was confirmed that superstimulated heifers with GnRH agonist implants can be induced to ovulate with LH. It was also demonstrated that ovulation is closely synchronized after injection of LH. Thus, a single, fixed-time insemination schedule could be used in a GnRH agonist-LH superovulation protocol, with significant practical and economic advantages for superovulation and embryo transfer programs.     

Ultrasonographic determination of ovarian follicular. Development in superovulated heifers pretreated with FSH-P at the beginning of the estrous cycle

On Day 3 of the estrous cycle (estrus = Day 0), dairy heifers were given either 10 mg i.m. FSH-P (FSH-P primed; n = 9) or a saline vehicle (saline primed; n = 9). On Day 10, all heifers were superovulated with FSH-P (total = 27.7 mg i.m.) in declining doses over 5 d. Heifers were inseminated artificially at estrus. From Day 2 until estrus, the number and size of follicles >2 mm were monitored daily by ultrasonography. The mean (+/- SEM) number of corpora lutea (CL) (6.2 +/- 1.5 vs 10.7 +/- 0.9; P<0.05) and the mean number of recovered embryos and unfertilized ova (3.6 +/- 1.7 vs 8.4 +/- 2.2; P<0.05) were lower in FSH-P-primed than in saline-primed heifers. Prior to initiation of superovulation, follicles >10 mm appeared on Days 6 to 7 in saline-primed heifers but only on Days 8 to 10 in FSH-P-primed heifers (P<0.05). Also, until Day 10, the mean number of follicles 4 to 6 mm and 7 to 10 mm was higher (P<0.05) in FSH-P-primed than in saline-primed heifers. After initiation of the superovulatory treatment (Day 10 to estrus), saline-primed heifers had a greater and faster increase in the mean number of follicles >10 mm (P<0.02) than FSH-P-primed heifers did. Depletion in the number of follicles 2 to 3 mm (P<0.001) between Day 10 and estrus and in the number of follicles 4 to 6 mm (P<0.05) between Day 12 and estrus occurred in both groups of heifers. Decreased superovulatory response and embryo recovery in FSH-P-primed heifers may have been due to the presence of large follicles (>10 mm) prior to the initiation of the superovulatory treatment which reduced the ability of small follicles to grow into larger size classes during superovulatory treatment.     

Effects of oxytocin on cloprostenol-induced luteolysis, follicular growth, ovulation and corpus luteum function in heifers

Twenty-five normally cyclic Holstein heifers were used to examine the effects of oxytocin on cloprostenol-induced luteolysis, subsequent ovulation, and early luteal and follicular development. The heifers were randomly assigned to 1 of 4 treatments: Group SC-SC (n=6), Group SC-OT (n=6), Group OT-SC (n=6) and Group OT-OT (n=7). The SC-SC and SC-OT groups received continuous saline infusion, while Groups OT-SC and OT-OT received continuous oxytocin infusion (1:9 mg/d) on Days 14 to 26 after estrus. All animals received 500 microg, i.m. cloprostenol 2 d after initiation of infusion (Day 16) to induce luteolysis. Groups SC-OT and OT-OT received oxytocin twice daily (12 h apart) (0.33 USP units/kg body weight, s.c.) on Days 3 to 6 of the estrous cycle following cloprostenol-induced luteolysis, while Groups SC-SC and OT-SC received an equivalent volume of saline. Daily plasma progesterone (P4) concentrations prior to cloprostenol-induced luteolysis and rates of decline in P4 following the induced luteolysis did not differ between oxytocin-infused (OT-OT and OT-SC) and saline-infused (SC-SC and SC-OT) groups (P >0.1). Duration of the estrous cycle was shortened in saline-infused heifers receiving oxytocin daily during the first week of the estrous cycle. In contrast, oxytocin injections did not result in premature inhibition of luteal function and return to estrus in heifers that received oxytocin infusion (OT-OT). Day of ovulation, size of ovulating follicle and time of peak LH after cloprostenol administration for oxytocin and saline-treated control heifers did not differ (P >0.1). During the first 3 d of the estrous cycle following luteal regression, fewer (P <0.01) follicles of all classes were observed in the oxytocin-infused animals. Day of emergence of the first follicular wave in heifers treated with oxytocin was delayed (P <0.05). The results show that continuous infusion of oxytocin during the mid-luteal stage of the estrous cycle has no effect on cloprostenol-induced luteal regression, timing of preovulatory LH peak or ovulation. Further, the finding support that an episodic rather than continuous administration of oxytocin during the first week of the estrous cycle results in premature loss of luteal function. The data suggest minor inhibitory effects of oxytocin on follicular growth during the first 3 d of the estrous cycle following cloprostenol-induced luteolysis.     

Effects of oxytocin on follicular development and duration of the estrous cycle in heifers

Holstein heifers were used to study effects of exogenous administration of oxytocin on luteal function and ovarian follicular development. Twelve heifers were monitored for 1 estrous cycle to confirm normal ovarian function. At the subsequent estrus, these animals were randomly assigned to 1 of 3 treatments: saline control, (Group 1, n=4), oxytocin (Group 2, n=4) and saline pregnant (Group 3, n=4). Group 2 received continuous infusion of oxytocin (1.9 mg/d) from Days 14 to 26 after estrus, while Groups 1 and 3 received saline infusion during the same period. Group 3 were artificially inseminated at estrus. Daily blood samples were collected for oxytocin and progesterone assay. Ovarian follicles and corpus luteum (CL) development were monitored daily by transrectal ultrasonography until Day 32 after estrus. Plasma progesterone (P4) concentrations prior to initiation of infusion were 7.6+/-1.3 ng/mL on Day 14. They then decreased to <1 ng/mL on Day 19 for Group 1 and on Day 28 for Group 2. The interestrous interval was longer (P <0.05) for heifers that received oxytocin infusion. During the infusion period P4 concentrations were not different (P >0.05) between Group 2 and 3 but declined gradually from Day 20 in Group 2 despite the presence of high plasma oxytocin concentrations. Control heifers had 2 waves of follicular growth, with the second dominant follicle ovulating. Three of the 4 oxytocin-infused animals had an additional wave, with the third dominant follicle ovulating. Oxytocin infusion had no effect on size of the ovulating follicle (P >0.05) and the number of Class 1 follicles (3 to 5 mm, P >0.1). Differences in the number of Class 2 follicles (6 to 9 mm) among treatments on Days 15 to 22 after estrus were not detected (P >0.1) except on Days 23 to 26, when Group 2 had fewer follicles than Group 3 (P <0.05). The results show that continuous infusion of oxytocin during normal luteolysis delays luteal regression without inhibiting follicular development.     

Response of prepubertal ewes primed with monensin or progesterone to administration of FSH

Prepubertal ewe lambs were treated with FSH after progesterone priming for 12 days (Group P), monensin supplementation for 14 days (Group M) or a standard diet (Group C). Serial blood samples were taken for LH and progesterone assay, and ovariectomy was performed on half of each group 38-52 h after start of treatment to assess ovarian function, follicular steroid production in vitro and the concentration of gonadotrophin binding sites in follicles. The remaining ewe lambs were ovariectomized 8 days after FSH treatment to determine whether functional corpora lutea were present. FSH treatment was followed by a preovulatory LH surge which occurred significantly later (P less than 0.05) and was better synchronized in ewes in Groups P and M than in those in Group C. At 13-15 h after the LH surge significantly more large follicles were present on ovaries from Group P and M ewes than in Group C. Follicles greater than 5 mm diameter from ewes in Groups P and M produced significantly less oestrogen and testosterone and more dihydrotestosterone, and had significantly more hCG binding sites, than did similar-sized follicles from Group C animals. Ovariectomy on Day 8 after the completion of FSH treatment showed that ewes in Groups P and M had significantly greater numbers of functional corpora lutea. These results indicate that, in prepubertal ewes, progesterone priming and monensin supplementation may delay the preovulatory LH surge, allowing follicles developing after FSH treatment more time to mature before ovulation. This may result in better luteinization of ruptured follicles in these ewes, with the formation of functional corpora lutea.(ABSTRACT TRUNCATED AT 250 WORDS)     

Superstimulation of ovarian follicular growth with FSH oocyte recovery, and embryo production from Zebu (Bos indicus) calves: effects of treatment with a GnRH agonist or antagonist

The capacity of heifer calves of a late sexually maturing Zebu (Bos indicus) genotype to respond to superstimulation with FSH at a young age and in vitro oocyte development were examined. Some calves were treated with a GnRH agonist (deslorelin) or antagonist (cetrorelix) to determine whether altering plasma concentrations of LH would influence follicular responses to FSH and oocyte developmental competency. Brahman calves (3-mo-old; 140 +/- 3 kg) were randomly assigned to 3 groups: control (n = 10); deslorelin treatment from Day -8 to 3 (n = 10); and cetrorelix treatment from Day -3 to 2 (n = 10). All calves were stimulated with FSH from Day 0 to 2, and were ovariectomized on Day 3 to determine follicular responses to FSH and to recover oocytes for in vitro procedures. Before treatment with FSH, heifers receiving deslorelin had greater (P < 0.001) plasma LH (0.30 +/- 0.01 ng/ml) than control heifers (0.17 +/- 0.02 ng/ml), while plasma LH was reduced (P < 0.05) in heifers treated with cetrorelix (0.13 +/- 0.01 ng/ml). Control heifers had a surge release of LH during treatment with FSH, but this did not occur in heifers treated with deslorelin or cetrorelix. All heifers had large numbers of follicles > or = 2 mm (approximately 60 follicles) after superstimulation with FSH, and there were no differences (P > 0.10) between groups. Total numbers of oocytes recovered and cultured also did not differ (P > 0.05) for control heifers and heifers treated with deslorelin or cetrorelix. Fertilization and cleavage rates were similar for the 3 groups, and developmental rates to blastocysts were also similar. Zebu heifers respond well to superstimulation with FSH at a young age, and their oocytes are developmentally competent.     

Exogenous estradiol reduces inhibition of luteinizing hormone by estradiol in prepubertal heifers

The hypothesis that high levels of exogenous estradiol administered to heifers during the prepubertal period would decrease subsequent negative feedback of estradiol on luteinizing hormone (LH) secretion was tested. Fourteen prepubertal heifers were ovariectomized on Day 0. Ovariectomized heifers received either no further treatment (OVX, n = 4), a single estradiol implant on Day 0 (OVXE, n = 5), or the single implant on Day 0 and two additional implants between Days 16 and 30 (OVXE+ E, n = 5). Ten ovary-intact heifers received either no treatment (INT, n = 5) or were administered the two estradiol implants between Days 16 and 30 (INT+ 5, n = 5). Comparison of LH secretion in OVXE to OVXE+E, and in INT to INT+E resulted in significant time-by-treatment interactions (p less than 0.05 for both). As pubertal age approached, mean concentration of LH (p less than 0.05) and pulse frequency (p less than 0.05) increased more rapidly in OVXE+E and INT+E than in OVXE and INT, respectively. Amplitude of LH pulses was unaffected by treatment. When data were standardized to day of puberty in INT and INT+E heifers, mean LH concentration and LH pulse frequency increased as puberty approached in both groups. These data confirm earlier reports indicating that secretion of LH increases gradually as puberty approaches in heifers. It was concluded that administration of estradiol during the prepubertal period hastened the decline in the subsequent negative feedback of estradiol. Precocious puberty was not induced in ovary-intact females.     

The effects of dose and duration of administration of pFSH during the first follicular wave on the ovulation rate of beef heifers

Four experiments were carried out to examine the effects of administration of pFSH (Vetrepharm) from Day 3 of the estrous cycle in conjunction with PG on Day 5 on follicular populations and ovulation rate in heifers. In Experiment 1, 47 heifers were allocated to 1 of 4 treatment groups (n = 11 to 12 per group): a) control, b) 1.5 mg pFSH, c) 2.0 mg pFSH or d) 2.5 mg pFSH until estrus. Heifers assigned to the 3 treatments had a higher ovulation rate than the controls (P < 0.05). In Experiment 2, 45 heifers were allocated to 1 of 5 treatment groups (n = 8 to 10 per group): a) control, b) 1.0 mg pFSH until PG, c) 1.0 mg pFSH until estrus, d) 1.5 mg pFSH until PG or e) 1.5 mg pFSH until estrus. From Day 5, heifers assigned to pFSH treatments had more large follicles than the controls (P < 0.05). There was no effect of treatment on the incidence of twin ovulations. In Experiment 3, 43 heifers were assigned to 1 of 3 groups (n = 11 to 16 per group): a) control, b) 1.0 mg pFSH until estrus or c) 1.5 mg pFSH until estrus. At slaughter, 14 d after administration of PG, the incidence of twin ovulations was 0/11, 7/16 and 8/16 for Groups a, b and c, respectively (P = 0.011). In Experiment 4, pFSH (1.5 mg) was administered to 3 groups during the development of the first dominant follicle: a) growth phase (n = 19); b) static phase (n = 17); and c) decline phase (n = 17). All pFSH-treated heifers had a higher ovulation rate than the controls (P < 0.05); heifers assigned to Group c had a higher ovulation rate than those in Groups a or b (P < 0.05). More heifers assigned to Group c (7/17) superovulated than in the other 2 groups (P < 0.05). In conclusion, administration of 1.0 or 1.5 mg pFSH twice daily beginning at Day 3 of the estrous cycle in association with the induction of luteolysis increased the ovulation rate significantly when pFSH treatment was continued to onset of estrus. The ovulation rate and the occurrence of multiple ovulations were significantly higher when pFSH was administered at the time that the first dominant follicle was in decline.     

Perturbation of estradiol-feedback control of luteinizing hormone secretion by immunoneutralization induces development of follicular cysts in cattle

We used immunoneutralization of endogenous estradiol to investigate deficiencies in the estradiol-feedback regulation of LH secretion as a primary cause of follicular cysts in cattle. Twenty-one cows in the prostaglandin (PG) F(2alpha)-induced follicular phase were assigned to receive either 100 ml of estradiol antiserum produced in a castrated male goat (n = 11, immunized group) or the same amount of castrated male goat serum (n = 10, control group). The time of injection of the sera was designated as 0 h and Day 0. Five cows in each group were assigned to subgroups in which we determined the effects of estradiol immunization on LH secretion and follicular growth during the periovulatory period. The remaining six estradiol-immunized cows were subjected to long-term analyses of follicular growth and hormonal profiles, including evaluation of pulsatile secretion of LH. The remaining five control cows were used to determine pulsatile secretion of LH on Day 0 (follicular phase) and Day 14 (midluteal phase). The control cows exhibited a preovulatory LH surge within 48 h after injection of the control serum, followed by ovulation of the dominant follicle that had developed during the PGF(2alpha)-induced follicular phase. In contrast, the LH surge was not detected after treatment with estradiol antiserum. None of the 11 estradiol-immunized cows had ovulation of the dominant follicle, which had emerged before estradiol immunization and enlarged to more than 20 mm in diameter by Day 10. Long-term observation of the six immunized cows revealed that five had multiple follicular waves, with maximum follicular sizes of 20-45 mm at 10- to 30-day intervals for more than 50 days. The sixth cow experienced twin ovulations of the initial persistent follicles on Day 18. The LH pulse frequency in the five immunized cows that showed the long-term turnover of cystic follicles ranged from 0.81 +/- 0.13 to 0.97 +/- 0.09 pulses/h during the experiment, significantly (P < 0.05) higher than that in the midluteal phase of the control cows (0.23 +/- 0.07). The mean LH concentration in the immunized cows was also generally higher than that in the luteal phase of the control cows. However, the LH pulse and mean concentration of LH after immunization were similar to those in the follicular phase of the control cows. Plasma concentrations of total inhibin increased (P < 0.01) concomitant with the emergence of cystic follicles and remained high during the growth of cystic follicles, whereas FSH concentrations were inversely correlated with total inhibin concentrations. In conclusion, neutralization of endogenous estradiol resulted in suppression of the preovulatory LH surge but a normal range of basal LH secretion, and this circumstance led to an anovulatory situation similar to that observed with naturally occurring follicular cysts. These findings provide evidence that lack of LH surge because of dysfunction in the positive-feedback regulation of LH secretion by estradiol can be the initial factor inducing formation of follicular cysts.     

Decreased pulsatile LH secretion in heifers superovulated with eCG or FSH

This study was designed to test the hypothesis that treatment with super-ovulatory drugs suppresses endogenous pulsatile LH secretion. Heifers (n=5/group) were superovulated with eCG (2500 IU) or FSH (equivalent to 400 mg NIH-FSH-P1), starting on Day 10 of the estrous cycle, and were injected with prostaglandin F(2alpha) on Day 12 to induce luteolysis. Control cows were injected only with prostaglandin. Frequent blood samples were taken during luteolysis (6 to 14 h after PG administration) for assay of plasma LH, estradiol, progesterone, testosterone and androstenedione. The LH pulse frequency in eCG-treated cows was significantly lower than that in control cows (2.4 +/- 0.4 & 6.4 +/- 0.4 pulses/8 h, respectively; P<0.05), and plasma progesterone (3.4 +/- 0.4 vs 1.8 +/- 0.1 ng/ml, for treated and control heifers, respectively; P<0.05) and estradiol concentrations (25.9 +/- 4.3 & 4.3 +/- 0.4 pg/ml, for treated and control heifers, respectively; P<0.05) were higher compared with those of the controls. No LH pulses were detected in FSH-treated cows, and mean LH concentrations were significantly lower than those in the controls (0.3 +/- 0.1 & 0.8 +/- 0.1, respectively; P<0.05). This suppression of LH was associated with an increase in estradiol (9.5 +/- 1.4 pg/ml; P<0.05 compared with controls) but not in progesterone concentrations (2.1 +/- 0.2 ng/ml; P>0.05 compared to controls). Both superovulatory protocols increased the ovulation rate (21.6 +/- 3.9 and 23.0 +/- 4.2, for eCG and FSH groups, respectively; P>0.05). These data demonstrate that super-ovulatory treatments decrease LH pulse frequency during the follicular phase of the treatment cycle. This could be explained by increased steroid secretion in the eCG-trated heifers but not in FSH-treated animals.     

Roles of the dominant follicle and the pattern of oestradiol in induction of preovulatory surges of LH and FSH in prepubertal heifers by pulsatile low doses of LH

Prepubertal crossbred beef heifers were injected (i.v.) with 50 micrograms bovine LH every 2 h for 48 h (first injection at 0 h). At 28 h, number and diameter of ovarian follicles were determined by ultrasonic scanning, and unilateral removal of either the ovary bearing the largest follicle (Group UL, N = 5) or the opposite ovary (Group UO, N = 4) was performed; control animals remained intact (Group I, N = 5). Blood samples were taken every 2 h (starting at 0 h) for a 60-h period to assess concentrations of gonadotrophins and oestradiol. Preovulatory-like surges of LH occurred in 0/5, 4/4 and 5/5 heifers for Groups UL, UO and I respectively; the time of the LH surge did not differ between animals in Groups I and UO (mean = 40 h). FSH in Group UL heifers rose to a plateau immediately after unilateral ovariectomy; this pattern was not observed in the other two groups (P less than 0.01). The area under the curve for FSH was significantly different (P less than 0.05) among groups after 28 h. Preovulatory-like surges of FSH occurred coincidently with those of LH, except for one Group I heifer. An increase in the concentrations of oestradiol between 0 and 28 h was detected in all animals. Profiles of oestradiol during this period did not differ between heifers that had an LH surge (Group UO and I) and those that did not (Group UL).(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of nutrition in the regulation of LH secretion during anestrus by the serotoninergic and dopaminergic systems in Mediterranean ewes treated with melatonin

The steroid-dependent inhibition of LH secretion involves dopaminergic and serotoninergic systems but it is unclear how the plane of nutrition affects this inhibition during anestrus in melatonin treated ewes. Melatonin implants (18 mg) were inserted (Day 0) into ovariectomized, estradiol treated adult Rasa Aragonesa ewes on a high (H; n = 8) or low energy diet (L; n = 6) which were applied in early anestrus (Day 29-57) and late anestrus (Day 90-104). Cyproheptadine (0.1 mg/ kg), a serotoninergic (SHT2) receptor antagonist, was administered in early and late anestrus (Day 50 and 107) followed by pimozide (0.08 mg/kg), a dopaminergic2 receptor antagonist (Day 57 and 114). The H ewes had significantly higher LH concentrations (P < 0.05) before cyproheptadine treatment in early anestrus. The H and L ewes responded in a similar way to the antagonists in both early and late anestrus, except for L ewes who had a higher LH pulse amplitude after pimozide treatment in both periods (P < 0.05). During early anestrus, cyproheptadine tended to increase (P = 0.06) LH pulse frequency in L ewes and LH concentrations in H ewes. The LH secretion also increased in L ewes after pimozide administration during early anestrus (P < 0.05 for mean LH concentrations and LH pulse frequency and amplitude). However, pimozide dramatically increased LH secretion during late anestrus (Day 114) irrespective of the plane of nutrition (P = 0.06-0.08 for LH pulse frequency and P < 0.05 for LH concentrations and pulse amplitude). In melatonin treated Mediterranean ewes, the plane of nutrition appeared to modify the effect of dopaminergic and serotoninergic systems on the steroid-dependent inhibition of LH secretion throughout anestrus.     

Progesterone (CIDR)-based timed AI protocols using GnRH, porcine LH or estradiol cypionate for dairy heifers: ovarian and endocrine responses and pregnancy rates

The overall objective was to compare the efficacy of GnRH, porcine LH (pLH) and estradiol cypionate (ECP), in a modified Ovsynch/fixed-time AI (FTAI) protocol that included a controlled internal drug [progesterone] release (CIDR) device. In Experiment 1, heifers received a CIDR on Day -10, and PGF (25mg) on Day -3. At CIDR insertion, heifers received 100 microg of GnRH (n=6), 0.5mg of ECP (n=6), 5.0mg of pLH (n=6) or 2 mL of saline (n=7); these treatments were repeated on Day -1, except for ECP, that was repeated on Day -2, concurrent with CIDR-removal. The 5.0 mg pLH was the least effective with a longer interval to ovulation than the other groups combined (102 versus 64 h; P<0.05). Overall mean LH concentrations (1.6 ng/mL) and area under the curve (AUC) did not differ among treatments, but mean peak LH concentration was lower in heifers given 5 mg of pLH compared to all other groups (4.5 versus 10.3 ng/mL; P<0.05). In Experiment 2, heifers on CIDR-based Ovsynch protocols were given 12.5mg pLH (n=6; pLH-low), 25.0 mg pLH (n=6, pLH-high), or 100 microg GnRH (n=5; control). Heifers in the pLH-high group had greater (P<0.01) plasma LH concentrations (between 12 and 20 h) than GnRH-treated heifers, but the pLH treatments did not differ (P>0.10). Area under the curve for LH (ng/32 h) was at least 50% greater (P<0.01) in pLH-treated heifers compared to GnRH-treated heifers (mean, 41.3, 56.3 and 20.3 for pLH-low, pLH-high and GnRH, respectively). Ovulation occurred in 15 of 17 heifers. Progesterone concentrations were higher on Days 9 and 14 in heifers given 25mg of pLH, suggesting enhanced CL function. In Experiment 3, 240 heifers were assigned to CIDR-based Ovsynch/FTAI protocols. The first and second hormonal treatments (with an intervening PGF treatment on Day -3) were GnRH/GnRH (100 microg), ECP/ECP (0.5 mg), pLH/pLH (12.5 mg) or GnRH/ECP, respectively; pregnancy rates were 58.7, 66.1, 45.9 and 48.3%, respectively (ECP/ECP>both pLH/pLH and GnRH/ECP; P相似文献   

Influence of pregnancy on the onset of oestrus and luteal function after prostaglandin-induced luteolysis in cattle

Luteolysis was induced by an injection of 500 micrograms cloprostenol (a prostaglandin (PG) analogue) in pregnant (P) Holstein heifers on Days 17 or 24 of gestation and in non-pregnant (NP) Holstein heifers on Day 17 of the oestrous cycle (oestrus = Day 0). Heifers in Groups P-17 (N = 8) and P-24 (N = 8) were inseminated twice whereas those in Group NP-17 (N = 8) were not inseminated. Immediately after PG injection, embryos were recovered by uterine flushing (400 ml) to confirm pregnancy in Groups P-17 and P-24. Uterine flushing with an equivalent volume of physiological saline was also done in Group NP-17. The interval from PG injection to oestrus and to the peak of luteinizing hormone (LH) as well as profile of increase in plasma oestradiol concentrations during that period did not differ (P greater than 0.1) among the groups. However, the proportion of heifers exhibiting abnormal luteal phases (primarily of short duration) during the oestrous cycle after PG injection was greater (P less than 0.01) in Group P-24 than in Groups NP-17 + P-17 pooled (6/8 vs 3/16). These results suggest that the previous presence of a conceptus did not have any effect on the onset of oestrus, or on plasma concentrations of oestradiol and LH after PG-induced luteolysis on Days 17 or 24 of gestation. However, luteal function during the subsequent oestrous cycle was impaired if heifers were 24 days pregnant when luteolysis was induced.     

Activation of quiescent ovaries by administration of PMSG after LH-RH analogue treatment in heifers

The effect of pregnant mare serum gonadotrophin (PMSG) treatment on activation of quiescent ovaries was examined in heifers. Groups of thirteen, twenty and twelve heifers which showed ovulation within 2 d and corpus luteum (CL) development after injection with a luteinizing hormone releasing hormone analogue (LH-RH-A) were supplementally injected with 500 IU of PMSG (Group I); 500 IU of PMSG and 500 mug of Prostaglandin F(2alpha) analogue (PGF(2alpha)-A; Group II); and 500 mug of PGF(2alpha)-A (Group III) on Day 6 after the injection of 200 mug of LH-RH-A (Day 0), respectively. Estrus appeared in 33.3 to 45.0% of the heifers of the respective groups after the treatment. Ovulation occurred at a significantly (P<0.01) higher rate in Groups I (100%) and II (90.0%) than in Group III (41.7%). The ovarian cyclic activity was initiated in all the heifers that ovulated. Plasma progesterone levels decreased significantly (P<0.05) to about 1 ng/ml on Day 8 and Day 7 in Group I and Groups II and III, respectively. Plasma estradiol-17beta (E(z)) levels increased significantly (P<0.05), reaching a peak on Days 7 to 7.5 in Groups I and II but not in Group III. It is concluded that PMSG treatment stimulates maturation and E(z) secretion of a follicle, thus promoting ovulation and the onset of ovarian cyclic activity.