Exogenous progesterone and progestins as used in estrous synchrony regimens do not mimic the corpus luteum in regulation of luteinizing hormone and 17 beta-estradiol in circulation of cows.

Our working hypothesis was that the low concentrations of progesterone (P4) and synthetic progestins administered in hormonal regimens to control estrous cycles of cows would have similar effects on secretion of LH and 17 beta-estradiol (E2). In addition, we hypothesized that concentrations of exogenous P4 typical of the midluteal phase of the estrous cycle and the corpus luteum (CL) would have similar effects on LH and E2, and the effects would be different from those of synthetic progestins and low concentrations of P4. Cows (n = 29) were randomly assigned to one of five treatment groups: 1) one Progesterone Releasing Intravaginal Device (1PRID; n = 6); 2) two PRIDs (2PRID; n = 6); 3) norgestomet, as in Syncro-Mate-B regimen (SMB; n = 6); 4) melengestrol acetate (MGA; 0.5 mg/day; n = 5); and 5) control (CONT; n = 6). Treatments were administered for 9 days (Day 0 = initiation of treatment). All cows from 1PRID, 2PRID, SMB, and MGA groups were injected with prostaglandin F2 alpha (PGF2 alpha) on Days 2 and 5 of the treatment period to regress CL. Cows in the 1PRID and SMB groups were also administered exogenous estrogen according to the respective estrous synchronization protocol for these products. Daily blood samples were collected from Day 0 to 35 to determine concentrations of P4. On Day 8, blood samples were collected at 15-min intervals for 24 h to determine pattern of LH secretion. On Day 9, all treatments ceased and cows in the CONT group received injections of PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)     

Frequency of luteinizing hormone pulses in cattle influences duration of persistence of dominant ovarian follicles,follicular fluid concentrations of steroids,and activity of insulin-like growth factor binding proteins

The objectives of the present study were to determine how varying frequency of LH pulses as controlled by varying treatments with progesterone (P4) in cattle would affect: (1) concentration of steroid hormones and activity of insulin-like growth factor binding proteins (IGFBPs) in the ovarian follicular fluid and blood plasma, and (2) duration of persistence of largest ovarian follicles. There were four treatment groups (n=7 per group) and a control group (n=5) of mature, non-lactating beef cows. Treatments were: (1) two progesterone releasing intravaginal devices (PRIDs) for 16 days (2PRID); (2) a half PRID for 16 days (0.5PRID); (3) two PRIDs for 8 days, then a half PRID for 8 days (2-0.5PRID); or (4) a half PRID for 8 days, then two PRIDs for 8 days (0.5-2PRID). Treatment was initiated on the fifth day of the estrous cycle, which was designated as Day 0, and continued for 16 days. All P4-treated females were administered prostaglandin F2alpha on Day 0 and 1 to regress their corpora lutea. Frequency of LH pulses was greater during treatment with the smaller dose of P4 compared with treatment with the larger dose of P4 and the control group. Ovarian follicles were classified into five categories based on ultrasonographic observations: growing (G); atretic (A); growing dominant (GD); growing persistent (GP); or atretic persistent (AP). At ovariectomy on Day 16, the largest and second largest follicles collected were re-classified into five categories based on follicular concentration of steroids. Classification of the largest follicle collected on Day 16 was influenced by treatment (P<0.005), with the 2PRID group having A follicles, the 2-0.5PRID group GP follicles, the 0.5-2PRID group AP follicles, and the 0.5PRID group GD and GP follicles. Concentrations of 17beta-estradiol (E2) were greatest in GD and GP follicles (P<0.05). There was less (P<0.05) activity of IGFBP-2 in GD follicles and less (P<0.05) activity of IGFBP-3 in GD and GP follicles than other follicles. Activity of IGFBP-4 and -5 was greater (P<0.05) in A and AP follicles than G, GD, and GP follicles. Maintenance of a frequent release of LH pulses over a 16-day period did not result in maintenance of persistent follicles throughout this period indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia is associated with greater activity of IGFBP-2, -4, -5, and greater concentrations of P4 in follicles, whereas growing dominant and persistent follicles contained greater concentrations of E2, androstenedione (A4), and less IGFBP-2 activity than follicles of other classes. Follicle classifications based on ultrasonography or follicular concentration of steroids did differ (P<0.05) for the largest follicles from the 2PRID group. Two follicles in this group appeared as GD follicles by ultrasonography, but these were atretic based on follicular steroid contents. Objective 1 of the present study yielded the conclusion that concentrations of steroid hormones in follicular fluid and blood plasma could be predictably controlled by regulating the frequency of LH pulses with varying doses of P4. Objective 2 yielded the conclusion that maintain frequent release of LH pulses over a 16-day period could not maintain persistent follicles throughout this period, indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia in the present study was associated with increased follicular fluid activity of IGFBP-2, -4, -5, and P4, whereas growing dominant and persistent follicles contained greater concentrations of E2, A4, and less IGFBP-2 activity than follicles of other classes.     

Estrus and ovulation in beef cows following use of progesterone-releasing devices, progesterone and estradiol valerate

Two hundred nonsuckling beef cows were treated with either 1) a progesterone-releasing intravaginal device (PRID) for 12 days; 2) PRID plus an IM injection of 200 mg progesterone (PRID-P); 3) PRID plus 5-mg IM injection of estradiol valerate (PRID-EV); or 4) PRID-EV-P. Cows were started on treatment on one of the first eight days of the estrous cycle. The number of cows which had P levels above 1 ng/ml one day after PRID removal was 12 to 50% lower in PRID-EV and PRID-EV-P groups than in PRID and PRID-P groups (P < 0.05). The proportion of cows showing estrus by 96 hours after PRID removal was 38, 36, 77, and 88% (P < 0.05) for the PRID, PRID-P, PRID-EV and PRID-EV-P groups, respectively. Thirty-one percent fewer cows treated with PRID on days 5 through 8 of the estrous cycle showed estrus by four days after PRID removal than those treated on days 1 through 4. In addition, 18 to 22% more cows had P levels above 1 ng/ml among cows treated with PRID or PRID-P on days 5 through 8 than among cows treated similarly on days 1 through 4. It was concluded that effective synchronization of estrus is achieved only when estrogen is used in conjunction with PRID in cows treated for twelve days during the first eight days of an estrous cycle.     

Development of persistent ovarian follicles during synchronization of estrus influences the superovulatory response to FSH treatment in cattle

The synchronization of estrus with synthetic progestins or progesterone (P(4)) results in the development of a large, persistent ovarian follicle. The objectives of the present study were to determine if development of a persistent ovarian follicle during synchronization of estrus suppresses recruitment of additional follicles during FSH treatment. On Day 5 of the estrous cycle (estrus = Day 0), beef cows were treated with 0.5 or 2.0 P(4) releasing intravaginal devices (PRIDs) for 8 d (Experiment 1, n = 20), 5 or 2 d (Experiment 2, n = 44) before initiation of FSH treatment. Prostaglandin F(2alpha) (25 mg) was administered on Days 5 and 6. Superovulation was induced with 24 mg of recombinant bovine FSH (rbFSH, Experiment 1) or 28 mg of FSH-P (Experiment 2) over a 3- or 4-d period, respectively. The PRIDs were removed concurrently with the 5th injection of rbFSH or FSH-P. There was a treatment-by-day interaction (P < 0.001) for the concentration of 17beta-estradiol in cows treated for 8, 5 or 2 d before FSH treatment. In Experiment 1, FSH treatment initiated 8 d after insertion of a 0.5 PRID did not affect the number of CL (6.9 +/- 1.4 vs 6.7 +/- 1.6), ova/embryos (3.7 +/-1.3 vs 3.0 +/- 1.3) and transferable embryos (2.4 +/- 0.9 vs 3.0 +/- 0.9) compared with that of the 2.0 PRIDs. In Experiment 2, FSH treatment initiated 5 d after insertion of a 0.5 PRID decreased the number of CL (4.0 +/- 0.5 vs 8.3 +/- 0.8; P < 0.001), ova/embryos (3.0 +/- 0.6 vs 5.9 +/- 1.2; P < 0.03) and transferable embryos (2.3 +/- 0.6 vs 5.1 +/- 1.0; P < 0.03) compared with that of a 2.0 PRID, respectively. Initiation of FSH treatment 2 d after insertion of a 0.5 PRID compared with a 2.0 PRID had no affect on the number of CL (8.0 +/- 2.1 vs 8.7 +/- 1.2), total ova (4.8 +/- 1.4 vs 6.9 +/- 1.4) and transferable embryos (2.9 +/- 1.2 vs 6.1 +/- 1.7). In conclusion, treatment with low doses of P(4) (0.5 PRID) for 5 d but not for 2 or 8 d before initiation of FSH treatment results in the development of a dominant ovarian follicle, which reduces recruitment of ovarian follicles, and the number of CL, total ova and transferable embryos.     

Physical properties of bovine cervical mucus during normal and induced (progesterone and/or PGF2alpha) estrus

Ninety two Friesian cows were used to determine physical properties of cervical mucus collected during normal estrus and estrus induced. Estrus was induced using either progesterone (P4) releasing intravaginal devices (PRID) and/or prostaglandin F2alpha (PGF2alpha). The animals were assigned to 4 groups (no treatment, a PRID for 12 days plus an injection of 1000 IU PMSG at the removal of the PRID, a double injection of 3 mL PGF2alpha 11 days apart, and a PRID for 7 days plus an injection of PGF2alpha 24 h before the removal of PRID). A number of cows with normal estrus exhibited three consecutive estrus cycles after calving. Cows that had not shown estrus for three months after calving had their reproductive system palpated twice at 10-day intervals, to determine their ovarian activity. Then PRID and/or PGF2alpha was administered to cows that were found to have a palpable corpus luteum in one of two palpations (cycling cows). The cows of the three induced estrous groups were artificially inseminated (AI) twice, while those with normal estrus received only a single AI. Cervical mucus samples were collected from all cows 5 to 30 min before the first AI. Additionally, samples of cervical mucus were collected from 20 cows at their first estrus after the induced estrus. The results are summarized as follows: 1) The physical properties of cervical mucus were similar in the first three normal consecutive estrus cycles after calving. 2) The physical properties of cervical mucus in normal estrus after calving were similar to those in the first estrus after an induced estrus. 3) The pH values for normal estrus were similar to those for induced estrus. 4) Viscosity of cervical mucus in the normal estrous group was significantly lower than that in the induced estrus. Furthermore, significant differences were noticed among the three induced estrous groups. 5) Spinnbarkeit, crystallization and receptivity of cervical mucus (penetration test) were significantly higher in the normal estrous group than in the induced estrous groups, while no difference was detected among induced estrus groups. 6) Pregnancy rates in the normal estrus group were the same as in the induced estrus groups. 7) The percentages of cows in the induced estrous groups that produced cervical mucus with similar viscosity, spinnbarkeit and receptivity (penetration test) characteristics as the normal estrus group, was very low.     

Endocrine, estrous and pregnancy response to varying dosages of Luprostiol in beef cows

Multiparous lactating beef cows were observed for estrus and randomly assigned to one of four Luprostiol (13, thia-PG-F(2)alpha analog) treatment groups receiving 3.8 (LI), 7.5 (LII), 15 (LIII) or 30 (LIV) mg Luprostiol, respectively, or to an untreated control group (C), or to a positive control group (E) receiving 500 mcg Estrumate. Cows received their respective treatments in a single dosage on Day 7, 8 or 9 of the estrous cycle (estrus = Day 0) and were artificially inseminated 12 h following the subsequent estrus. Blood samples were collected from all groups immediately prior to treatment and at 12-h intervals to 48 h post treatment and analyzed for progesterone (P(4)). Blood samples were collected at 3-h intervals from 24 to 72 h post treatment for animals in Group LIII and for 48 h (or observed estrus) starting on Day 19 of the estrous cycle for animals in Group C. These samples were analyzed for estradiol-17beta(E(2)), follicle stimulating hormone (FSH) and luteinizing hormone (LH). Treatment with Luprostiol at doses >/= 7.5 mg resulted in a synchronous estrous response during the first 5 d post treatment in 75 to 95% of cows treated. Luteal function, as evaluated by systemic P(4) concentration, paralleled results observed for estrous response. Treatment with a 15 or 30 mg dose of Luprostiol resulted in greater overall pregnancy rate at synchronized estrus. No biologically significant differences were found in blood levels of E(2), FSH or LH around the time of estrus between cows in Groups C and LIII. Results from these studies indicate treatment with Luprostiol at doses >/= 7.5 mg resulted in a synchronous estrus during the first 5 d after treatment. Pregnancy rates and endocrine changes were similar to those observed in control and Estrumate-treated cows.     

Effect of progesterone on basal LH and episodic LH and FSH secretion in heifers

Heifers between Days 6 and 10 of the cycle were allocated at random to groups of 8 and treated with (i) a 4% progesterone-releasing intravaginal device (PRID) + oestrogen capsule for 12 days; (ii) 4% PRID for 12 days; (iii) 20% PRID for 12 days; (iv) 4% for 14 days; or (v) 20% PRID for 14 days. Blood was obtained daily during treatment and at 2- or 4-h intervals for 72 h after removal of PRIDs. Some animals were sampled every 20 min for 4.676 h on the 3rd day after PRID insertion, and 1 day before and 36 h after removal of the PRID insertion, and 1 day before and 36 h after removal of the PRID. During progesterone treatment there was: (i) no correlation between concentrations of progesterone and LH within days; (ii) a significant negative correlation between progesterone and days (P less than 0.01) and also between progesterone and LH over days (P less than 0.01); (iii) the overall correlation co-efficient between LH and days was positive (P less than 0.05). The amplitude of LH or FSH episodes was not affected as progesterone concentrations declined during PRID treatment, but the number of LH (but not FSH) episodes was increased (p less than 0.01). After PRID removal, the amplitude of both LH and FSH episodes increased (P less than 0.01). We suggest that progesterone is part of a negative feedback complex on LH secretion in cattle and that this effect is apparently mediated through frequency of episodic LH release.     

The postpartum induced corpus luteum: functional differences from that of cycling cows and the effects of progesterone pretreatment

Anestrous postpartum (PP) Hereford cows (n = 41) were used to compare corpora lutea (CL) from gonadotropin-releasing hormone (GnRH)-induced ovulation with CL from cycling cows. Postpartum cows were injected i.m. daily with 100 mg progesterone (P4) or oil on Days 25 through 28 PP and then given 200 micrograms GnRH i.m. on Day 30 PP. Corpora lutea were removed from one-half of the PP cows in the oil- and P4-treated groups 6.5 days after GnRH injection, and from the cycling cows 7 days after estrus. Intact PP cows were used to evaluate cycle length. Blood was collected daily from all PP cows from Day 25 PP through luteectomy and on Days 9, 11, and 13 post-GnRH from the oil- and P4-intact cows to determine short (SHORT) versus normal (NORM) luteal phases. Cycling cows were bled daily from estrus until CL removal NORM PP cows had higher (P less than 0.001) P4 levels than did SHORT PP cows from Day 7 through Day 13 post-GnRH, and more (P less than 0.05) P4-intact cows were NORM compared with oil-intact cows (45.5% vs. 14.3%, respectively). Corpora lutea from cycling cows were heavier (P less than 0.05) and had a higher luteinizing hormone (LH) receptor concentration (P less than 0.05), but CL P4 concentration did not differ from PP cows. Corpora lutea weight, LH receptor and P4 concentration, and in vitro P4 production were similar in the oil-and P4-treated PP cows. NORM cows had heavier CL (P less than 0.05) than SHORT cows, although P4 content and LH receptor concentration did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to estrus in cattle

Two trials involving 85 heifers and 67 cows were conducted to determine the effect of estrous cycle stage at the time of Syncro-Mate-B((R)) (SMB) treatment on interval to estrus following implant removal and on conception rate at the synchronized estrus. In Trial 1, 57 beef and 28 dairy heifers were treated with SMB on each representative day of a 22-d estrous cycle (estrus = Day 0). Beef heifers were artificially inseminated approximately 48 h after implant removal, whereas dairy heifers were inseminated 0 to 12 h after detection of estrus. Inseminations were scored by the inseminator according to their difficulty. Interval to the onset of estrus was not different between heifers treated early ( Day 11) in the cycle (35.2 +/- 7.2 h). Conception rate at the synchronized estrus was slightly higher in early-cycle heifers (22 47 = 47% ) compared to late-cycle heifers (14 38 = 37% , P = 0.2). Heifers that were difficult to inseminate had lower (P < 0.01) conception rates (2 11 = 18% ) at the synchronized estrus than heifers considered normal (21 51 = 41% ) or easier than normal to inseminate (13 23 = 57% ). In Trial 2, of the 131 beef cows synchronized, 67 that were estimated to be either early or late in the estrous cycle by progesterone analysis were utilized. Cows were treated with SMB and inseminated without regard to estrus 48-h after implant removal. Inseminations were scored as in Trial 1. Calves were separated from cows from the time of implant removal to insemination. Conception rate was higher (P < 0.05) in cows treated with SMB early ( Day 11, 16 35 = 46% ). Cows that were difficult to inseminate had a lower (P < 0.01) conception rate (0 8 = 0% ) than cows that were normal (43 94 = 46% ) or easier than normal to inseminate (13 29 = 45% ).     

Studies of FSH-P induced follicular growth in cows

Because cow ovaries do not contain a dominant follicle before Day 3 of the estrous cycle, we hypothesized that gonadotropin treatment early in the estrous cycle would induce growth of multiple follicles and could be used to induce superovulation. In Experiment 1, when 16 cows were treated with FSH-P beginning on Day 2 of the estrous cycle and were slaughtered on Day 5, all cows responded to gonadotropin treatment by exhibiting a large number ( approximately 19) of estrogenactive follicles >/= 6 mm. In Experiment 2, in response to FSH-P treatment from Day 2 to Day 7, and fenprostalene treatment on Day 6, 11 of 15 cows exhibited estrus and had a mean ovulation rate of 23.7 +/- 1.5. In Experiment 3, an FSH-P treatment regimen identical to that used in Experiment 2 was administered to cows beginning either on Day 2 (Day-2 cows; n=14) or Day 10 (Day-10 cows; n=11) of the estrous cycle. Twelve of 14 Day-2 cows and all Day-10 cows exhibited estrus after fenprostalene treatment. Day-2 cows exhibited 34.3 +/- 7.0 ovulations, which was less (P < 0.05) than that exhibited by Day-10 cows (48.3 +/- 4.4). However, the proportion of embryos recovered per corpus luteum was about 2-fold greater (P < 0.05) for Day-2 cows than for Day-10 cows (0.49 +/- 0.08 vs 0.27 +/- 0.06). These data indicate that beginning gonadotropin treatment early in the estrous cycle, when a dominant follicle is not present, provides an efficacious means to induce growth of multiple follicles and superovulation in cows. However, when FSH was administered for 6 d, beginning the treatment on Day 10 also resulted in a consistent and efficacious response.     

Relationships between insulin and glucose metabolism and pituitary-ovarian functions in fasted heifers

The effects of fasting between Days 8 and 16 of the estrous cycle on plasma concentrations of luteinizing hormone (LH), progesterone, cortisol, glucose and insulin were determined in 4 fasted and 4 control heifers during an estrous cycle of fasting and in the subsequent cycle after fasting. Cortisol levels were unaffected by fasting. Concentrations of insulin and glucose, however, were decreased (p less than 0.05) by 12 and 36 h, respectively, after fasting was begun and did not return to control values until 12 h (insulin) and 4 to 7 days (glucose) after fasting ended. Concentrations of progesterone were greater (p less than 0.05) in fasted than in control heifers from Day 10 to 15 of the estrous cycle during fasting, while LH levels were lower (p less than 0.01) in fasted than in control heifers during the last 24 h of fasting. Concentrations of LH increased (p less than 0.01) abruptly in fasted heifers in the first 4 h after they were refed on Day 16 of the fasted cycle. Concentrations (means +/- SEM) of LH also were greater (p less than 0.05) in fasted (11.2 +/- 2.6 ng/ml) than in control (4.7 +/- 1.2 ng/ml) heifers during estrus of the cycle after fasting; this elevated LH was preceded by a rebound response in insulin levels in the fasted-refed heifers, with insulin increasing from 176 +/- 35 pg/ml to 1302 +/- 280 pg/ml between refeeding and estrus of the cycle after fasting. Concentrations of LH, glucose and insulin were similar in both groups after Day 2 of the postfasting cycle. Concentrations of progesterone in two fasted heifers and controls were similar during the cycle after fasting, whereas concentrations in the other fasted heifers were less than 1 ng/ml until Day 10, indicating delayed ovulation and (or) reduced luteal function. Thus, aberrant pituitary and luteal functions in fasted heifers were associated with concurrent fasting-induced changes in insulin and glucose metabolism.     

Effect of estradiol on secretion of luteinizing hormone during the follicular phase of the bovine estrous cycle

Mean concentrations of luteinizing hormone (LH) increase during the follicular phase of the estrous cycle in cows. The working hypotheses in the present study were (1) that increasing concentrations of 17 beta-estradiol (E2) during the follicular phase of the estrous cycle cause an increase in mean concentration of LH by increasing amplitude of pulses of LH, and (2) that increasing E2 concentrations during this stage of the estrous cycle decrease frequency of pulses of LH in bovine females. Day of estrus was synchronized in seventeen mature cows. Treatments were initiated on Day 16 of the experimental estrous cycle (Day 0 = estrus). At Hour 0 (on Day 16), 4 cows were lutectomized. Lutectomy of these cows (EE; n = 4) allowed for endogenous secretion of E2. The remaining cows were ovariectomized at Hour 0 and were assigned to one of three E2 treatments: luteal phase E2 (LE, n = 5), increasing then decreasing E2 (DE, n = 5), and no E2 (NE, n = 3). Cows in the group that received LE were administered one E2 implant at Hour 0, which provided low circulating concentrations of E2 similar to those observed during the luteal phase of the estrous cycle. Cows in the group that received DE were administered one E2 implant at Hour 0, and additional implants were administered at 8-h intervals through Hour 40; then, two implants were removed at Hours 48 and 56, and one implant was removed at Hour 64.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chemical properties of bovine cervical mucus during normal estrus and estrus induced by progesterone and/or PGF2alpha

Ninety-two Friesian cows were used to determine the chemical properties of cervical mucus during normal estrus and estrus induced by progesterone (P4)-releasing intravaginal devices (PRID) and/or prostaglandin F2alpha. The animals were assigned to 4 groups (no treatment, a PRID for 12 days plus injection of 1000 IU PMSG at the removal of PRID, a double i.m. injection of PGF2alpha 11 days apart, or PRID for 7 days plus an im injection of PGF2alpha 24 h before the removal of PRID). A number of cows with normal estrus exhibited three consecutive estrous cycles after delivery. Cows that had not shown estrus for 3 months after delivery had their ovaries palpated twice at 10-day intervals, to determine their ovarian activity. Then PRID and/or PGF2alpha was administered in cows that had a palpable corpus luteum in one of the two palpations (cyclic cows). A double artificial insemination (AI) was performed to the cows of the three induced-estrus groups, while the cows with normal estrus received only one AI. Cervical mucus samples were collected from all cows 5 to 30 min before the first AI. Additionally, samples of cervical mucus were collected from 20 cows during their first estrus after the induced one. The results are summarized as follows: 1) The biochemical properties of cervical mucus in the first three estrus periods after delivery were similar. 2) These properties were similar both in normal estrus after delivery and in the first estrus after an induced one. 3) Glucose and fructose concentrations for normal estrus were similar to those for induced estrus groups. 4) Total protein and cholesterol concentrations were significantly lower (P < 0.001) in normal than in induced estrus, while no difference was found among the induced estrus groups. 5) Pregnancy rates of the cows did not differ significantly among the normal and the induced-estrus groups. 6) The percentages of cows in the induced-estrus groups that produced cervical mucus with total protein and cholesterol concentrations similar to those for the normal estrus groups was very low.     

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)     

Inhibition of estrus and corpora lutea function with Norgestomet

Forty-five nonpregnant, nonlactating, Angus and Brangus cows were utilized to determine how long a Norgestomet ear implant would inhibit estrus when administered at various stages of an estrous cycle. All cows completed a nontreated estrous cycle to ensure normal cyclicity. At the second observed estrus (estrus = Day 1), cows were randomly allotted to be treated at metestrus (Day 3 or Day 4, n = 15); at diestrus (Day 9 or Day 10, n = 14); or at proestrus (Day 15 or Day 16, n = 16). All cows received a 2-ml intramuscular injection of 3 mg of Norgestomet accompanied by a 6-mg Norgestomet ear implant, which remained in situ for 21 days, or until individual cows were observed in estrus. Estrus was inhibited for a mean (+/- SEM) of 18.7 +/- 0.7, 19.9 +/- 0.8, and 17.0 +/- 0.8 days, respectively, when cows were treated at metestrus, diestrus, and proestrus (metestrus and diestrus vs proestrus; P < 0.05). Estrus was inhibited for an entire 21-day implantation period in 27, 50, and 38% of cows treated at metestrus, diestrus, and proestrus, respectively (P > 0.10). Norgestomet inhibited estrus in all cows for 11, 17, and 11 days after implantation when treatment was initiated at metestrus, diestrus, and proestrus, respectively (P > 0.10). These data indicate that a 6-mg Norgestomet ear implant effectively inhibits estrus in all cows for a maximum of 11 days, with some cows exhibiting estrus by Day 12 with the Norgestomet implant in situ.     

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.     

Influence of reproductive stage at PRID insertion on synchronization of estrus and ovulation in mares

In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus (n=6), estrus (n=11) and diestrus (n=11). Plasma concentrations of progesterone at insertion (Day 1) of PRID differed among treatment groups (anestrus: 0.2-0.6 ng mL(-1), estrus: 0.2-0.5 and diestrus: 1.6-10.8 ng mL(-1); P<0.001). Total secretion of progesterone (area under curve (AUC)) during treatment period revealed highest values in diestrus (38.2+/-3.1 ng mL(-1)h(-1)) followed by estrus (25.1+/-2.7) and anestrus (21.0+/-0.4 ng mL(-1)h(-1); P<0.05). Progesterone area under curve (AUC) was positively correlated with initial progesterone concentrations (R=0.5; P<0.05), but it did not correlate with the interval from PRID removal to ovulation. Plasma concentrations of LH during treatment period, were significantly lower in anestrous mares (184.6+/-28.6 ng mL(-1)h(-1)) when compared to estrous and diestrous mares (349.7+/-53.3 and 370.5+/-40.3 ng mL(-1)h(-1); P<0.05). Follicular size at PRID insertion had no effects on the intervals from PRID removal to subsequent estrus and ovulation. Follicle diameters at removal of PRID were significantly correlated with the interval from coil removal to estrus (R=-0.55, P<0.05) and ovulation (R=-0.72, P<0.0004) in cyclic mares. In anestrus 0 of 6 (0%) mares, in estrus 5 of 11 (45.5%) and in diestrus 6 of 11 (54.5%) mares ovulated within a defined interval of 1 day before to 1 day after mean interval from PRID removal to ovulation. In cyclic mares, response to treatment was significantly higher when compared to anestrous mares: almost all mares responded with estrus and ovulation independent from the stage of the estrous cycle at the start of treatment. However, accuracy of synchronization was still unsatisfactory. In cyclic mares, the plasma progesterone concentrations at insertion of PRID seem to be more important for the efficacy of the treatment than the assignment to estrous cycle stages.     

Induction of estrus and ovulation in non-cyclic buffalo (Bubalusbubalis) heifers with progesterone-releasing intravaginal device and pregnant mare serum gonadotrophin and their gonadotrophin profile

A study was undertaken to induce estrus among 15 non-cyclic Murrah buffalo heifers at a relatively early age of 2.5 to 3 yr by progesterone releasing intravaginal device (PRID) application. On Day 13, the PRID was removed and the animals were divided into two groups (A and B). Group B received 1000 IU of pregnant mare serum gonadotrophin (PMSG) intramuscularly (i.m.) immediately after removal of the PRID, whereas Group A was given no further treatment. Circulating gonadotrophin profiles (luteinizing hormone (LH) and follicle stimulating hormone (FSH) were quantified during and after the PRID treatment, as well as during the induced estrous cycle. LH and FSH levels before, during, and after PRID treatment were in the range of 0.5 to 3.0 ng/ml and 10 to 45 ng/ml, respectively, and could be considered basal levels. The peak FSH levels of Group B (PRID + PMSG) during estrus ranged from 69.44 to 337.06 ng/ml, much higher than the levels recorded in Group A (PRID). None of the animals in Group A showed peak LH levels during estrus, whereas two animals in Group B had peak LH levels of 15.84 and 16.93 ng/ml at 0 h and 12 h after detection of estrus. The higher LH and FSH levels obtained in Group B animals compared with Group A animals was possibly due to the superimposed effect of PMSG over PRID. All of the 14 animals exhibited estrus. None of the animals in Group A conceived whereas three out of seven animals in Group B conceived, indicating that PMSG following PRID resulted in ovulatory estrus.     

Ovarian follicular development following administration of progesterone or aspiration of ovarian follicles in Holstein cows

The objective of this study was to compare the effects of administration of a single injection of progesterone (P4) and follicle aspiration on Day 7 of the estrous cycle on the timing and synchrony of follicular wave emergence, time of ovulation, and concentrations of P4, estradiol and FSH in Holstein cows. Twenty cows were assigned to 4 groups (n=5 cows per group) in a 2 by 2 factorial arrangement. Cows were treated on Day 7 (Day 0 = estrus) of the estrous cycle with either sham follicular aspiration and an oil vehicle administered intramuscularly (control), aspiration of ovarian follicles (aspiration), 200 mg of P4 im, or aspiration and 200 mg of P4 im (aspiration + P4). On Day 11, PGF(2alpha)(25mg) was administered to all groups. Synchrony of ovulation was less variable in each of the treatment groups compared with the control group (P<0.05), whereas ovulation was delayed in cows in the P4 group (P<0.05). Day of follicular wave emergence was delayed in the cows of the P4 group compared with cows in the aspiration and aspiration + P4 groups (P<0.01), whereas variability in wave emergence was less among both groups of aspirated cows compared with the cows in the control group (P<0.01). More follicles 4 to 7 mm in diameter were detected in the 2 aspiration groups compared with the cows in the control and P4 group (P<0.05). No difference was detected among groups in the maximum concentration of FSH associated with follicular wave emergence. We conclude that both the administration of P4 and the aspiration of follicles on Day 7 of the estrous cycle improves the synchrony of ovulation when luteolysis is induced on Day 11 and results in similar concentrations of FSH at the time of follicular wave emergence, but the timing of wave emergence and the number of follicles post-emergence differ.     

The synchrony of prostaglandin-induced estrus in cows was reduced by pretreatment with hCG

The induction of optimal synchrony of estrus in cows requires synchronization of luteolysis and of the waves of follicular growth (follicular waves). The aim of this study was to determine whether hormonal treatments aimed at synchronizing follicular waves improved the synchrony of prostaglandin (PG)-induced estrus. In Experiment 1, cows were treated on Day 5 of the estrous cycle with saline in Group 1 (n = 25; 16 ml, i.v., 12 h apart), with hCG in Group 2 (n = 27; 3000 IU, i.v.), or with hCG and bovine follicular fluid (bFF) in Group 3 (n = 21; 16 ml, i.v., 12 h apart). On Day 12, all cows were treated with prostaglandin (PG; 500 micrograms cloprostenol, i.m.). In Experiment 2, cows were treated on Day 5 of the estrous cycle with saline (3 ml, i.m.) in Group 1 (n = 22) or with hCG (3000 IU, i.v.) in Group 2 (n = 20) and Group 3 (n = 22). On Day 12, the cows were treated with PG (500 micrograms in Groups 1 and 2; 1000 micrograms in Group 3). Blood samples for progesterone (P4) determination were collected on Day 12 (Experiment 1) or on Days 12 and 14 (Experiment 2). Cows were fitted with heat mount detectors and observed twice a day for signs of estrus. Four cows in Experiment 1 (1 cow each from Groups 1 and 2; 2 cows from Group 3) had plasma P4 concentrations below 1 ng/ml on Day 12 and were excluded from the analyses. In Experiment 1, cows treated with hCG or hCG + bFF had a more variable (P = 0.0007, P = 0.0005) day of occurrence of and a longer interval to estrus (5.9 +/- 0.7 d, P = 0.003 and 6.2 +/- 0.8 d, P = 0.005) than saline-treated cows (3.4 +/- 0.4 d). The plasma P4 concentrations on Day 12 were higher (P < 0.0001) in hCG- and in hCG + bFF-treated cows than in saline-treated cows (9.4 +/- 0.75 and 8.5 +/- 0.75 vs 4.1 +/- 0.27 ng/ml), but there was no correlation (P > 0.05) between plasma P4 concentrations and the interval to estrus. In Experiment 2, cows treated with hCG/500PG and hCG/1000PG had a more variable (P = 0.0007, P = 0.002) day of occurrence of and a longer interval to estrus (4.2 +/- 0.4 d, P = 0.04; 4.1 +/- 0.4 d, P = 0.03) than saline/500PG-treated cows (3.2 +/- 0.1 d). The concentrations of plasma P4 on Days 12 and 14 of both hCG/500PG- and hCG/1000PG-treated cows were higher (P < 0.05) than in saline/500PG-treated cows (7.3 +/- 0.64, 0.7 +/- 0.08 and 7.7 +/- 0.49, 0.7 +/- 0.06 vs 5.3 +/- 0.37, 0.5 +/- 0.03 ng/ml). The concentrations of plasma P4 on Days 12 or 14 and the interval to estrus were not correlated (P > 0.05) in any treatment group. The concentrations of plasma P4 on Days 12 and 14 of hCG/500PG- or hCG/1000PG-treated cows were correlated (r = 0.65, P < 0.05; r = 0.50, P < 0.05). This study indicated that treatment of cows with hCG on Day 5 of the estrous cycle reduced the synchrony of PG-induced estrus and that this reduction was not due to the failure of luteal regression.