Oestrous cycles and the breeding season of the Père David's deer hind (Elaphurus davidianus)

Reproductive cycles were studied in a group of tame Père David's deer hinds. The non-pregnant hind is seasonally polyoestrous and, in animals studied over 2 years, the breeding season began in early August (2 August +/- 3.3 days; s.e.m., N = 9) and ended in mid-December (18 December +/- 5.7 days; N = 8) and early January (6 January +/- 3.2 days; N = 11) in consecutive years. During the anoestrous period, plasma progesterone concentrations were low (0.2 +/- 0.01 ng/ml) or non-detectable. There was a small, transient increase in progesterone values before the onset of the first cycle of the breeding season. In daily samples taken during an oestrous cycle in which hinds were mated by a marked vasectomized stag, progesterone concentrations remained low (less than 0.5 ng/ml) for a period of about 6 days around the time of oestrus, showed a significant increase above oestrous levels by Day 4 (Day 0 = day of oestrus) and then continued to increase for 18 +/- 2.8 days to reach mean maximum luteal levels of 3.5 +/- 0.6 ng/ml. The plasma progesterone profiles from a number of animals indicated that marking of the hinds by the vasectomized stag did not occur at each ovulation during the breeding season and therefore an estimate of the cycle length could not be determined by this method. In the following year, detection of oestrus in 5 hinds was based on behavioural observations made in the absence of the stag. A total of 19 oestrous cycles with a mean length of 19.5 +/- 0.6 days was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of fasting on luteal function, leptin and steroids concentration during oestrous cycle of the goat in natural photo-status

The effect of fasting during oestrous cycle on the occurrence of oestrous and concentration of leptin and steroid hormones was investigated in goats. Sixteen Ardi goats of 10-12 month of age were split into two groups (control and fasting). Oestrous was synchronized with intravaginal progesterone sponges and detected 24h after sponge removal. Blood samples were collected at the days 5, 10, 15 of each cycle. Fasting of mature goats twice for 4 days starting on day 10 of two successive oestrous cycles inhibited oestrous behaviour and resulted in reduced concentration of leptin, progesterone and testosterone with different timing. Day 5 of the second cycle showed significant decrease in the plasma level of leptin (1.6+/-0.15 ng/ml) and progesterone (1.6+/-0.1 ng/ml) as compared to control group (3.2+/-0.15 ng/ml and 4.1+/-0.2 ng/ml, respectively). Testosterone started to decrease from day 10 of the second cycle (35.0+/-12.0 pg/ml) as compared to control group (65.0+/-15.0 pg/ml); the decrease in this hormone was significant in day 15 of the second cycle (65.0+/-16.0 pg/ml) as compared to the control (320.0+/-50.0 pg/ml). These data suggest that fasting-induced inadequate corpus luteum function, hence, lowering progesterone plasma level may partly be more leptin-dependent than the following decrease in plasma level of testosterone.     

Social influences on oestrous cycle length and plasma progesterone concentrations in the female lesser mouse lemur (Microcebus murinus)

Plasma progesterone concentrations were recorded during one breeding season in 19 lesser mouse lemur females living in different social conditions. The oestrous cycle length and the progesterone profile mainly depended on the social environment of the female. For totally isolated females, the oestrous cycle lasted 38 +/- 5.7 days and included a 25-30-days spontaneous luteal phase with a progesterone peak about 100 ng/ml between the 20th and 25th days after oestrus, and a prolonged preovulatory period of 10-15 days which could be considered equivalent to the follicular phase of a menstrual cycle. When females were able to communicate through olfactory, visual and auditory signals, the oestrous cycle was significantly lengthened (53.7 +/- 5.9 days). When females had tactile contacts, the oestrous cycle was further lengthened (62.7 +/- 0.8 days). This lengthening of the oestrous cycle was related to an extension of the luteal phase associated with a decrease in progesterone concentrations during this period. In females maintained with one male (paired) or with males and females (heterosexually grouped), large individual variations were shown in cycle lengths or in progesterone concentrations. In these females, cycle lengths and progesterone concentrations were inversely correlated to plasma cortisol concentrations.     

Sex hormones correlated with sex skin swelling and rectal temperature during the menstrual cycle of the pigtail macaque (Macaca nemestrina).

Daily measurement of serum luteinizing hormone, estradiol-17beta, and progesterone were made during the menstrual cycle in nine pigtail macaques (Macaca nemestrina). All data were normalized to the day of the luteinizing hormone peak. Serum estradiol-17beta increased from approximately 100 pg/ml during the early follicular phase to 442 +/- 156 pg/ml during the maximum midcycle concomitant with the luteinizing hormone peak, and a small increase in serum estradiol-17beta was observed during the luteal phase coincident with the progesterone peak. Serum progesterone values increased slightly at the time of the luteinizing hormone peak and increased from 0.2-0.3 ng/ml during the midfollicular phase to peak levels of 8.3 +/- 1.75 ng/ml 9 days after the luteinizing hormone surge. Serum luteinizing hormone remained low and relatively constant throughout the early and midcycle, then sharply increased approximately four-fold to peak values of 6.25 +/- 0.9 ng/ml. Sex skin swelling increased slowly during the follicular phase and declined slowly throughout the early luteal phase. Rectal temperature did not change significantly throughout the menstrual cycle. The similarity of plasma sex hormone changes during the menstrual cycle between women and the pigtail macaque suggested that this nonhuman primate should be a useful animal model for studying human reproduction.     

Plasma concentrations of progesterone and testosterone in captive woolly opossums (Caluromys philander)

Plasma testosterone and progesterone concentrations were measured in captive woolly opossums, a didelphid marsupial originating from neotropical forests in French Guyana. Although not exposed to cyclic environmental conditions as in the field, both sexes exhibited spontaneous circannual changes in sexual hormones. Males showed synchronous variations in plasma testosterone characterized by significant elevated concentrations during April and September (8.6 +/- 1 ng/ml, N = 5) and lower levels from May to July (3.6 +/- 0.4 ng/ml). In females, synchronous periods of 2-3 successive oestrous cycles occurred. Between these periods, females remained acyclic. The oestrous cycle, determined by urogenital smears, lasted 28-45 days (n = 14) and included a 20-day spontaneous luteal phase in which progesterone concentrations reached 30-40 ng/ml plasma. Even though testosterone concentrations in paired males increased significantly in response to oestrous periods of the paired females, spontaneous circannual rhythms of sexual activity were not well synchronized between the sexes in captivity. When compared to field data, sexual activity of captive animals followed a pattern similar to that in wild animals, without any changes in males but with a delay of 3 months in females.     

Progesterone profile in buffaloes during various stages of oestrous cycle using radioimmunoassy technique

Investigation were carried out to study the norms of progesterone concentration in the blood serum of buffaloes during various phases of oestrous cycle. Twenty four animals (12 heifers and 12 cows) were used. The blood serum samples were stored at -20 degrees C until processed for progesterone assay. The progesterone concentrations were measured by the radioimmunoassay technique. The progesterone levels were 0.360 +/- 0.062 and 0.334 +/- 0.066 ng/ml on the day of oestrus in buffalo-heifers and buffalo-cows, respectively. The values were around 1 ng/ml till day 6, followed by a gradual increase to a peak average value of 4.888 +/- 0.399 and 5.119 +/- 0.415 ng/ml on day 15 of the cycle in heifers and cows, respectively. Thereafter, the progesterone concentration fell abruptly to a level similar to that at oestrus. The mean progesterone value a day before oestrus was 0.488 +/- 0.067 and 0.577 +/- 0.053 ng/ml in buffalo-heifers and buffalo-cows, respectively. The mean progesterone concentration of different days of the cycle (except day 16) did not differ significantly (P / -0.01) between heifers and cows.     

Extension of oestrous cycles and prolonged secretion of progesterone in non-pregnant cattle infused continuously with oxytocin

The experimental objective was to evaluate how continuous infusion of oxytocin during the anticipated period of luteolysis in cattle would influence secretion of progesterone, oestradiol and 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM). In Exp. I, 6 non-lactating Holstein cows were infused with saline or oxytocin (20 IU/h, i.v.) from Day 13 to Day 20 of an oestrous cycle in a cross-over experimental design (Day 0 = oestrus). During saline cycles, concentrations of progesterone decreased from 11.0 +/- 2.0 ng/ml on Day 14 to 2.0 +/- 1.3 ng/ml on Day 23; however, during oxytocin cycles, luteolysis was delayed and progesterone secretion remained near 11 ng/ml until after Day 22 (P less than 0.05). Interoestrous interval was 1.6 days longer in oxytocin than in saline cycles (P = 0.07). Baseline PGFM and amplitude and frequency of PGFM peaks in blood samples collected hourly on Day 18 did not differ between saline and oxytocin cycles. In Exp. II, 7 non-lactating Holstein cows were infused with saline or oxytocin from Day 13 to Day 25 after oestrus in a cross-over experimental design. Secretion of progesterone decreased from 6.8 +/- 0.7 ng/ml on Day 16 to less than 2 ng/ml on Day 22 of saline cycles; however, during oxytocin cycles, luteolysis did not occur until after Day 25 (P less than 0.05). Interoestrous interval was 5.9 days longer for oxytocin than for saline cycles (P less than 0.05). In blood samples taken every 2 h from Day 17 to Day 23, PGFM peak amplitude was higher (P less than 0.05) in saline (142.1 +/- 25.1 pg/ml) than in oxytocin cycles (109.8 +/- 15.2 pg/ml). Nevertheless, pulsatile secretion of PGFM was detected during 6 of 7 oxytocin cycles. In both experiments, the anticipated rise in serum oestradiol concentrations before oestrus, around Days 18-20, was observed during saline cycles, but during oxytocin cycles, concentrations of oestradiol remained at basal levels until after oxytocin infusion was discontinued. We concluded that continuous infusion of oxytocin caused extended oestrous cycles, prolonged the secretion of progesterone, and reduced the amplitude of PGFM pulses. Moreover, when oxytocin was infused, pulsatile secretion of PGFM was not abolished, but oestrogen secretion did not increase until oxytocin infusion stopped.     

Characterization of the oestrous cycle and mating season of squirrel monkeys from copulatory behaviour.

Observations of the behaviour of squirrel monkeys, including 8 opposite-sex pairs during daily 30-min social encounters and 2 mixed-sex permanent groups during daily 30-min observation sessions, over a 14-month period were used to determine the periodicity of the oestrous cycle and annual mating season. The median and modal length of the oestrous cycle was 8 days, within which copulations were limited to a 1--2 day period. In a cyclic female, plasma progesterone levels over a 24-day period dropped from 85--151 ng/ml to 25 ng/ml 2 days before oestrus. In non-cyclic females plasma progesterone values were less than 15-4 ng/ml. Males exhibited a 6-8--19-7 week 'season' of copulation and ejaculation. The onset of this 'mating season' in August coincided with the annual peak in male body weight (the 'fatted male' phenomenon).     

Circulating progesterone and oestradiol-17 beta concentrations in cyclic Cape porcupines, Hystrix africaeaustralis

The general pattern of steroid secretion during the 30-day oestrous cycle of the Cape porcupine is that of a surge (25-176 pg/ml) in oestradiol-17 beta secretion at the time of perforation of the vaginal closure membrane, followed by an increase in progesterone concentrations, the latter attaining peak values (mean 5.9 +/- 2.1 ng/ml) 8-19 days (13.8 +/- 2.8 days) after vaginal opening. Copulation occurred after the oestradiol-17 beta surge and the length of the luteal phase of the cycle varied from 21 to 35 days (29.3 +/- 4.7 days), this representing 93% of the length of the cycle. Perforation of the vaginal closure membrane was not always accompanied by an increase in oestradiol-17 beta levels and some instances (19%) of vaginal opening were not followed by an increase in progesterone secretion. The hormonal characteristics of the oestrous cycle of females housed with vasectomized males were similar to those of females housed with intact males.     

Effect of high progesterone concentrations during the early luteal phase on the length of the ovulatory cycle of goats

The effect of exogenous progesterone exposure early in the oestrous cycle on the duration of the interovulatory interval was studied in dairy goats. A controlled intravaginal drug release (CIDR-G) device was inserted for 5 days starting at day 0 (D0 group, n=6) or day 3 (D3 group, n=5) postovulation. A third group was composed of untreated control goats (control group, n=7). Daily transrectal ultrasound was carried out during the interovulatory interval to assess the ovarian dynamics. Oestrous behaviour was checked twice a day and serum progesterone levels were assayed in daily jugular blood samples. Treated goats showed two different responses. In three D0 goats and one D3 goat, progesterone concentrations fell immediately after CIDR withdrawal and this was followed by oestrus and ovulation between days 8 and 11 (short cycles). In the other three D0 goats and in four D3 goats the treatment significantly reduced the interovulatory interval (18.3+/-0.3 and 18.5+/-0.3 days, respectively) (shortened cycles) compared with the control group (20.0+/-0.2 days; P<0.05), but the intervals with progesterone concentrations over 1 ng/ml were not different (15.7+/-0.3, 15.8+/-0.7 and 16.0+/-0.5 days for D0, D3 and control goats, respectively). In all D0 goats with a short cycle response, the ovulatory follicle arose from the first follicular wave but in the D3 goat with a short cycle it arose from the second follicular wave. These results showed that premature progesterone exposure early in the ovulatory cycle of the goat affected its length inducing short or shortened cycles. The effect of progesterone could either affect luteotropic support of the corpus luteum (CL) and/or stimulate a premature release of the luteolysin.     

Prolactin administration during the luteal and follicular phase of the oestrous cycle of gilts

In Exp. I infusions of prolactin (0.5 mg in 2 ml sterile saline) were repeated every 2 h for 36 h on Days 12-13 of the cycle. In Exp. II infusions of prolactin were administered from Days 17 to 19 (60 h) at 2-h intervals. Control gilts were given 2 ml sterile saline at similar intervals during the same period. Basal prolactin concentrations before initiation of infusions ranged from 1.3 +/- 0.1 to 5.6 +/- 2.2 ng/ml in both experiments. By 5 min after a prolactin infusion, mean plasma prolactin concentration ranged from 74.9 +/- 5.8 to 113.0 +/- 9.5 ng/ml, but then declined to approximately equal to 10 ng/ml just before the next infusion of prolactin. Administration of prolactin during the luteal phase of the oestrous cycle of the gilts had no effect on basal levels of progesterone, oestradiol or LH. During the follicular phase there were no differences (P greater than 0.05) between control and prolactin-treated gilt progesterone and LH concentrations, but oestradiol plasma values were decreased (P less than 0.05) on the 2nd and 3rd day of prolactin treatment. Our results would indicate that prolactin does not play a major role in the regulation of the oestrous cycle of the pig.     

Effect of presence of the male on initiation of estrous cycle activity of goats

Serum progesterone concentrations and behavioral estrus were determined in two groups of 17 mixed breed dairy does at the beginning of the breeding season. The treatment group was pastured adjacent to two mature bucks while two teaser bucks ran with the group. The control group was pastured without exposure to bucks. Goats were observed for estrus daily for 35 days and samples of jugular blood were collected every other day for radioimmunoassay of progesterone. Signs of estrus were observed in 16 of 17 does in the treatment group within a mean +/- S.E. of 5.5 +/- 1.3 days after introduction of the bucks. Thirteen does demonstrated a progesterone profile characteristic of a normal estrous cycle with peak progesterone concentrations of 5.9 +/- 0.5 ng/ml. Signs of behavioral estrus were not observed in the control group. One control doe demonstrated a progesterone profile characteristic of a normal estrous cycle attaining a peak progesterone concentration of 3.9 ng/ml. Progesterone concentrations in the remaining 16 control does were at or near the lower limits of sensitivity of the assay for the duration of the experiment. Fifteen of the control does exhibited estrus within 7 +/- 1.5 days after exposure to bucks at the end of the experiment. These results clearly demonstrated a profound influence of the male on estrous cycle activity during the beginning of the breeding season.     

Concentration of steroids in bovine peripheral plasma during the oestrous cycle and the effect of betamethasone treatment.

Testosterone, oestradiol and progesterone were measured in peripheral plasma during the oestrous cycle of 6 heifers. Oestradiol and progesterone results confirmed earlier reports. Concentration of testosterone on the day of oestrus was 40+/-3 pg/ml (mean+/-S.E.M.), and two peaks were detected during the cycle, one 7 days before oestrus (1809+/-603 pg/ml) and the other (78+/- 7 pg/ml) on the day before the onset of oestrus. The concentration of progesterone declined in most cases 1 day after the maximum concentration of testosterone. Betamethasone treatment in 5 heifers extended luteal function by an average of 10 days: plasma androstenedione and oestradiol concentrations were unaltered; cortisol values were depressed for at least 16 days after treatment; testosterone concentrations were lowered by 13+/-2-4% during treatment, and except in one heifer the peak on Day -7 was abolished.     

Hormonal evidence for induced ovulation in Monodelphis domestica.

Breeding activity in the South American grey opossum, Monodelphis domestica, is stimulated by the presence of males. This study presents the first analysis of changes in concentrations of plasma progesterone during pregnant and nonpregnant cycles. In Expt 1, females were paired with either intact or vasectomized males to stimulate a reproductive cycle, or were isolated from males. Within 4-8 days of pairing, females showed marked changes in the size of the urogenital opening (vulva), which were paralleled by similar changes in body weight (11.4 +/- 2%; mean +/- SEM; n = 13). There was a second increase and decrease in body weight (21.7 +/- 3.3%; n = 13) in pregnant and nonpregnant cycles during the luteal phase of the cycle. Changes in concentrations of plasma progesterone, determined from samples collected three times a week, were similar in pregnant and nonpregnant cycles. Plasma progesterone concentration, which was increased for 15-18 days, showed two distinct peaks. The first peak, 3-4.5 ng ml-1, occurred immediately after the decrease in vulval swelling, and the second peak (1-2 ng ml-1) occurred 8-12 days later. Concentrations of plasma progesterone were low before parturition occurred. Females isolated from males for 35 days showed no changes in body weight or vulval swelling and concentrations of plasma progesterone remained undetectable. In Expt 2, concentrations of luteinizing hormone (LH) in plasma were determined twice a day for the first few days after pairing. In three of five females an LH peak was detected coincident with the maximal swelling of the vulva.     

Relation between progesterone concentrations during the early luteal phase and follicular dynamics in goats

We studied the relationship between progesterone (P4) concentrations early in the estrus cycle and follicular dynamics in dairy goats. We used seven untreated goats (control group) and six progesterone treated goats (P group) with a controlled internal drug release device from Days 0 to 5 (Day 0: day of ovulation). We performed daily ultrasonograph during the interovulatory interval to determine ovarian change and took daily blood samples to determine serum estradiol 17beta (E2) and P4 concentrations by RIA. We divided the control goats into 3- (n = 4) and 4-wave goats (n = 3), according to the number of follicular waves recorded during the ovulatory cycle. Mean progesterone concentrations between Days I and 5 were higher and mean estradiol concentrations between Days 3 and 5 were lower in 4-wave goats (P4: 3.8+/-0.2 ng/ml; E2: 1.6+/-0.2 pg/ml) than in 3-wave goats (P4: 2.0+/-0.5 ng/ml, P < 0.05; E2: 4.4+/-0.9 pg/ml, P < 0.05). Wave 2 emerged earlier in 4-wave (Day 4.2+/-0.3) than in 3-wave goats (Day 7.3+/-0.3, P < 0.05). Three out of six of the progesterone-treated goats had short cycles (mean 8.0+/-0.0 days) and ovulated from Wave 1. The other three goats had shorter cycles (mean 18.3+/-0.3 days) than the control group (20.0+/-0.2 days; P < 0.05), although they were within the normal range of control cycles (shortened cycles). In the three treated goats with shortened cycles (two with four waves, one with three waves), mean progesterone concentrations between Days I and 5 were higher (4.7+/-0.6 ng/ml) than in the 3-wave control goats. In these goats, Wave 2 emerged at Day 4.3+/-0.3, similar to the time observed in 4-wave goats but earlier (P < or = 0.05) than in 3-wave control goats. Overall results confirm a relationship between the progesterone levels and the follicular wave turnover during the early luteal phase in the goat. Higher progesterone concentrations may accelerate follicular turnover probably by an early decline of the negative feedback action of the largest follicle of Wave 1. This is followed by an early emergence of Wave 2.     

Progesterone and testosterone concentrations during oestrous cycle and pregnancy in the common vole (Microtus arvalis Pallas)

Serum progesterone and testosterone concentrations were measured during different stages of oestrous and pregnancy in paired and unpaired female common voles (Microtus arvalis). Hormone concentrations were measured by ELISA, and cycle stages were determined by vaginal smears. Paired females usually had serum progesterone concentrations of more than 10 ng/ml in the oestrous cycle. A significant maximum was detected in prooestrous (51.70 +/- 7.84 ng/ml, mean +/- S.D.). Serum progesterone concentrations increased from about 40 ng/ml at the beginning of pregnancy to about 70 ng/ml on days 15 and 16. The last 2 days before parturition (days 19 and 20) were characterised by a decrease of progesterone concentrations to ca. 30 ng/ml. The maximum concentration of testosterone was found in prooestrous (1.58 +/- 0.31 ng/ml). Concentrations during pregnancy varied between 1.5 and 2.1 ng/ml. In two of three cases unpaired females exhibited progesterone values below 10 ng/ml, but with varying vaginal smear patterns. The combination of progesterone concentrations and vaginal smear patterns was found to be regular in only 23.8% of the cases. The most frequent cycle stage found was the oestrous (44.2%). Mean concentrations of progesterone (10.43 +/- 13.81 ng/ml) and testosterone (0.85 +/- 1.11 ng/ml) in unpaired females were significantly lower than in paired females, thereby denoting reproductive inactivity in the former. The study presents basic data for several parameters of the reproductive biology in the common vole and confirms the importance of combining hormone assays and vaginal smear monitoring in reproductive research.     

Social suppression of ovarian cyclicity in captive and wild colonies of naked mole-rats, Heterocephalus glaber

To investigate the endocrine cause of reproductive suppression in nonbreeding female naked mole-rats, animals from 35 colonies were studied in captivity. Urinary and plasma progesterone concentrations were elevated in pregnant females (urine: 10.0-148.4 ng/mg Cr, 27 samples from 8 females; plasma: 3.6-30.0 ng/ml, 5 samples from 5 females; Days 21-40 of pregnancy) and cyclic breeding females (urine: 0.5-97.8 ng/mg Cr, 146 samples from 7 females; plasma: less than 1.0-35.4 ng/ml, 25 samples from 7 females). The latter group showed cyclic patterns of urinary progesterone, indicating a mean ovarian cycle length of 34.4 +/- 1.6 days (mean +/- s.e.m.) with a follicular phase of 6.0 +/- 0.6 days and a luteal phase of 27.5 +/- 1.3 days (19 cycles from 9 breeding females). In non-breeding females urinary and plasma progesterone values were undetectable (urine: less than 0.5 ng/mg Cr, 232 samples from 64 females; plasma: less than 1.0 ng/ml, 7 samples from 6 females). Breeding females had higher (P less than 0.001) plasma LH concentrations (3.0 +/- 0.2 mi.u./ml, 73 samples from 24 females) than did non-breeding females (1.6 +/- 0.1 mi.u./ml, 57 samples from 44 females). Urinary and plasma progesterone concentrations in non-breeding females from wild colonies situated near Mtito Andei, Kenya, were either below the assay sensitivity limit (urine: less than 0.5 ng/mg Cr, 11 females from 2 colonies; plasma: less than 1.0 ng/ml, 25 females from 4 colonies), or very low (plasma: 1.6 +/- 0.6 ng/ml, 15 females from 4 colonies). In captivity, non-breeding females removed from their colonies (i.e. the dominant breeding female) and either paired directly with a non-breeding male (N = 2), or removed and housed singly for 6 weeks before pairing with a non-breeding male (N = 5) may develop a perforate vagina for the first time in as little as 7 days. Urinary progesterone concentrations rose above 2.0 ng/mg Cr (indicative of a luteal phase) for the first time 8.0 +/- 1.9 days after being separated. These results suggest that ovulation is suppressed in subordinate non-breeding female naked mole-rats in captive and wild colonies, and show that plasma LH concentrations are significantly lower in these non-breeding females. This reproductive block in non-breeding females is readily reversible if the social factors suppressing reproduction are removed.     

Effect of dietary intake on pattern of growth of dominant follicles during the oestrous cycle in beef heifers

Friesian x Hereford heifers (n = 19; mean +/- s.e.m. body weight (BW) = 375 +/- 5 kg) were used in a randomized incomplete block design. Heifers were fed 0.7 (n = 7; L), 1.1 (n = 7; M) or 1.8% (n = 5; G) of BW in dry matter (DM)/day for 10 weeks. Ovaries were examined by ultrasound, for one oestrous cycle, from week 5 of treatment. Maximum diameter of dominant follicles was smaller (P less than 0.05) in L (11.8 +/- 0.1 mm) than in M (13.7 +/- 0.2 mm) or G (13.2 +/- 0.3 mm) heifers. Growth rate (mm/day) of dominant follicles during the oestrous cycle was not affected (P greater than 0.05) by dietary intake. Persistence of dominant follicles was shorter (P less than 0.05) in L (9.8 +/- 0.2 days) than in M (11.9 +/- 0.3 days) or G (12.7 +/- 0.4 days) heifers. Three dominant follicles were identified during the oestrous cycle of 5 of 7 L, 3 of 7 M and 1 of 5 G heifers (P less than 0.10); 2 dominant follicles were identified in the remaining heifers (n = 2 of 7, 4 of 7 and 4 of 5, respectively). Length of the luteal phase and luteal-phase concentrations of progesterone were not affected (P greater than 0.05) by treatment. Low dietary intake reduced the diameter and persistence of dominant follicles during the oestrous cycle of beef heifers and tended to increase the proportion of oestrous cycles with 3 dominant follicles.     

Endocrine changes during pregnancy, parturition and the early post-partum period in the llama (Lama glama)

Mean (+/- s.d.) pregnancy length for the 14 llamas in this study was 350 +/- 4.5 days. Plasma progesterone concentrations increased by 5 days after mating and remained elevated (greater than 2.0 ng/ml) throughout most of pregnancy. At about 2 weeks before parturition, plasma progesterone concentrations began to decline, dropped markedly during the final 24 h before parturition, and returned to basal concentrations (less than 0.5 ng/ml) by the day of parturition. The combined oestrone + oestradiol-17 beta and oestradiol-17 beta concentrations varied between 6 and 274 pg/ml and 4 and 114 pg/ml, respectively, during the first 9 months of pregnancy. Concentrations increased between 9 months after mating and the end of pregnancy with peak mean concentrations of 827 +/- 58 (s.e.m.) pg oestrone + oestradiol-17 beta/ml (range: 64-1658) and 196 +/- 10 pg oestradiol-17 beta/ml (31-294) during the last week of pregnancy. Concentrations then declined to 87 +/- 14 pg oestrone + oestradiol-17 beta/ml (7-488) and 25 +/- 5 pg oestradiol-17 beta/ml (2.5-142) during the first week post partum. Plasma cortisol concentrations varied between 2.6 and 51.9 ng/ml (14.0 +/- 0.5) from mating until 2 weeks before parturition when the concentrations began to decline. Only a slight increase in plasma cortisol concentrations was observed in association with parturition. Plasma triiodothyronine concentrations varied between 0.5 and 4.5 ng/ml (1.9 +/- 0.1) throughout pregnancy and the periparturient period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian and luteal blood flow, and peripheral plasma progesterone levels, in cyclic guinea-pigs

Ovarian and luteal blood flow rates were studied using radioactive microspheres in guinea-pigs between Day 6 of the oestrous cycle and Day 1 of the following cycle. Peripheral plasma progesterone levels were measured by radioimmunoassay on the same days of the oestrous cycle. Ovarian blood flow was greatest between Days 9 and 12 and had fallen by Day 16 both in absolute (ml . min-1) and relative (ml.min-1.g-1) terms. Luteal weight and blood flow were also greatest between Days 9 and 12 and had fallen sharply by Day 16. The highest mean (+/- s.d.) luteal flows measured were 0.10 +/- 0.04 ml.min-1 per corpus luteum, and 24.26 +/- 9.3 ml.min-1.g-1 luteal tissue on Day 10 of the cycle. Mean peripheral plasma progesterone levels reached a maximum of 3.66 +/- 1.1 ng/ml at Day 12 of the cycle and fell thereafter, reaching 0.74 +/- 0.5 ng/ml by Day 1 of the following cycle. Plasma progesterone levels declined significantly between Days 12 and 14 of the cycle, whereas no significant drop in luteal blood flow was demonstrable until after Day 14. These data do not support the idea that declining luteal blood flow is an initiating mechanism in luteal regression in the guinea-pig.