PMS Injection Research Articles

Effects of Tokishakuyakusan, Keishibukuryogan and Unkeito on DNA polymerase alpha activity in PMS-treated immature rat uterus incubated in vitro.

We have recently found that Tokishakuyakusan (TS), Keishibukuryogan (KB) or Unkeito (UT) inhibits in vivo DNA polymerase alpha activity in the rat uterus stimulated by PMS. In this study, uteri resected 24 h after injection of PMS on day 27 of age were incubated in vitro with 20 micrograms/ml of extract of TS, KB or UT for 4 h. The DNA polymerase alpha activity in uteri tended to decrease after the addition of TS, KB or UT with significant difference (P < 0.05) compared with TS-, KB- and UT-untreated control groups. These results suggest that TS, KB or UT, especially KB, tends to inhibit directly the enzyme activity in rat uterus.

Endothelin-1 and Endothelin-3 Stimulate Ovarian Steroidogenesis

The possible direct involvement of endothelin (ET) in preovulatory follicular steroidogenesis was investigated in vitro. Follicular development in immature rats was induced by pregnant mare's serum gonadotropin (PMS). Twenty-four and 48 h after PMS injection, ovarian follicles were incubated in vitro with or without 4 x 10(-11) to 4 x 10(-5) M endothelin-1 (ET-1) or endothelin-3 (ET-3) for 2 h, or perifused in vitro with 4 x 10(-7) M of ET-1 or ET-3 for 3 h. In the incubation study, ET-1 and ET-3 significantly stimulated progesterone, testosterone, and 17 beta-estradiol production by follicles 24 and 48 h after PMS injection. Progesterone, testosterone, and 17 beta-estradiol were increased in a dose-dependent manner by 4 x 10(-11) to 4 x 10(-6) M ET-1 or ET-3; in the case of ET-3, this increase occurred only at 24 h after PMS injection. In addition, ET-1 stimulated ovarian steroid production more effectively than ET-3. In addition to their effects on ovarian steroidogenesis, both ET-1 and ET-3 increased tissue cyclic adenosine-3',5'-monophosphate (cyclic AMP) production. The steroidogenic effect of ET-1 or ET-3 was most pronounced by follicles 48 h after PMS injection. In the perifusion experiment, ET-1 and ET-3 also stimulated progesterone, testosterone, and 17 beta-estradiol secretion. These indicate the involvement of ET-1 or ET-3 in the regulation of ovarian differentiation by stimulating steroidogenesis, at least partially through the mediation of cyclic AMP.

Hachimijiogan and Tokishakuyakusan enhance deoxyribonucleic acid alpha-nucleotidyltransferase activity in relationship to DNA synthesis by ovarian follicles via a cyclic AMP system.

The ovaries resected from twenty-nine day old female rats primed with 10 IU of PMS for 48 hours were incubated for 120 minutes with 2-20 micrograms/ml of Hachimijiogan (HZ) and Tokishakuyakusan (TS). The animals in another group were injected intravenously with 20 micrograms of HZ and TS 48 hours after PMS injection, and 20 minutes later decapitated. Deoxyribonucleic acid (DNA) alpha-nucleotidyltransferase activity and cyclic AMP accumulation in ovarian tissue were significantly increased by HZ and TS. These results suggest that HZ and TS enhance DNA alpha-nucleotidyltransferase activity via cyclic AMP by ovarian follicles.

Lifespan of Corpora Lutea Induced in Estrous-Synchronized Cycling and Anestrous ewes2

The effect of pretreatment with flurogestone acetate (FA) on the lifespan of corpora lutea induced with pregnant mare serum gonadotropin (PMS) was examined in cycling and anestrous ewes. Cycling ewes received one of three treatments: 750 IU PMS 2 d before expected estrus (P), FA-impregnated vaginal sponges for 16 d (F), and FA sponges for 16 d and 750 IU PMS 2 d before sponge removal (FP). A fourth group served as controls (C). When compared with d 12 means within treatment, plasma progesterone means were lower (P less than .05) on d 16 in control ewes, on d 15 in P and F ewes, and on d 14 in FP ewes. Only 44% of ewes receiving FA treatment alone exhibited estrus (P less than .05) compared with 100% of untreated ewes. The FP treatment increased ovulation rate compared with controls (P less than .01). The decrease in luteal lifespan observed in cycling ewes suggests a possibility of asynchrony between the uterus and embryo, which could result in failure of an embryo to prevent luteal regression, thus resulting in reduced fertility. None of the seasonally anestrous ewes that received PMS alone and only 55% of those treated with FA sponges for 8 d before PMS injection exhibited estrus. Ewes pretreated with FA exhibited higher plasma progesterone concentrations on d 10 through 16 after PMS injection. There were no differences in luteal lifespan as measured by peripheral plasma progesterone patterns. Although FA treatment did not alter luteal lifespan in anestrous ewes, the increased plasma progesterone concentrations observed with FA treatment suggest that progestogen pretreatment may be essential for optimal luteal function.

Effects of pregnant mare's serum gonadotrophin administered in vivo on steroid accumulation by isolated rabbit ovarian follicles.

Various doses (5, 50 and 100 IU) of pregnant mare's serum gonadotrophin (PMS) were administered to sexually mature female rabbits and steroids measured in follicular fluid, ovarian pieces and in incubation media of isolated follicles treated with ovine luteinizing hormone (LH). Follicular fluid progesterone, oestradiol and androgen were increased after PMS injection. Ovarian progesterone content was increased by all doses of PMS, and androgen and oestradiol content only by 50 and 100 IU PMS. Medium sized follicles from rabbits treated with 50 and 100 IU PMS accumulated more progesterone than all follicles from rabbits treated with saline or 5 IU PMS. Androgen accumulation by small follicles from 50 and 100 IU dose rabbits was higher than that by follicles from other treatment groups. Oestradiol accumulation mimicked androgen accumulation. The addition of LH to the medium stimulated the accumulation of progesterone and androgen by all follicles. LH caused an increase in oestradiol accumulation by medium follicles from saline and low dose PMS treated animals. No effect of LH on oestrogen accumulation was seen with large or medium follicles from animals treated with 100 IU PMS or 50 IU PMS for 2 or 3 days. These results suggest that priming of small follicles with PMS can increase their ability to produce androgen which is probably aromatized to oestrogen.

Ovarian C17,20-lyase: Changes in intact and hypophysectomized immature rats treated with pregnant mare's serum gonadotropin

The steroid C17,20-lyase activity of immature rat ovarian microsomal (105,000 g pellet), mitochondrial (10,000 g pellet) and combined fractions was measured using progesterone and 17-hydroxyprogesterone as substrates. Steroid 17α-hydroxylase was measured, using progesterone as substrate, in some of the preparations for comparison. With progesterone about 3.5 times more product (acetic acid) was formed than with 17-hydroxyprogesterone as substrate. The half-time for lyase activity following hypophysectomy was 51.8 h, while that for 17α-hydroxylase was 51.3 h. Following an intravenous injection of 20 iu of pregnant mare's serum gonadotropin (PMS) into immature hypophysectomized rats lyase activity decreased for 12 h followed by recovery during the next 12 h with a rapid increase between 24 and 72 h. In contrast, a subcutaneous injection of the same dose produced an initial rise in activity with a decline between 12 and 24 h, followed by a second large increase. In intact animals injection (s.c.) of PMS produced an initial fall in lyase activity followed by an increase beginning 12 h later. A dramatic decrease in activity occurred between 48 and 72 h concomitant with ovulation; hypophysectomy at 48 h not only prevented the decrease, but produced an increase in activity. The changes in ovarian C17,20-lyase activity following administration of PMS mimic those of 17α-hydroxylase.

Brain dopamine variations in gonadotropin-treated immature rat.

The cortex, cerebellum, caudate nucleus, and hypothalamus of immature rats treated with pregnant mare's serum gonadotropin (PMS) were isolated and analyzed for dopamine (DA) content at 6-h intervals for 72 h. Results showed that PMS injection caused significant elevation in DA levels in all brain regions studied.

Effect of adrenocorticotropin on progesterone, 20alpha-OH- progesterone and adenosine 3',5'-monophosphate in isolated luteal cells from rat ovaries

The present investigation was designed to study the effect of synthetic ACTH on the synthesis of progesterone, 20 alpha-OH-progesterone and adenosine-3', 5'-monophosphate (cAMP) in isolated luteal cells. Experiments were conducted on rats from three groups. Group I: PMS primed immature rats. Group II: PMS plus hCG primed immature rats. Group III: pregnant rats. Luteal cells were isolated by the Kumai Method (7) using a sucrose density gradient after digestion with trypsin and collagenase. Luteal cells were divided into three fractions; S-1, S-2 and S-3. Following an 18 hr-incubation of S-1 cells of day 7 after PMS injection, a significant increase in progesterone release by ACTH lasted from 6 to 18 hr, whereas 20 alpha-OH-progesterone decreased significantly by ACTH from 8 to 18 hr. There were no differences in progesterone and 20 alpha-OH-progesterone releases from S-2 cells of day 7 between media with and without ACTH. Progesterone release without ACTH reached the peak on day 7 in Group I and on day 6 in Group II. ACTH stimulated progesterone and inhibited 20 alpha-OH-progesterone releases in Groups I and II. The maximum effect of ACTH in both Groups was noted on days 6 and 7. There were no differences in the Effective Dose (ED50) and the Inhibitory Dose (ID50) of ACTH between Group I and Group II. In Group III, releases of progesterone and 20 alpha-OH-progesterone from S-1 cells to media with or without ACTH decreased remarkably after 11 days of gestation. On days, 3, 5 and 8 of gestation, a significant increase in progesterone release from S-1 cells was noted by the ACTH addition. 20 alpha-OH-progesterone release from S-1 cells to media with or without ACTH decreased as the pregnancy advanced. Total cAMP of intra- and extra-cellular S-1 cells (Group II) on day 5 after PMS injection was assayed. ACTH induced an increase in intracellular cAMP. The present results indicate the following: (1) In Group I and Group II, progesterone release increased with the age of the luteal cells and ACTH dose. In Group III, ACTH stimulated progesterone release in a dose-dependent manner in early gestation. (2) 20 alpha-OH-progesterone release decreased by ACTH dose in Group I and Group II, and decreased in Group III as the gestation advanced. (3) Intracellular cAMP increased by ACTH in Group II.

Importance of catecholestrogens in the regulation of the ovarian cycle.

Using highly stabilized catecholestrogen preparations-ascorbic acid added to the free alcohols or benzoic acid derivatives — 2- and 4-hydroxyestrogens were tested in simple, clearly defined animal models: As index for the peripheral action the influence on vaginal opening and uterus weight gain was monitored after continuous s.c. administration for 6 days (minipumps) in immature intact rats resulting in a relative estrogenic potency (estradiol = 100%) of 70–100% for 4-hydroxyestradiol and less than 30% for 2-hydroxyestradiol. As index for the central action LH levels were measured in adult ovx rats leading to the same relations in the relative potencies. As index for both central and peripheral actions LH levels and the formation of corpora lutea were investigated in animals with an intact but prepubertal feed-back loop, i.e. in 25-day-old immature rats. 4-Hydroxyestradiol in this model clearly triggered LH surges and induced ovulations, its potency being in the same range as that of estradiol. 2-Hydroxyestradiol, in comparable doses, again showed no significant effect. Finally, female immature animals known to ovulate 3 days after PMS injection were treated concomitantly with either primary or catecholestrogen-antibody preparations. Whereas the primary estrogen antibody significantly blocked ovulation, the 2- and 4-hydroxyestrogen antibodies were ineffective. If, however, PMS and estrogen-antibody treated animals were supplemented with 4-hydroxyestrogens, ovulations could be restored. Thereby, it was inferred that peripheral 4-hydroxyestrogens, though not essential for the physiology of reproduction, can completely replace the physiologically essential peripheral estradiol at central target sites.

Steroid 17 alpha-hydroxylase activity of ovarian granulosa cells from hypophysectomized immature rats treated with pregnant mare's serum gonadotropin (PMS).

Immature hypophysectomized rats were injected with 2mg of diethylstilbestrol to increase granulosa cell numbers and with 20 IU of PMS to stimulate ovarian growth. Steroid 17 alpha-hydroxylase activity of cultured granulosa cell, harvested from mature follicles 48 h after injection of PMS, was demonstrated using a tritium exchange assay with 17 alpha 3H-pregneneolone as substrate. For comparison, aromatase activity of the same cells was examined by a similar assay using 1 beta 3H-testosterone as the substrate. The activities of the two enzymes were similar when expressed in terms of the amount of substrate converted per unit time. While an NADPH generating system in the incubation medium was essential for demonstrating any hydroxylase activity, 10-15% of the total aromatase activity could be found without added cofactor. Attempts to alter hydroxylase activity of granulosa cells by inclusion of LH, FSH or prolactin in the incubation medium were unsuccessful. However, activity could be change by prostaglandins (PG) or agents which can alter PG synthesis. Activity was increased by low concentrations of phospholipase A2 (PLA2), histamine, and arachidonic acid (AA). Large doses of PLA2, or AA, were inhibitory. PGE2, but not PGF2 alpha, increased, while indomethacin decreased, hydroxylase activity. The results clearly indicate that granulosa cells in the rat have a potent 17-hydroxylase system and therefore do not support the widely held contention that lack of this enzyme is one of the bases for the need for two kinds of cells for ovarian estrogen production.

Preovulatory depletion of ovarian catecholamines in the rat.

The purpose of the present investigation was to correlate changes in ovarian catecholamines and serum pituitary hormones and sex steroids. As the experimental model we used the prepubertal rat injected with 7.5 IU PMS on day 28 at 0900 h. Within 24 h after the injection, ovarian weight increased, and on day 30 at 2400 h, it was twice that of controls. On day 31, all of the PMS-treated rats but none of the controls had ovulated, and the average number of ova was 9. Serum estradiol in these rats was elevated significantly on the afternoon of day 30 and was followed by a preovulatory surge of LH and FSH. Serum progesterone was also increased on the evening of day 30, and an elevation in serum PRL on the morning of day 30 in the PMS-treated rats was evident, whereas serum GH was unchanged. Ovarian norepinephrine (NE) dropped from 65.5 +/- 6.9 pg/mg ovary (mean +/- SE) before the PMS injection of 14.4 +/- 1.5 pg/mg ovary on the evening of day 30. This depletion proceeded in two apparent phases: an initial drop within 12 h after PMS injection, and a further reduction coincident with the gonadotropin surge. Throughout this period, ovarian NE in the controls increased 50--60%. There was a 2-fold reduction in ovarian dopamine in the PMS-primed rats, but the levels were 10-fold lower than those of NE. The data document that the hormonal profiles and the number of ovulating follicles of the prepubertal rat primed with a low dose of PMS resemble those of the normal cycling rat. A significant depletion of ovarian catecholamines was observed during the preovulatory period, which is temporally related to increases in serum gonadotropins.

Inhibitory effect of progesterone on follicular growth and induced superovulation in the rat.

We investigated the effect of exogenous progesterone on follicular growth and pregnant mares' serum gonadotropin and human chorionic gonadotropin (PMS-HCG) induced superovulation in intact and hypophysectomized immature rats. Although the administration of progesterone during PMS-HCG injections had no effect on superovulation, the administration of progesterone beginning 3 days before PMS injection inhibited superovulation in both intact and hypophysectomized rats. In order to study the mechanism of inhibition of superovulation by pretreatment with progesterone, an autoradiographic study using tritiated thymidine was done in hypophysectomized rats just before PMS injection. The labelling indices of granulosa cells were significantly decreased by the administration of progesterone (p < 0.001). Treatment with progesterone resulted in an increase of the follicles in early stages of atresia with pycnotic nuclei in granulosa cells surrounding apparently normal oocytes. Ovarian histology and serum and ovarian tissue concentrations of estradiol were then examined in hypophysectomized rats 20 h after HCG injection. Large Graafian follicles and corpora lutea were rarely seen in rats previously given progesterone, whereas many large Graafian follicles and corpora lutea were observed in the control rats. The concentrations of estradiol in the progesterone-pretreated rats were significantly reduced in serum (p < 0.02) and slightly reduced in ovarian tissues when compared with controls.

The involvement of serotonin in induced ovulation in the immature rat

In pregnant mare's serum gonadotropin (PMS) treated immature rats the cortex, cerebellum, caudate nucleus and hypothalamus were isolated and analyzed for their serotonin (5-HT) content at 6-h intervals for 72 h. Results showed a general trend of significant variation occurring in days 1 and 3 after PMS injection with no major variations observed on the second day. The results obtained suggest a possible involvement of 5-HT in the control of ovulation.

Intrafollicular cumulus cell transformations associated with oocyte maturation following gonadotrophic hormone stimulation of adult mice.

AbstractEffects of gonadotrophic hormones on the intrafollicular morphological transformation of cumulus cells were examined in adult mice. Formation of transformed cumulus masses was examined during both the pre‐ and post‐ovulatory course of gonadotrophic (PMS or PMS + HCG) induction of follicular synchronization and ovulation. Within nine hours of PMS injection and prior to ovulation, transformed cumulus cell masses were present within ovaries. Injection of HCG within 48 hours of the PMS injection stimulated the formation of additional and increased numbers of pre‐ovulatory transformed cumulus cell masses. Ovulation occurred within 24 hours of both the PMS injection and the HCG injection when given to animals previously stimulated with PMS. Oocytes isolated from transformed cumulus cell masses following PMS or HCG injection had invariably undergone meiotic maturation. Transformed cumulus masses were also recovered from ovaries following induced ovulation; however, their numbers were decreased. Follicles stimulated by PMS remained sensitive to HCG (underwent ovulation) for approximately four days following a single injection of PMS. Results indicate that identifiable morphological and physiological changes in cumulus cells precede ovulation and are strongly correlated with the induction of the meiotic maturation process in the enclosed oocytes. The presence of mature oocytes in transformed cumulus masses following ovulation furthermore indicates that asynchrony of the oocyte maturation and ovulatory events are induced by the gonadotrophic hormones. Intrafollicular cumulus cell transformations are discussed in relation to dissociation of the somatic and germ cells, the mechanisms of meiotic induction and the process of atresia. Results suggest that the simple morphological changes described provide a quantitative and selective indicator of gonadotrophic action within the ovary.

Active Immunization of Female Rats with Luteinizing Hormone Releasing Hormone (LHRH)

Cycling rats were immunized against LHRH. In most of these rats, antibody to LHRH became detectable 20 days after the first immunizing injection and reached a maximum level about 40 days later. The elevation of antibody titers, accompanied by the lengthening of the estrous cycle, resulted in continuous anestrus approximately 50 days after the first injection. Peripheral serum LH declined to nondetectable levels but prolactin was not significantly altered throughout the experimental period. The presence of circulating antibody to LHRH was confirmed by the blockade of ovulation in cycling hamsters after i.v. injection of serum from the immunized rats. About 60 days after the establishment of anestrus, the ovaries of the actively immunized rats weighed one-fifth those of the normal cyding rats, but were significantly heavier than the ovaries of rats hypophysectomized for 2 months. The ovaries of immunized anestrous rats consisted mostly of small- to medium-sized follicles; occasionally follicles with small antra were encountered. In immunized rats LHRH content of the hypothalami remained at the level of normal cycling rats; however, LH concentration of the pituitary was lower than that in normal rats. In the immunized rats an i.v. injection of a large dose of LHRH caused a small rise in LH but did not induce ovulation. Ovulation was induced by injection of PMS followed by LH. Cervical stimulation after ovulation evoked an elevation of peripheral progesterone comparable to that in normal pseudopregnant rats until Day 5. These results suggest that rats actively immunized with LHRH provide a model which has low levels of LH and relatively unimpaired levels of prolactin.

Pregnant Mare Serum and Human Chorionic Gonadotropin Stimulate Ovarian ∆5-3β-Hydroxysteroid Dehydrogenase in Aged Mice

Aged (12- to 14-month-old) estrous and diestrous C57BL mice exhibited lower histochemically demonstrable ovarian delta5-3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity in thecal, luteal, and interstitial cells, and lower (P less than 0.01) ovarian 3beta-HSD concentration and total content than did young (3-month-old) estrous animals. Administration of pregnant mare serum (PMS, 10 IU subcutaneously), followed in 40 hours by human chorionic gonadotropin (HCG, 5 IU subcutaneously) or HCG (2 IU daily for 4 days) alone, restored luteal and interstitial 3beta-HSD in aged mice. Follicular, lutea, and interstitial 3beta-HSD activity was increased in aged mice by a single PMS injection (10 IU). The total ovarian dehydrogenase concentration was increased 100% in aged animals by PMS and/or HCG administration. Restoration of histochemically demonstrable ovarian 3beta-HSD and total enzyme content in aged mice by PMS and/or HCG indicates ovarian sensitivity to gonadotropin and subnormal tropic hormone stimulation of the ovary in situ.

Ovarian LDH activity in gonadotropin-treated immature rats.

Lactate dehydrogenase (LDH) activity was studied in the ovaries of immature rats treated with pregnant mare serum gonadotropin (PMS). LDH activity increased sharply at 36 h after PMS injection in the ovarian tissue as well as in the blood. It was suggested that the increase of LDH activity in the ovary may be related to its increasing ability to secrete estrogen.

Stimulation of the estrogen synthesizing system of the immature rat ovary by exogenous and endogenous gonadotropins

Immature rat ovaries increase their secretion of estradiol (E 2) when stimulated by gonadotropins but only after a lag period of several hours. Once established, estrogen secretion can be maintained, or increased, by the continued presence of gonadotropin. A combination of ovine FSH+LH given at 2 hr intervals stimulated the estrogen synthesizing system ( ESS ) of the ovary and serum E 2 showed a pronounced rise between 16 and 20 hrs after the initial injection. When given every 2 hrs for 5 doses (0–8 hrs) serum E 2 was undetectable. However, it was increased if 20 IU PMS was injected at the time of the last dose of FSH+ LH. Endogenous FSH&LH, increased by hourly injections of LH-releasing hormone for a period of 8 hrs, stimulated the ESS ; serum E 2 increased at the expected time when this treatment was followed by an injection of PMS. Anti-PMS antiserum given 12 hrs after PMS, prevented the expected rise in serum E 2 at 24 hrs. However, FSH, LH or a combination of the two given every 2 hrs beginning at the time of the anti-PMS produced an increase in E 2 secretion; the combination was more effective than either hormone alone. These results are consistent with the interpretation that a combined FSH-LH action is responsible for induction of the ESS in the immature rat ovary. The combination of hormones is also very effective in maintaining estrogen secretion but some function appears possible with FSH or LH alone.

Hypothalamic releasing hormones and fertility regulation with emphasis on ovulation induction before puberty

The nature, mode of action, and neuroendocrine mechanisms of hypothalamic releasing hormones have been reviewed, LH releasing hormones can be used for (a) basic research in neuroendocrinology, (b) diagnostic tool to differentiate hypothalamic and pituitary disorders in clinical gynecology; and (c) to induce ovulation in mature and immature females.Prepubertal female rats of 28, 32 and 39 days of age were treated with a single dose 0–300 μg of LRF, and examined for oviductal ova 20 h later. Ovulation was not induced in all the females within 24 h. Doses less than 300 μg had no effect on ovarian and uterine weight. In 28 and 32 day old rats treated with 300 μg of LRF, an increase in ovarian and uterine weight was equivalent to the increase resulting from 1 mg of LH. To determine the effective dose of LRF for ovulation, 23 day old rats were primed with 5 I.U. of PMD, ovulation occurred 2 h following LRF treatment, as in rats injected with 1 mg of LH. In another experiment, rats 18–23-days of age were injected with 0–80 μg of LRF about 56 h following 5 i.u. of PMS injection. The response was age-dependent: 5μg of LRF caused ovulation in 21-day-old rats, whereas 10 μg evoked this response in 18-day-old rats.A possible relationship between folliculogenesis and LRF-induced ovulation was examined. Twentyone and 25-day-old rats were primed with 5 I.U. of PMS and a single injection of LRF (40 μg) at 24, 30, 36 and 42 h after PMS treatment. The females were examined for ovulation 20 h later. Ovulation occurred only in a few 25-day olds when LRF treatment was given after 24 h of priming, whereas all ovulated when priming was done for 36 h after PMS treatment; however, ovulation was induced by 1 mg of LH. Only 20 and 50% of the rats showed ovulation when primed 30 and 36 h respectively. Estradiol has a stimulating effect on the release of LH in adult rats. Twenty-five-day-old rats were primed first with 10 μg of estradiol, and a single dose of LRF (0–100 μg) about 48 h. then autopsied 24 h later. Vaginal opening was observed in all of the rats but ovulation did not occur in all. The possible interaction between various doses of estrogen and the time of LRF injection after estrogen priming will be examined. Sexual maturity in the female involves an interaction between the synthesis and the release of hypothalamic releasing hormones and functional integrity of the hypothalamo-hypophysealovarian axis.

Some consequences of high flock prolificacy in an intensive grassland sheep production system

SummaryAn intensive sheep production system using flocks of 100 Scottish Halfbred (SHB), 100 Welsh Speckleface (WSF) and 100 Finn Blackface (FBF) ewes maintained by 8, 4 and 6 ha grassland respectively for a 5-year period, was investigated to establish the consequences of high flock prolificacy and the measures taken to achieve it, including PMS administration. Mating occurred in late October/November at ewe: ram ratios of 25 or 33: 1. Ewes were housed in winter and fed silage, with supplementary cereals in late pregnancy. Lambs in excess of 2 (SHB) and 1 (WSF and FBF) per ewe were artificially reared and fattened indoors; ewes and lambs at grass were rotationally grazed (with forward creep grazing by the lambs). Prolificacy in the SHB breed was 225 lambs born per 100 ewes mated for untreated ewes and 237 for hormone-treated ewes; 119 and 155 respectively for WSF ewes; and 255 for FBF ewes (all untreated). Lambs sold per 100 ewes mated were: for SHB, 200 and 177; WSF, 102 and 107; FBF, 201.Good ewe condition and heavy live weights at mating were associated with appetite problems on silage in late pregnancy; PMS injection with a failure to secure conception rates above 80% at the critical oestrus and a markedly lower prolificacy for ewes conceiving at later oestruses; mating in the middle of the breeding season and March/April lambing with slow lamb growth rates on grass in July and August. Hormone-induced high prolificacy was associated with a greater proportion of large multiple litters than natural high prolificacy, and consequent smaller lamb birth weights and more perinatal mortality. There was a significant negative regression relating fleece weight with litter size. The results suggest the existence of an optimal level of prolificacy for the system employed.