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

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

Immediate and delayed effects of heat stress on follicular development and its association with plasma FSH and inhibin concentration in cows

The aim of this study was to characterize the immediate effects of heat stress on plasma FSH and inhibin concentrations, and its involvement in follicular dynamics during a complete oestrous cycle, and to examine a possible delayed effect of heat stress on follicular development. Holstein dairy cows were oestrous synchronized and randomly assigned to either cooled (n = 7) or heat-stressed (n = 6) treatment groups. During a complete oestrous cycle, control cows, which were cooled, maintained normothermia, whereas heat-stressed cows, which were exposed to direct solar radiation, developed hyperthermia. At the end of this oestrous cycle (treated cycle), both groups were cooled and maintained normothermia for the first 10 days of the subsequent oestrous cycle. Throughout this period, follicular development was examined by ultrasonography, and plasma samples were collected. During the second follicular wave of the treated oestrous cycle, a significantly larger cohort of medium sized follicles (6-9 mm) was found in heat-stressed cows than in cooled cows (P < 0.05). The enhanced growth of follicles in this wave in heat-stressed cows was associated with a higher plasma FSH increase which lasted 4 more days (days 8-13 of the oestrous cycle; P < 0.05), and coincided with a decrease in the plasma concentration of immunoreactive inhibin (days 5-18 of the oestrous cycle; P < 0.05). During the follicular phase (days 17-20 of the treated cycle), heat-stressed cows showed an increase in the number of large follicles (>/= 10 mm), and the preovulatory plasma FSH surge was significantly higher in heat-stressed cows than in cooled cows (P < 0.01). The effect of heat stress was also observed during the first follicular wave of the subsequent cycle: the postovulatory plasma FSH concentration was higher (P < 0.01), but fewer medium follicles developed, and the first follicular wave decreased at a slower rate in previously heat-stressed cows than in cooled cows (0.40 and 0.71 follicles per day, respectively). This study shows both immediate and delayed effects of heat stress on follicular dynamics, which were associated with high FSH and low inhibin concentrations in plasma. These alterations may have physiological significance that could be associated with low fertility of cattle during the summer and autumn.     

Effect of intrauterine infusion of Escherichia coli on hormonal patterns in gilts during the oestrous cycle

The aim of this study was to determine the effect of intrauterine Escherichia coli infusion on the patterns of plasma LH, prolactin, progesterone, androstenedione, testosterone, oestrone, oestradiol-17beta, cortisol and 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM) in gilts during the oestrous cycle. On day 4 of the oestrous cycle (day 0), 25 mL of saline or 25 mL of Escherichia coli suspension, containing 10(7) colony forming units x mL(-1), was infused once into the each uterine horn in group I or II respectively. The control gilts developed a new oestrous cycle at the expected time but not bacteria-treated. Endometritis and vaginal discharge developed in all gilts after Escherichia coli infusion. The administration of Escherichia coli resulted in a reduction of plasma levels of LH, prolactin, oestrone and oestradiol-17beta (P < 0.05-0.001), mainly on days 15-18 after treatment (expected perioestrous period). During this time, the plasma androstenedione level was elevated (P < 0.05-0.001) after bacteria infusion. In the gilts receiving bacteria, progesterone concentration decreased from day 8 after treatment and was low until the end of the study (P < 0.05-0.001). On days 8-12 after bacteria administration, the level of PGFM was higher (P < 0.001) than that found in the control group. These results suggest that the developing inflammatory process of the endometrium in gilts following Escherichia coli infusion significantly affects the pituitary-ovarian axis function as well as prostaglandin production leading to anoestrus.     

Ovarian follicular population changes with the advance of the breeding season in intact and unilaterally ovariectomized ewes

In ewes at the 1st, 2nd or 4th oestrous cycle after unilateral ovariectomy, the ovulation rate remained constant at 1.5 in the control (sham-operated) ewes, but increased from 1.3 to 2.0 in unilaterally ovariectomized ewes. In control ewes, the proportion of preantral follicles declined significantly (P less than 0.05) with each oestrous cycle while the antral follicles increased as the breeding season progressed (P less than 0.05). In contrast, after unilateral ovariectomy, the proportion of preantral and antral follicles remained constant throughout the cycles studied. The rate of atresia of antral follicles, especially those from small size classes, decreased significantly after one cycle of unilateral ovariectomy (P less than 0.05). Larger antral follicles had a different rate of atresia as the breeding season advanced. It is concluded that unilateral ovariectomy acutely decreased the rate of atresia and maintained the within-ovary equilibrium between preantral and antral follicles which otherwise would have decreased due to the depletion of preantral follicles with the advance of the breeding season.     

Episodic secretion of gonadotrophins and ovarian steroids in jugular and utero-ovarian vein plasma during the follicular phase of the oestrous cycle in gilts

Blood samples were collected simultaneously from the jugular and utero-ovarian veins of 13 gilts from Days 11 through 16 of the oestrous cycle. A luteolytic dose (10 mg) of PGF-2 alpha was given on Day 12 to facilitate the natural occurrence of luteolysis and standardize the associated decrease in concentrations of progesterone. The mean interval from PGF to oestrus was 5.5 +/- 0.7 days (mean oestrous cycle length = 17.5 +/- 0.7 days). Mean concentrations, pulse amplitudes and pulse frequencies of oestradiol and progesterone were greater (P less than 0.05) in the utero-ovarian than jugular vein. Secretory profiles of LH and FSH were similar (P greater than 0.05) in plasma collected simultaneously from both veins. Based on these data, temporal relationships among hormonal patterns of FSH and LH in the jugular vein and oestradiol and progesterone in the utero-ovarian vein were examined. Concentrations of progesterone declined (P less than 0.05) between Days 12 and 14, while all secretory variables for oestradiol increased (P less than 0.05) from Day 12 through 16 of the oestrous cycle. The pulsatile secretion of FSH remained relatively constant during the experiment. However, both pulse amplitude and mean concentration tended (P less than 0.2) to be lower on Day 16 compared with Day 12. The episodic secretion of LH shifted from a pattern characterized by high-amplitude, low-frequency pulses to one dominated by numerous pulses of diminishing magnitude between Days 13 and 14. From Days 14 to 16 of the oestrous cycle, 91% of all oestradiol pulses were temporally associated with gonadotrophin pulses composed of both FSH and LH episodes. However, pulses of oestradiol (52%) not associated with an episode of LH and/or FSH were observed on Days 12 and 13. These data demonstrate that during the follicular phase of the pig oestrous cycle substantial oestradiol production occurred coincident with luteolysis and before the shift in the episodic secretion of LH. The pool of follicles which ovulated was probably the source of this early increase in the secretion of oestradiol. Therefore, we propose that factors in addition to FSH and LH are involved in the initial selection of follicles destined to ovulate during the early stages of the follicular phase of the pig oestrous cycle. In contrast, high-frequency, low-amplitude pulses composed of LH and FSH were the predominant endocrine signal associated with oestradiol secretion during the second half of the oestrous cycle.(ABSTRACT TRUNCATED AT 400 WORDS)     

Changes in gonadotrophin secretion and ovarian antral follicular activity in seasonally breeding sheep throughout the year

Overall, significantly more antral follicles greater than or equal to 1 mm diameter were present in Romney ewes during anoestrus than in the breeding season (anoestrus, 35 +/- 3 (mean +/- s.e.m.) follicles per ewe, 23 sheep; Day 9-10 of oestrous cycle, 24 +/- 1 follicles per ewe, 22 sheep; P less than 0.01), although the mean numbers of preovulatory-sized follicles (greater than or equal to 5 mm diam.) were similar (anoestrus, 1.3 +/- 0.2 per ewe; oestrous cycle, 1.0 +/- 0.1 per ewe). The ability of ovarian follicles to synthesize oestradiol did not differ between anoestrus and the breeding season as assessed from the levels of extant aromatase enzyme activity in granulosa cells and steroid concentrations in follicular fluid. Although the mean plasma concentration of LH did not differ between anoestrus and the luteal phase of the breeding season, the pattern of LH secretion differed markedly; on Day 9-10 of the oestrous cycle there were significantly more (P less than 0.001) high-amplitude LH peaks (i.e. greater than or equal to 1 ng/ml) in plasma and significantly fewer (P less than 0.001) low amplitude peaks (less than 1 ng/ml) than in anoestrous ewes. Moreover, the mean concentrations of FSH and prolactin were significantly lower during the luteal phase of the cycle than during anoestrus (FSH, P less than 0.05, prolactin, P less than 0.001). It is concluded that, in Romney ewes, the levels of antral follicular activity change throughout the year in synchrony with the circannual patterns of prolactin and day-length. Also, these data support the notion that anovulation during seasonal anoestrus is due to a reduced frequency of high-amplitude LH discharges from the pituitary gland.     

The rat pinealocyte during the oestrous cycle. A morphometric study

The involvement of the pineal gland in the oestrous cycle seems to be clear nowadays according to various types of studies, although its exact functional mechanism remains unknown. The lack of morphological studies on the pineal gland throughout the oestrous cycle has drawn us into the quantification of the surface of pinealocyte nucleoli and nuclei and lipid contents (expressed in mean area of lipid droplets with respect to the total area of pinealocytes) in each of one of the four days of the oestrous cycle: Prooestrous, oestrous, metoestrous and dioestrous. The measures of nuclei and lipid droplets were taken on photographs that were obtained from 1 micron thick sections by means of an image analyzer and the measures of nucleoli were obtained from micrography by means a point-counting analysis. One-way analysis of variance showed significant differences among nucleolar surface during the four days of the cycle. Nucleolar surface in prooestrous and oestrous was significantly smaller than in metoestrous and dioestrous and nuclear surface showed higher values in dioestrous and proestrous than oestrous and metoestrous. The relative value of lipid surface with respect to pinealocyte surface showed significant differences between oestrous and the other three days, with their minimum value in oestrous and maximum in metoestrous. We conclude that the pinealocyte have a rhythmic activity during the oestrous cycle, with a minimum close to ovulation, where the pituitary gonadotropins and ovarian hormonal levels presents a surge.     

Acid phosphatase and leucine aminopeptidase activity in the uterine flushings of non-pregnant and pregnant gilts

The activities of uteroferrin, measured as acid phosphatase (AP), and an aminoacylpeptidase (AA) were measured in uterine flushings collected from gilts on Days 6, 8, 10, 12, 14, 15, 16 and 18 of the oestrous cycle and pregnancy (N = 37). Changes in AP (P less than 0.05) were associated with day for both specific and total AP in non-pregnant and pregnant gilts. For pregnant and non-pregnant gilts, AP activity was greatest between Days 14 and 16 and then decreased to Day 18. The AA specific activity increased (P less than 0.01) between Days 10 and 12 of the oestrous cycle and pregnancy, but neither effects of pregnancy nor day by pregnancy status interaction were detected. The AA total activity was greater for pregnant gilts (P less than 0.01). These data suggest an inhibitory effect of oestrogens of blastocyst origin on synthesis and/or secretion of uteroferrin, but not AA.     

Monitoring ovarian function and pregnancy in Eld's deer (Cervus eldi thamin) by evaluating urinary steroid metabolite excretion

Direct radioimmunoassays (RIA) for urinary oestrone conjugates and pregnanediol-3 alpha-glucuronide (PdG) were used to study ovarian activity patterns and pregnancy in Eld's deer. In 2 does, urinary metabolite patterns were compared to temporal patterns of plasma LH, oestradiol-17 beta and progesterone. Preovulatory LH peaks occurred coincident with behavioural oestrus, and plasma progesterone secretion paralleled PdG excretion. Although plasma oestradiol-17 beta levels fluctuated between 5 and 10 pg/ml throughout the oestrous cycle, no preovulatory oestrogen surge was observed. Based on PdG excretion, non-conception oestrous cycles averaged 21.5 +/- 2.1 days (+/- s.e.m., n = 65); however, 2 of 13 does exhibited prolonged oestrous cycles (30.1 +/- 4.4 days; range 14-62 days, n = 14) characterized by sustained PdG excretion. Excluding these 2 females, the mean oestrous cycle was 18.5 +/- 0.3 days (range 14-23 days, n = 51). Behavioural oestrus (12-24 h duration) was observed in 42 of 65 cycles (64.6%), and always corresponded with intercyclic troughs in PdG excretion (2-5 days duration). Mean gestation duration (n = 10) was 33.5 +/- 0.4 weeks. PdG concentrations increased (P less than 0.05) by Week -32 (3rd week of gestation), plateaued between Weeks -31 and -25, increased (P less than 0.05) markedly by Week -22 and then rose steadily until parturition, declining (P less than 0.05) rapidly thereafter. Mean excretion of oestrone conjugates remained low until Week -30, increased (P less than 0.05) steadily to Week -24 (P less than 0.05) and then returned to baseline by Week -17. Increased (P less than 0.05) oestrone conjugates concentrations were detected again by Week -4 followed by a rapid increase to peak pregnancy levels by Week -1, declining (P less than 0.05) precipitously after parturition. The results confirm that the Eld's deer is seasonally polyoestrous with onset (January-March) and cessation (August-October) of regular, cyclic ovarian activity coinciding with increasing and decreasing daylengths, respectively. Urinary PdG excretion accurately reflects cyclic ovarian activity and markedly elevated concentrations of this metabolite provide an accurate index of pregnancy. The simultaneous monitoring of oestrone conjugates appears useful for estimating the stage of pregnancy and predicting parturition onset.     

Factors affecting number of surface ovarian follicles and oocytes yield and quality in Egyptian buffaloes

Three experiments were conducted to evaluate factors affecting number of surface ovarian follicles and oocytes yield and quality in buffalo. In Experiment 1, ovaries (n = 126) were collected in pairs from slaughtered anoestrus, early pregnant and cyclic buffaloes. Ovarian follicles (1-3, 4-9 and > or = 10 mm diameter) were counted, aspirated and oocytes were recovered and evaluated. In Experiment 2, ovaries were divided into 2 groups. Group 1, ovaries bearing a CL (n = 74) and Group 2 non-bearing CL (n = 74), ovarian follicles (2-8 mm) were counted, aspirated and oocytes evaluated. In Experiment 3, oocytes were recovered using aspiration or slicing methods. In all experiments, oocytes were classified into good, fair, poor and denuded. Results showed that the development of small and total ovarian follicles are continuous and independent in early pregnant or cyclic buffalo cows, however, it significantly decreased (P < 0.01) in the ovaries of anoestrus buffaloes. Number of medium and large size follicles was significantly increased (P < 0.01) in cyclic buffaloes on Days 10-16 and 17-22 of oestrous cycle, while large follicles was significantly decreased (P < 0.01) in the ovaries of pregnant buffaloes. A significantly higher (P < 0.01) percentage of poor and denuded oocytes were recovered from ovaries of anoestrus and pregnant buffalo. While, the highest (P < 0.01) percentage of good quality oocytes were recovered from ovaries of cyclic buffaloes on Days 1-3 and 10-16 of oestrous cycle, eliciting that the stage of oestrous cycle is affecting the quality of buffalo oocytes. In addition, the presence of a CL stimulates the development of a significantly higher (P < 0.01) number ovarian follicles which produced a significantly higher (P < 0.05) number of good quality oocytes. Slicing of buffalo ovaries produced a significantly higher number of fair, poor and denuded oocytes. In conclusion, number of ovarian follicles and yield and quality of oocytes were affected by the reproductive status, stage of the oestrous cycle, presence of a CL and the method of oocytes retrieval.     

Plasma,milk and faecal progesterone concentrations during the oestrous cycle of lactating dairy cows with different milk yields

The hypotheses tested in this study were that neither average progesterone (P4) concentrations in plasma and milk nor average progesterone metabolites concentrations in faeces would differ during an oestrous cycle in two groups of cows with differing daily milk yields. High producing (HP = 8) and low producing (LP = 8) dairy cows were selected randomly for the study. Their oestrous cycles were initially synchronised using P4 and prostaglandin F2alpha. Chromic oxide capsules were administered twice daily to measure total faecal output. Samples of blood, faeces and milk were taken daily throughout one oestrous cycle, plasma and milk P4, and faecal progesterone metabolites (FP4M) assayed. The average daily milk yields in the two groups were 30.8 and 21.9l per day, respectively (P < 0.0001), although daily faecal output was similar in both the groups (HP, 7.7 versus LP, 6.9 kg DM; P = 0.24). Mean plasma and milk P4 concentrations were similar in both the groups (plasma P4, 4.12 versus 4.05 ng/ml; P = 0.3; milk P4, 8.2 versus 8.3; P = 0.9) during dioestrus. Average daily excretion of P4 to the milk was greater in HP than LP cows (252 versus 185 microg, P = 0.04). Neither concentration nor the daily yield of FP4Ms was affected by level of milk yield (concentration: 12.2 versus 11.5 microg/g; daily yield: 89.1 versus 82.9 mg per day; P > 0.05). These data showed that the concentrations of P4 in plasma and milk, and the concentrations and daily yields of FP4M were not affected by the level of daily milk yields which differed by about 41% of the LP average of 21.9l.     

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.     

Hormone studies on ewes grazing an oestrogenic (Yarloop clover) pasture during the reproductive cycle.

The endocrine function of Merino and Corriedale ewes grazing an oestrogenic (Yarloop clover) pasture has been studied during the oestrous cycle, pregnancy and parturition, and the results compared with those from a study of similar ewes grazing a neighbouring grass pasture. Plasma progesterone, oestrogen and corticoids were measured using competitive protein binding assay procedures. During the oestrous cycle clearly anomalous patterns in hormone content were evident in ewes grazing Yarloop, and this related to their significantly poorer (P less than 0.001) fertility. The first mating, when ewes were 1-1/2 years of age, was particularly affected. Successful conception took place in only 27% of ewes mated on Yarloop, compared with 95% on grass. Evidence of disturbance in the normal patterns of both plasma oestrogen and progesterone was found in infertile ewes, including a shortened period of luteal function. Disturbance of endocrine function caused by Yarloop clover ingestion was also found in pregnant ewes, with the mean plasma progesterone concentrations during the latter half of pregnancy reduced (P less than 0.05) and the plasma oestrogen and corticoid levels tending to be higher in these animals. In detailed hormone studies in the periparturant period, both groups showed a similar fall in plasma progesterone and rise in plasma oestrogen prior to parturition. Where excessive time was taken for parturition (more than 30 min) this was reflected in higher plasma corticoid levels (P less than 0.05) within 8 h of birth.     

Gonadotrophins, fecundity genes and ovarian follicular function

The Booroola Merino is a sheep breed having a major gene(s) (F) influencing its ovulation-rate. Homozygous (FF), heterozygous (F+) and non-carriers (++) of the gene have ovulation-rates of greater than or equal to 5, 3 or 4 and 1 or 2 respectively with the durations of each oestrous cycle and oestrous behaviour being similar in all genotypes. Although the principal site(s) of gene expression are obscure, FF genotypes have mean plasma concentrations of FSH and LH which are higher than in the F+ ewes, which in turn are higher than in the ++ animals. Thus, the FF and F+ animals provide a unique system in which to examine ovarian function under continual exposure to elevated gonadotrophin concentrations. At the ovarian level, F gene-specific differences in follicular development and function were noted. In small follicles (0.1-1.0 mm dia.), the basal levels of cAMP and the in vitro synthesis of cAMP, progesterone, androstenedione and oestradiol-17 beta in response to LH and FSH were significantly influenced by genotype (FF greater than F+ greater than ++; P less than 0.05). In larger follicles (1-4.5 mm dia.) the granulosa cells from FF and F+ ewes were more responsive to FSH and/or LH than in ++ ewes with respect to cAMP synthesis and they also had higher levels of aromatase activity. In vivo, the ovarian secretion-rates of oestradiol from greater than or equal to 5 ("oestrogenic") follicles in FF ewes, 3-4 such follicles in F+ ewes, and 1-2 such follicles in ++ animals during the follicular phase were similar. In FF and F+ ewes, the preovulatory follicles ovulated at a smaller diameter (i.e. 3-5 mm) than in ++ ewes (greater than 5 mm diam.) and also produced smaller corpora lutea. Thus, after continual exposure to elevated levels of gonadotrophins, follicles may synthesize steroid and mature at smaller diameters compared to those exposed to normal levels of FSH and LH.     

Oocyte maturation inhibitor, inhibin and steroid concentrations in porcine follicular fluid at various stages of the oestrous cycle

Oocyte maturation inhibitor (OMI), inhibin, progesterone and oestradiol 17 beta concentrations were measured in fluid collected from small (less than 3 mm), medium size (3-6 mm) and large (greater than 6 mm) porcine ovarian follicles, which were obtained on Days 5, 10, 15 and 18 of the oestrous cycle and at 24 h after the onset of oestrus. Concentrations of OMI decreased with increasing follicle diameter (P less than 0.05), independent of the stage of the oestrous cycle. Concentrations of inhibin showed a tendency to decrease with increasing follicle diameter on Days 10, 15 and 18, but not on Day 5 of the cycle. Concentrations of OMI and inhibin in the largest follicles were low before the onset of oestrus, and were essentially unaltered 24 h later. A positive correlation was found between OMI and inhibin concentrations, whereas the correlation between inhibin concentration and log (progesterone concentrations) was negative.     

Seasonal variations in post-partum plasma progesterone levels and conception in primiparous and multiparous dairy cows

Progesterone concentrations in peripheral plasma of 18 primiparous and 34 multiparous dairy cows were determined by radioimmunoassay every 4 days, from 10 days post partum until the next conception. The interval from parturition to the first progesterone peak (greater than 4 ng/ml plasma) was significantly longer (P less than 4 ng/ml plasma) was significantly longer (P less than 0.01) in primiparous than in multiparous cows. The progesterone concentrations on Days 4-15 of the oestrous cycle were significantly lower (P less than 0.025) during the summer than in cycles occurring in winter. The conception rate during the summer was lower than in winter. In cows inseminated in summer, conception was related to the shape of the progesterone curve in the cycle preceding insemination.     

Effect of level of dietary n-3 polyunsaturated fatty acid supplementation on systemic and tissue fatty acid concentrations and on selected reproductive variables in cattle

Reproductively normal crossbred beef heifers were individually offered a diet of barley straw and concentrate supplemented with one of four levels of a fish oil (FO) enriched supplement. Following oestrous cycle synchronisation, blood samples were collected at appropriate intervals for the measurement of progesterone (P(4)), oestradiol (E(2)), fatty acids, insulin-like growth factor 1 (IGF-1) and metabolites. On days 15 and 16 of the cycle, oxytocin was administered intravenously and the prostaglandin F(2alpha) (PGF(2alpha)) response was measured as venous concentrations of 13,14-dihydro-15-keto PGF(2alpha) (PGFM). The heifers were slaughtered on days 17 or 18 of the oestrous cycle and endometrial tissue, rumen fluid and follicular fluid were collected for determination of fatty acid concentrations. In general there was no effect (P>0.05) of diet on plasma P(4) or E(2) concentrations. Increasing FO supplementation increased CL diameter on day 7 post-oestrus (P<0.0001) but had no effect on diameter on day of slaughter (P>0.05). On day 15, PGFM concentration was greater on the highest level of FO supplementation compared to controls (P<0.05), however, there were no differences between other diet comparisons (P>0.05). There was no effect of diet on PGFM concentration on day 16 (P>0.05). There was a strong positive relationship between plasma and uterine endometrial concentrations of both EPA (R(2)=0.86; P<0.0001) and total n-3 PUFA (R(2)=0.77; P<0.0001). IGF-1 concentrations increased on all diets and were greatest at the highest level of n-3 PUFA supplementation (P<0.05).     

Histamine and increased ovarian blood flow mediate LH-induced superovulation in the cyclic hamster

Constant infusion of LH (400 micrograms NIH-S24) through an osmotic minipump inserted on Day 1 (oestrus) of the cycle in the hamster resulted in spontaneous superovulation (approximately equal to 29 ova) at the next expected oestrus, increased blood flow (P less than 0.001) to the ovary on Day 3, and slight depletion (0.1 greater than P greater than 0.05) of histamine in the ovary. Treatment with antihistamine (alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, or cimetidine, an H2 blocker) by injections or by infusion using separate osmotic minipumps significantly (P less than 0.01) reduced the number of ova shed in the LH-treated hamsters. Infusion of LH with alpha-fluoromethylhistidine in the same osmotic minipump reduced the bioactivity of the LH. Infusion of antihistamine alone did not alter the normal number of ova shed. The results suggest that the LH-induced superovulation involves stimulation of histamine release; the histamine than may increase ovarian blood flow thus allowing more gonadotrophins to reach the ovary.     

Binding and action of insulin-like growth factors and insulin in bovine luteal tissue during the oestrous cycle.

The effect of insulin-like growth factors (IGFs) and insulin on the release of progesterone and oxytocin from bovine corpus luteum was investigated at early (days 5-7), mid- (days 8-12) and late (days 15-18) luteal phases of the oestrous cycle in an in vitro microdialysis system. The expression of specific receptors was evaluated in bovine corpora lutea of the respective luteal stages. A 30 min infusion of IGF-1, IGF-2 (1.3, 13 and 130 nmol l-1) or insulin (13, 130 and 1300 nmol l-1) caused a stimulation of the release of progesterone (P < 0.05). IGF-1 was most effective in releasing progesterone. Oxytocin release from corpora lutea was stimulated by insulin at all doses tested (13-1300 nmol l-1), whereas the IGFs were only effective at the highest dose (130 nmol l-1) applied. The high doses of IGFs (130 nmol l-1) and insulin (1300 nmol l-1) stimulated the release of progesterone and oxytocin throughout the luteal phase (P < 0.05). For all three peptides, greatest stimulation was seen during the late luteal phase (days 15-18 of the oestrous cycle) with the peak of progesterone release directly related to peptide infusion (P < 0.05). In addition, IGF-1 stimulated total release of progesterone (units in 4 h) after the beginning of the stimulation during this phase (P < 0.05). IGF-1 caused a gradual increase of progesterone even beyond the time of peptide perfusion, whereas IGF-2 and insulin stimulated progesterone release only during the peptide perfusion. Distinct receptors for IGF-1 and IGF-2 were present in corpora lutea membrane preparations at all stages investigated. Specific binding for insulin was also seen in all stages of the cycle without any cycle-dependent changes in the amount of binding. The displacement of labelled insulin by unlabelled IGF-1 and IGF-2 did not show the rank of order that has been described as typical for insulin receptors (i.e. insulin > IGF-1 > IGF-2), but comparable binding affinities were observed for the three unlabelled ligands. Specific binding of IGF-2 was markedly higher than that of IGF-1 or insulin throughout the cycle (1.9- and 4.9-fold higher compared with IGF-1 and insulin, respectively). Receptor specificity did not change during luteal development. Binding affinity and capacity of IGF-1 receptor was constant throughout the oestrous cycle. Specific IGF-2 binding increased and showed a positive co-operativity towards the end of the cycle. Specific binding of insulin was not significantly different in the three luteal stages examined.