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PubMed2002

Myometrial activity around estrus in sows: spontaneous activity and effects of estrogens, cloprostenol, seminal plasma and clenbuterol.

A new, nonsurgical, open-end catheter technique was used to study spontaneous uterine activity around estrus in sows, and the effects of estrogens, seminal plasma, cloprostenol, and clenbuterol on uterine activity. In the first experiment, uterine activity was studied in 14 multiparous, cyclic sows, during one or more estrous cycles, from day -4 to day 4 of the cycle (day 0: first day of standing estrus). From a few days before estrus until estrus, the percentage of sows showing any uterine contractions increased from 55 to 100%, and frequency and mean amplitude of uterine contractions for these sows increased from 15 to 22/h, and from 20 to 40 mmHg on average. After estrus, uterine activity decreased. There were large differences between sows in uterine activity, which were consistent over the days of the cycle. In the second experiment, 11.5 microg of estrogens in 100 ml saline (n = 17), 100 ml seminal plasma (n = 5), 1 mg cloprostenol in 100 ml saline (n = 10), 0.30 mg clenbuterol in 100 ml saline (n = 11), or 100 ml saline (n = 5) was infused IU, after recording spontaneous activity. Infusion with saline or seminal plasma did not affect uterine activity. Estrogens increased frequency of contractions. Cloprostenol increased both frequency and amplitude of contractions. Clenbuterol reduced both frequency and amplitude of contractions. In conclusion, this study shows that spontaneous uterine activity in sows is increased around estrus, and it supports the role of estrogens in boar seminal plasma in affecting uterine activity around mating. Further, this study has yielded possible tools to study the relation between uterine activity and sperm transport.

Adrenergic beta-Agonists↗
PubMed2002

Evaluation of steroid microspheres for control of estrus in cows and induction of puberty in heifers.

Two trials were designed to test whether a single treatment with a microsphere formulation of progesterone (P) could simulate the luteal phase of the estrous cycle and lead to estrus and subsequent luteal development. The first experiment was to characterize the pattern of serum P concentrations and estrus in cows treated with a microsphere formulation (P + E) that contained 625 mg P and 50 mg estradiol (E). Four cows with palpable corpora lutea were treated with 25 mg prostaglandin F2 m. Each cow was given P + E (i.m.) 12 h later. Tail vein blood samples were taken on Days 1 and 2 following P + E treatment and then three times weekly for 24 days. Serum P increased from 0.8 +/- 0.1 ng/ml at P + E treatment to 4.7 +/- 0.6 ng/ml on Day 1, declined gradually to 4.1 +/- 0.3 ng/ml on Day 7 and then declined more rapidly to 0.6 +/- 0.1 ng/ml on Day 13. Treated cows showed estrus 16.25 +/- 0.7 days after P + E treatment. Thereafter, serum P increased beginning on Day 20 after P + E treatment, as expected following estrus. In Experiment 2, Angus and Simmental heifers (10.5-11.5 months of age) were administered i.m. either the vehicle (controls), E (50 mg), P (625 mg) or P + E (n = 13 per group). While treatment with E resulted in behavioral estrus (1-2 days after treatment) in each treated heifer, it did not (P > 0.5) initiate estrous cycles as indicated by subsequent increased serum P. In contrast, the P and P + E treatments increased (P < 0.05) the proportion (11/13) of heifers that showed estrus by 21 days after treatment followed by elevated serum P. We conclude that the microsphere formulation of P simulated the pattern of serum P concentrations during the luteal phase of the estrous cycle and initiated estrous cycles in peripubertal heifers with or without E.

Animals↗
PubMed2003

Estrus induction following PGF2alpha treatment in the superovulated buffalo (Bubalus bubalis).

Early return-to-estrus after embryo collection would shorten the interval between consecutive superovulations and improve efficiency of embryo production. Following superovulation and embryo collection, 80 buffaloes were treated with 15.0mg Luprostiol (PGF2alpha analogue) for the induction of luteolysis and early return-to-estrus. A total of 67.5% donor animals returned to estrus, on average 11.8+/-0.84 days after the PGF2alpha treatment. The number of ovulations ( 5 CL) had no significant effect on the percentage of donors returning to estrus within 30 days, as 70% of the buffaloes with 5 CL returned to estrus during this time. However, an increase in the number of ovulations significantly delayed the return to estrus as this duration was 9.7+/-0.93 days in the buffaloes with 5 CL.

Animals↗
PubMed2007

Differential estradiol requirement for the induction of estrus behavior and the luteinizing hormone surge in two breeds of sheep.

For a better understanding of the mechanisms that lead to the preovulatory GnRH/LH surge and estrus behavior, the minimum estradiol (E) requirements (dose and duration) to induce each of these events were determined and compared between two breeds of ewes having either single (Ile de France) or multiple (Romanov) ovulations. The ewes were initially studied during a natural estrus cycle, and were then ovariectomized and run through successive artificial estrus cycles. For these artificial cycles the duration and amplitude of the follucular phase E increase were manipulated by E implants. Under all conditions, the onset of estrus behavior was similar in the two breeds, although its duration was longer in Romanov ewes. While a moderate E signal (6 cm for 12 h) induced an LH surge in 10/10 Ile de France ewes, a larger E signal (12 cm for 12 h) was minimally effective in Romanov ewes (4/10). Additional studies revealed that a small E signal (3 cm for 6 h) induced full estrus behavior in all Romanov ewes but was completely ineffective in Ile de France animals (0/10). Higher doses and mostly longer durations of the E signal (12 cm for 24 h) were required to induce a surge in all the Romanov ewes. These results demonstrate a clear difference in the E requirement for the induction of estrus behavior and the LH surge between breeds of ewes that have different ovulation rates. These data provide compelling evidence that, in one breed, the neuronal systems that regulate both events require different estrogen signals.

Animals↗
PubMed1985

Pulsatile administration of gonadotropin-releasing hormone to anestrous sows: endocrine changes associated with GnRH-induced and spontaneous estrus.

This experiment determined whether pulsatile administration of gonadotropin-releasing hormone (GnRH) would induce estrus and ovulation in seasonally anestrous primiparous sows and compared endocrine responses of GnRH-induced sows with those of primiparous sows that exhibited spontaneous estrus after weaning. Seventeen primiparous Landrace X Large White sows farrowed in August 1982, lactated 23.8 +/- 0.4 days (mean +/- SEM), and weaned 9.0 +/- 0.3 pigs per litter. Blood for determination of progesterone, luteinizing hormone (LH), and estradiol-17 beta (E) was collected every 6 h from 1 day before to 12 days after weaning. Twelve sows exhibited spontaneous estrus 135 +/- 9 h after weaning, and these sows were considered to be normal. Five sows were anestrous for at least 23 days postweaning and failed to ovulate, as indicated by concentrations of progesterone that were less than 1.0 ng/ml in blood samples collected daily during this period. From Day 0 to Day 30 postweaning, levels of estradiol in anestrous sows varied between 3 and 30 pg/ml, concentrations of LH were low, and preovulatory-like LH surges did not occur. Beginning on Day 30 postweaning, four anestrous sows were given 1.5 micrograms GnRH (i.v.) hourly until onset of estrus and blood was collected every 6 h during GnRH treatment. The average interval from beginning of GnRH treatment to onset of estrus was 84 +/- 5 h (range 72 to 96 h). Patterns of estradiol and LH secretion around estrus were similar in normal sows and those treated with GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

The effects of pheromonal stimuli on estrus and peripheral plasma estradiol in female gray short-tailed opossums (Monodelphis domestica).

Exposure to male pheromones is associated with the activation of vaginal estrus in gray short-tailed opossums. The effects of such exposure on peripheral plasma estradiol-17 beta (E) levels in this marsupial species were examined in this study. Mean E levels of 27.8 pg/ml +/- 4.4 in diestrous females living in a room containing only females were similar to those seen in other marsupials. Direct naso/oral exposure to pheromonal cues provided by males resulted in vaginal estrus in 75% of these females within 4 11 days. None of the females exposed to clean cages came into vaginal estrus. Animals that were in estrus at the time of blood sampling or came into estrus over the experimental period had significantly higher E levels (58.1 +/- 12.6 pg/ml) than females in the pheromone-exposed and control groups that did not come into estrus (23.3 +/- 8.2 pg/ml). These findings are discussed with respect to other marsupial and eutherian species.

Animals↗
PubMed2006

Progestin concentrations are increased following paced mating in midbrain, hippocampus, diencephalon, and cortex of rats in behavioral estrus, but only in midbrain of diestrous rats.

BACKGROUND: The progesterone (P(4)) metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), acts in the midbrain ventral tegmental area (VTA) to modulate the intensity and duration of lordosis. 3alpha,5alpha-THP can also have anti-anxiety and anti-stress effects in part through actions in the hippocampus. Separate reports indicate that manipulating 3alpha,5alpha-THP levels in the VTA or hippocampus respectively can influence lordosis and affective behavior. 3alpha,5alpha-THP levels can also be altered by behavioral experiences, such as mating or swim stress. Whether endogenous levels of 3alpha,5alpha-THP modulate and/or are increased in response to affective and/or reproductively-relevant behaviors was investigated. METHODS: In Experiment 1, rats in behavioral estrus or diestrus were individually tested sequentially in the open field, elevated plus maze, partner preference, social interaction, and paced mating tasks and levels of 17beta-estradiol (E(2)), P(4), dihydroprogesterone (DHP), and 3alpha,5alpha-THP in serum, midbrain, hippocampus, diencephalon, and cortex were examined. In Experiments 2 and 3, rats in behavioral estrus or diestrus, were individually tested in the battery indicated above, with, or without, paced mating and tissues were collected immediately after testing for later assessment of endocrine measures. RESULTS: In Experiment 1, behavioral estrous, compared to diestrous, rats demonstrated more exploratory, anti-anxiety, social, and reproductive behaviors, and had higher levels of E(2) and progestins in serum, midbrain, hippocampus, diencephalon, and cortex. In Experiment 2, in midbrain and hippocampus, levels of 3alpha,5alpha-THP and its precursor DHP were increased among rats in behavioral estrus that were mated. In diencephalon, and cortex, DHP levels were increased by mating. In Experiment 3, in midbrain, levels of 3alpha,5alpha-THP and its precursor DHP were increased among diestrous rats that were tested in the behavioral battery with mating as compared to those tested in the behavioral battery without mating. CONCLUSIONS: Increased levels of 3alpha,5alpha-THP in behavioral estrus versus diestrous rats are associated with enhanced exploratory, anti-anxiety, social, and reproductive behaviors. Rats in behavioral estrus that are mated have further increases in 3alpha,5alpha-THP and/or DHP levels in midbrain, hippocampus, diencephalon, and cortex than do non-mated rats in behavioral estrus, whereas diestrous rats only show 3alpha,5alpha-THP increases in midbrain in response to behavioral testing that included mating.

Animals↗
PubMed1978

Induction of persistent estrus by constant light: effects of neonatal constant light and Harderian gland function.

The effect of constant light on the age at onset of persistent estrus was compared in rats exposed to constant light since birth (LL-0) and those exposed beginning at 70 days of age (LL-70). Persistent estrus occurred about 27 days later in the LL-0 rats than in the LL-70 rats. Exposure to LL for just the 1st 15 days of life (LL-0-15) and then subsequent exposure to LL at 71 days also delayed the induction of persistent estrus. Neonatal injection of a Harderian gland (HG) homogenate to LL-0-15 rats reduced the age of vaginal opening and 1st estrus and reduced the delayed onset of persistent estrus caused by the neonatal LL. Harderianectomy of LL-0 or hematoporphyrin injections in LL-0-15 rats had no effect on the onset of LL-induced persistent estrus.

Animals↗
PubMed1997

The antiprogestins RU486 and ZK98299 affect follicle-stimulating hormone secretion differentially on estrus, but not on proestrus.

Previous in vivo studies from our laboratory indicated that administration of the antiprogestin RU486 on proestrus suppresses both the preovulatory gonadotropin surges and the secondary FSH surge, suggesting a role for the progesterone receptor (PR) in the generation of these surges. The present study was designed to test the effects of another antiprogestin, ZK98299, which has been reported to block the PR through a mechanism different from that of RU486, on gonadotropin secretion in vivo. RU486 and ZK98299 (2 and 6 mg/kg) were administered s.c. at 1230 h on proestrus; uterine intraluminal fluid content, serum gonadotropins, and gonadotropin subunit messenger RNAs (mRNAs) were determined at 1830 h on proestrus and at 0900 h on estrus. At 1830 h on proestrus, both RU486 and ZK98299 at both doses caused equal suppression of the preovulatory FSH surge and FSHbeta mRNA. Both antiprogestins also equally attenuated the preovulatory LH surge at this time, with the higher doses causing greater suppression. In contrast, at 0900 h on estrus, the antiprogestins affected serum FSH differentially; only RU486 suppressed the secondary FSH surge despite the fact that both drugs prevented the release of uterine intraluminal fluid, confirming blockade of progesterone action at the level of the uterus. Neither drug had a significant effect on FSHbeta mRNA at 0900 h on estrus. ZK98299 at the higher dose caused a small, but significant, increase in serum LH. In a subsequent experiment, we compared the effects of RU486 and ZK98299 (6 mg/kg, s.c.), administered at 1230 h on proestrus, on serum FSH raised above the natural secondary FSH surge on the morning of estrus by passive immunization with an antiserum to inhibin-alpha (anti-I) at 1700 h on proestrus. Consistent with the results of the first experiment, both antiprogestins blocked the release of uterine intraluminal fluid, but only RU486 lowered serum FSH in both the normal sheep serum-treated controls and anti-I-treated rats; in contrast, ZK98299 actually increased serum FSH in the normal sheep serum-treated control animals. ZK98299 also increased FSHbeta mRNA in the control group; RU486, on the other hand, reduced FSHbeta mRNA only in the anti-I group. The results demonstrate unequivocally that whereas the effects of the two antiprogestins on serum FSH and FSHbeta mRNA are similar on proestrus, they are divergent on estrus. The data suggest that the functional state of the PR/transcriptional activation complex in the gonadotrope on the morning of estrus is different from that on the evening of proestrus.

Animals↗
PubMed2006

Induction of estrus by prostaglandin F2alpha administration in the vaginal vestibules of miniature pigs.

Estrus induction is an important step in embryo production. It has been difficult to induce estrus in miniature pigs by intramascular (i.m.) injection of prostaglandin F2alpha (PGF2(2alpha)) in the early luteal stage of the estrous cycle. In the present study, we injected two different doses of PGF2(2alpha) i.m. and into the submucosa of the vaginal vestibule (i.ves.) of miniature pigs, and examined the effect of these treatments on estrus induction. Fifteen miniature pigs were divided into five experimental groups (control, saline injected i.m.; PGF2alpha treated, 1.0 or 1.5 mg of PGF2alpha injected twice i.m. or i.ves.), and the estrus length and concentrations of 17beta-estradiol (E2) and progesterone (P) in the blood were examined. Estrus length was significantly shortened by a large amount of PGF2alpha injected i.ves. In addition, the concentration of P in the blood significantly decreased after two injections of PGF2alpha (i.m. or i.ves.). These results suggest that in miniature pigs, administration of at least 3.0 mg of PGF2alpha is required for the induction of luteolysis and injection of PGF2alpha into the vaginal vestibule is a useful method of estrus induction.

Administration, Intravaginal↗
PubMed1993

Prevention of estrus in bitches by subcutaneous implantation of chlormadinone acetate.

The efficacy and clinical safety of chlormadinone acetate (CAP) in preventing estrus were assessed in bitches on condition that CAP was subcutaneously implanted in silastic silicon rubber. To evaluate the long-term efficacy of implantation, 19 bitches were divided into 4 groups given doses of 2.5, 5, 10 and 25 mg/kg, respectively. Although estrus was observed within 13 months after implantation in all of the bitches given CAP in the 2.5 mg/kg dose, and in 13 to 15 months in 3 of the 5 bitches given the 5 mg/kg dose, it was prevented for at least 24 months in all of the bitches given doses of 10 mg/kg or more. Plasma progesterone levels remained low throughout the period of estrus prevention, indicating a close correlation with the effect of CAP. The mean body weight of the bitches in groups receiving higher doses increased slightly over the course of the experiment. Except this, no clinical, hematology or biochemistry abnormalities were found in any of the treated bitches. Another 6 bitches were given 10 to 30 mg/kg of CAP, but the implants were removed to observe the recurrence of estrus and to measure the amount of CAP in the removed implant. Estrus recurred after removal even in the bitch given 30 mg/kg. The concentrations of CAP in the plasma and the amounts of CAP remaining in the implants demonstrated the sustained release of CAP from the implants. The concentrations of CAP in the individual bitches indicated that the lowest concentration effective in preventing estrus is 0.7 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1975

Correlation between sexual maturation and induction of persistent estrus by continuous illumination.

The rats brought up under continuous illumination from the neonatal day persist in the rhythmic estrous cycle for long time and do not easily reveal so-called continuous vaginal estrus. On the contrary, immature rats at about 30 days of age show the persistent estrus soon after exposure to continuous illumination as well as adult rats. The purpose of this paper was to examine the relation of the age placed under continuous illumination and the time required to reach the persistent estrus. As the results, it was found that the younger rats need proportionally the longer time to reach the persistent estrus; the rats which were transferred into continuously illuminated environment at 0 (group A), 5 (group B), 10 (group C), 15-16 (group D) and 30 (group E) days of age required a mean time of 132.1 +/- 8.4, 126.8 +/- 8.9, 89.7 +/- 6.2, 91.5 +/- 3.8 and 70.3 +/- 3.0 days after birth to reach the persistent estrus, respectively. In the present data, a significant difference was seen between group B and C. Though all rats were killed after the same length of persistently estrous periods, actual endocrine level appeared to differ among the groups; the rats required longer time to reach the persistent estrus had smaller ovaries and adrenals.

Age Factors↗
PubMed1990

A review of synchronization of estrus in postpartum cattle.

Estrus has been synchronized in cattle with progestogens, prostaglandins (prostaglandin F2 alpha and its analogues), progestogen-estrogen combinations and progestogen-prostaglandin combinations. Progestogens administered for 14 to 20 d are effective in synchronizing estrus; however, fertility at the synchronized estrus is subnormal. Duration of progestogen treatment can be reduced by combining it with an estrogen. Syncro-Mate B is a progestogen-estrogen combination that results in a tightly synchronized estrous response. Prostaglandins can be used in double- or single-injection programs. Fertility of the estrus after prostaglandin treatment is similar to that of controls. Estrus also has been synchronized effectively by combining a 5- to 9-d progestogen treatment with prostaglandin at or near the end of treatment. When prostaglandin is used alone, cattle in the late stages of the luteal phase (d 11 to 15 of the estrous cycle) at the time of prostaglandin injection have a higher estrous response and may be more fertile than those injected with prostaglandin in the early part (d 6 to 9) of the luteal phase. More recently, a 14-d progestogen treatment has been combined with a prostaglandin injection given 16 to 18 d after progestogen withdrawal. This system places cattle in the late luteal phase of the estrous cycle at the time of prostaglandin injection and has resulted in an estrus with greater fertility than that immediately following progestogen treatment.

Animals↗
PubMed1990

Postpartum interval to estrus and patterns of LH and progesterone in first-calf suckled beef cows exposed to mature bulls.

Two trials were conducted in which Angus x Hereford first-calf cows were assigned randomly at calving to one of two treatments: exposure to mature penile-blocked bulls (BE) or isolation from bulls (NE). In Trial 1 (BE, n = 38; NE, n = 37), cow to bull ratio increased from 12:1 to 19:1 over a 14-d period; in Trial 2 (BE, n = 25; NE, n = 24), this ratio was maintained at 13:1. In both trials, blood samples were collected weekly for progesterone and ovaries and uteri of cows were examined rectally. Cows were observed for estrus twice daily (am:pm) beginning 10 d after calving. In Trial 2, intensive blood sampling for LH began 10 d after calving (eight cows per treatment) and continued at weekly intervals until estrus or the end of the trial. Postpartum weight change, condition score change and time to uterine involution did not differ (P greater than .10) between treatments in either trial. Interval to estrus was shorter (P less than .05) for BE cows than for NE cows in both trials. A greater proportion (P less than .05) of BE cows exhibited estrus by 60 and 90 d after calving and showed an increase in progesterone before first estrus. Mean and baseline LH concentrations and amplitude, frequency and duration of LH pulses were not altered (P greater than .10) by bull exposure. In conclusion, exposing first-calf suckled beef cows to bulls after calving hastened resumption of estrous cycles. Bull exposure did not alter patterns of LH concentrations but did increase proportions of cows that showed increased progesterone before first estrus.

Animals↗
PubMed1999

Control of the weaning-to-estrus interval in sows using gonadotropins and prostaglandins during lactation.

Two experiments were conducted to examine the effectiveness of various strategies using gonadotropins to induce ovulation during lactation as a means of controlling the weaning-to-estrus interval in sows. The objective of Exp. 1 was to examine the efficacy of various gonadotropin regimens for induction of ovulation during lactation. Primiparous (n = 60) and multiparous (n = 83) crossbred sows were assigned, before farrowing, to one of four treatments: no injection (control); 1,000 IU hCG on d 0 (hCG-0; d 0 = day of farrowing); P.G. 600 + 1,000 IU hCG 4 and 7 d after farrowing, respectively (hCG-7); or P.G. 600 + 1,000 IU hCG 11 and 14 d after farrowing, respectively (hCG-14). Sows were weaned on 18 +/- 2 d after farrowing and monitored daily for estrus via exposure to mature boars. The criterion for determining the induction of ovulation was a sustained increase in serum progesterone concentrations above 4.0 ng/mL. The most consistent response to exogenous gonadotropins was on d 0, with an 80% response in primiparous sows (12/15) and a 71% response in multiparous sows (15/21). Weaning-to-estrus intervals for multiparous sows were longer (P = .05) for hCG-14 and hCG-7 than for control and hCG-0 sows. Weaning-to-estrus intervals for primiparous sows were longer (P = .05) for the hCG-14 than for the hCG-0 treatment. The objective of Exp. 2 was to ascertain the effects of postpartum treatment with hCG (1,000 IU) on d 0 and PGF2alpha (10 mg) at d 14 on the weaning-to-estrus interval in multiparous sows weaned at d 14 after birth. Before farrowing, sows (n = 60) were randomly assigned to one of four treatments: positive control, weaning at d 21; negative control, weaning at d 14; hCG within 24 h after farrowing, weaning at d 14; or hCG within 24 h after farrowing and PGF2alpha at weaning, weaning at d 14. Weaning-to-estrus intervals were longer (P = .05) in sows receiving PGF2alpha than in the other treatments. Results indicate that it is possible to induce ovulation immediately after farrowing, using a single injection of hCG, and this strategy can be used to uncouple weaning from the resumption of reproductive activity. However, the administration of PGF2alpha at 14 d after farrowing did not consistently cause regression of the induced corpora lutea.

Animals↗
PubMed2001

Effectiveness of GnRH plus prostaglandin F2alpha for estrus synchronization in cattle of Bos indicus breeding.

Postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding at three locations were studied to determine the efficacy of GnRH + PGF2alpha combinations for synchronization of estrus and(or) ovulation. Cows were equally distributed to each of three treatments by body condition score at the start of the experiment (d 0). All cows received 100 microg of GnRH on d 0 and 25 mg of PGF2alpha 7 d later. The three insemination protocols included 1) AI 12 h after exhibiting estrus during d 7 to 12 of the experiment (Select-Synch; n = 197); 2) timed-AI + 100 microg of GnRH on d 9 of the experiment (CO-Synch; n = 193); 3) AI 12 h after exhibiting estrus during d 7 to 10 of the experiment. Cows not exhibiting estrus by d 10 were timed-AI and injected with 100 microg of GnRH on d 10 of the experiment (Hybrid-Synch; n = 200). The percentage of cows exhibiting estrus during d 7 to 12 of the experiment was lower (P < 0.05) for CO-Synch (17.6%) cows than for Select-Synch or Hybrid-Synch (45.2 and 33.0%, respectively) cows, which did not differ (P > 0.05). For the Select-Synch and Hybrid-Synch cows that exhibited estrus during d 7 to 10 of the experiment and were artificially inseminated, conception rates were similar across treatments (50.5%). Pregnancy rates were greater (P < 0.01) for CO-Synch and Hybrid-Synch (31.0 and 35.5%, respectively) cows than for Select-Synch (20.8%) cows. A greater (P < 0.01) percentage of cycling cows became pregnant (34.5%) than noncycling cows (25.9%) across all treatments. The CO-Synch and Hybrid-Synch synchronization protocols resulted in greater pregnancy rates compared with the Select-Synch protocol in postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding.

Animals↗
PubMed2003

The effects of varying the interval from follicular wave emergence to progestin withdrawal on follicular dynamics and the synchrony of estrus in beef cattle.

The objective of this experiment was to examine the effects of varying the interval from follicular wave emergence to progestin (controlled internal drug-releasing insert, CIDR) withdrawal on follicular dynamics and the synchrony of estrus. A secondary objective was to assess the effects of causing the dominant follicle (DF) to develop in the presence or absence of a corpus luteum (CL) on follicular dynamics and the synchrony of estrus and ovulation. The experiment was designed as a 2 x 2 x 2 factorial arrangement of treatments with injection of GnRH or estradiol-17 beta and progesterone (E2 + P4) at treatment initiation, duration of CIDR treatment, and injection of PG (prostaglandin F2 alpha) or saline at the time of CIDR insertion as main effects. Estrous cycles (n = 49) in Angus cows were synchronized, and treatments commenced on d 6 to 8 of the estrous cycle. Cows were randomly assigned to receive a CIDR containing 1.9 g of P4 for 7 or 9 d. Approximately half the cows from each CIDR group received either GnRH (100 micrograms) or E2 + P4 (1 mg of E2 + 100 mg of P4) at CIDR insertion. Cows in GnRH or E2 + P4 groups were divided into those that received PG (37.5 mg) or saline at CIDR insertion. All cows received PG (25 mg) 1 d before CIDR removal. Daily ovarian events were monitored via ultrasound. The intervals from GnRH or E2 + P4 treatment to follicular wave emergence were 1.4 and 3.3 d, respectively (P < 0.05). The interval from follicular wave emergence to CIDR removal was longer (P < 0.05) for cows treated with GnRH (6.6 d) than those treated with E2 + P4 (4.7 d) and longer (P < 0.05) for those fitted with a CIDR for 9 d (6.5 d) than those with a CIDR in place for 7 d (4.8 d). Cows treated with PG or GnRH at CIDR insertion had a larger (P < 0.05) DF at CIDR removal than those treated with saline or E2 + P4. Treatment with a CIDR for 9 d also resulted in a larger (P < 0.07) DF at CIDR removal compared with cows fitted with a CIDR for 7 d. The interval from CIDR removal to estrus was shorter (P < 0.05) in cows treated with PG than those treated with saline. The synchrony of estrus and ovulation was not affected by any of the treatments (P > 0.05). Altering the interval from follicular wave emergence to progestin removal or creating different luteal environments in which the DF developed caused differences in the size of the DF at CIDR removal and the timing of the onset of estrus, but it did not affect the synchrony of estrus or ovulation.

Animals↗
PubMed2003

Resynchronization of estrus in cattle of unknown pregnancy status using estrogen, progesterone, or both.

Our objective was to develop treatments applied to cattle of unknown pregnancy status that would resynchronize the repeat estrus of nonpregnant females. In Exp. 1, previously inseminated dairy and beef heifers were assigned randomly to each of three treatments 13 d after AI: 1) no treatment (controls; n = 44); 2) 0.5 mg of estradiol cypionate (ECP) i.m. on d 13 and 20 at the time of insertion and removal of a used intravaginal progesterone (P4)-releasing insert (CIDR; P4 + ECP; n = 44); and 3) same as P4 + ECP without injections of ECP (P4; n = 42). The P4 + ECP (>90%) and P4 (>75%) protocols effectively synchronized repeat periods of estrus to 2 d and did not harm established pregnancies. In Exp. 2, treatments similar to those in Exp. 1 were applied to previously inseminated beef heifers (n = 439). Feeding 0.5 mg of melengestrol acetate (MGA) from d 13 to 19 after AI replaced the CIDR as a source of progestin. Of those heifers not pregnant (n = 65) after the initial AI, more than 86% were reinseminated, but conception was decreased (P < 0.05) by 28 to 39% compared with controls. In Exp. 3, previously inseminated lactating beef cows at four locations were assigned within herd to each of three treatments: 1) no treatment (control; n = 307); 2) same as in Exp. 1, but with P4 + 1 mg of estradiol benzoate on d 13 and 20 (P4 + EB; n = 153); and 3) same as in Exp. 1, P4 + ECP (n = 149). Treatments with P4 plus estrogen did not decrease conception rates in pregnant cows at any location, but increased (P < 0.05) the percentage of nonpregnant cows returning to estrus between 19 and 23 d after timed AI from 29% in controls to 86% in P4 + EB and 65% in P4 + ECP cows. Conception rates at the return estrus were not decreased when treatments occurred between d 13 and 20. In Exp. 4, lactating beef cows were assigned as in Exp. 3 to each of three treatments: 1) no treatment (controls; n = 51); 2) P4 + ECP (n = 47), as in Exp. 1; and 3) a single injection of ECP on d 13 (n = 48). Previously established pregnancies were not harmed (P = 0.70), and return rates of nonpregnant cows did not differ (P = 0.78) among treatments. In summary, in both heifers and lactating beef cows, the P4-based resynchronization treatments increased synchronized return rates when estrus detection rates were low, had no negative effects on established pregnancies, and decreased or tended to decrease conception rates at the resynchronized estrus.

Administration, Intravaginal↗