Extension of short cycles in postpartum beef cows by intrauterine treatment with catecholestradiol

Induction of ovulation in postpartum suckled beef cows: a review

Prolonged postpartum acyclicity in suckled beef cows reduces the calf crop, and causes economic loss to beef cattle producers. Once anterior pituitary LH stores have been replenished between Days 15 and 30 post partum in suckled beef cows, methods to initiate cyclicity include non-hormonal methods such as weaning of calves (either complete, temporary or partial), or exposure to bulls, and hormonal methods such as administration of GnRH (either single injection, intermittent injections, or continuous infusion), gonadotropins (eCG, FSH, hCG), and steroids (estrogens, anti-estrogens, and progestogens). Weaning is costly, reduces growth rate of weaned calves, and short cycles are common after weaning-induced ovulation. Exposure of cows to bulls is not practical and its effect is not predictable. Repeated injections of GnRH, or a single injection of hCG are not always effective; ovulation is always followed by a short cycle, and usually a return to acyclicity. Estrogens and anti-estrogens do not consistently shorten postpartum anestrus. Exogenous progestogens include intravaginal devices, such as controlled-internal drug release (CIDR) or progesterone-releasing intravaginal device (PRID), norgestomet implants, and the feed-additive melengestrol acetate (MGA). Administration of exogenous progestogens is more practical than, and offers more advantages over, other treatments to shorten postpartum acyclicity in suckled beef cows. Mimicking the short cycle after Week 3 post partum, by maintaining circulating progesterone at subluteal concentrations or circulating progestin at intermediate concentrations, extends the life-span and allows terminal maturation of the postpartum dominant follicle as in cyclic cows, by initiating endogenous GnRH and LH pulses. This is followed by an LH surge, ovulation and normal cycles. The benefit from using exogenous progestogens after Week 3 post partum in suckled beef cows is that ovulation is induced, cyclicity is initiated, the resulting CL has a normal life-span and function, and there is no need to change management, such as weaning of calves. We present a model for the induction of ovulation and initiation of cyclicity using exogenous progestogens after Week 3 post partum in suckled beef cows.

Short-term effects of exogenous estradiol-17 beta on blastocyst development during the period of elongation in swine

Objectives were to examine the effects of a single dose (4 mg) of estradiol-17 beta (E2) on blastocyst development around the period of elongation. Proestrus gilts were induced to ovulate with 750 IU of hCG and were mated before ovulation (normal mating, 24 to 32 h post-hCG) or after ovulation had begun (delayed mating, 43 h post-hCG). This difference in time of mating has been demonstrated to result in approximately a 7-h difference in time of blastocyst elongation. Normally and delay-mated gilts were ovariohysterectomized at 278 h post-hCG or injected with E2 or vehicle (corn oil) at 278 h and then ovariohysterectomized at 290 h post-hCG (five or six gilts per group). Blastocyst size was measured and concentrations of E2, retinol, uteroferrin, insulin-like growth factor-I (IGF-I), uterine plasmin/trypsin inhibitor (UPTI) and protein in uterine flushings were quantified. Blastocyst size and components of uterine flushings did not differ (P > 0.05) between normally and delay-mated gilts at 278 h post-hCG. However, at 290 h post-hCG, normally mated gilts had larger (P < 0.01) blastocysts (small spheres to filamentous) and their flushings tended to contain less (P < 0.07) amounts of retinol than those of delay-mated gilts whose blastocysts ranged from small spheres to ovoidals. Normally mated gilts receiving E2 at 278 h had smaller (P < 0.01) blastocysts and less (P < 0.05) amounts of retinol at 290 h post-hCG than gilts receiving vehicle. Conversely, delay-mated gilts treated with E2 or vehicle did not differ (P > 0.05) in blastocyst size and amounts of components of uterine flushings at 290 h post-hCG. Normally mated gilts treated with vehicle had litters in the process of elongating at 290 h post-hCG. Mean blastocyst size (P < 0.001) and amounts of components of uterine flushings (except for IGF-I) in these gilts were greater (P < 0.05, UPTI = 0.06) than in normally mated gilts at 278 h post-hCG, whose blastocysts were spherical. Among gilts not treated with E2 (278 h and 290 h pooled), mean blastocyst size was positively correlated (P < 0.05) with amounts of retinol, E2, uteroferrin and total protein. Results indicated that a single dose of E2 given before elongation altered blastocyst development depending on how close blastocysts were to onset of elongation at the time of E2 treatment.

Effect of the rate of progesterone decline at luteolysis on the ovulatory follicles and subsequent estrous cycle length in ewes

Follicular and interestrous characteristics were examined in 34 ewes after experiencing either a rapid decline in plasma concentrations of progesterone at luteolysis [prostaglandin F2 alpha (PGF2 alpha)-induced] or a slow rate of decline, lasting over 72 h. All ewes were given PGF2 alpha on day 10 (day 0 = estrus). A slow rate of decline was established in 17 ewes by the intravenous infusion of progesterone initially at 72 ml h-1, delivering 4.5 mg progesterone h-1, then decreasing the infusion rate by 1 ml h-1 for the next three days. Seventeen additional ewes, predestined to experience a rapid decline in progesterone, were infused with vehicle. In Experiment 1, after infusion, ewes (6 ewes/group) were necropsied at the onset of estrus and follicle diameter was determined, follicular fluid was aspirated and the remaining follicular wall was microscopically examined to determine the number of granulosa cell layers. In Experiment 2, the interestrous interval, after infusion, was observed in both groups of ewes (11 ewes/group). Ewes experiencing a rapid rate of progesterone decline at luteolysis had no differences in follicle diameter nor follicular concentration of progesterone or estradiol but their ovulatory follicles contained fewer (P < 0.01) granulosa cell layers and the resulting estrous cycle was longer (P < 0.05) than ewes experiencing a slow rate of progesterone decline.

Influence of catecholestradiol on short-lived corpora lutea in beef cows

The influence of intrauterine administration of catecholestradiol (4-hydroxylated estradiol) on lifespan of the initial postpartum corpus luteum was evaluated in suckled beef cows. In experiment 1, postpartum cows (n = 23) were untreated (CONTROL) or received intrauterine infusions (0700 and 1700 hr) of either vehicle (SAL) or catecholestradiol (CATE; 4 micrograms) from day 15 to 22 (day 0 = parturition). Blood samples were collected three times weekly (day 15 to 100) and analyzed for progesterone. In experiment 2, cows received twice daily intrauterine infusions of either vehicle (n = 18), or catecholestradiol (n = 19), from day 25 +/- .5 to day 30 +/- .5. Following the final infusion, calves were temporarily weaned from all cows for 48 hr. At the end of the 48 hr weaning period, cows in each infusion group received either an i.m. injection of 1,000 IU hCG (SAL+hCG, n = 9; CATE+hCG, n = 9) or no further treatment (SAL, n = 9; CATE, n = 10). Blood samples were collected daily for 21 d following calf removal and 3 times weekly through 100 d postpartum. In both experiments, the initial postpartum elevation in peripheral progesterone concentrations was characterized as either a short (< 5 d) or extended (> 8 d) luteal phase. In experiment 1, postpartum anestrous interval (60 +/- 3.4 d) and incidence of short luteal phases (77%) were similar among CONTROL, SAL and CATE treatments. In experiment 2, luteal phases were induced within 10 d of onset of weaning in 90, 100, 56 and 60% of cows in SAL+hCG, CATE+hCG, SAL and CATE treatments, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a nonsteroidal aromatase inhibitor on in vitro and in vivo secretion of estradiol and on the estrous cycle in ewes

Three experiments were performed to study effects of decreased concentrations of estradiol-17 beta (E2) on lifespan and function of ensuing ovine corpora lutea (CL). In experiment 1, 52 follicles were collected from 10 ewes and placed into individual culture with 0 or .01 microCi 3H-androstenedione (10 ng; 3H-A) and 0, 10(-11), 10(-9), 10(-7), or 10(-5) M of a nonsteroidal aromatase inhibitor, CGS16949A (CGS). Concentrations of E2 secreted into the medium, and synthesis of estrogens as estimated by formation of 3H-water from 3H-A were decreased by 10(-5) and 10(-7) (P < .01), but not 10(-9) or 10(-11) M CGS. In experiment 2, luteolysis was induced in 24 ewes by injection of PGF2 alpha on days 5 to 10 of the estrous cycle (0 hr). Ewes received 0, 0.5, 1.0, 2.0 or 4.0 mg CGS per kg BW i.v. at -12, 0, 12 and 24 hr, and an ovulatory dose of hCG at 36 hr. Jugular (P < .001) and vena caval (P < .001) concentrations of E2 were decreased by CGS at all doses tested for 8 to 10 hr, but had returned to levels similar to control ewes by the time of the next injection. Concentrations of E2 around the time of the LH surge were similar in control and treated ewes. During the subsequent luteal phase, concentrations of progesterone (P4) were similar in control and treated ewes. Thus, transient decreases in E2 during the follicular phase were not deleterious to the subsequent luteal phase. In experiment 3, luteolysis was induced in 18 ewes by injection of PGF2 alpha on days 6 or 7 (0 hr) of the estrous cycle. Ewes received 0 or 1 mg CGS per kg BW i.v. every 8 hr from 0 to 40 hr. Ovulation was induced with hCG at 36 hr. CGS reduced jugular (P < .001) and vena caval (P < .001) concentrations of E2, prevented an endogenous surge of LH (P < .05) and increased (P < .001) concentrations of FSH. All ewes had ovulated a marked follicle by 72 hr, but onset of the luteal phase, as assessed by concentrations of P4, was delayed (P < .01) in ewes receiving CGS. Delayed luteal phases were not solely attributable to the presence of new CL or to luteinization of follicular cysts. When data were aligned according to the day ewes were observed in estrus, profiles of P4 did not differ with treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of estradiol on duration of anestrus and incidence of short estrous cycles in postpartum cows

The influence of exposure to exogenous estradiol on the interval from parturition to first ovulation, luteinizing hormone (LH) secretion and luteal function was examined in cows. Cows were assigned at parturition to one of three treatments. Cows received either a 3.0 (1-E; n = 30) or .75 cm (1/4-E; n = 28) implant containing 17 beta-estradiol or served as untreated control animals (C; n = 33). Implants were administered within 2 days following parturition and removed on day 40 postpartum (day 0 = day of parturition). Single blood samples were collected twice weekly and analyzed for progesterone to determine length of postpartum anestrus and duration of the initial increase in progesterone. Sequential blood samples were collected on day 35 +/- .1 postpartum (15 min intervals for 18 hrs) from 5 cows in each treatment and analyzed for LH. Concentrations of estradiol were higher (P less than .01) in the 1-E (5.3 +/- .24) than in C (3.9 +/- .23) or 1/4 E (3.9 +/- .25) cows on day 35 postpartum. The interval from parturition to the first estrous cycle of normal duration was similar for cows in the C and 1-E treatment (53 +/- 2.4 and 56 +/- 2.4 days, respectively). Cows in the 1/4-E treatment had a longer (P less than .05) interval (68 +/- 2.5 days). Secretion of LH was similar among treatments on day 35 postpartum. The first normal luteal phase after parturition was preceded by a transient rise in progesterone in 81, 64 and 85% of the cows in the C, 1-E and 1/4-E treatments, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)