Effect of grazing sorghum (Sorghum bicolor) infected with ergot (Claviceps africana) on beef cattle.
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Animal Feed↗
Biomedical subjects
J A Downing
Publications and source records attributed to J A Downing.
The effects of exogenous growth hormone on follicular steroid secretion and ovulation rate in sheep.
Growth hormone (GH) has diverse actions in many tissues, including the follicle. This paper summarizes three experiments that examined the effects of GH and insulin-like growth factor (IGF)-I on the ovary. Ewes given oGH and pregnant mane serum gonadotrophin were compared with control and pregnant mane serum gonadotrophin-treated ewes. Ewes, with synchronized cycles, were given varying doses of pregnant mane serum gonadotrophin and/or oGH to determine if oGH is able to augment ovulation rate (Experiment 1). Experiments 2 and 3 used the ovarian autotransplant model. Ewes were infused via the ovarian artery with oGH (Experiment 2) or insulin-like growth factor I (IGF-I) (Experiment 3). Both were administered for 12 hr on Day 10. In Experiment 2, ewes were given intravenous gonadotropin releasing hormone (150 ng i.v.) at -2.5 and 10.5 hr relative to infusion. Ovarian and jugular venous blood was collected every 15 min from -30 to 150 min relative to gonadotropin releasing hormone. In Experiment 3, luteolysis was induced at the end of infusion. Ovarian and jugular venous blood was collected every 3 hr from before and until 84 hr after the infusion. Estradiol and androstenedione were assayed in ovarian venous plasma and GH in jugular venous plasma. In Experiment 1, treatment with oGH increased the jugular venous concentration of GH. However, in Experiment 2 treatment with oGH via the ovarian artery did not increase jugular venous GH but did increase ovarian venous GH. Treatment with oGH had no effect on ovulation rate (Experiment 1) or the secretion of androstenedione and estradiol (Experiment 2). Infusion of IGF-I (Experiment 3) increased the secretion of estradiol during the follicular phase. These data show that short-term treatment of sheep with GH had no in vivo effects on the follicle and that IGF-I was a potent stimulator of follicular steroidogenesis in vivo.
Androstenedione↗
Effect of progesterone on the GnRH-induced secretion of oestradiol and androstenedione from the autotransplanted ovary of the anoestrous ewe.
Two experiments were conducted during the anoestrous period in Border Leicester x Merino ewes with ovarian autotransplants to study the effects of a single injection of 20 mg progesterone on follicular steroid secretion. The aim of these experiments was to determine whether pretreatment with a 20 mg intramuscular injection of progesterone could reduce GnRH-induced ovarian steroid secretion in anoestrous ewes. In both experiments, an injection of 150 ng GnRH induced an LH pulse in all ewes with a maximum concentration 10 min (the first post-injection sample) after injection. Oestradiol and androstenedione secretion increased progressively after the GnRH-induced LH pulse and reached maximum rates of secretion between 60 and 90 min before decreasing slowly to pre-injection rates at 150 min. There were no differences in the pattern of secretion of oestradiol (measured in both experiments) or androstenedione (measured only in Expt 2). In Expt 1, the injection of progesterone 72 h before the challenge with GnRH had no effect on the maximum rate of oestradiol secretion from the autotransplanted ovary. However, in Expt 2, when progesterone was given either 36 or 60 h before GnRH, there was a significant suppression in the maximum rate of secretion of both oestradiol and androstenedione between 60 and 90 min after GnRH injection. These data show that pretreatment of anoestrous sheep with progesterone can suppress LH-stimulated steroid secretion from the ovary and indicate that progesterone may have a direct effect on oestrogenic follicles in sheep.
Analysis of Variance↗
The effect of a direct arterial infusion of insulin and glucose on the ovarian secretion rates of androstenedione and oestradiol in ewes with an autotransplanted ovary.
Improving ewe nutrition even for short periods will increase ovulation rate. The increased nutrients must in some way affect the number of follicles that develop to the pre-ovulatory stage. One possible mechanism is that a nutrient or a metabolic hormone that responds to nutrition might act directly on the ovary to influence follicle development and/or follicle selection. In the study described here, insulin and glucose, alone or together, were infused directly into the ovarian artery of ewes with an autotransplanted ovary, for 13.5 h on day 11 of the oestrous cycle. The pattern of androstenedione and oestradiol secretion in response to a GnRH-stimulated LH pulse was measured 2.5 h before and 12.5 h and 24.5 h after the start of the infusion. Glucose or insulin infused alone had no effect on the secretion of androstenedione and oestradiol. However, when infused together, they decreased significantly the secretion of androstenedione and, to a lesser extent, oestradiol. We suggest that the sudden availability of additional glucose and insulin increases insulin-stimulated glucose uptake by the follicle. This leads to an inhibition of LH-stimulated steroidogenesis by the ovarian follicle which occurs in the absence of any detectable changes in circulating plasma concentrations of FSH. These results show that insulin and glucose act together to influence ovarian function directly and suggest that the effects of short-term nutrition on ovulation rate may be mediated by a direct ovarian action of insulin and glucose.
Analysis of Variance↗
Ovulation rate and the concentrations of LH, FSH, GH, prolactin and insulin in ewes infused with tryptophan, tyrosine or tyrosine plus phenylalanine during the luteal phase of the oestrous cycle.
Dietary amino acid precursors for cathecholamineric and serotonergic neurotransmitters may be important in the mechanism of nutritional effects on ovulation rate. This paper reports the results of three experiments that examined the effect of such amino acids on ovulation rate and the concentrations of FSH and LH in sheep. In three separate experiments, groups of ewes were infused, over Days 9 to 13 of the oestrous cycle, with either tryptophan (n = 11), tyrosine (n = 11) or a mixture of tyrosine and phenylalanine (n = 11). Control ewes (n = 12 in each experiment) were infused with a vehicle over the same period. None of the amino acids infused effected ovulation rate or plasma concentrations of LH, FSH, GH or prolactin. The infusion of a mixture of tyrosine and phenylalanine increased insulin concentrations. The infusion of these amino acids was not associated with changes in gonadotrophin concentrations and therefore the effect of nutrition on ovulation rate in ewes does not seem to involve an increase in the availability of tryptophan, tyrosine or phenylalanine. Increasing the uptake of other amino acids that compete with tryptophan, tyrosine or phenylalanine for the large neutral amino acid transporter may cause a decrease in the availability of tryptophan, tyrosine or phenylalanine thereby eliciting the effects of nutrition on ovulation rate. However, this hypothesis remains to be tested.
Animals↗
The circulating concentrations of FSH, LH and prolactin in the oestradiol-implanted ovariectomized ewe treated with caffeine.
Caffeine, a trimethylxanthine alkaloid, is a psycho-active drug that effects a wide range of physiological systems, including the reproductive system. Reports of infants with intra-uterine growth retardation and lowered birth weight as a result of in utero exposure to caffeine, are increasing. The drug is also known to alter steroidogenesis but it is not certain whether this is a direct and/or an indirect effect with the involvement of the central nervous system. Thus, an experiment was designed to determine the effect of acute caffeine administration on the circulating concentrations of gonadotrophins and prolactin in the ovariectomized oestradiol-implanted ewe. A single intravenous dose of caffeine (20 mg kg-1 bodyweight) did not affect circulating gonadotrophin concentrations with the parameters for the pulsatile secretion of luteinizing hormone (LH) and the mean concentration of follicle stimulating hormone (FSH) being similar in both experimental and control groups. Circulating prolactin levels, on the other hand, were significantly (P < 0.01) elevated following intravenous treatment with caffeine. The effect was immediate following caffeine administration with elevated concentrations being maintained over the next 3 h before their return to pre-treatment concentrations. The response was bi-phasic with peaks of prolactin concentrations at 1 and 3 h. The results of this experiment show that acute caffeine exposure does not affect the secretion of gonadotrophins from the anterior pituitary gland. Furthermore, they show that acute administration of caffeine stimulates prolactin secretion via an action that is independent of oestradiol feedback and which we suggest, may involve the ACTH/adrenal axis.
Animals↗
The distribution of ovulations from the ovaries of merino and Border Leicester x merino ewes and its effect on the survival of their embryos.
The distribution of ovulation between the right and the left ovary was recorded using endoscopy, in 2806 ewes over a 5-year period. Fifteen separate tests were conducted as part of the development programme for a commercial twinning vaccine. There were significantly more ovulations on the right ovary (53.4%) compared to the left ovary (46.6%; P < 0.001). The distribution of ovulation between the ovaries was not influenced by either the breed of sheep or prior immunisation against the steroid hormones androstenedione or testosterone. These findings suggest that the hormonal control of folliculogenesis and ovulation rate is modulated by unknown local factors within the ovary and its vasculature. The site of ovulation had no effect on embryo survival, and embryos from unilateral ovulations were just as likely to survive as were embryos from bilateral ovulations. However, embryo survival was influenced by ovulation rate, and ewes with ovulation rates of four or more had reduced litter sizes and lower embryo survival.
Animals↗
The ovarian secretion of androstenedione and oestradiol during late pregnancy and the early postpartum period in sheep with an autotransplanted ovary.
During late pregnancy in the ewe, ovarian function is suppressed by placental steroids and following parturition ovarian function is restored. This experiment determined the ovarian secretion of oestradiol and androstenedione during late pregnancy and the early postpartum period in ewes. Six ewes with ovarian autotransplants were transplanted with three day 6 embryos and three gave birth on day 147. Ovarian and jugular blood sampled were collected on three different occasions. On each occasion a 4 h period of sampling was followed by a 6 or 8 h period during which the ewes were challenged with 150 ng of gonadotropin-releasing hormone (GnRH). Basal secretion of oestradiol and androstenedione was 0.3 +/- 0.1 and 10.5 +/- 3.0 ng min-1, respectively, on day 120 of pregnancy. Oestradiol secretion remained low on days 7 and 21 postpartum (0.4 +/- 0.3 and 0.3 +/- 0.1 ng min-1, respectively). Androstenedione secretion (ng min-1) on days 7 and 21 postpartum was 2.5 +/- 0.5 and 4.1 +/- 1.8, respectively. The injection of GnRH on day 121 of pregnancy produced luteinizing hormone (LH) release with a peak concentration of 0.6 +/- 0.1 ng mL-1, that did not stimulate steroid secretion. On day 8 postpartum GnRH injection induced LH release with a peak concentration of 3.9 +/- 1.1 ng mL-1 that stimulated secretion of oestradiol (0.2 +/- 0.1 to 2.1 +/- 0.9 ng min-1; P < 0.01) and androstenedione (2.3 +/- 0.6 to 17.1 +/- 6.9 ng min-1; P < 0.001). Similar effects were seen on day 22 postpartum; GnRH injection induced LH release with a peak concentration of 4.7 +/- 1.4 ng mL-1 that stimulated secretion of oestradiol (0.2 +/- 0.1 to 3.7 +/- 1.1 ng min-1; P < 0.001) and androstenedione (4.2 +/- 2.6 to 29.5 +/- 9.2 ng min-1; P < 0.01). These results suggest that the suppression of ovarian function during late pregnancy in the ewe is reversed by 7 days postpartum.
Androstenedione↗
The effects of N-methyl-D,L-aspartic acid and aspartic acid on the plasma concentration of gonadotrophins, GH and prolactin in the ewe.
Aspartic acid is a neurotransmitter in the central nervous system that acts via the glutamate receptor and the analogue, N-methyl-D,L-aspartic acid (NMA) is an agonist that stimulates GnRH secretion. Under normal dietary conditions, the plasma concentration of aspartic acid in ewes is low and if increased by improved nutrition may increase the brain concentration of aspartic acid leading to increased gonadotrophin secretion. In two experiments we investigated the effects of NMA on pituitary hormone concentrations and the effects of aspartic acid on ovulation rate and pituitary hormone concentrations. The intravenous injection of NMA into cycling ewes resulted in an immediate (within 15 min) release of a pulse of LH and of GH and a prolonged (up to 1 h) suppression of prolactin secretion. There were marked differences in responsiveness to NMA between individual ewes. The intravenous infusion of aspartic acid for 5 days in the late luteal phase of the oestrous cycle did not affect ovulation rate but reduced the mean LH (P < 0.05) and FSH (P < 0.05) concentrations in plasma. The frequency of LH pulses also tended to be lower (P < 0.1) in ewes infused with aspartic acid. It is suggested that the decrease in gonadotrophin secretion in ewes infused with aspartic acid is due to effects on the hypothalamus or the anterior pituitary gland which are not related to increased levels of ovarian feedback. These changes are likely to involve decreased GnRH secretion.
Animals↗
Ovulation rate and the concentrations of gonadotrophic and metabolic hormones in ewes fed lupin grain.
An experiment in which a lupin grain supplement was fed to ewes (n = 11) over days 2-13 of the oestrous cycle was carried out. A group of 12 ewes was used as a control and not fed the supplement. Plasma concentrations of LH and GH (20 min intervals) and FSH, insulin and prolactin (hourly intervals) were determined in plasma samples collected every 20 min over 24 h on day 11 of the oestrous cycle. The changes were related to increases in ovulation rate. Ovulation rate was increased (2.5 +/- 0.2 versus 1.9 +/- 0.2 for lupin-supplemented and control groups, respectively; P = 0.073) in the group that received the lupin supplement, but this increase was not associated with significant changes in either LH or FSH concentrations on day 11 of the oestrous cycle. Lupin supplementation had significant effects on the plasma concentrations of prolactin, GH and insulin. There was a transient increase (P < 0.05) in the concentration of prolactin 4-8 h after feeding, whereas insulin concentrations were increased immediately after feeding (P < 0.02) and were still high 24 h later (P < 0.02). Growth hormone concentrations were reduced in ewes fed with lupin grain (P < 0.001). These metabolic responses initiated by feeding a high energy and protein supplement such as lupin grain may be related to changes in ovulation rate. In particular, the sustained increases in insulin concentrations suggest that an increased supply of glucose to the follicle mediates nutritionally stimulated increases in ovulation rate.
Amino Acids↗
A mixture of the branched chain amino acids leucine, isoleucine and valine increases ovulation rate in ewes when infused during the late luteal phase of the oestrous cycle: an effect that may be mediated by insulin.
The positive relationship between nutritional state and ovulation rate in sheep may involve the action of specific nutrients on gonadotrophin release. LH and FSH secretion is controlled in part by hypothalamic GnRH, which is in turn influenced by central adrenergic and serotonergic neuronal systems. In this experiment the branched chain amino acids (BCAAs) leucine, isoleucine and valine were examined for effects on LH and FSH secretion. A mixture of the three amino acids was infused into ewes for 5 days immediately before luteolysis, a time when nutritional effects on ovulation rate occur. The infusion significantly increased ovulation rate without any associated increase in FSH or LH. However, the infusion did increase plasma insulin concentrations and this effect, together with the high levels of blood urea observed, suggests that these amino acids had increased the supply of energy substrates to the follicles. An increase in insulin-mediated glucose uptake by follicles could be the stimulus responsible for the increase in ovulation rate. The ability of the animal to utilize BCAAs for energy metabolism may be an important component of the ovulation responses to nutrition.
Amino Acids, Branched-Chain↗
The in vivo effects of fibroblast growth factor and epidermal growth factor on the secretion of oestradiol, androstenedione and progesterone by the autotransplanted ovary in the ewe.
An experiment was conducted to determine the effects of epidermal growth factor (EGF) and fibroblast growth factor (FGF), infused into the ovarian artery, on the secretion of ovarian steroids during the mid-luteal phase in ewes with an autotransplanted ovary. The infusion of EGF (5 micrograms/h) for 12 h suppressed the secretion of oestradiol and androstenedione during the infusion and for up to 30 h after the infusion. The secretion of progesterone tended to be lower immediately after the infusion (not significant) but had recovered by 24 h after the end of the infusion and then increased significantly (P < 0.05) to rates higher than in control animals. There were no effects of the infusion of EGF on the characteristics of pulsatile LH secretion. FSH concentrations increased 24 h after the end of the infusion probably as an indirect consequence of the changes in oestradiol secretion and not as a consequence of a direct effect of EGF on the hypothalamo-pituitary axis although this latter possibility cannot be unequivocally eliminated. The infusion of FGF (1.5 microgram/h) for 12 h also suppressed the secretion of oestradiol and androstenedione during and for up to 30 h after the infusion. The infusion of FGF had no detectable effect on the secretion of progesterone or the characteristics of pulsatile LH secretion. FSH concentrations increased steadily during the infusion but declined rapidly to below pre-infusion concentrations after the end of the infusion. These data provide tentative in vivo evidence for paracrine and autocrine effects of EGF and FGF on follicular and luteal function in sheep.
Androstenedione↗
Ovulation rate and the concentrations of gonadotrophins and metabolic hormones in ewes infused with glucose during the late luteal phase of the oestrous cycle.
The positive relationship between nutrition and ovulation rate was investigated in sheep infused intravenously with glucose. Ovulation rate increased (2.0 +/- 0.0 vs 2.4 +/- 0.3) when ewes were given an infusion of glucose (60-65 mM/h) for five days in the late luteal phase of the oestrous cycle. The effect of glucose was obtained without any significant change in LH secretion. The concentration of FSH in glucose-infused ewes was lower during the infusion (luteal phase) but higher during the early follicular phase. These data suggest that the change in ovulation rate occurred without increased gonadotrophin support to the follicle during the late luteal phase, which is the period of the sheep oestrous cycle during which improved nutrition increases ovulation rate. There were no changes in GH or prolactin, but changes in circulating glucose and insulin levels were detected. We conclude that insulin, because of its role in cell growth and metabolism, is involved in mediating ovulation responses to nutritional stimuli, either directly or more likely by the stimulation of insulin-mediated glucose uptake.
Animals↗
Changes in progesterone secretion following treatment with transforming growth factor alpha (TGF-alpha) during the follicular phase of the sheep oestrous cycle.
The effects of transforming growth factor alpha (TGF-alpha) on ovarian steroid secretion were investigated. Three crossbred ewes synchronized for oestrus with ovarian autotransplants were infused with TGF-alpha (30 micrograms in 12 h) via the ovarian artery for 12 h before withdrawal of progestagen pessary. Three ewes were used as controls. Jugular and ovarian venous blood samples were taken at intervals of 10 min at two stages during the follicular phase (21-27 h and 38-42 h after pessary withdrawal) and every 2 h from 44 to 86 h. Plasma LH and FSH concentrations, and ovarian secretion rates of inhibin, androstenedione, oestradiol and progesterone were determined using radioimmunoassays. LH pulse amplitude increased in ewes treated with TGF-alpha in the early follicular phase (0.92 +/- 0.25 micrograms l-1 in controls versus 3.10 +/- 0.35 micrograms l-1 in TGF-alpha treated ewes; P < 0.05) and remained high in the late follicular phase. Plasma FSH concentrations were high during the follicular phase in ewes treated with TGF-alpha (P < 0.05). The infusion of TGF-alpha had no significant effect on the ovarian rate of secretion of androstenedione and, although the secretion rates of oestradiol and inhibin were consistently lower in TGF-alpha-infused ewes, the differences were not significant. The ratio of secretion of androstenedione to oestradiol was greater during the follicular phase in TGF-alpha-treated ewes (P < 0.05), suggesting that the efficiency of aromatization had been impaired.(ABSTRACT TRUNCATED AT 250 WORDS)
Androstenedione↗
A model for follicle selection and the determination of ovulation rate in the ewe.
A model for folliculogenesis is proposed that is based as far as possible on a knowledge of physiological, rather than anatomical, changes taking place during follicle development. The model is therefore functional, rather than descriptive, and consists of five classes of follicles that have been defined by their dependency and sensitivity to gonadotrophins. These classes are: primordial, committed, gonadotrophin-responsive, gonadotrophin-dependent and ovulatory. The model is an attempt to encourage discussion and to promote the integration of morphological models of folliculogenesis with recent advances in the molecular endocrinology of the ovarian follicle. Two hypotheses for the mechanisms that determine ovulation rate are developed in light of the model. In the first, multiple ovulation results when the viability of gonadotropin-dependent follicles is enhanced. In the second, multiple ovulation is caused by increasing the number of gonadotrophin-responsive follicles available for further development; this results from the increasing rate of folliculogenesis and the throughput of follicles. The final section of this paper examines how these two hypothetical mechanisms, which are not mutually exclusive, appear to account for most of the known genetical and environmental effects on ovulation rate of sheep. In particular, the effects of nutrition, genotype, exogenous gonadotrophins, immunity to both oestrogens and androgens, and immunity to inhibin are discussed.
Animal Nutritional Physiological Phenomena↗
Epidermal growth factor acts directly on the sheep ovary in vivo to inhibit oestradiol-17 beta and inhibin secretion and enhance progesterone secretion.
Epidermal growth factor (EGF) is a potential intra-ovarian modulator of gonadotroph action on differentiated follicular cells. Specific binding sites have been identified in the ovary and functional differentiation in cultured granulosa cells can be modulated by treatment with EGF. The aim of this study was to determine if EGF was capable of altering ovarian function in vivo during the follicular phase of the sheep oestrous cycle. Fourteen cross-bred ewes with ovarian autotransplants were treated with progestagen pessaries for 12 days. Three ewes were infused with murine EGF (mEGF) via the jugular vein (75 micrograms/kg bodyweight per 12 h) during the 12 h preceding progestagen pessary withdrawal, and received an injection of a prostaglandin analogue at 0 h to induce luteolysis. Over the same time-period, two doses of EGF were administered to other groups of ewes by infusion into the ovarian artery (low: 6 micrograms/12 h, n = 3 and high: 60 micrograms/12 h, n = 3). The remaining five ewes were not infused with EGF (controls). Jugular and ovarian venous blood samples were taken at 10-min intervals at two stages during the follicular phase (21-27 h and 38-42 h after pessary withdrawal) and every 2 h from 44 to 76 or 86 h. mEGF, LH, FSH, inhibin, androstenedione, oestradiol-17 beta and progesterone concentrations in plasma were determined using radioimmunoassays. The secretion rates of androstenedione, oestradiol, progesterone and inhibin by the ovary were calculated. EGF acted directly on the ovary in a dose-dependent manner. Oestradiol secretion was inhibited following treatment with EGF but androstenedione secretion was unaffected. EGF appears therefore to act within the granulosa cells to inhibit aromatization. Inhibin secretion was also suppressed by treatment with EGF, though it was not possible to determine if this was caused by a direct or indirect action of EGF on granulosa cells. The rate of progesterone secretion increased in ewes receiving systemic (i.e. via the jugular vein) and high-dose intra-arterial infusions of EGF, even though a preovulatory LH surge was not observed in these animals during the entire experimental period. Concomitant increases in both LH and FSH secretion were associated with these effects of EGF on ovarian function. In conclusion, EGF appears to act directly on the granulosa cells of the follicle to inhibit aromatization and also to inhibit inhibin production. The low levels of oestradiol and inhibin in the presence of high levels of gonadotrophin indicate that atresia may have been induced in medium to large antral follicles.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Increased ovulation rate in androstenedione-immune ewes is not due to elevated plasma concentrations of FSH.
Two experiments were undertaken to determine the hormonal response of Merino ewes to immunization against androstenedione (Fecundin). In Exp. 1 peripheral concentrations of LH, FSH and progesterone were monitored in spontaneously cycling ewes (20 immunized and 21 controls). In Exp. 2 (10 immunized and 10 controls) the same hormones were measured in ewes before and after prostaglandin (PG)-induced luteolysis and, in addition, the pattern of pulsatile LH secretion was determined during the luteal (PG + 12 days), early follicular (PG + 24 h) and late follicular (PG + 40 h) phase of the oestrous cycle. Ovulation rates were measured in both experiments. The results of these experiments indicate that androstenedione-immune animals have elevated ovulation rates (0.6-0.7 greater than control animals; P less than 0.05) associated with elevated plasma concentrations of LH and progesterone. The magnitude of the increase in plasma progesterone was correlated with androstenedione antibody titre (r = 0.6, P less than 0.001). LH pulse frequency of androstenedione-immune ewes tended to be higher at all stages of the oestrous cycle, but this difference was only significant (P less than 0.05) during the luteal phase. Mean plasma concentrations of FSH did not differ significantly between immunized and control ewes at any stage of the cycle. Analysis of periodic fluctuations in FSH during the luteal phase revealed that androstenedione-immune animals had a similar number of fluctuations of a similar amplitude to those of control animals, but the nadir of these fluctuations was lower (P less than 0.05) in immunized animals. A significant (P less than 0.05) negative correlation existed between androstenedione antibody titre and the interval between FSH peaks (r = -0.49) and androstenedione antibody titre and FSH nadir concentrations (r = -0.46). It is concluded that plasma FSH concentrations are not a determinant of ovulation rate in androstenedione-immune ewes and that increased LH concentrations, or perturbation of normal intraovarian mechanisms, may be responsible for the increase in ovulation rate observed in ewes immunized against androstenedione.
Androstenedione↗
Nutrient effects on ovulation rate, ovarian function and the secretion of gonadotrophic and metabolic hormones in sheep.
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Animal Nutritional Physiological Phenomena↗