Treatment with progesterone and 17 beta-oestradiol to induce emergence of a newly-recruited dominant ovulatory follicle during oestrus synchronisation with long-term use of norgestomet in Brahman heifers

The aim of this study was to determine the effect on ovarian follicular growth and atresia, of acute treatment with either 100 mg of progesterone (n = 10), 200 mg of progesterone (n = 10), 10 mg of oestradiol + 100 mg of progesterone (n = 10), 10 mg of oestradiol (n = 10) or no treatment (n = 10), given on Day 10 of a 17-day treatment with a norgestomet implant in randomly cycling Bos indicus heifers. The fate of the dominant follicle on Day 10, emergence of the new cohort of follicles and the intervals from implant removal to ovulation were recorded by ultrasonography. Plasma concentrations of Luteinizing hormone (LH), progesterone and oestradiol were determined during the time when the norgestomet implant was in place. All treatments resulted in the emergence of a new cohort of follicles within 5 days of administration. The day of emergence of the ovulatory follicle tended to be delayed after treatment with 100 mg of progesterone (2.7 +/- 0.3 days after treatment), 200 mg of progesterone (3.7 +/- 0.5 days after treatment), 10 mg of oestradiol + 100 mg of progesterone (4.4 +/- 0.2 days after treatment) and 10 mg of oestradiol (4.6 +/- 0.4 days after treatment) compared to control heifers (1.4 +/- 1.4 days after time of treatment). The mean interval from implant removal to onset of oestrus was significantly shorter after treatment with 100 mg of progesterone (38.4 +/- 2.6 h) than after treatment with 200 mg of progesterone (61.5 +/- 3.9 h) but otherwise, the mean interval from implant removal to onset of oestrus did not differ. Oestrus synchrony, measured by the sample standard deviation of oestrus onset, was tighter in all treatment groups compared to untreated control heifers. The mean interval from implant removal to ovulation did not differ significantly between groups. The synchrony of ovulation, measured by the sample standard deviation of the interval from implant removal to ovulation, was significantly tighter after treatment with 100 mg of progesterone, 200 mg of progesterone and 10 mg of oestradiol compared to control heifers. Treatment with 10 mg of oestradiol resulted in ovulation in seven of 10 heifers before implant removal, three of which failed to ovulate after implant removal. Progesterone administered on Day 10 lowered plasma LH concentrations (P < 0.05), whereas treatment with oestradiol caused a surge of LH and ovulation. Progesterone administered with oestradiol prevented the LH surge. A combination treatment of oestradiol and progesterone given on Day 10 of a 17-day norgestomet treatment in a range of follicular states resulted in the consistent emergence of a new cohort of follicles which included the eventual ovulatory follicle.     

Fate of the dominant follicle, embryonal survival, and pregnancy rates in dairy cattle treated with prostaglandin F2 alpha and progestins in the absence or presence of a functional corpus luteum

Our objective was to examine the role of progestin type on serum concentrations of progesterone (p4) and estradiol-17 beta (E2), ovarian follicular dynamics, and fertility in cattle in the presence or absence of a corpus luteum (CL) in an estrus synchronization scheme using progestin and PGF2 alpha. In Exp. 1, 325 cows and heifers were given one injection of PGF2 alpha (d 0) and then assigned randomly within parity to five treatments: to receive a second PGF2 alpha injection 14 d later (control); to receive norgestomet (NORG) for 7 d beginning on d 8, with a second PGF2 alpha injection given either 1 d (NORG + no CL) or 6 d (NORG + CL) after insertion; or to receive a P4-releasing intravaginal device (PRID) in lieu of norgestomet at comparable times. Presence or absence of a CL was based on concentrations of serum P4 on d 14. Pregnancy rates after insemination were greater (P < .01) with luteal treatments than with nonluteal treatments. Embryonal survival between two stages of pregnancy was 87.6%. In Exp. 2, ovarian structures in 50 cows were examined daily using ultrasonography and the same five treatments. Diameter of the ovulatory follicle was greater (P < .05) with the nonluteal treatments (NORG and PRID + no CL) than with the control and luteal treatments (PRID and NORG + CL). Replacement of the dominant follicle during progestin treatment was altered by treatment (luteal status) and stage of the estrous cycle. Fertility was not enhanced by exogenous progestins when a CL was present. In the absence of a CL, progestin (P4 less than NORG at the doses used) reduced fertility by increasing E2 and the diameter of the ovulatory follicle and decreasing turnover of dominant follicles.     

Effects of melengestrol acetate on onset of puberty, follicular growth, and patterns of luteinizing hormone secretion in beef heifers

Our objective was to test the hypothesis that short-term (8 days) treatment of prepubertal heifers with melengestrol acetate (MGA) and subsequent steroid withdrawal would stimulate LH secretion and follicular growth. Angus heifers were divided randomly into two groups; MGA-treated (n = 8) or control (CON; n = 9). Puberty was determined by monitoring circulating concentrations of progesterone and ovarian morphology during a 14-day period following MGA withdrawal. LH secretory patterns were assessed upon initiation of MGA (Day 0), during MGA (Day 7), and 1 day after withdrawal of MGA (Day 9). All MGA-treated heifers, versus four CON heifers, exhibited corpora lutea and luteal phase concentrations of progesterone within 10 days after treatment (p = 0.01). Mean LH and LH pulse frequency increased (p = 0.005 and 0.0001, respectively) between Days 0 and 9 in MGA-treated heifers. In CON heifers, mean LH concentrations and pulse frequencies did not change. During the same period, diameter of the largest follicle increased in MGA-treated animals (p = 0.003) but did not change in the CON heifers. On the basis of these results, we suggest that MGA withdrawal enhances onset of puberty by stimulating pulsatile LH secretion that accelerates follicle growth to the preovulatory stage.     

Norgestomet implants synchronize estrus and enhance fertility in beef heifers subsequent to a timed artificial insemination

Three trials involving 128 heifers were conducted to determine whether norgestomet implants administered during the mid- and late luteal phases after breeding could be used to synchronize a second estrus in nonpregnant, inseminated heifers without adversely affecting pregnancy in pregnant heifers. All heifers were initially synchronized with Syncro-Mate B and artificially inseminated 47 h after implant removal. On d 9 (Trial 1) or d 12 (Trial 2) after the timed AI, the heifers were randomly assigned to treated or control groups. Treated heifers received two silicone implants containing 10.0 mg of norgestomet each (Trial 1) or one silicone implant containing 3.6 mg of norgestomet (Trial 2). Silicone implants were removed on d 21 after the initial AI. In Trial 1, the calving rate to the initial AI of the control heifers was 35 vs 55% for the norgestomet-implanted heifers (P > .05). In Trial 2 the calving rate to the initial AI of the control heifers was 9 vs 45% in the treated heifers (P < .01). At the return estrus 52% of the control heifers returned to estrus within a 3-d period, whereas 93% of the norgestomet-treated heifers returned to estrus within a 3-d period (P < .01). Norgestomet treatment had no effect on serum progesterone concentrations of the pregnant heifers on d 21 after the initial AI. In Trial 3, both control and treated heifers were administered silicone implants containing 3.6 mg of norgestomet on d 12; additionally, the treated heifers received an injection containing 3.0 mg of norgestomet and 5.0 mg of estradiol valerate. Norgestomet implants were removed on d 21.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selection, dominance and atresia of follicles during the oestrous cycle of heifers

This study examined the correlation between measurement of follicle growth by ultrasound, and measurement of intrafollicular ratios of oestradiol and progesterone concentrations and the serum concentrations of FSH during selection, dominance and atresia or ovulation of dominant follicles in heifers. Heifers were ovariectomized on days 0 (before LH surge), 1 (after LH surge, preovulation), 1 (postovulation), 3, 6 and 12 of the oestrous cycle. Blood samples were collected at 4-6 h intervals. After ovariectomy all follicles > or = 5 mm were measured and follicular fluid was aspirated. Follicles were classified by size according to ultrasound (F1, largest; F2, second largest; F3, all remaining follicles > or = 5 mm) and by the ratio of oestradiol:progesterone concentrations. During the follicular phase, a single dominant oestrogen-active follicle increased in diameter while serum concentrations of LH increased and FSH decreased (P < 0.05). On day 1 (after LH surge, preovulation), serum LH and FSH decreased to pre-surge concentrations (P < 0.0001), while follicle size and intrafollicular progesterone concentration increased and oestradiol concentration decreased (P < 0.05). A dominant nonovulatory follicle, classified as oestrogen-active on days 1, 3 and 6 and oestrogen-inactive on day 12, increased in size from day 1 to day 7 and lost dominance during days 10-12, coincident with the growth of multiple oestrogen-active follicles. The serum FSH concentration increased transiently (P < 0.05) before each new wave of dominant follicular growth. The overall correlation of ultrasound measurements of follicle diameter with measures of follicle size after ovariectomy was high.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics of prolonged dominant versus control follicles: follicle cell numbers, steroidogenic capabilities, and messenger ribonucleic acid for steroidogenic enzymes

Cattle with low (subluteal) levels of plasma progesterone develop a persistent dominant follicle; plasma estradiol and LH pulse frequency are elevated, and fertility subsequent to the ovulation of a prolonged dominant follicle is compromised. The hypotheses were 1) that prolonged dominant follicles produce more estradiol because they have theca and granulosa cells with an enhanced capacity to produce androgen and estradiol, respectively, and 2) that these changes in steroidogenic capacity are paralleled by concomitant changes in mRNA for the appropriate steroidogenic enzymes. Prolonged dominant follicles were induced by treating Holstein heifers with exogenous progesterone via an intravaginal controlled internal drug-release device (CIDR) from Day 14 to 28 of the cycle. Prolonged dominant follicles were collected just before (CIDRb, Day 28; n=4) or 24 h after (CIDRa, Day 29; n=4) CIDR removal, and their steroidogenic capacity was compared to that of growing, control dominant follicles obtained just before (CONTb, n=4) or 24 h after (CONTa, n=4) a luteolytic injection of prostaglandin F2alpha during the late luteal phase. After natural luteolysis, CIDR heifers maintained subluteal concentrations of progesterone (1-2 ng/ml) and had higher estradiol and LH pulse frequency than control heifers, as expected. In CIDR heifers, prolonged dominant follicles were present on the ovary for a longer time, reached a larger diameter, and had more granulosa cells and a larger mass of theca than dominant follicles from control heifers (p < 0.05). Concentrations of steroids in follicular fluid, estradiol secretion by granulosa cells in vitro, and levels of mRNA for steroidogenic enzymes in theca and granulosa cells provided no evidence for greater capacity of theca and granulosa cells of CIDR follicles to produce androgen and estradiol. In fact, follicular fluid estradiol and mRNA for P450 aromatase were higher after luteolysis than before in control animals (p < 0.05) but not after CIDR removal in treated animals. Therefore, the data do not support the hypotheses. Rather it is suggested that prolonged dominant follicles produce more estradiol because they have more granulosa cells and a larger mass of theca than control dominant follicles. In contrast, progesterone concentrations in the follicular fluid increased in CIDRa relative to CIDRb follicles (p < 0.05), a change that did not occur in control follicles; and granulosa cells from CIDRa follicles secreted more progesterone than granulosa cells from any other group. The increased capacity of CIDRa follicles to secrete progesterone suggests premature luteinization, which could contribute to decreased fertility in cattle that ovulate a prolonged dominant follicle.     

Luteolysis during two stages of the estrous cycle: subsequent endocrine profiles associated with radiotelemetrically detected estrus in heifers

Our objective was to correlate hormonal changes with the timing and onset of estrus in heifers before and after luteolysis was induced with PGF2 alpha at two stages of the estrous cycle: d 6 to 9 (early; n = 10) or d 14 to 15 (late; n = 10). Blood was collected at intervals of 2 or 12 h to quantify serum concentrations of progesterone, estradiol-17 beta, and LH while heifers were observed visually for estrus and monitored for standing activity by pressure-sensitive, radiotelemetric devices. Although the concentrations of estradiol-17 beta that were associated with the putative appearance of the first dominant follicle declined before luteolysis was induced early in the cycle, some heifers that were given PGF2 alpha were in estrus as early as 35 h. Compared with heifers treated late in the estrous cycle, heifers that were treated early in the cycle produced less progesterone before PGF2 alpha treatment and had greater peak concentrations of estradiol-17 beta at estrus. In addition, heifers that were treated early in the cycle had shorter intervals from PGF2 alpha treatment to estrus, to peak estradiol-17 beta, and to peak LH and to initiation of estrus after the peak in estradiol-17 beta than did heifers treated later in the cycle. The increase in estradiol-17 beta associated with the putative first-wave follicle of the subsequent cycle and the duration of that cycle in early cycle heifers was less than after late cycle luteolysis. Results indicated that greater concentrations of estradiol-17 beta during estrus may be related to the durations of previous cycles and less progesterone exposure before luteolysis. The onset of estrus corresponded closely to, but preceded, the preovulatory LH surge by approximately 3 h.     

Norgestomet implants prevent pregnancy in beef heifers on pasture

The efficacy of erodible norgestomet implants for preventing pregnancy in postpubertal heifers was evaluated in two experiments at five locations each. Heifers (n = 896) within each study location were stratified by weight and allotted randomly to receive an ear implant containing either 0, 24, 36, or 48 mg of norgestomet (d 0). Heifers were exposed to fertile bulls immediately after implantation for 75 d (d 0 to 74) in Exp. 1 (n = 476) or for 80 d (d 75 to 154) in Exp. 2 (n = 420). Weights were recorded on d 0 and 74 (Exp. 1 and 2) and d 154 (Exp. 2). Each heifer was palpated rectally for pregnancy at the end of each experiment. Pregnancy rates were higher (P < .01) for control heifers (0 mg implant) than for heifers that received 24, 36, or 48 mg of norgestomet. In Exp. 1, pregnancy rates were 96, 29, 6, and 4% for heifers that received 0, 24, 36, and 48 mg implants of norgestomet, respectively. In Exp. 2, pregnancy rates were 85, 36, 19, and 9% for heifers that received 0, 24, 36, and 48 mg implants of norgestomet, respectively. Estrous activity during the first 3 wk of bull exposure was reduced (P < .05) among heifers that received norgestomet implants compared to control heifers but was not completely abolished at any dosage in Exp. 1. During the first 75 d of Exp. 1 and 2, heifers treated with 36 or 48 mg norgestomet implants gained weight faster (P < .05) than control heifers. Combined across both experiments, ADG during the first 74 d were .53, .56, .59, and .60 kg/d for heifers treated with 0, 24, 36, and 48 mg implants of norgestomet, respectively. These data indicate that norgestomet implants increased rate of weight gain, reduced estrous activity, and reduced the occurrence of pregnancy in heifers on pasture.     

Timing of in vivo maturation of equine preovulatory oocytes and competence for in vitro maturation of immature oocytes collected simultaneously

The objects of this study were to monitor the development of the cumulus complex and nuclear maturation in oocytes recovered from preovulatory follicles following treatment to induce ovulation and to investigate the in vitro maturation competence of oocytes recovered from smaller nonpreovulatory follicles of varying size. All follicles > or =5 mm in pony mares were individually punctured at 0, 6, 12, 24 and 35 h after an injection of LH to induce ovulation. The recovery rates of oocytes were 64% from 55 preovulatory follicles, 22% from 32 subordinate follicles and 52% from 227 small follicles. Cumulus expansion of the preovulatory oocytes occurred at 12 h post LH treatment while the metaphase I and II components of nuclear maturation were not completed until 24 and 35 h post LH respectively. For nonpreovulatory follicles, the frequency of atresia and oocyte competence for in vitro nuclear maturation both increased with increasing follicular size.     

Decline in serum follicle-stimulating hormone concentrations alters key intrafollicular growth factors involved in selection of the dominant follicle in heifers

Declining FSH after a transient rise coincides with selection of a dominant follicle (DF) and atresia of the remaining cohort follicles (subordinates) in cattle. The objectives of this study were to determine 1) whether intrafollicular amounts of inhibins, activin-A, insulin-like growth factor I (IGF-I), and IGF-I-binding proteins (IGFBP) are altered during selection of the first-wave dominant follicle (DF1) and 2) whether these biochemical markers are FSH dependent. Beef heifers received six or eight 6-h injections of saline (controls) or eight 6-h injections of recombinant bovine FSH (1 mg/injection) at 38 to 42 h after estrus (Day 0). Daily ultrasound scanning was used to define selection of DF1. Controls (n = 6 per group) were ovariectomized 1) on Day 3 of the estrous cycle before DF1 selection (preselection follicles) and 2) after DF1 selection on Day 4.8 +/- 0.5. In controls, FSH declined between Days 2 and 3 and selection of DF1 occurred between Days 3 and 5. During this interval, intrafollicular estradiol concentrations increased > 5-fold in DF1, yet declined 4-fold in subordinates (p < 0.05). In DF1, total IGF-I increased 1.3-fold (p < 0.05), whereas the amounts of the 40- to 47-kDa and the 35-kDa IGFBP (ligand hybridization) decreased 2.4- and 2.5-fold, respectively (p < 0.05), compared to values in preselection follicles on Day 3; total dimeric inhibin-A decreased 1.8-fold (p < 0.05). In contrast, amounts of the 30- to 32-kDa IGFBP increased 12.4-fold (p < 0.05) in subordinates on Day 4.8 compared with preselection follicles on Day 3, while the amount of inhibins > 34 kDa decreased 4- to 9-fold (p < 0.05). In FSH-treated heifers, both selection of DF1 and atresia of subordinates were delayed by 2.2 days. Preselection follicles recovered on Day 4.9 +/- 0.1 from FSH-treated heifers were similar (p > 0.05) in almost all biochemical parameters to preselection follicles from control heifers; however, they differed markedly from both DF1 and subordinate follicles recovered from control heifers on Day 4.8 +/- 0.5. In conclusion, the decline in FSH beginning after Day 2 of the heifer estrous cycle causes differential alterations in FSH-dependent growth factors and hormones within the cohort of preselection follicles, simultaneously inducing growth and enhanced estradiol-producing capacity of the DF and atresia of subordinate follicles.     

Follicle size-dependent induction of prostaglandin G/H synthase-2 during superovulation in cattle

Under physiological conditions, prostaglandin G/H synthase-2 (PGHS-2) is induced in bovine preovulatory follicles by the endogenous surge of gonadotropins. To characterize the pattern of follicular PGHS-2 expression during superovulation in cattle, heifers were treated with exogenous FSH and ovulation was induced with hCG. Animals were ovariectomized 0, 18, and 24 h post-hCG, and extracts of follicles > or = 6 mm were analyzed by Western blotting. Follicular fluid concentrations of prostaglandin (PG) E2, PGF2alpha, progesterone, and estradiol-17beta were determined by RIAs, and the morphology of the cumulus oocyte complex was examined. Results showed that PGHS-2 protein was absent in all follicles isolated at 0 h post-hCG (n = 119) and in small follicles (6 to < 8 mm) isolated between 0 and 24 h post-hCG (n = 27 follicles). In contrast, 12.3% of medium (8 to < 10 mm) and 43.7% of large (> or = 10 mm) follicles were PGHS-2-positive at 18 h post-hCG, and these percentages rose at 24 h to 45.9% and 91.0% in medium and large follicles, respectively (p < 0.05). Follicular fluid concentrations of PGE2 and PGF2alpha were low in follicles isolated at 0 h and increased only in PGHS-2-positive follicles isolated 24 h post-hCG (p < 0.05). Concentrations of progesterone and estradiol-17beta at 0 h were 28.2 +/- 5.8 and 291.8 +/- 13.0 ng/ml, respectively, and a shift from estradiol-17beta to progesterone dominance (luteinization) occurred at 24 h post-hCG only in PGHS-2-positive follicles. Also, expansion of the cumulus oocyte complex was detected at 24 h post-hCG only in PGHS-2-positive follicles. Lack of PGHS-2 induction in follicles of ovulatory size (> 8 mm) was associated with an apparent failure to respond to hCG (absence of luteinization and cumulus expansion). Collectively, these results demonstrate the presence of a time- and follicle size-dependent induction of PGHS-2 in bovine follicles during superovulatory treatment and suggest that PGHS-2 expression can be used as a marker for follicular commitment to ovulation during ovarian hyperstimulation protocols.     

Endocrine activity of induced persistent follicles in sheep

This experiment was designed to examine gonadotropin requirements for the induction and maintenance of persistent ovarian follicles in sheep. At the time of prostaglandin (PG) treatment on the tenth day of an induced estrous cycle, 8 ewes (with one ovary autotransplanted to the neck) received an injection of a GnRH antagonist ([Ac-d-Nal1, d-4-C-1-Phe2, d-Trp3, d-Arg6, d-Ala10] GnRH.HOAc; 50 microg/kg s.c.), and continuous hourly injections of exogenous ovine LH (equivalent to 1.25 microg NIH-oLH-S26) began simultaneously with this first antagonist injection (time zero). Antagonist was given three times at 3-day intervals. On Day 6, LH injections were stopped in 4 ewes (group 2) but continued in 4 other ewes (group 1) until the end of the 10-day experiment. Ovarian vein blood was sampled daily every 15 min for a 2-h period around two injections of exogenous LH (this sampling included group 2 after Day 6). Additional jugular and ovarian vein blood samples were collected every 8 h throughout the experiment. Daily ultrasound examination revealed the presence of at least one large follicle (range 4- to 7.5-mm diameter) from Day 3 to Day 10 in all ewes, but no new growing follicles (> 2 mm) were detected for at least 6 days. After Day 2, secretion of estradiol was positively correlated with that of inhibin (r = 0.83, p < 0.001), whereas FSH concentrations were inversely related to inhibin (r = -0.71, p < 0.001) and estradiol (r = -0.81, p < 0.001). In the absence of an LH surge, estradiol and androstenedione secretion (range 5-20 ng steroid/min) was maintained from Day 1 to Day 8 in group 1; but in group 2, secretion decreased abruptly when the LH injections stopped. Thus, continued low-amplitude, high-frequency LH pulses were required to maintain estradiol secretion when concentrations of FSH were < 0.5 ng/ml. However, estradiol and androstenedione secretion decreased (and FSH concentrations increased) between Days 8 and 10 in the ewes that received continued LH injections (group 1), showing that atresia in estrogenic follicles was not due to a lack of gonadotropin availability but to changes within the follicle. For the first 3 days after administration of PG, androstenedione secretion was greater than that of estradiol (p < 0.05), but from Day 4 to 6 the secretion rates were similar (p < 0.1), suggesting that aromatase may be limiting in the first 3 days whereas provision of androstenedione precursors was altered as the follicle persisted. In group 2 on Days 7 and 8 when hourly LH injections had stopped, neither androstenedione nor estradiol secretion increased after one test injection of LH; in contrast, androstenedione but not estradiol secretion increased after a second LH test injection 1 h later, suggesting that secretion of androstenedione is controlled by repeated exposure to LH. In conclusion, persistent estrogenic follicles were produced in the follicular phase in sheep by treatment with a combination of GnRH antagonist and hourly pulses of LH. Secretion of estradiol was dependent on continued hourly LH pulses of approximately 1 ng/ml and the follicles remained estrogenic for 8 days, after which time the ability to secrete estradiol and androstenedione declined even with continued LH injections.     

Acute infectious purpura fulminans: pathogenesis and medical management

The aims of this study were to determine: (1) if short-term treatment of Bos indicus heifers with progesterone (P4) while implanted with a s.c. norgestomet implant for 17 days would influence the time interval to oestrus and increase fertility of the synchronised oestrus, and (2) whether the response to treatment with P4 would differ between heifers treated with a norgestomet implant for 17 vs. 11 days when short-term treatment with P4 is applied 3 days prior to implant removal. B. indicus heifers at two separate sites (A and B) were allocated to three groups at each site. Heifers in two groups (NG and NGP4 groups) were given a single s.c. norgestomet implant on the first day of treatment (day 0) while heifers in a third group (NGP4PG group) were implanted on day 6. A single P4 releasing Controlled Internal Drug Release device (CIDR) was inserted on day 14 in heifers in the NGP4 and NGP4PG groups and was removed 23.5 +/- 0.07 h later (day 15). Heifers in the NGP4PG group were administered an analogue of prostaglandin F2 alpha (PGF2 alpha) at the time of CIDR removal to regress corpora lutea. Implants were removed from all heifers on the same day (day 17) and a 400 IU of equine chorionic gonadotrophin (ECG) was administered s.c. Animals were artificially inseminated 11.1 +/- 0.17 h after detection of oestrus, using frozen semen from one bull at site A and one of five bulls at site B. Inseminations were carried out by one of two technicians. Treatment with P4 delayed oestrus and reduced the synchrony of oestrus at site A (hours to oestrus +/- SD: NG group, 39.0 +/- 13.7; NGP4 group, 66.3 +/- 24.4; NGP4PG group, 58.9 +/- 20.5 h; P < 0.05) but not at site B (41.4 +/- 15.2, 42.5 +/- 10.1, 45.4 +/- 10.3 h; P > 0.05). Pregnancy rates 6 weeks after insemination were found to be significantly associated with bull (P < 0.001), treatment group (P = 0.013) and insemination technician (P = 0.033). Pregnancy rates were greater in the heifers in the NGP4 group than heifers in the NG group [50.3% (78/155) vs. 36.4% (60/165); odds ratio = 1.83, 95% CI = 1.14 to 2.96] and similar between heifers in the NGP4 and NGP4PG groups [50.3% (78/155) vs. 51.1% (63/117); odds ratio = 1.06, 95% CI = 0.67 to 1.69]. It was concluded that acute treatment with P4 can improve pregnancy rates in B. indicus heifers treated for 17 days with norgestomet implants. Reducing the duration of norgestomet treatment to 11 days and administration of PGF2 alpha at the time of ending treatment with a CIDR device resulted in no differences in fertility, mean intervals to oestrus or synchrony of oestrus.     

Changes in ovarian function and gonadotropin secretion preceding the onset of nutritionally induced anestrus in Bos indicus heifers

The aim of this study was to monitor endocrine and ovarian changes immediately preceding the onset of nutritionally induced anestrus. Daily blood samples were obtained from 14 postpubertal heifers for one estrous cycle (initial estrous cycle). Subsequently, heifers designated "restricted" were given a limited diet (n = 9), and daily blood samples were obtained for approximately 21 days preceding onset of anestrus (anovulatory cycle). Controls were allowed ad libitum dietary intake (n = 5), and daily blood samples were collected for a complete estrous cycle during a time period that coincided with that preceding onset of anestrus in restricted heifers. Plasma samples were assayed for LH, FSH, progesterone, and estradiol-17 beta. The ovaries of all heifers were examined daily using transrectal ultrasonography from the initial until the final or anovulatory estrous cycles to determine changes in growth of follicles and corpora lutea. Anestrus was defined as failure of ovulation of the dominant follicle following luteolysis. When anovulatory and initial estrous cycles in restricted heifers were compared, mean concentrations of LH were lower (p < 0.01), and diameters of dominant follicles were smaller (p < 0.01); mean concentrations of estradiol-17 beta were also lower in the three days following luteolysis (p = 0.06), but concentrations of FSH appeared to be higher (p = 0.003); maximum diameters of corpora lutea were smaller (p < 0.001), but duration of luteal phases and concentrations of progesterone preceding luteolysis were similar (p > 0.10). In controls, no differences were found between estrous cycles for any of these variables. It is concluded that failure of ovulation, following reduced dietary intake, resulted from insufficient circulating LH to stimulate maturation of the ovulatory follicle.     

Effect of an ovulatory dose of luteinizing hormone on the concentration of oestrone, oestradiol and progesterone in the rabbit ovarian follicles

This study was done to determine the effect of an ovulatory dose of LH on the concentration of oestrone, oestradiol and progesterone in the follicular tissue and in follicular fluid of ovaries of sexually mature female rabbits. Eight animals were sacrificed without treatment while others (4 to a group) were sacrificed at 1, 3, 4, 6, 8 and 10 h after administration of LH (50 mug). In each animal follicles from both ovaries were pooled and the follicular tissue was separated from the fluid. Determination of oestrone, oestradiol and progesterone was done by radioimmunoassay separately in the follicular tissue and in fluid. One hour after LH treatment oestrogen levels were found elevated, as compared to the control, in the fluid but not in the tissue. Thereafter oestrogen levels declined and reached levels much below control at times nearing ovulation. On the other hand, progesterone levels were elevated over the control in both the tissue and fluid at 1 and 3 h. The tissue progesterone levels were, however, below control at and after 6 h. The sustained high concentrations of tissue progesterone in the earlier period after LH stimulation could play a role in the chain of events leading to follicular rupture.     

Effects of dietary gossypol consumption on metabolic homeostasis and reproductive endocrine function in beef heifers and cows

Our objectives were to determine the effects of incremental increases in dietary gossypol on metabolic homeostasis and reproductive endocrine function in postpubertal beef heifers and the long-term effects of elevated dietary gossypol on various metabolic and reproductive endocrine characteristics in mature cows. In Exp. 1, heifers (n = 6/group) were fed either 0, .5, 2.5, 5, 10, or 20 g.animal-1 x d-1 of dietary free gossypol for 62 d. Erythrocyte membrane osmotic fragility was increased (P < .0001) in both the 10- and 20-g groups. Slight alterations in plasma concentrations of sorbitol dehydrogenase and K+ were also detected in the latter group. Treatment did not affect ADG, body condition scores, or concentrations of progesterone during the estrous cycle; however, mean concentrations of LH were higher (P < .001) in heifers fed 20 g/d of gossypol than in heifers in all other groups. In Exp. 2, lactating cows (n = 17) exhibiting regular estrous cycles were fed a control (no gossypol, n = 8) or high-gossypol (20 mg.kg BW-1 x d-1 free gossypol, n = 9) diet for 33 wk. Mean BW and body condition scores did not differ during the feeding period. Erythrocyte membrane fragility was greater (P < .05) in the high-gossypol than in the control group. Magnitude of the preovulatory LH surge, luteal phase concentrations of progesterone, follicular fluid concentrations of estradiol and progesterone, in vitro granulosa cell estradiol production, and 60-d pregnancy rates were similar between groups. The amounts of gossypol fed in these experiments are not likely to affect reproductive performance adversely in beef heifers or cows.     

Fertility in estrus-cycling and noncycling virgin heifers and suckled beef cows after induced ovulation

A procedure was developed to either induce or synchronize ovulation in heifers and suckled cows. Beef females were assigned to two breeding programs: 1) two injections of prostaglandin F2alpha (PGF2alpha) given 14 d apart to synchronize estrus (PGF2alpha control; n = 179), with inseminations 12 to 16 h after detected estrus or at 80 h in the absence of estrus, or 2) two injections of PGF2alpha (d -14 and 0) plus 100 microg of GnRH on d -7 when 6 mg of norgestomet was implanted (PGF2alpha/NORG/GnRH treatment; n = 173). Implants were removed 24 h after the second PGF2alpha injection (d +1) and females were inseminated 12 to 16 h after detected estrus until 54 h after PGF2alpha. The remaining cattle were given a second 100-microg GnRH injection 54 h after PGF2alpha and inseminated 18 to 20 h later. Percentages of noncycling females with subsequently elevated progesterone (P4) on d 0 or +1 were not different between treatment groups (20.4 vs 25%), but conception rate was greater (P < .05) in noncycling treated females than in noncycling controls (55 vs 12.8%). Conception rates in cycling (59.2%) and noncycling (62.2%) treated females were similar to those in cycling controls (56.2%) but greater (P = .06) than those in noncycling controls (26.5%). Conception rates in treated females inseminated 12 to 16 h after detected estrus (63.1%) or at one fixed time (58.3%) were similar to those in controls inseminated 12 to 16 h after detected estrus (68.7%). This treatment procedure produced fertility after one timed insemination that was equal to controls inseminated after detected estrus and induced equally fertile ovulations in noncycling heifers and cows.     

How does daily treatment with human chorionic gonadotropin induce superovulation in the cyclic hamster?

Daily s.c. injection of 2.0 IU hCG per day, begun on Day 1 of the cycle (estrus), results in hamsters ovulating 20.7 +/- 0.7 eggs instead of the normal number of 13.3 +/- 0.5 (SEM). This is associated with a reduced rate of follicular atresia so that more of the 10 developing follicles per ovary (large preantral stages) normally recruited on Day 1 of the cycle mature and go on to ovulate. The hCG-treated follicles were larger than control follicles, but contained similar amounts of DNA/follicle; increased size of the antral cavity accounted for their greater size. Moreover, DNA synthesis was significantly reduced in the hCG follicles on Days 2 and 4. Thecal vascularity as judged by the number of red blood cells retained in the theca or microsphere uptake by follicles indicates that on Day 2, thecal blood flow was significantly lower in the hCG-treated animals than in controls. On the other hand, after hCG treatment begun on Day 1, serum levels and in vitro incubation of individual follicles revealed that on Day 2 and beyond, androstenedione (A) and estradiol (E2) levels were elevated. After hCG treatment, the elevated serum E2 correlated with reduced serum LH on Days 3 and 4 whereas FSH was unaffected. To study in vitro steroid accumulation, the 10 largest follicles (the developing follicles) were dissected from alternate left and right ovaries from control and hCG-treated animals and incubated individually, and their histology was then compared with the steroid profiles. Accumulation of A and E2 was significantly greater in the hCG-treated follicles than in controls in a 1-h basal incubation and after the addition of 50 ng LH. Progesterone accumulation usually did not differ between the control and hCG-treated follicles. Early stage 1 atretic follicles (judged by histology) were still capable of producing A and E2 in vitro, comparable to control follicles; but, as atresia progressed, the follicles synthesized only progesterone. This is consistent with the temporal pattern previously observed in a model of induced follicular atresia in the hamster [Greenwald, Biol Reprod 1989; 40:175-181]. It is concluded that superovulation resulting from hCG injections is due to thecal production of androgens from follicles normally destined for atresia. For the untreated cyclic hamster, the critical time for thecal androgen production is the first 2 days of the cycle. The aromatizable androgens are then converted into estrogens, which in turn may maintain the microenvironment of the antral cavity, which is essential for viability of the granulosa cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effect of hormone replacement therapy alone and in combination with simvastatin on plasma lipids of hypercholesterolemic postmenopausal women with coronary artery disease

Follicular growth, lifespan of the corpus luteum, and antioxidant status of lactating Holsteins that experienced heat stress were monitored. Eleven multiparous cows, 60 to 110 d in milk, were maintained from 0800 to 1800 h daily in environmental chambers from d 11 to 21 of the estrous cycle. Cows were randomly assigned to a heat stress (mean dry bulb temperature peaked at 38.3 degrees C) or control treatment (mean dry bulb temperatures varied from 20.8 to 25.6 degrees C). Rectal temperature and respiration rates of heat-stressed cows were higher at 1600 h than were those of control cows. The length of the estrous cycle and the interval from estrus until luteolysis were not different between treatments. Two of 6 control cows and 1 of 5 heat-stressed cows had extended cycles (> 24 d). Heat-stressed cows had more class 1 (2 to 5 mm) follicles from d 11 to 15 of the estrous cycle. Numbers of class 2 (6 to 9 mm) and class 3 (> or = 9 mm) follicles were similar between treatments. Plasma progesterone concentrations were higher for heat-stressed cows until d 19 of the estrous cycle. Treatment did not affect concentrations of alpha-tocopherol, beta-carotene, retinol, retinyl palmitate, or total protein in plasma or concentrations of malondialdehyde in muscle. In conclusion, heat stress did not extend luteal function or the length of the estrous cycle of lactating Holstein cows but did affect follicular growth and progesterone concentrations in plasma. Heat stress did not appear to increase lipid peroxidation or decrease lipid-soluble antioxidant concentrations in blood.