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PubMed1982

Analysis of the estrous cycle of the laboratory-housed Senegal galago (Galago senegalensis senegalensis): natural and induced cycles.

The natural estrous cycle of captive Senegal galagos was analyzed from daily records of 11 cycling females for 18 months, and induction of vaginal estrus and ovulation by gonadotropins and estrogen were examined in 9 females. No seasonal trend in cycling was indicated, as at least 5 of the 11 cycling females exhibited vaginal estrus during each month. Cycle lengths and duration of estrus were consistent for each female but varied significantly among females. Individuals' average cycle lengths ranged from 29.2 +/- 0.8 to 39.3 +/- 3.4 days, and duration of estrus from 4.8 +/- 0.2 to 6.7 +/- 0.4 days. Vaginal estrus was induced by PMSG and PMSG-HCG combinations, and by estradiol. The gonadotropins also induced growth and ovulation of more than one follicle.

Animals↗
PubMed2003

Determination of the estrous cycle phases of rats: some helpful considerations.

The short length of the estrous cycle of rats makes them ideal for investigation of changes occurring during the reproductive cycle. The estrous cycle lasts four days and is characterized as: proestrus, estrus, metestrus and diestrus, which may be determined according to the cell types observed in the vaginal smear. Since the collection of vaginal secretion and the use of stained material generally takes some time, the aim of the present work was to provide researchers with some helpful considerations about the determination of the rat estrous cycle phases in a fast and practical way. Vaginal secretion of thirty female rats was collected every morning during a month and unstained native material was observed using the microscope without the aid of the condenser lens. Using the 10 x objective lens, it was easier to analyze the proportion among the three cellular types, which are present in the vaginal smear. Using the 40 x objective lens, it is easier to recognize each one of these cellular types. The collection of vaginal lavage from the animals, the observation of the material, in the microscope, and the determination of the estrous cycle phase of all the thirty female rats took 15-20 minutes.

Animals↗
PubMed1995

Evidence of ovulation in goats (Capra hircus ) with short estrous cycle and its occurrence in the tropics.

The influence of season and exposure to buck on the length of the estrous cycle were determined in 32 normally cycling native goats of different ages and parity. The estrous cycle durations were classified as short, medium and long. Ten goats (31%) exhibited medium length estrous cycles; 22 animals (69%) exhibited a combination of short, medium and long estrous cycles. Of the 155 estrous cycles studied, 15% were short, 72% were medium and 13% were long. Short estrous cycles were significantly shorter (P < 0.01) in estrus duration than medium or long estrous cycles. Significant differences (P < 0.05) for estrous cycle length and estrus duration were found between does but not within does. The presence of a buck for 8 to 16 h showed no significant effect on the length of the estrous cycle or on estrus duration, but a 24-h exposure period to a buck yielded shorter estrous cycles and estrus duration than found in the unexposed control group. Estrous cycles were significantly shorter (P < 0.01) in October, when rainfall is 57.9% of the annual total, and significantly longer (P < 0.01) in February, when rainfall is low at 0.2% of the annual total. A negative linear relationship (r = -0.87) was observed between estrous cycle and rainfall. Twenty-eight (90.3 %) of the short estrous cycles were ovulatory. The short cycles had a relatively lower ovulation rate than medium and long estrous cycles. The results indicate that the short estrous cycle in goats is associated with ovulation, and its occurrence in the tropics is related to rainfall.

Journal Article↗
PubMed2006

Variations in opioid peptide levels during the estrous cycle in Sprague-Dawley rats.

The estrous cycle, with its various hormonal conditions, may provide us with the means of understanding how endocrine states relate to opioid mechanisms. There has been increasing experimental support for interaction between sex steroids and opioid peptides in the central nervous system. Here, we describe fluctuations in endogenous brain immunoreactive (ir) peptide levels during various phases of the estrous cycle in the female Sprague-Dawley rat. Ir levels of dynorphin A, dynorphin B, Leu-enkephalin-Arg(6), Met-enkephalin-Arg(6)Phe(7) and nociceptin/orphanin FQ were measured in the pituitary gland and in 10 areas of the brain during the diestrus, proestrus and estrus phase. In several areas of the brain, basal levels of endogenous opioid peptides showed variation during the course of the estrous cycle. Significant differences were found between the diestrus state and the proestrus and/or estrus conditions, particularly in the nucleus accumbens, caudate putamen and the substantia nigra. The ir levels of the endogenous peptide nociceptin/orphanin FQ became altered in only one of the areas measured, indicating less variance during the estrous cycle. Correlation analyses revealed that significant associations between dynorphin A or dynorphin B and Leu-enkephalin-Arg(6) were found more often during estrus than during the diestrus and proestrus conditions. The ratio between the ir levels of Leu-enkephalin-Arg(6), a cleavage product of the enzymatic conversion of dynorphin peptides into shorter peptides in vivo, and dynorphin peptides was calculated. The significantly lower ratio between Leu-enkephalin-Arg(6) and dynorphin B in diestrus than in proestrus and estrus also indicates cyclic fluctuations in the enzymatic cleavage of dynorphin. These findings are discussed in relation to the possible role of interactions between sex steroids and opioid peptide mechanisms during the normal estrous cycle.

Animals↗
PubMed2004

Acute stress impairs spatial memory in male but not female rats: influence of estrous cycle.

We investigated how sex and estrous cycle influenced spatial recognition memory in the Y-maze after exposure to acute restraint stress. In Experiment 1, intact male and female rats were restrained for 1 h and then 2 h after the start of restraint, rats were trained on the Y-maze. After a 4 h delay, hippocampal-dependent spatial recognition memory was assessed. Acute stress produced opposite patterns between the sexes with spatial memory being impaired in males and facilitated in females. Serum corticosterone measures indicated that both sexes showed a robust corticosterone response after restraint and a moderate corticosterone response after Y-maze exposure. Serum corticosterone levels in response to restraint and Y-maze were not statistically different between the sexes. Experiment 2 examined the influence of the estrous cycle on spatial memory ability after acute stress. Acute stress facilitated spatial memory in females compared to controls, regardless of the estrous cycle phase (estrus and proestrus). Moreover, females in proestrus showed higher serum corticosterone levels during restraint compared to females in estrus. No differences in corticosterone levels were observed at baseline or following 2 h of recovery from restraint. These data show important differences in how sex and estrous cycle influence cognitive functions following acute stress.

Acute Disease↗
PubMed1978

Possible relations between the secretory cycle of the neurosecretory cells in the rat paraventricular nucleus and the estrous cycle.

The ultrastructure of neurosecretory cells in the paraventricular nucleus of the female rat in various stages of the estrous cycle was studied by electron microscopy. On account of the secretory cycle, the neurosecretory neurons were classified into four types, and the incidence of each type was counted throughout the estrous cycle. In proestrous afternoon, neurons at the phase of protein synthesis (Type I neuron) increased in number. In estrus and metestrus, neurons at the phase of granule production (Type II neuron) and granule storage (Type III neuron) increased in number. In diestrus and in early morning of the proestrus, neurons at the phase of granule transport (Type IV neuron) and Herring bodies increased in number and in size. The secretory cycle in the paraventricular nucleus of the female rat was intimately related to the estrous cycle. We also observed the neurons in the supraoptic nucleus, but there were no changes accompanying the estrous cycle.

Animals↗
PubMed1980

Short estrous cycles and associated serum progesterone levels in beef cows.

Short estrous cycles in beef cows were investigated in two experiments. In trial 1, breeding dates from 2,854 fall-calving Angus cows were used to determine the incidence of short estrous cycles. Of 198 cycles of less than 17 days, 170 were between the first and second detected estrus. Estrous cycles of 7 to 10 days occurred more frequently (P<.005) than other short estrous cycles. Eight-day estrous cycles were most frequent. In the second experiment, calves were weaned from 25 of 33 anestrous spring-calving, crossbred Simmental cows. Compared to herdmates still nursing calves, an increased percentage of cows which had calves weaned were observed in estrus within 10 and 25 days after the date of weaning (P<.005) and a higher percentage had 7- to 10-day estrous cycles. Cows that were observed in estrus within 10 days after weaning were inseminated with Angus semen at their first estrus and with Simmental semen at their second estrus. No cows conceived on the first estrus of 7- to 10-day estrous cycles; 61.5% conceived on the second estrus. Serum progesterone was higher (P<.01) before the second estrus than the first.

Journal Article↗
PubMed2004

Prostaglandin F2alpha-induced estrus in ewes exhibiting estrous cycles of different duration.

Effects of prostaglandin F(2alpha) (PGF(2alpha)), administered during the mid-luteal phase of the estrous cycle, were examined in ewes exhibiting estrous cycles classified as short (< or =16.5 days, short-cycle ewes, n = 10) or long (> or =18 days, long-cycle ewes, n = 9) based on the durations of two estrous cycles (cycles -2 and -1) before treatment. The ewes received (i.m.) 20mg of PGF(2alpha) on day 10 of the third estrous cycle (cycle 0) followed, 36 h later, by 25 microg of gonadotropin releasing hormone (GnRH) to time the events of ovulation. Duration of subsequent estrous cycles +1 and +2 were recorded, and then the ewes were treated with the same combination of PGF(2alpha) and GnRH beginning on day 10 of estrous cycle +3. Ovaries were recovered 6h after GnRH administration to assess development of pre-ovulatory follicles. The proportion of ewes that exhibited estrus after PGF(2alpha) and GnRH treatment on cycle 0 was not different (P > 0.05) between short- and long-cycle ewes. Onset of estrus occurred sooner (P < 0.05) after PGF(2alpha) injection in short-cycle ewes than in long-cycle ewes (1.9 +/- 0.1 days and 2.3 +/- 0.1 days, duration of cycle 0 was 11.9 and 12.3 days, respectively). Duration of estrous cycle +1 was 1.2 days longer (P < 0.01) than cycle -1 in short-cycle ewes. However, duration of estrous cycle +1 did not change (P > 0.05) after PGF(2alpha) and GnRH administration in ewes having long cycles. Pre-ovulatory follicles did not differ (P > 0.05) in numbers, diameter, layers of granulosa cells nor concentrations of progesterone and estradiol-17beta in follicular fluid between short- and long-cycle ewes after PGF(2alpha) and GnRH treatment. In conclusion, ewes having short or long estrous cycles responded differently to PGF(2alpha) and GnRH treatment with respect to the interval to onset of estrus and duration of the subsequent estrous cycle.

Animals↗
PubMed1990

Immunoreactive somatostatin diurnal rhythms in rat pineal, retina and harderian gland: effects of sex, season, continuous darkness and estrous cycle.

Diurnal profiles of the content of immunoreactive somatostatin (IRS) in the male and female rat pineal, Harderian gland and retina have been studied. Supplementary experiments have been performed to elucidate a possible effect of infradian cycles, namely estrous and seasonal cycles, and continuous dark on IRS concentration. Results demonstrate that the IRS content in the rat pineal gland, Harderian gland and retina is submitted to diurnal variations, but not under all studied conditions. A sexual dimorphism exists between male and female animals: male rats showed higher IRS content in pineal (103.8 +/- 4.7 vs 32.3 +/- 1.8 pg IRS/gland), but lower in retina (1,362.1 +/- 82.7 vs 2,176 +/- 102.2 +/- pg IRS/mg of protein) and Harderian gland (10.3 +/- 0.8 vs 30.6 +/- 3.5 pg IRS/mg of protein). Additionally, seasonal differences appeared: in male and female animals pineal IRS content was lower in spring than in November. This decrease also appeared in female retina IRS concentration. Estrous cycle did not seem to change IRS content in the three studied tissues. Finally, pineal IRS rhythm persisted after continuous dark for a week. These results demonstrate, in the rat, sexual differences in the IRS content of the various tissues studied and suggest a physiological role for somatostatin, possibly related to seasonal adaptation.

Animals↗
PubMed2001

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

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

Animals↗
PubMed1983

Uptake of serotonin and norepinephrine in hypothalamic and limbic brain regions during the estrous cycle and the effect of neurotoxin lesions on estrous cyclicity.

The temporal pattern of hypothalamic and limbic aminergic activity during the estrous cycle has been measured by changes in the serotonergic and noradrenergic neuronal uptake during the regular estrous cycle. Significant changes (p = 0.006, 0.01) in the uptake of 3H 5-HT and 3H NE were recorded in the suprachiasmatic nuclei (SCN) at 1200 hours on proestrus. Significant changes (p = 0.01, 0.018) in the uptake of 3H 5-HT in the preoptic area (POA) were found at 1200 hours on both diestrus and proestrus while median eminence (ME) 5-HT showed a significant increase only during proestrus (p = 0.001). In the amygdala (AMYG) 3H 5-HT uptake was significantly different at 1200 hours on diestrus and proestrus while 3H NE uptake was significant (p = 0.001) at 1200 hours only during proestrus. The plasma proestrous luteinizing hormone surge occurred at 1700 hours. The serotonin neurotoxin, 5,7-dihydroxytryptamine, was stereotaxically injected through a 30 gauge needle in concentrations of 5-10 micrograms/microliters/minute for 1 minute in various nuclear regions. In the SCN 4 or 5 day estrous cyclicity was interrupted by diestrus for average periods of up to 15 days; in the POA for periods of 10 days; in the ME for periods of 13 days; and in the AMYG for periods of up to 6 days. Sham injections of 5% ascorbic acid had no effect on cyclicity and following these periods of acyclicity rats resumed normal cycles. These lesion effects and patterns of uptake suggest a common timing mechanism utilizing serotonergic raphe systems for neuroendocrine control. Lesions with 5,7-DHT in all four brain regions disrupt cyclicity, but the greatest delays occur in the SCN and ME regions which are particularly critical to intrinsic neuroendocrine rhythms. Patterns of increase in reuptake capacity in all 4 regions occur 3 hours prior to the critical period for the plasma LH surge and may be an important mechanism for many types of neuroendocrine events including ovulation.

5,7-Dihydroxytryptamine↗
PubMed1979

Relationship of the estrous cycle to milk composition.

The relationship of the estrous cycle to milk composition was examined in 15 Holstein cows in first lactation which were approximately 45 days postpartum. Composite milk samples were collected twice daily and analyzed for progesterone, fat, protein, total solids, sodium, potassium, magnesium, calcium, and somatic cells. Milk progesterone was minimal (less than ng/ml) from day -1 to day 2 (day 0 = estrus) of the estrous cycle and then increased at a relatively constant rate through day 15. Milk yield and sodium and magnesium concentrations of the milk varied with days of the estrous cycle. Mean milk yield was highest and sodium and magnesium concentrations were lowest on day 1. However, sodium concentration of the milk was the only component that varied significantly during the 3 days centered on estrus (days -1, 0, and 1). No other milk component changed significantly during the estrous cycle. Although milk yield and composition varied during the estrous cycle, none of these components appeared to be a practical indicator of estrus.

Animals↗
PubMed2006

Nuclear estrogen and progesterone receptors in the oviduct of heifers under natural and superovulated estrous cycles.

Oviducts from 22 crossbred heifers were examined for the presence of nuclear estrogen (ERalpha) and progesterone (PR) receptors at different phases (estrus, metaestrus and diestrus) of naturally occurring estrous cycles and estrous cycles during which superovulation was induced. Receptors were detected by immunohistochemistry in the epithelial cells, connective tissue and muscular layer of oviductal infundibulum, ampulla, ampullary/isthmic transition and isthmus. Epithelial ERalpha was found along the entire oviduct regardless of the cycle phase and of the circulating concentrations of 17beta-estradiol (E(2)) and progesterone (P(4)). Epithelial PR was found mainly at the ampullary-isthmic transition and isthmus and more intensely at the estrus phase but their amount was not correlated with P(4) concentrations. ERalpha in the connective tissue was more abundant at the infundibulum and ampulla, regardless of the phase of the estrous cycle and of E(2) and P(4) circulating concentrations. PR in the connective tissue was found mostly at the ampulla, regardless of the estrous cycle phase but no correlations were found between amount and P(4) concentrations. ERalpha staining intensity in the muscular layer was similar at all phases of the estrous cycle and at all anatomical segments of the oviducts. However, PR staining was more intense at the isthmus during the metaestrus phase and it was negatively correlated with P(4) concentrations. In general, data from the present research suggest that P(4) exerts an inhibitory role upon ERalpha and PR. Also, no differences were found between animals subjected or not to superovulation.

Animals↗
PubMed2003

Premature prostaglandin F2alpha secretion causes luteal regression in GnRH-induced short estrous cycles in cyclic dairy heifers.

This study aimed to confirm that the luteolysis in normal-cycling dairy heifers seen during short estrous cycles induced with cloprostenol (Clp) and GnRH administered 24h apart is caused by a premature release of prostaglandin F(2alpha) (PGF(2alpha)). A further aim was to study the PGF(2alpha) release pattern more closely to determine whether it resembles the spontaneous release occurring during normal regression of the corpus luteum (CL) or whether PGF(2alpha) is continuously secreted after the induced ovulations, leading to short estrous cycles. Twenty-four Ayrshire heifers were allotted to four equally sized groups. After estrus synchronization with 0.5mg of Clp, a new luteolysis was induced with 0.5mg of Clp on Day 6 (groups T-d6 and C-d6) or Day 7 (groups T-d7 and C-d7) after ovulation. Gonadorelin (0.1mg i.m.) was given to groups T-d6 and T-d7 to induce premature ovulation 24h later. Groups C-d6 and C-d7 served as controls. Ovaries were examined daily by transrectal ultrasonography, while blood samples (for progesterone and 15-ketodihydro-PGF(2alpha) analyses) were obtained via a jugular catheter every 3h, starting from the second Clp treatment and continuing for 9 days postovulation. Unresponsiveness to Clp or anovulation resulted in 4 C-d6 heifers being excluded. Four heifers in group T-d6 and three in group T-d7 had a short estrous cycle of 8-12 days, while all others had a cycle of normal length. Significant elevations in 15-ketodihydro-PGF(2alpha) concentrations with recurrent high peaks coincided with a decrease in progesterone concentration and were detected in all heifers that showed a short estrous cycle, but not in any heifers with normal estrous cycles in groups T and C. In conclusion, a premature release of PGF(2alpha), which closely resembles its release during spontaneous luteolysis, causes luteal regression in these short cycles.

Animals↗
PubMed1979

Estrogen and progesterone concentrations in bovine milk during the estrous cycle.

Estrogen and progesterone concentrations in milk during the estrous cycle were estimated in 18 normally cycling Holstein dairy cows. The estrogen and progesterone concentrations in milk during the estrous cycle followed the pattern described for them in blood in the corresponding period. During most of the estrous cycle, estrogen concentration remained at approximately 200 pg/ml and reached a proestrous peak of 360 +/- 127 pg/ml on day 19. The progesterone concentration in milk during the estrous cycle increased to a peak on day 13 (45.5 +/- 6.6 ng/ml) and thereafter declined towards estrus. Estrus detection/prediction based on milk progesterone concentrations appears feasible in view of the significant differences in milk progesterone concentrations between the early luteal (post-ovulatory), luteal and rapid follicular growth periods of the estrous cycle.

Journal Article↗
PubMed1983

Ovarian activity during normal and abnormal length estrous cycles in the goat.

Ovarian and behavioral cyclicity were studied during 3-5 estrous cycles in a group of 10 multiparous, Nubian does. Changes in ovarian morphology throughout the estrous cycle were identified and photographed laparoscopically. Forty-eight estrous cycles were observed during the study and of these, 21 were abnormally short in duration (mean +/- SEM, 6.5 +/- 0.5 days). Mean duration of the estrous cycle for the 27 normal length cycles was 21.5 +/- 0.8 days. Eighteen/21 (86%) of the short cycles and 6/27 (22%) of the normal cycles were initiated during early breeding season (between September 1st and October 15th). There were no differences (P greater than 0.05) in the duration of estrus for the short (mean, 2.9 +/- 0.3 days) and normal (mean, 2.8 +/- 0.8 days) cycle groups. A total of 6/11 (55%) of the short duration cycles examined laparoscopically appeared to be anovulatory, but ovulation was observed in all normal cycles examined. The number of corpora lutea (CL) observed during normal length and short estrous cycles was 3.1 +/- 0.2 and 2.2 +/- 0.2, respectively (P less than 0.01). The cumulative percentage of does that showed morphological evidence of ovulation by the first, second and fifth day after the onset of estrus was 30%, 60% and 100%, respectively. Based on distinct differences in morphology and development, 2 types of CL were identified. The maximum visible diameter of Type I and Type II CL was 9.4 +/- 0.6 mm and 5.1 +/- 0.5 mm, respectively. These data document ovarian morphology throughout the normal and abnormal duration estrous cycle of the goat and indicate that 1) short estrous cycles observed early in the breeding season are associated with prematurely regressing CL or anovulation and 2) the ovary produces 2 morphologically distinct types of CL which differ not only in size and appearance, but also potentially in postovulatory function and longevity.

Animals↗
PubMed2001

Effects of mild food deprivation on the estrous cycle of rats.

It has long been known that severe food deprivation disrupts the estrous cycle. One of the main problems with behavioral tasks that use food for reinforcement is the requirement that the animal be food deprived. This manipulation could be problematic in studies using female animals, since it may interfere with the estrous cycle of the animals. The purpose of the present study was to investigate: (1) the effect of mild food deprivation on four different strains of rats, (2) factors in the food deprivation procedure that could affect the estrous cycle, and (3) the possible effect of enriched diets during food deprivation on the estrous cycle. A comparison of the estrous cycle in four different rat strains revealed differences in the reliability of the estrous cycle even before the onset of food deprivation. Fischer, Long-Evans, and Sprague-Dawley rats all showed reliable cycle patterns. This was not the case for Brown Norway rats. During food deprivation, the cycle of the Fischer rats was disrupted, whereas the Long-Evans and Sprague-Dawley animals continued to cycle. Both the rate of weight loss and the percent of ad libitum body weight were related to cessation of the estrous cycle. However, enriching an animal's diet with sugar or oil additives delayed the disruption of the estrous cycle. Additionally, animals resumed cycling when returned to ad libitum weight levels. The present findings suggest that when animals need to be food deprived, preference should be given to using Long-Evans or Sprague-Dawley rats. If Fischer rats must be used, they should not be deprived below 90-95% of their ad libitum body weight. Strategies for future food deprivation studies are discussed, as well as a comparison of the effects of mild and severe food deprivation.

Aging↗
PubMed1988

Plasma luteinizing hormone and progesterone concentrations in goats with estrous cycles of normal or short duration after prostaglandin F2 alpha administration during diestrus or pregnancy.

Plasma luteinizing hormone (LH) and progesterone concentrations were compared in does experiencing short-duration estrous cycles and in does with estrous cycles of normal duration. The short-duration estrous cycles were observed immediately after induction of abortion in pregnant does by use of prostaglandin (PG) F2 alpha. Intramuscular administration of 5 mg of PGF2 alpha was accomplished in 8 does that were 52 to 63 days into gestation and in 9 cycling does at 7 to 10 days after estrus. In both groups, the mean plasma concentration of progesterone decreased from a luteal phase concentration immediately before to less than 1 ng/ml by 24 hours after PGF2 alpha administration. Of the 8 does that aborted, 6 experienced short-duration estrous cycles, and 4 of these 6 had an LH surge during the time of blood sample collection. The mean time from PGF2 alpha administration to the LH surge was significantly (P less than 0.05) longer in does with short-duration estrous cycles (71 hours) than that in does with estrous cycles of normal duration (58 hours). The mean area under the LH concentration curve was significantly (P less than 0.005) less for does with short-duration estrous cycles. Short-duration estrous cycles were associated with delayed preovulatory LH surges of reduced magnitude.

Abortion, Induced↗