Influence of reproductive state on pituitary-adrenal activity in the ewe

Plasma corticosteroid concentrations are altered in pregnancy, during the reproductive cycle and by ovariectomy in many species. This study was designed to examine basal ACTH and cortisol in ewes of four different reproductive statuses: ovariectomized, nonpregnant cycling, nonpregnant noncycling, and pregnant. Blood samples were drawn every 4 hr for 48 hr from ewes during quiet, undisturbed conditions and analyzed for plasma ACTH, cortisol and progesterone concentrations. There were no significant changes in ACTH, cortisol or progesterone over time. Mean progesterone concentrations were significantly greater in the pregnant ewes than in all other ewes, and were greater in cycling ewes than noncycling or ovariectomized ewes. Mean ACTH was significantly greater in pregnant ewes than noncycling ewes, and mean cortisol was significantly greater in cycling ewes than in nonpregnant cycling or noncycling ewes. Ovariectomized ewes also had significantly greater mean cortisol concentrations than cycling ewes. The results demonstrate that there is an increase in basal ACTH and cortisol in ovine pregnancy.

Hypothalamic sites of catecholamine inhibition of luteinizing hormone in the anestrous ewe

Norepinephrine (NE) and dopamine (DA) actively inhibit the release of LH in anestrous ewes. This can be detected as an increase in LH pulse frequency following i.v. injection of NE and DA antagonists. The objective of this study was to determine the sites of these inhibitory actions in the ovine hypothalamus by using local administrations of the NE antagonist, phenoxybenzamine (PBZ), or the DA antagonist, pimozide (PIM), into specific hypothalamic areas. Each neurotransmitter antagonist was administered via a chronically implanted steel guide tube into either the preoptic area (POA), retrochiasmatic area (RCh), or the median eminence region (ME). Blood samples were taken every 15 min for 2 h before and 4 h during implantation of these drugs and were analyzed for LH and prolactin by RIA. Control (no treatment) samples were obtained similarly from the same animals on another day. Placement of PBZ into the POA significantly increased LH pulse frequency and mean LH concentrations over control values whereas PIM did not. In contrast, PIM significantly increased LH pulse frequency and mean LH concentrations when placed in the ME or in the RCh, but PBZ did not. No effects of PIM on prolactin concentrations were detected. These results suggest that an NE neural system operates in the POA and that a DA system acts in the medial basal hypothalamus (RCh or ME) to suppress GnRH pulse frequency in the ovary-intact anestrous ewe.

Effect of FSH on ovarian inhibin secretion in anoestrous ewes

In Exp. 1, 7 Finn-Merino ewes which had one ovary autotransplanted to a site in the neck had jugular and timed ovarian venous blood samples collected at 10-min intervals for 2 h before and 3 h after injection of 5 micrograms NIAMDD-oFSH-S16. In Exp. 2, 8 Finn-Merino ewes with ovarian autotransplants had jugular and timed ovarian venous blood samples collected at 15-min intervals for 2 h before and 12 h after bolus injection of 40 micrograms NIAMDD-oFSH-S16 and infusion of oFSH-S16 at 6 micrograms/min for 4 h. In Exp. 2 the follicular population of the ovary was assessed by real-time ultrasound at the beginning and end of the experimental period. In both experiments the secretion rates of inhibin (1-3 ng/min) and oestradiol (0.5-8 ng/min) were similar to those observed during the luteal phase of the cycle in the breeding season, indicating significant follicular development in these animals. In Exp. 1 there was no change in the secretion of oestradiol or inhibin after the injection of FSH which resulted in a 25% increase (P less than 0.05) in the concentration of FSH in plasma. Inhibin secretion was pulsatile but there was no difference in inhibin pulse frequency before (1.6 +/- 0.2 pulses/h) or after (1.2 +/- 0.5 pulses/h) injection of FSH. In Exp. 2 injection of FSH resulted in an increase (P less than 0.001) in plasma concentrations of FSH in the sample taken 10 min after injection from a baseline of 1.2 +/- 0.2 ng/ml to a peak of 10.6 +/- 1.0 ng/ml (mean +/- s.e.m.).(ABSTRACT TRUNCATED AT 250 WORDS)

Onset of luteal activity in non-foaling mares during the early breeding season in Finland

The luteal activity in mares was studied in the Equine Research Station (ERS) and in trotting stables (TS) in South-Finland. The mares were Standardbreeds in the TS and mainly Finnhorses in the ERS. Between January and June blood was collected once a week for serum progesterone determinations. The mares in the ERS were distributed in 1 of 3 groups: three-years old not yet in training (N = 38), brood mares (N = 21) and mares in training (N = 47). A 4th group was the mares in training in the trotting stables (N = 73). Every 5th mare in the ERS and every 4th mare in the trotting stables were cycling already at the beginning of the year. Onset of luteal activity in anoestrous mares was most common in the middle of May. Over 95% of the mares were cycling at the beginning of June. In the ERS 40% of the Finnhorse mares in training were cycling through the winter. The three-years old and the brood mares were all anoestrous during winter. They started to cycle on average before the middle of May. Anoestrous training mares started before the middle of April. Anoestrous Finnhorse mares began to cycle later than warm blooded mares in all of the groups studied. Mares which had foaled the previous year were more often anoestrous during the winter than dry mares. The time of year when cycling began in a particular mare tended to be the same from year to year (p less than 0.01).

Hypothyroidism affects reproductive refractoriness and the seasonal oestrous period in Welsh Mountain ewes

Welsh Mountain ewes (n = 6) were rendered hypothyroid by daily treatment with methylthiouracil (35 mg/kg), beginning in early August and ending in late February. Plasma thyroxine levels were reduced by mid-September to about 33% of those in untreated ewes (n = 6). The two groups of ewes were held under natural daylengths until 5 October, then on 12 h light: 12 h darkness (12L:12D) until 28 February when the photoperiod was reduced to 8L:16D. The onset of reproductive cyclicity in October was similar in both groups of ewes but the end of the reproductive period occurred later (P less than 0.05) in the hypothyroid ewes (29 January +/- 7 days (S.E.M.] than in the untreated controls (6 January +/- 7 days). As a result, the duration of the seasonal reproductive period was significantly (P less than 0.05) longer in the hypothyroid (122 +/- 9 days) than in the untreated ewes (91 +/- 10 days). The number of oestrous cycles (duration 15.4 and 15.7 days in the hypothyroid and untreated ewes respectively) was 7.0 +/- 0.6 in the hypothyroid ewes and 5.0 +/- 0.5 (P less than 0.05) in the normal ewes. Reducing the photo-period overcame the reproductive refractoriness and anoestrus in both groups, the hypothyroid ewes beginning to cycle on 13 April (+/- 0.5 days) after an anoestrous period of 72.8 +/- 7.1 days. The untreated ewes began to cycle 2 weeks later on 26 April (+/- 1.7 days) after an anoestrous period of 112.0 +/- 8.5 days (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of photoperiod on gonadotrophin-releasing hormone stimulated luteinising hormone release in the anoestrous mare

The transition from anoestrus to oestrus in mares is controlled by photoperiod. The present study examined whether additional daylength would accelerate the mares' response to gonadotrophin-releasing-hormone (GnRH). Nine anoestrous mares were placed under ambient or artificial long lighting on 7th January. The four month experimental period was divided into a three-day sequence which was repeated at 21 day intervals. Ovaries were palpated rectally on Day 1; saline was injected (1 ml intravenously [iv]) on Day 2; GnRH was administered (0.59 microgram/kg bodyweight iv) on Day 3. Blood was taken at -60, 0, 15, 30, 60 and 120 mins relative to saline or GnRH treatment. Serum luteinising hormone (LH) was determined by a homologous equine radioimmunoassay (RIA). Several criteria were employed to define a positive response to GnRH and the results were analysed by Fisher's exact probability test. Treatment with artificial light allowed a response to GnRH within six weeks whereas the mares in ambient lighting took 12 weeks to respond to GnRH. The advancement in the time of response to GnRH under the long photoperiod could be related to changes in pituitary LH content, accelerated follicular activity or alterations in other brain-pituitary hormone levels.

The estradiol-induced surge of gonadotropin-releasing hormone in the ewe

Previous studies suggest two roles for estradiol in inducing the LH surge in ewes: a neural action to evoke a sudden release of GnRH and a pituitary action to maximize response to GnRH. We tested two hypotheses: a follicular phase estradiol rise induces a GnRH surge; and the surge-inducing action of estradiol does not vary with season. In the breeding season, ewes in the midluteal phase of the estrous cycle were ovariectomized and treated with implants producing luteal phase levels of estradiol and progesterone, and an apparatus was surgically installed for later sampling of pituitary portal blood. At the normal time of luteolysis (1 week later), progesterone implants were removed, simulating luteal regression. Ewes were divided into two groups: estradiol implants also removed (n = 6) and estradiol implants added 16 h after progesterone removal to produce a rise in estradiol to levels that mimic those that circulate in the late follicular phase (n = 6). In anestrus, the estradiol rise treatment was replicated in ewes (n = 5) after an artificial luteal phase produced by sequential insertion and subsequent removal of progesterone implants. Regardless of season, the LH surge induced by estradiol was invariably accompanied by a massive GnRH surge, ranging from 73- to 394-fold over presurge values. The GnRH and LH surges began together, but the GnRH surge continued well beyond the surge of LH. There was no seasonal difference in time course or amplitude of the GnRH surge. Control ewes not treated with estradiol exhibited regular pulses of LH and GnRH every 1-2 h, but no surge of either hormone. We conclude that, regardless of season, a rise in estradiol to late follicular phase levels initiates a large and abrupt GnRH surge coincident with the onset of the LH surge. The LH surge ends despite continued elevation of GnRH.

Role of photorefractoriness in onset of anoestrus in Rambouillet x Dorset ewes

An experiment was conducted to determine the extent to which refractoriness to short daylength is involved in the onset of anoestrus in Rambouillet x Dorset ewes. Ovary-intact ewes (N = 36) were exposed to ambient photoperiod (C) or to a photoperiod equal to the winter solstice (S) beginning on 21 December 1986 and continuing until 21 April 1987. Samples of serum were obtained at weekly intervals and assayed for progesterone to assess ovarian activity, and for prolactin to assess response to photoperiod treatment. In addition, ovariectomized (ovx) ewes with implants containing oestradiol were housed with C(Covx) and S (Sovx) ewes (N = 4 per treatment). The concentration of LH was determined in serum collected biweekly from all ovariectomized ewes throughout the treatment period as an index of reproductive status. Time-trends for concentrations of LH differed (P less than 0.005) for ewes in Groups Covx and Sovx with LH decreasing on the order of about 8-fold in Group Covx through the treatment period, while not changing appreciably in Group Sovx. Intact ewes in both treatments began to become anoestrous by the 9th week of treatment (about the last week in February). However, fewer Group S than Group C ewes were anoestrous at 13 and 14 weeks of treatment (P = 0.09). Time-trends for concentrations of prolactin also differed for the Group C and S ewes (P less than 0.005), probably reflecting the divergence in duration of photoperiod between the two treatments by the end of the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Estradiol feedback inhibition of luteinizing hormone concentrations in the anestrous sow

The suppressive effects of exogenous 17 beta-estradiol (E2) on LH concentrations in sows that remained anestrus following weaning and in those that returned to estrus were evaluated. Four anestrous and four cyclic sows were treated subcutaneously with silastic implants containing E2 at 13 d after ovariectomy (d 0). Three anestrous and six cyclic sows received silastic implants without E2. Blood was collected at 6-h intervals from d -1 to d 12 and at 15-min intervals for 8 h on d -1, 2, 7 and 12. Sows were treated with 1 microgram GnRH/kg BW at the completion of each 8-h frequent sampling period. Blood was collected at intervals of 10 to 30 min for 3 h after GnRH treatment. Concentrations of E2 remained less than 5 pg/ml in sham-treated sows and were between 20 and 25 pg/ml in E2-treated females. Pulsatile LH concentrations was similar between anestrous and cyclic sows prior to implant treatment. Sham-treated anestrous sows had greater (P less than .05) pulse frequency and mean LH concentrations than E2-treated anestrous sows on d 2, 7 and 12. Differences in pulsatile LH concentrations between E2-treated and sham-treated cyclic sows were not detected. Pulse frequency was less (P less than .05) in E2-treated anestrous sows than in E2-treated cyclic sows on d 7 and 12. Peak LH concentrations were greater (P less than .05) in E2-treated cyclic sows than in E2-treated anestrous sows at each GnRH challenge. These results suggest that the hypothalamo-hypophyseal axis is more sensitive to the negative feedback effects of E2 in anestrous sows than in cyclic sows. In addition, chronic E2 treatment reduces pituitary responsiveness to GnRH to a greater extent in anestrous than in cyclic sows. Failure to return to estrus in swine may be due, at least in part, to an increased sensitivity of the hypothalamo-hypophyseal axis to the negative feedback effect of estradiol.

Decreased availability of metabolic fuels induces anestrus in golden hamsters

Food deprivation inhibits ovulation and estrous behavior in golden hamsters. In experiment 1, the effects of phasic starvation (food deprivation on days 1 and 2 of the 4-day estrous cycle) depended on prior body weight and fat content. Starvation-induced anestrus, which occurs after only one cycle of phasic starvation in lean hamsters, did not occur until after three or more cycles in fat hamsters. None of the fat hamsters became anestrous until their body weights had declined to the level of lean hamsters. However, in experiment 2, we found evidence that changes in reproductive status were not signaled by any dimension of body size per se but instead by the general availability of metabolic fuels. Estrous cycles of thin hamsters were not significantly affected by food deprivation and weight loss when the hamsters were provided with either a 25% glucose solution or with vegetable shortening. In experiment 3, simultaneous pharmacological reduction of both fatty acid oxidation and glycolysis inhibited estrous cycles in hamsters fed ad libitum. Estradiol treatment restored estrous behavior, but not ovulation, in food-deprived, lean hamsters and in hamsters in which both fatty acid oxidation and glycolysis were reduced. Decreased availability of utilizable metabolic fuels may inhibit follicular development, which may in turn lead to circulating estradiol levels that are insufficient to stimulate estrous behavior.

Physiological mechanisms controlling anestrus and infertility in postpartum beef cattle

Postpartum infertility is caused by four factors: general infertility, lack of uterine involution, short estrous cycles and anestrus. The general infertility component is common to any estrous cycle and reduces potential fertility by 20 to 30%. Incomplete uterine involution prevents fertilization during the first 20 d after calving but is not related to anestrus. Short estrous cycles prevent fertility during the first 40 d after calving by causing the cow to return to estrus before pregnancy recognition occurs. Anestrus is the major component of postpartum infertility and is affected by several minor factors: season, breed, parity, dystocia, presence of a bull, uterine palpation and carryover effects from the previous pregnancy as well as two major factors: suckling and nutrition. These major factors have direct effects on anestrus but also interact with one or more other factors to control postpartum anestrus. Physiological mechanisms associated with anestrus involve blockage of the GnRH "pulse generator" in the hypothalamus, but other pathways also must be involved because bypassing the pulse generator is not an effective treatment for all cows. The primary cause of anestrus probably is different for different stages of anestrus. The mediating mechanisms for anestrus are not involved with prolactin, oxytocin, the adrenal or direct neural input from the mammary gland but are at least partially involved with blood glucose and the endogenous opioid peptide system. Management options to decrease the impact of anestrus and infertility include: 1) restrict breeding season to less than or equal to 45 d; 2) manage nutrition so body condition score is 5 to 7 before calving; 3) minimize effects of dystocia and stimulate estrous activity with a sterile bull and estrous synchronization; and 4) judicious use of complete, partial or short-term weaning.

Suckling as a regulator of postpartum rebreeding in cattle: a review

An extended and variable period of anovulation and anestrus occurs in suckled beef cows following parturition. This imposes both biological and economic constraints on the efficiency of beef production. A large body of knowledge has linked these phenomena to an attenuation of neuroendocrine signals that subserve gonadal function. During late gestation, high concentrations of placental estrogen inhibit the synthesis of LH, and pituitary stores of LH are depleted at parturition. Maximum pituitary stores of LH, releasable pools of LH and the ability of hypothalamic centers to respond to positive feedback effects of estradiol occur within 3 to 4 wk after calving in suckled cows. However, the requisite pattern of pulsatile LH secretion, which accompanies similar changes in nonsuckled cows within 2 to 3 wk after calving, occurs in only 30 to 50% of suckled animals. The period of acyclicity that continues in the remainder is exacerbated by poor body condition and may persist in some females for periods exceeding 100 d. Utilizing data from the cow, as well as other species, a model for suckling-induced inhibition of pulsatile LH release is proposed. The biological and economic impact of current and future techniques for controlling suckling-induced anestrus also is considered, including a conceptual analysis of nonbiological limitations.

Continuous exposure of Suffolk ewes to an equatorial photoperiod disrupts expression of the annual breeding season

The objective was to determine if "clamping" ewes onto a 12L:12D photoperiod resulted in expression of circannual rhythms of reproductive activity. On 24 February, 1986, two groups of 6 yearling ewes each were placed in isolated adjacent photochambers under a 12L:12D photoperiod and controlled temperature. Six control ewes were kept outdoors. Blood samples taken thrice weekly were analyzed for progesterone. Data from Days 0-1056 are reported. The mean number of cycles by control and 12L:12D ewes did not differ (32.8 +/- 1.7 vs. 29.7 +/- 4.0). The ranges were 27-39 vs. 4-51, respectively. Ten 12L:12D ewes started cycling coincidentally or later than the controls, and then cycled either regularly or irregularly throughout the study. Two of the 12L:12D ewes cycled continuously. The mean number of cycles during the period 15 April-15 August (anestrus) in Years 1, 2, and 3 were 0.7, 0.7, 0.2 for controls versus 0.3, 5.1, and 4.5 for 12L:12D ewes. The mean number of cycles during the period 15 September-15 January (breeding season) in Years 1, 2, and 3 were 7.3, 7.7, and 7.3 for controls versus 2.8, 4.8, and 4.0 for 12L:12D ewes. All controls showed distinct, alternating annual periods of anestrus and ovarian cycles whereas only two 12L:12D ewes showed a similar pattern. Estrous cycles were distributed nonrandomly in all controls and in 2 ewes exposed to 12L:12D. In the 12L:12D ewes, melatonin concentrations rose immediately after the lights-off and fell immediately after on. Lengths of the luteal phases of the cycles did not differ between groups. In summary, estrous cycles of most ewes clamped on a 12L:12D photoperiod occurred throughout the year at variable intervals rather than in distinct breeding seasons.

[Changes in the follicle system and the population of tertiary follicles in sheep after the administration of PMSG in anestrus]

The total quantitative changes of ovaries, proportion of atretic and non atretic follicles and changes of tertiary follicles in sheep after administration of increasing doses of PMSG during the anoestrous period were observed. In experimental groups the statistically significant increase of average weight, volume and dimensions of ovaries in comparison with control group were determined biometrically. The average number of tertiary follicles was greater in experimental groups but at the same time we observed a higher proportion of atretic follicles (64% of the total number in the control group; 71-77% in the experimental groups). In the group of sheep administered a dose of 1500 m.u. PMSG we determined a high proportion of luteinized follicles (as much as 21% of the total number of atretic follicles). The total number of small follicles in the so called transient phase in the comparison of experimental and control groups was not changed significantly. In the experimental group an increased incidence of preovulatory follicles and a reduction of tertiary follicle dimensions in the period of follicle cavity formation was determined.

[Enhanced ovarian sensitivity to gonadotropins in anestrus in sheep]

Superovulatory doses of PMSG and hCG, injected to anestrus crossbred ewes, induced more intensive luteinization of large follicles and progesterone secretion in ewes, lambed by twins (9) at first pregnancy, then in the cases of singleton lambed ewes or nonlambing ones (12). The ovaries of 2 ewes, lambed by twins, have healthy follicles, with increased estradiol concentration in their follicular fluid despite the presence of ovulatory follicles, giving corpora lutea. It is concluded that enhanced ovarian reactivity at anestrus can be related to the reserves of the reproductive system in more prolific ewes.

Computer modeling of sheep reproduction: I. An algorithm for quantifying anestrous cycles in ewes

An algorithm that mathematically describes annual estrous activity in ewes is given. The function fitted as the ordinate is similar to a normal distribution function related to date as the abscissa. The data used were collected from literature on different breeds and from different locations of the world; all studies had been specifically conducted to study estrous activity in ewes in these locations. Parameters estimated in an iterative procedure from the algorithm were length of time during which estrous cycles occurred (SA), a measure of asymmetry (SD), day of mid-estrous (DE), highest incidence of estrus (MX) and lowest incidence of estrus (MN), day of lowest incidence of estrus (DN) and day of mid-anestrous season (DA). Incidence of estrus is defined as the proportion of ewes exhibiting an active estrus. These parameters were estimated for several breeds and locations. The data, as collected, were inadequately cross-classified to allow for unconfounded estimation. However, analyses of fitted parameters that describe the curves gave quantitative results about the influences of breed of sheep, location, latitude and altitude and indicated which parameters were associated with these factors. Breeds differed significantly for SA, DE, MX and DA. Locations differed for DE, MX and DA. Latitude was associated with differences in DE, DN and DA with altitude also associated with differences in DE and DA. There were no significant effects on SD even though breeds differed sizably in SD.

Nutritional anestrus in beef cows: body weight change, body condition, luteinizing hormone in serum and ovarian activity

Multiparous Hereford cows (n = 22) with moderate to good body condition scores (BCS) were randomly allotted to maintenance (M) or restricted (R) diets under drylot conditions. Cows on M diets received adequate feed to maintain initial BW, whereas R cows were fed to lose 1% of their initial BW weekly until luteal activity ceased. When most of the R cows became anestrous, their diet was increased to allow BW gain and resumption of ovarian cyclicity. Body weights and BCS were recorded weekly and luteal activity was assessed by weekly determination of progesterone in plasma. Concentrations of LH in serum were quantified in weekly samples and in samples obtained frequently at four selected times. Restricted cows had reduced BW (P less than .01) by 5 wk and reduced BCS (P less than .01) by 15 wk compared with M cows. Luteal activity ceased after 26 +/- 1 wk of reduced nutrient intake in 91% of the R cows; R cows had lost 24.0 +/- .9% of their initial BW and had a BCS of 3.5 +/- .3. Lack of luteal activity was associated with absence of behavioral estrus. Estrous cycles resumed 9 +/- 2 wk after the diet of R cows was increased, at which time R cows weighed 12 +/- 3% less than at the start of the experiment and had a BCS of 4.6 +/- .2. Concentrations of LH in serum samples obtained weekly were reduced (P less than .01) in R cows compared with M cows. In addition, LH pulse frequency was reduced (P less than .05) when R cows were initiating anestrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of prostaglandin F-2 alpha and oxytocin in the regression of GnRH-induced abnormal corpora lutea in anoestrous ewes

Anoestrous Romney Marsh ewes with (+P) and without (-P) progesterone pretreatment were induced to ovulate by multiple low-dose injection of GnRH followed by a bolus injection of GnRH. Luteal function was assessed by twice daily measurement of plasma progesterone. Animals were slaughtered on Days 3 or 5 after the end of GnRH treatment and CL and endometrium were recovered. In all Day-5 ewes, blood samples were collected at 30-min intervals for 8 h on Days 3 and 5 for measurement of PGFM and oxytocin. At slaughter 92% of the Group +P ewes had ovulated compared with 54% of the Group -P ewes. The ovaries of some of the Group -P ewes only contained luteinized cysts either alone or in association with CL. In the ewes that ovulated, progesterone profiles were normal in all Group +P ewes, whereas Group -P ewes had 'normal' or 'abnormal' profiles in which plasma progesterone was declining prematurely. All of the CL from ewes with abnormal progesterone profiles were associated with follicular cysts, and were significantly smaller and with a lower progesterone content on Day 5. PGFM levels decreased (P less than 0.05) between Days 3 and 5 in ewes in Groups +P and -P with 'normal' CL but increased (P less than 0.01) in Group -P ewes with 'abnormal' CL. Oxytocin levels were lower in Group -P ewes with 'abnormal' CL on Day 5, than in 'normal' ewes in Groups -P (P less than 0.01) or +P (P less than 0.05). In 3/5 Day-5 ewes with 'abnormal' CL there was a clear association between a major peak of oxytocin and a rise in PGFM during the frequent sampling period on Day 3 or Day 5, and endometrial oxytocin binding sites were present at slaughter. This suggests that the premature regression of 'abnormal' CL occurs via the normal luteolytic mechanism. Although ewes in Groups +P and -P with 'normal' CL had similar progesterone profiles, plasma oxytocin was significantly higher (P less than 0.05) in the Group -P ewes and oxytocin binding sites were present only in this group, suggesting that progesterone pretreatment can influence the production of both oxytocin and its receptor.

Annual profiles of sex steroids in blood plasma and ovarian tissue of wild female musk shrew, Suncus murinus

Relative ovarian weights with bursa and annual profiles of sex steroids have been described in the female musk shrew, Suncus murinus, collected in the vicinity of Rawalpindi, Pakistan. The relative gonadal weight was basal (23.20 +/- 1.20 mg/100 g) during anoestrus but enhanced (39.93 +/- 2.73 mg/100 g) abruptly at the onset of the breeding season. Plasma progesterone concentrations, measured during different parts of the year, indicated elevated levels during the late pregnant stage (p less than 0.01). The ovarian progesterone was also comparatively higher in late pregnant animals. No significant difference was observed in plasma and ovarian oestradiol.

Effect of transportation and relocation in post-weaning anoestrous primiparous sows

The object of this investigation was to study the clinical and endocrine responses to transportation and relocation in 8 post-weaning anoestrous sows. They had been anoestrous for at least 24 days after weaning before transportation/relocation was performed. Laparoscopy, performed at the beginning of the experiment, revealed that the ovaries contained many follicles (less than or equal to 6 mm in diameter), but no corpora lutea. Blood samples, taken before and after transportation/relocation, showed that LH activity was low at the beginning of the experiment and increased after transportation/relocation in the majority of the sows. Peripheral plasma concentrations of of oestradiol-17 beta increased 1-4 days after transportation/relocation in 6 out of 8 sows which was followed by oestrus and ovulation. Progesterone concentrations were also below the practical detection limit until the end of oestrus. This study has demonstrated that a change in environment by transportation and relocation can induce oestrus by increasing the LH activity in post-weaning anoestrous sows.

Effects of immunization against recombinant bovine inhibin alpha subunit on circulating concentrations of gonadotrophins in ewes

Immunization of ewes against a pure recombinant preparation of the alpha subunit of bovine inhibin (alpha-bI) resulted in a three- to fourfold increase in ovulation rate, associated with antibodies in plasma recognizing pure native 31 kDa inhibin. The aim of this study was to examine the effects of this immunization on basal and GnRH-stimulated plasma concentrations of FSH and LH in ewes during the anoestrous and breeding seasons. The groups were untreated control ewes (n = 5), control ewes treated with keyhole limpet haemocyanin (KLH alone, n = 4), ewes treated with alpha-bI alone (n = 4) and alpha-bI-KLH conjugate-treated ewes (n = 3). There were no effects of immunization on basal FSH or LH in anoestrous ewes, despite the presence of antibodies recognizing 31 kDa inhibin. In the breeding season, immunization against alpha-bI resulted in increased basal (follicular phase, P less than 0.1; luteal phase P less than 0.05) and GnRH-stimulated (follicular phase only, P less than 0.001) release of FSH, but not LH. The data are compatible with the hypotheses that the increase in ovulation rate in immunized ewes is due to an increase in circulating FSH concentrations and that inhibin may only have a major peripheral influence on FSH in sheep during the breeding season.

Milk production in concurrently pregnant and lactating goats mated out of season

Five lactating goats which had kidded normally in March were mated during seasonal anoestrus in May, at the time of peak milk production, after ovulation had been induced using gonadotrophin-releasing hormone (Knight et al. 1988). Milk yield was unaffected by the hormone treatment, and decreased at the same rate as that of control (non-pregnant) goats for the first 8 weeks of the pregnancy. Thereafter yield declined more quickly in the test goats and just before parturition (in October) was 57% of the control value. Following parturition in the test animals, yield rose rapidly as the second lactation was established. None became 'dry' at any stage. Yield continued to decline with advancing lactation in the controls, which were mated normally in October or November and dried-off in December. During their second ('extra') lactation in the winter the test animals produced 12% less than in a normal second lactation in summertime; during the year the extra lactation meant that the test animals produced 73% more milk than the controls. In some, a second concurrent pregnancy was established during the extra lactation, with the result that three lactations were obtained in the time normally taken for two. Mammary cell number and proliferation rate were both higher in the pregnant animals than in the controls in week 23 of the first lactation.

Treatment with bovine follicular fluid suppresses follicular development in gonadotrophin-releasing hormone-treated anoestrous ewes

The role of FSH in gonadotrophin-releasing hormone (GnRH)-induced follicular development in anoestrous ewes was investigated using injections of bovine follicular fluid (bFF) to reduce plasma FSH levels. Groups of five animals were treated for 12 h with GnRH (250 ng at 2-h intervals) alone, GnRH plus bFF or saline alone, or for 36 h with GnRH alone, GnRH plus bFF or bFF alone. The administration of bFF (1.5 ml s.c. at 8-h intervals) significantly (P less than 0.05) reduced mean plasma FSH levels, but with the exception of animals treated with bFF alone, had no effect on LH levels. Treatment with bFF alone for 36 h resulted in a significant (P less than 0.05) increase in LH concentrations. There was considerable variation in the number of follicles greater than or equal to 2 mm in diameter in the treatment groups. The mean diameter, oestradiol secretion and number of 'oestrogenic' follicles were significantly (P less than 0.01) reduced in ewes treated with GnRH plus bFF or bFF alone for 36 h compared with those treated with GnRH alone. Testosterone secretion by the follicles was not affected by treatment. These results confirm previous findings that treatment with bFF decreases circulating FSH levels in anoestrous ewes and, moreover, that concurrent administration of bFF and GnRH inhibits the follicular maturation that is induced by treatment with GnRH alone, suggesting that FSH as well as LH is required for follicular maturation in the ewe.

Effect of hysterectomy on the short life-cycle corpus luteum produced after GnRH-induced ovulation in the anoestrous ewe

Anoestrous Romney Marsh ewes were treated with small-dose (250 ng) multiple injections of GnRH. Ewes in Groups 1 and 3 were hysterectomized 2 weeks before treatment, while those in Groups 2 and 4 were intact controls. Groups 1 and 2 were primed with progesterone (+P) and treated with 2 h injections of GnRH (250 ng) for 36 h, while Groups 3 and 4 were not pretreated (-P) but were given 2 h injections of GnRH (250 ng) for 18 h. Both treatment regimens were terminated with a bolus injection of GnRH (125 micrograms), given to synchronize the timing of the LH surge and subsequent luteal progesterone production. The plasma progesterone profiles of 5/5 animals in Group 2 (+P controls) and 2/5 animals in Group 4 (-P controls) were indicative of normal luteal function, while the remaining 3/5 animals in Group 4 produced plasma progesterone profiles typical of abnormal luteal function. However, in all the hysterectomized animals (Groups 1 and 3) peripheral plasma progesterone concentrations rose to reach a mean peak value of 1.3 ng/ml plasma on Day 8 which was maintained in all animals irrespective of progesterone pretreatment. The absence of a fall in progesterone concentrations precluded the identification of any animal in Group 4 showing abnormal luteal function. It was also noted that, after hysterectomy, although the corpus luteum was maintained, it was with reduced secretory capacity. The prevention of the expected proportion (70%) of -P animals from displaying a decline in plasma progesterone concentration after hysterectomy provides firm evidence that the uterus is involved in the premature regression of the short-cycle corpus luteum.

Function of abnormal corpora lutea in vivo after GnRH-induced ovulation in the anoestrous ewe

Anoestrous Romney Marsh ewes with and without progesterone treatment (+P, -P) were treated with small-dose (250 ng) multiple injections of GnRH at 2-h intervals for 48 h. Animals were slaughtered on Days 4, 5, 7 and 11 after the end of GnRH treatment and luteal function was assessed by the measurement of daily plasma progesterone concentrations. In all animals which ovulated (29/32, 91%) peripheral progesterone concentrations rose to 0.5-1.0 ng/ml within 3 days of the end of GnRH treatment. In 7/7 (100%) +P animals and 5/22 (23%) -P animals, progesterone concentrations continued to rise and were maintained at levels greater than 1.5 ng/ml until slaughter. In the remaining -P animals, plasma progesterone concentrations declined to reach basal levels by Day 5. Corpora lutea recovered from these animals showed signs of premature regression on Day 5 and were fully regressed by Day 7. Progesterone priming delayed the occurrence of the LH surge which occurred 39.1 +/- 3.6 h after the end of GnRH treatment in the +P animals compared to 20.2 +/- 1.74 h (P less than 0.001) in the -P animals in which luteal function was abnormal and 22.4 +/- 4.35 h in the -P animals in which luteal function was normal. These results show that abnormal luteal function occurs in the majority of GnRH-treated ewes in the absence of progesterone pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)