Superovulatory responses in dairy cows following ovulation of the dominant follicle of the first wave

In the present study we investigated the effect of hCG administration on Day 7 (Day 0 = day of standing estrus) to ovulate the dominant follicle of the first wave and the associated increase in progesterone concentration on subsequent superovulatory response in dairy cows. Twenty cyclic lactating cows were allocated at random to 2 groups: control (n = 10) and hCG-treated (n = 10). The ovaries of each cow were scanned using an ultrasound scanner on Day 7, to confirm the presence of the dominant follicle and thereafter every other day until embryo recovery. All cows received a total dose of 400 mg Folltropin-V in decreasing amounts for 5 days (Days 9 to 13) and 35 mg PGF(2alpha) on Day 12. In addition, the treated cows received 1000 IU hCG on Day 7. All cows were inseminated twice during estrus, and the embryos were collected 7 days later by a nonsurgical procedure. Blood smaples were taken at different times of the treatment period for progesterone determination. All cows possessed a dominant follicle at Day 7, and all but one of the hCG-treated cows ovulated the dominant follicle and formed an accessory corpus luteum. Plasma progesterone concentrations were significantly higher (P<0.01) in hCG-treated cows than control cows on the first day of Folltropin treatment and on the day of PGF(2alpha) injection. The mean number of follicles at estrus, the number of ovulations, the total number of embryos and the number of transferable embryos were not different (P>0.05) between control and hCG-treated cows.     

Effects of injection of hcg during the estrous cycle on follicle development and the inter-estrous interval

Pseudopregnancy in pigs can be induced by the administration of a single dose of hCG at Day 12 of the estrous cycle. However, the resulting length of pseudopregnancy can be extremely variable. In this study, it was investigated whether time of hCG administration (day of the cycle) and degree of follicle growth after hCG administration were related to the length of inter-estrous interval (pseudopregnancy). In the first experiment, groups of cyclic gilts were given 1500 IU hCG at either Day 11 (D 11; n=14) or Day 12 (D12; n=14) after onset of estrus, or not treated (Control; n=13). Follicle development was assessed daily using transcutaneous ultrasonography. Follicle size in the Control gilts remained relatively constant between Days 11 and 17, whereas in the treated gilts, follicle size increased (P < 0.001) within 4 days (D11) and 2 days (D12) after treatment. The inter-estrous interval was increased (P < 0.01) in the hCG-treated gilts (34.7+/-6.3 and 37.6+/-11.1 days in the D11 and D12 gilts, respectively), compared to Controls (22.3+/-5.2 d). About two-thirds of the treated gilts returned to estrus between Days 32 and 39 after onset of first estrus. No relationships were found between follicle development after treatment and length of the inter-estrous interval. In a second experiment, 16 cyclic gilts were treated with 1500 IU hCG at Day 12 and Day 15 of the estrous cycle. Follicle development was assessed at Days 12, 15 and 18. At Day 18, average follicle size was 8.4+/-2.0 mm. The inter-estrous interval was 39.7+/-5.4 days and 14 of 16 gilts returned to estrus between Days 34 and 44 after onset of first estrus. Again, no relationships were found between follicle development after treatment and the duration of the inter-estrous interval. We conclude that, based on the duration of the inter-estrous interval, administration of hCG during the luteal phase induced a short pseudopregnancy. However, the induction of accessory corpora lutea or follicular luteinization cannot be discounted.     

Ovarian follicular activity and hormonal profile during estrous cycle in cows: the development of 2 versus 3 waves

Most estrous cycles in cows consist of 2 or 3 waves of follicular activity. Waves of ovarian follicular development comprise the growth of dominant follicles some of which become ovulatory and the others are anovulatory. Ovarian follicular activity in cows during estrous cycle was studied with a special reference to follicular waves and the circulating concentrations of estradiol and progesterone. Transrectal ultrasound examination was carried out during 14 interovulatory intervals in 7 cows. Ovarian follicular activity was recorded together with assessment of serum estradiol and progesterone concentrations. Three-wave versus two-wave interovulatory intervals was observed in 71.4% of cows. The 3-wave interovulatory intervals differed from 2-wave intervals in: 1) earlier emergence of the dominant follicles, 2) longer in length, and 3) shorter interval from emergence to ovulation. There was a progressive increase in follicular size and estradiol production during growth phase of each wave. A drop in estradiol concentration was observed during the static phase of dominant anovulatory follicles. The size of the ovulatory follicle was always greater and produced higher estradiol compared with the anovulatory follicle. In conclusion, there was a predominance of 3-wave follicular activity that was associated with an increase in length of interovulatory intervals. A dominant anovulatory follicle during its static phase may initiate the emergence of a subsequent wave. Follicular size and estradiol concentration may have an important role in controlling follicular development and in determining whether an estrous cycle will have 2 or 3-waves.     

The effect of a GnRH analogue on the dynamics of follicular development and synchronization of estrus in lactating cyclic dairy cows

A GnRH analogue was used to synchronize ovarian follicular development prior to an injection of PGF(2alpha) for the synchronization of estrus in lactating Holstein cows. On Day 12 (estrus = Day 0) of the experimental cycle, cows (n = 8) were injected with 8 mug Buserelin (BUS group), followed by 25 mg PGF(2alpha) 7 d later (Day 19). Control cows (n = 7) received PGF(2alpha) on Day 12 (PGF group). Ovaries were scanned daily via ultrasonography, and plasma progesterone and estradiol concentrations were determined. Sizes of all visible follicles were recorded. Follicles were classified as small (3 to 5 mm), medium (6 to 9 mm), or large (>/= 10 mm). Between Days 12 and 16 of the cycle, the number of large follicles in PGF cows remained unchanged (1.2), whereas in the BUS group, the number of large follicles decreased from 1.3 on Day 12 to 0.5 on Day 15. Only 4 of 7 PGF cows ovulated a second-wave dominant follicle. In the BUS group, 7 of 8 cows ovulated a GnRH analogue induced dominant follicle that was first identified on Day 15. During the follicular phase (last 5 d prior to estrus), plasma progesterone declined in association with CL regression in both groups, and estradiol concentrations increased, reaching higher (P<.0.05) preovulatory peak concentration in BUS cows than in PGF cows (14.0 +/- 1.0 vs 10.4 +/- 1.1 pg/ml). The number of medium-size follicles was smaller and the number of small-size follicles tended to be higher in BUS cows than in the PGF-treated group. On the day of estrus, the size of the ovulatory follicle (16.1 vs 13.3 mm) and the size difference between the ovulatory and second largest follicle (11.4 vs 6.2 mm) were both larger in BUS cows than in PGF-treated cows, suggesting a more potent dominance effect of the ovulatory follicle in the BUS cows. This study suggests that a GnRH analogue can alter follicular development prior to synchronization of estrus with an injection of PGF(2alpha) in lactating dairy cows.     

Ovarian function in Nelore (Bos taurus indicus) cows after post-ovulation hormonal treatments

Maternal recognition of pregnancy in the cow requires successful signaling by the conceptus to block luteolysis. Conceptus growth and function depend on an optimal uterine environment, regulated by luteal progesterone. The objective of this study was to test strategies to optimize luteal function, as well as prevent a dominant follicle from initiating luteolysis. Nelore (Bos taurus indicus) beef cows (n=40) were submitted to a GnRH/PGF(2alpha)/GnRH protocol. Cows that ovulated from a dominant ovarian follicle (ovulation=Day 0) were allocated to receive: no additional treatment (G(C); n=7); 3000IU of hCG on Day 5 (G(hCG); n=5); 5mg of estradiol-17beta on Day 12 (G(E2); n=6); or 3000IU of hCG on Day 5 and 5mg of estradiol-17beta on Day 12 (G(hCG/E2); n=5). Ultrasonographic imaging of the ovaries, assessment of plasma progesterone concentration, and detection of estrus were done daily from Day 5 to the day of subsequent ovulation. Treatment with hCG induced an accessory CL, increased CL volume, and plasma progesterone concentration throughout the luteal phase (P<0.01). Estradiol-17beta induced atresia and recruitment of a new wave of follicular growth; it eliminated a potentially estrogen-active, growing ovarian follicle within the critical period for maternal recognition of pregnancy, but it also hastened luteolysis (Days 16 or 17 vs. Days 18 or 19 in non-treated cows). In conclusion, the approaches tested enhanced luteal function (hCG) and altered ovarian follicular dynamics (estradiol-17beta), but were unable to extend the life-span of the CL in Nelore cows.     

Luteotrophic influence of early bovine embryos and the relationship between plasma progesterone concentrations and embryo survival

This study was carried out to evaluate the luteotrophic influence of early (before Day 7 as well as after Day 7; Day 0=estrus) bovine embryos and the relationship between plasma progesterone (P4) concentrations and embryo survival. Virgin Holstein dairy heifers (n=325) from a single herd were randomly allocated to be nonbred, bred by artificial insemination (AI) or by embryo transfer (ET). Bred heifers were either treated with 1500 IU human chorionic gonadotrophin (hCG) on Day 7 of the estrous cycle or received no hCG treatment. Plasma P4 concentrations on Days 0, 5, 7, 10, 13, 15, 17, 19 and 21 were similar in pregnant AI- and ET-bred heifers and, this was observed in both hCG-treated and untreated females. Nonbred, AI- and ET-bred nonpregnant heifers (both hCG-treated and untreated) presented similar plasma P4 concentrations. Plasma P4 concentrations of pregnant heifers significantly deviated from those of nonpregnant and nonbred heifers on Day 17. In hCG-treated heifers, plasma P4 concentrations and Day 28 pregnancy rate were significantly higher in females with an induced accessory corpus luteum (CL) than in those females without an induced accessory CL. Treatment with hCG, although inducing the formation of accessory CL and significantly increasing plasma P4 concentrations had no significant effect on Day 28 pregnancy rate. In conclusion, this study does not support the existence of any peripherally detectable luteotrophic influence from early embryos (Days 5-7). Plasma P4 was only significantly related to embryo survival on Day 17, the time of expected onset of luteolysis.     

Modification of follicular dynamics by exogenous FSH and progesterone, and the induction of ovulation using hCG in postpartum beef cows

Follicular growth and ovulation in response to FSH, progesterone and hCG were evaluated in postpartum beef cows. In Experiment 1, on Day 21 post partum, cows received an injection of either saline (control; n = 6), FSH (200 mg; n = 6), or a PRID (n = 5) for 10 d. Both FSH and PRID prolonged maintenance of a dominant follicle (15.5 +/- 1.16 and 14.4 +/- 1.29 d, respectively, vs 8.4 +/- 1.22 d in control; P < 0.01), and increased the maximum diameter of the dominant follicle (14.0 +/- 0.91 and 16.4 +/- 1.01 mm, respectively, vs 10.9 +/- 0.95 mm in control; P < 0.05). The PRID-maintained dominant follicle ovulated in 60% of cows, followed by normal estrous cycles (vs 0% in control; P = 0.01), whereas the dominant follicle ovulated in 33% of FSH-treated cows (P = 0.08). The PRID regimen shortened the interval to first ovulation preceding a normal cycle and continued cyclicity (44 +/- 4.1 vs 60 +/- 4.4 d in control; P = 0.02). In Experiment 2, on Day 21 post partum, cows received either saline (control), saline + PRID, or FSH + PRID (n = 16/group). Sixty hours after PRID withdrawal, cows received either saline or hCG (1,500 IU, n = 8/treatment). The FSH + PRID regimen increased the number of large (> 10 mm in diameter) follicles (3.6 +/- 0.43 vs 1.9 +/- 0.39 in control; P = 0.005). Both PRID and FSH + PRID prolonged maintenance of the largest follicle (11.0 +/- 0.82 and 11.2 +/- 0.91 d, respectively, vs 8.7 +/- 0.81 d in control; P < 0.05). The PRID-maintained dominant follicle ovulated in 50% of cows, followed by normal estrous cycles. The FSH + PRID-maintained largest follicle had become atretic at PRID withdrawal and was anovulatory. The FSH + PRID + hCG regimen increased the incidence of ovulation preceding a cycle of normal duration and continued cyclicity (100 vs 50% in PRID; P = 0.03), and reduced the interval to first ovulation preceding a cycle of normal duration and continued cyclicity (38 +/- 6.5 vs 58 +/- 6.3 d in control; P = 0.04). The area under the progesterone curve during the induced cycle was reduced after (PRID +/- FSH) + hCG than after PRID +/- FSH (P = 0.002). These results indicate that PRID alone or with FSH/hCG has the potential to modify the dominant follicle and initiate cyclicity in postpartum beef cows.     

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.     

Ability of induced corpora lutea to maintain pregnancy from the third month of gestation to term in cattle

The local relationship between the pregnant uterine horn and the CL during maternal recognition of pregnancy is well-documented. It continues beyond that time; pregnancies were maintained in lutectomized cows when CL were induced on the ovary ipsilateral, but not contralateral, to the uterine horn of pregnancy during Days 28-53. This study evaluated factors affecting maintenance of pregnancy by CL induced after Day 53, in lutectomized cows that had received exogenous progesterone from Day 29 to 15 days after induction of a CL. Twenty-four suckled beef cows were lutectomized on Day 29 of gestation; pregnancy was maintained with progesterone from two controlled internal drug releasing (CIDR) inserts, exchanged every 5 days. Beginning on Day 53, ovaries and viability of pregnancy were evaluated by ultrasonography every 5 days. When a follicle >or=10 mm in diameter was present ipsilateral to the fetus, each cow received 1,000 IU of hCG. Following induction of a CL (20 of 24), progesterone was reduced to a single CIDR for 5 days, then removed. Retention of pregnancy was confirmed by rectal palpation and calving. Cows with induced CL maintained pregnancy to term, including four with the CL contralateral to the fetus. Three cows failed to form normal CL by Day 98 and lost pregnancy after removal of exogenous progesterone. One cow that did not respond to hCG lost pregnancy during exogenous progesterone. In conclusion, CL induced after Day 53 maintained pregnancy to term, even when induced contralateral to the pregnant uterine horn.     

Prostaglandin F-2 alpha causes regression of an hCG-induced corpus luteum before day 5 of its lifespan in cattle

The experimental objective was to evaluate how a spontaneously formed corpus luteum (CL) differed in its response to prostaglandin (PG) F-2 alpha, given during the first 5 days after ovulation, from a CL induced during dioestrus with hCG. Sixteen Holstein heifers were used during each of 2 consecutive oestrous cycles. During the first cycle (sham cycle), heifers were given no PGF-2 alpha (control) or PGF-2 alpha (25 mg, i.m.) on Day 2, 4 or 6 (oestrus = Day 0). During the second cycle (hCG-treated cycle), heifers were given hCG (5000 i.u., i.m.) on Day 10, followed by no PGF-2 alpha (control) or PGF-2 alpha on Day 12, 14 or 16, corresponding to 2, 4 or 6 days after the ovulatory dose of hCG. A new ovulation was induced in 13 of 16 heifers given hCG on Day 10. Luteolysis did not occur immediately in heifers given PGF-2 alpha on Day 2 or 4 during the sham cycle, but concentration of progesterone in serum during the remainder of the cycle was lower in heifers given PGF-2 alpha on Day 4 than in sham controls or heifers given PGF-2 alpha on Day 2 (P less than 0.05). Luteolysis occurred immediately in heifers given PGF-2 alpha on Day 6 of the sham cycle or on Day 12, 14 or 16 of the hCG-treated cycle, with concentration of progesterone in serum decreasing to less than 1 ng/ml within 2 days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dominant follicle removal before superstimulation on follicular growth, ovulation and embryo production in Holstein cows

This study was to investigate whether removing the dominant follicle 48 h before superstimulation influences follicular growth, ovulation and embryo production in Holstein cows. After synchronization, ovaries were scanned to assess the presence of a dominant follicle by ultrasonography with a real-time linear scanning ultrasound system on Days 4, 6 and 8 of the estrus cycle (Day 0 = day of estrus). Twenty-six Holstein cows with a dominant follicle were divided into 2 groups in which the dominant follicle was either removed (DFR group, n=13) by ultrasound-guided follicular aspiration or left intact (control group, n=13) on Day 8 of the estrus cycle. Superovulation treatment was initiated on Day 10. All donors were superovulated with injections of porcine FSH (Folltropin) twice daily with constant doses (total: 400 mg) over 4 d. On the 6th and 7th injections of Folltropin, 30 mg and 15 mg of PGF2alpha (Lutalyse) were given. Donors were inseminated twice at 12 h and 24 h after the onset of estrus. Embryos were recovered on Day 6 or 7 after AI. During superstimulation, the number of follicles 2 to 5 mm (small), 6 to 9 mm (medium) and > or = 10 mm (large) was determined by ultrasonography on a daily basis. At embryo recovery, the number of corpora lutea (CL) was also determined by ultrasonography and blood samples were collected for analysis of progesterone concentration. Follicular growth during superstimulation was earlier in the DFR group than in the control group. The number of medium and large follicles was greater (P < 0.01) in the DFR group than in the control group on Days 1 to 2 and Days 3 to 4 of superstimulation, respectively. The numbers of CL (9.6+/-1.1 vs 6.1+/-0.9) and progesterone concentration (30.9+/-5.4 vs 18.6+/-3.5 ng/mL) were greater (P < 0.05) in the DFR group than in the control group, respectively. The numbers of total ova (7.7+/-1.3 vs 3.9+/-1.0) and transferable embryos (4.6+/-0.9 vs 2.3+/-0.8) were also greater (P < 0.05) in the DFR group than in the control group, respectively. It is concluded that the removal of the dominant follicle 48 h before superstimulation promoted follicular growth, and increased ovulation and embryo production in Holstein cows.     

Oxygen and steroid concentrations in preovulatory follicles of lactating dairy cows exposed to acute heat stress

Maternal heat stress reduces oocyte competence for fertilization and post-fertilization development, but the mechanism is unknown. The present experiment investigated two potential mechanisms: (1) reduced oxygen delivery to the preovulatory follicle (due to increased thermoregulatory vascular perfusion of skin and respiratory tract); (2) reduced follicular steroid synthesis. These hypotheses were tested by measuring the fractional concentration of oxygen and concentrations of estradiol-17beta and progesterone in follicular fluid of the preovulatory follicle of lactating Holstein cows. Estrous cycles were synchronized using GnRH on Day -9 and PGF(2alpha) on Day -2. On Day 0, all cows without a CL and with a large preovulatory follicle were assigned to control or heat stress treatments for 1d (beginning at 1030 h). Between 4 and 6 h after treatment (1430-1630 h), follicular fluid was aspirated by transvaginal puncture, and fractional oxygen concentration in follicular fluid of the dominant follicle was determined with a fluorometric fiber-optic oxygen sensor. There was no significant effect of heat stress on follicular fluid P(O2) or concentrations of estradiol-17beta or progesterone among cows that had follicular fluid steroid concentrations considered typical of a preovulatory follicle. Follicular oxygen concentration was 6.9+/-0.4% for control cows and 7.3+/-0.3% for heat-stressed cows. Oxygen concentration tended to be inversely correlated to follicular diameter (P=0.09). In conclusion, it was unlikely that reduced oocyte competence due to acute heat stress was caused by reductions in follicular concentrations of oxygen, estradiol-17beta, or progesterone.     

Effects of recombinant bovine somatotropin on luteinizing hormone and ovarian function in lactating dairy cows

Thirty-two lactating Holstein cows were assigned to 1 of 4 groups in a randomized block design using a 2 X 2 factorial arrangement of treatments. Recombinant bovine growth hormone (rbSt; 25 mg/day) or placebo was administered beginning at Day 35 or 70 postpartum. All cows began treatment approximately 3 days post-estrus. Blood samples were collected at least once daily for a 70-day period to determine the concentration of progesterone and the duration of the luteal and follicular phases. During estrous cycles 1 and 3, frequent blood samples were taken (every 10 min for 8 h) 24 and 60 h after the onset of luteal regression. These samples were assayed for luteinizing hormone (LH), and samples coincident with the second LH pulse detected were assayed for estradiol. Ultrasonography was used to determine the size of the largest ovarian follicle from Day 17 until ovulation in estrous cycles 1 and 3. Luteal life span, length of the follicular phase, and diameter of the largest follicle were not affected by treatment with rbSt. Administration of rbSt increased the concentration of progesterone in plasma during the first two luteal phases (p less than 0.01). Progesterone was elevated during the mid-luteal phase of cycle 3 in rbSt-treated cows that began treatment about Day 35 postpartum but not in cows that began treatment on Day 70 postpartum (Treatment X Stage X Day, p less than 0.01). During the first follicular phase studied, LH pulse frequency was higher (p = 0.06) in rbSt-treated cows than in cows receiving the placebo.(ABSTRACT TRUNCATED AT 250 WORDS)     

Standardization and validation of an induced ovulation model system in buffalo cows: Characterization of gene expression changes in the periovulatory follicle

In bovines characterization of biochemical and molecular determinants of the dominant follicle before and during different time intervals after gonadotrophin surge requires precise identification of the dominant follicle from a follicular wave. The objectives of the present study were to standardize an experimental model in buffalo cows for accurately identifying the dominant follicle of the first wave of follicular growth and characterize changes in follicular fluid hormone concentrations as well as expression patterns of various genes associated with the process of ovulation. From the day of estrus (day 0), animals were subjected to blood sampling and ultrasonography for monitoring circulating progesterone levels and follicular growth. On day 7 of the cycle, animals were administered a PGF(2alpha) analogue (Tiaprost Trometamol, 750 microg i.m.) followed by an injection of hCG (2000 IU i.m.) 36 h later. Circulating progesterone levels progressively increased from day 1 of the cycle to 2.26+/-0.17 ng/ml on day 7 of the cycle, but declined significantly after PGF(2alpha) injection. A progressive increase in the size of the dominant follicle was observed by ultrasonography. The follicular fluid estradiol and progesterone concentrations in the dominant follicle were 600+/-16.7 and 38+/-7.6 ng/ml, respectively, before hCG injection and the concentration of estradiol decreased to 125.8+/-25.26 ng/ml, but concentration of progesterone increased to 195+/-24.6 ng/ml, 24h post-hCG injection. Inh-alpha and Cyp19A1 expressions in granulosa cells were maximal in the dominant follicle and declined in response to hCG treatment. Progesterone receptor, oxytocin and cycloxygenase-2 expressions in granulosa cells, regarded as markers of ovulation, were maximal at 24h post-hCG. The expressions of genes belonging to the super family of proteases were also examined; Cathepsin L expression decreased, while ADAMTS 3 and 5 expressions increased 24h post-hCG treatment. The results of the current study indicate that sequential treatments of PGF(2alpha) and hCG during early estrous cycle in the buffalo cow leads to follicular growth that culminates in ovulation. The model system reported in the present study would be valuable for examining temporo-spatial changes in the periovulatory follicle immediately before and after the onset of gonadotrophin surge.     

Administration of human chorionic gonadotropin at embryo transfer induced ovulation of a first wave dominant follicle, and increased progesterone and transfer pregnancy rates

We hypothesized that administration of hCG to recipients at embryo transfer (ET) would induce accessory CL, increase serum progesterone concentrations, and reduce early embryonic loss (as measured by increased transfer pregnancy rates). At three locations, purebred and crossbred Angus, Simmental, and Hereford recipients (n = 719) were assigned alternately to receive i.m. 1,000 IU hCG or 1 mL saline (control) at ET. Fresh or frozen-thawed embryos were transferred to recipients with a palpable CL on Days 5.5 to 8.5 (median = Day 7) of the cycle (Locations 1 and 2), or on Day 7 after timed ovulation (Location 3). Pregnancy diagnoses (transrectal ultrasonography) were done 28 to 39 d (median = 35 d) and reconfirmed 58 to 77 d (median = 67 d) post-estrus. At Location 1 (n = 108), ovaries were examined at pregnancy diagnosis to enumerate CL. More (P < 0.001) pregnant hCG-treated cows (69.0%) had multiple CL than pregnant controls (0%). Serum progesterone (ng/mL) determined at Locations 1 and 2 (n = 471) at both pregnancy diagnoses in pregnant cows was greater (P ≤ 0.05) after hCG treatment than in controls (first: 8.1 ± 0.9 vs 6.1 ± 0.8; second: 8.8 ± 0.9 vs 6.6 ± 0.7), respectively. Unadjusted pregnancy rates at the first diagnosis were 61.8 and 53.9% for hCG and controls. At the second diagnosis, pregnancy rates were 58.6 and 51.3%, respectively. Treatment (P = 0.026), embryo type (P = 0.016), and BCS (P = 0.074) affected transfer pregnancy rates. Based on odds ratios, greater pregnancy rates occurred in recipients receiving hCG, a fresh embryo (66.3 vs 55.5%), and having BCS >5 (62.3 vs 55.3%). We concluded that giving hCG at ET increased incidence of accessory CL, serum progesterone in pregnant recipients, and transfer pregnancy rates. Furthermore, we inferred that increased progesterone resulting from hCG-induced ovulation reduced early embryonic losses after transfer of embryos to recipients.     

The ability of subordinate follicles of the second follicular wave to become dominant is lost by day 15 of the estrous cycle in cattle

Generally, unilateral ovariectomy before a critical period in the latter part of the estrous cycle induces a transitory increase in plasma FSH, which causes subordinate follicles to develop and maintain ovulation rates characteristic of the species. A limiting period for subordinate follicles to assume dominance and from which ovulation occurs has not been shown for cattle. Growth and/or regression of subordinate follicles were characterized following removal of the dominant follicle at different days of the luteal phase of the estrous cycle in cattle in this study. In the mid-luteal phase (Day 13 or 15), the ovary with the dominant follicle of the second wave was ablated via unilateral ovariectomy; the corpus luteum also was removed. In the late luteal phase (Day 17 or 19), the dominant follicle was ablated with an ultrasonically guided 20 gauge needle. When the dominant follicle was removed on Day 13, the largest subordinate follicle of the second wave of follicular development became dominant and ovulation occurred from this follicle in 4 of 4 animals. However, when the dominant follicle was removed on Day 15, 17 or 19, a new wave of follicular development was induced in 14 of 15 animals. Moreover, the recovered subordinate follicle of the second wave of follicular development had similar growth characteristics to naturally occurring dominant follicles. In conclusion, the subordinate follicle in the second follicular wave in cattle retained the ability to become dominant, but this ability was lost by Day 15 of the estrous cycle. However, cattle then were able to maintain ovulation by developing a new wave of follicular growth.     

Follicle-stimulating hormone plays a role in the induction of ovarian follicular cysts in hypophysectomized rats.

Unabated stimulation by low doses of LH-like activity produces ovarian follicular cysts in both progesterone-synchronized immature rats and pregnant rats. Serum FSH is maintained in both of these models at values similar to those observed on diestrus. To determine whether unabated stimulation by basal serum FSH affects the ability of LH-like activity to induce cystic ovaries, immature hypophysectomized (HYPOXD) rats were given either no hormone (control); 2 micrograms ovine FSH (oFSH) once daily for 14 days beginning on Day 27; 0.5 IU hCG twice daily for 13 days beginning on Day 28 of age; or both oFSH and hCG (FSH + hCG) beginning on Day 27 and Day 28, respectively. By the end of the in vivo treatments (Day 40 of age), the largest follicles in the ovaries of control and hCG-treated HYPOXD rats were at the preantral stage of development, whereas the largest follicles present in ovaries from FSH-treated animals were atretic and at the small antral stage of development. In contrast, ovaries from rats treated with FSH + hCG displayed large follicular cysts by Day 37 of age. Of the serum steroids analyzed, only estradiol and androstenedione concentrations for animals treated with FSH + hCG were consistently elevated above values observed for control HYPOXD rats. Serum testosterone and dihydrotestosterone values were similar for hCG-treated and control HYPOXD rats throughout the in vivo treatments. In contrast, these steroids were elevated between Days 3 and 5 of FSH treatment (+/- hCG treatment). Serum progesterone and estrone values for all in vivo gonadotropin treatment groups were similar to those of controls. Serum insulin concentrations were not affected by any in vivo treatment. Incubates of follicles/cysts from FSH + hCG-treated HYPOXD rats contained more progesterone, androstenedione, and estradiol than incubates of follicles from any other in vivo treatment group. Follicles from all in vivo treatment groups responded to 8-bromo cAMP (cAMP) with increased in vitro progesterone accumulation. However, only follicles from FSH-treated and FSH + hCG-treated rats responded to cAMP with increased androstenedione and estradiol accumulation in vitro. Inclusion of 400 ng of either androstenedione or testosterone in the incubation medium enhanced progesterone accumulation in follicular incubates from control, hCG-treated, and FSH-treated HYPOXD rats, but did not enhance progesterone accumulation in follicular incubates from FSH + hCG-treated animals. Both androstenedione and estradiol production increased markedly under these conditions for follicles from all in vivo treatment groups.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of buserelin injection and deslorelin (GnRH-agonist) implants on plasma progesterone, LH, accessory CL formation, follicle and corpus luteum dynamics in Holstein cows

The influence of Buserelin injection and Deslorelin (a GnRH analogue) implants administered on Day 5 of the estrous cycle on plasma concentrations of LH and progesterone (P4), accessory CL formation, and follicle and CL dynamics was examined in nonlactating Holstein cows. On Day 5 (Day 1 = ovulation) following a synchronized estrus, 24 cows were assigned randomly (n = 4 per group) to receive 2 mL saline, i.m. (control), 8 micrograms, i.m. Buserelin or a subcutaneous Deslorelin (DES) implant in concentrations of 75 micrograms, 150 micrograms, 700 micrograms or 2100 micrograms. Blood samples were collected (for LH assay) at 30-min intervals for 2 h before and 12 h after GnRH-treatment from cows assigned to Buserelin, DES-700 micrograms and DES-2100 micrograms treatments and thereafter at 4-h intervals for 48 h. Beginning 24 h after treatment, ovaries were examined by ultrasound at 2-h intervals until ovulation was confirmed. Thereafter, ultrasonography and blood sampling (for P4 assay) was performed daily until a spontaneous ovulation before Day 45. A greater release of LH occurred in response to Deslorelin implants than to Buserelin injection (P < 0.01). Basal levels of LH between 12 and 48 h were higher in DES-700 micrograms group than in DES-2100 micrograms and Buserelin (P < 0.05). The first wave dominant follicle ovulated in all cows following GnRH treatment. Days to CL regression did not differ between treatments, but return to estrus was delayed (44.2 vs 27.2 d; P < 0.01) in cows of DES-2100 micrograms group. All GnRH treatments elevated plasma P4 concentrations, and the highest P4 responses were observed in the DES-700 micrograms and DES-2100 micrograms groups. The second follicular wave emerged earlier in GnRH-treated than in control cows (9.9 vs 12.8 d; P < 0.01). However, emergence of the third dominant follicle was delayed in cows of DES-2100 micrograms treatment (37.0 d) compared with DES-700 micrograms (22.2 d), Buserelin (17.8 d) or control (19.0 d). In conclusion, Deslorelin implants of 700 micrograms increased plasma P4 and LH concentrations and slightly delayed the emergence of the third dominant follicle. On the contrary, Deslorelin implants of 2100 micrograms drastically altered the P4 profiles and follicle dynamics.     

Fertility of dairy cattle treated with human chorionic gonadotropin (hCG) to stimulate progesterone secretion

Two experiments were conducted to determine if progesterone secretion and fertility would be affected by administration of human chorionic gonadotropin (hCG) before or after the first insemination. In Experiment 1, 48 Holstein heifers received 1000 IU of hCG or 1 ml of saline on Days 2, 3, and 4 of an estrous cycle. They were inseminated at the subsequent estrus. In Experiment 2, 110 Jersey and 105 Holstein cows received a single injection of 5000 IU of hCG or 5 ml of saline on Day 3 after estrus. These cows were first inseminated either at the estrus immediately preceding treatment or at the subsequent estrus. In both experiments, blood samples for determination of progesterone were collected thrice weekly for 3 to 4 wk following treatment. In Experiment 1, progesterone concentrations during mid-cycle were higher in hCG-treated heifers than in saline-treated controls. Treatment with hCG resulted in an 11% increase in the first service conception rate (P < 0.48). In Experiment 2, hCG-treated cows displayed higher progesterone secretion during mid-cycle than saline-treated herdmates. The conception rate of cows inseminated prior to hCG-treatment was not affected by treatment, but cows inseminated after treatment had a marginally lower fertility rate. The conception rate of cows receiving a repeat insemination following hCG treatment was higher than for the controls. We conclude that treatment with hCG did not improve the conception rate at the first insemination, but it may be beneficial for cows that require a repeat service.     

Effect of eCG on early resumption of ovarian activity in postpartum dairy cows

The purpose of the present study was to hasten the resumption of ovarian activity early postpartum in lactating dairy cows, using equine chorionic gonadotropin (eCG), to enhance follicular growth, followed by hCG, to induce ovulation. Primiparous Holstein dairy cows (n=21) were assigned equally into eCG, eCG-hCG and Control groups. Cows in the eCG and eCG-hCG groups received an i.m. injection of eCG (500 IU Folligon?) on Day 6 postpartum. Cows in the eCG-hCG group were also given an i.m. injection of hCG (500 IU Chorulon?), once dominant follicle reached the diameter of 13-16 mm following eCG injection. Cows in Control group did not receive any treatment. Daily blood sampling and ultrasound examination were conducted, starting at Day 6 postpartum until confirming the third ovulation. Follicles ≥10 mm in diameter were detected on Day 11.5±1.48, 10.1±0.52 and 11.1±1.36 after calving in Control, eCG and eCG-hCG groups, respectively (P>0.05). The first wave dominant follicle ovulated in 71.4% of cows treated with eCG and eCG-hCG. In contrast, none of the first wave dominant follicles ovulated in Control cows. By Day 20 postpartum, all cows in eCG group, 6/7 cows in eCG-hCG group and none of the cows in Control group ovulated (P<0.05). Short estrous cycles (≤16 days) were detected in 2/7, 1/7 and 6/7 cows in eCG, eCG-hCG and control groups, respectively (P<0.05). In conclusion, injection of eCG on Day 6 postpartum could assist the early resumption of ovarian activity by enhancing ovarian follicle growth and early ovulation in postpartum cows. In this context, subsequent hCG injection may not provide any more beneficial effect.