Effects of season on the reproductive organs and steroid hormone profiles in guinea hens (Numida meleagris).

The study documented gross anatomical and histological differences in the reproductive organs of 28 breeding and non-breeding female guinea fowls. Peripheral progesterone and 17ß-oestradiol concentrations were also compared in breeding and non-breeding hens. In non-breeding females, all ovarian and oviducal gross anatomical features had significantly regressed. Histologically, some of the changes in a regressing oviduct include systematic changes in height and size of all epithelial cells in all regions of the duct, absence/sparse ciliation of portions of surface epithelium in the magnum, isthmian and uterine regions, general loss of cytoplasmic mass, reduction in size and degeneration of tubular glands. Mucosal folds in all regions of the oviduct except the infundibular lip were higher in breeding females. No difference was found between the two groups in plasma progesterone concentrations. Breeding females, however, had higher peripheral oestradiol concentrations than non-breeding females. About 2 h prior to oviposition, plasma oestradiol concentrations peaked at 2.4-fold (230 pg/ml) compared with baseline concentration and plasma progesterone concentrations by nearly 9-fold (5.29 ng/ml) of baseline. Significant regression and changes in the histological structure of the ovary and oviduct had occurred in non-breeding females, and lower peripheral oestrogen concentrations may be responsible for this phenomenon.

Effects of season on the reproductive organ and plasma testosterone concentrations in guinea cocks (Numida meleagris).

The physiological basis of seasonal breeding in the guinea fowl (Numida meleagris) still remains unknown, despite the socioeconomic importance of these birds, particularly in Ghana. A study involving a total of 50 local guinea cocks was conducted, and documented gross anatomical and histological differences in the reproductive organs of breeding and non-breeding male guinea fowls. The study also compared peripheral testosterone concentrations in breeding and non-breeding cocks. Seasonal differences in variables measured were determined using two-tailed t-test/Mann-Whitney U-test. All comparisons were made at 5% level of significance. Breeding males had significantly (P = 0.000) higher anatomical biometric parameters than their non-breeding counterparts. Also, breeding birds had thicker (P = 0.000) phalli than their non-breeding counterparts. Histologically, regressing testis was characterized by the presence of sloughed off cells and increased debris in the tubular lumen and within the excurrent duct system, collapsed tubules and reduction in tubular lumen. Germ and Sertoli cell populations and nuclear diameters and actual seminiferous tubular diameter and length in regressing testes were significantly (P = 0.000) lower than in active testes. Leydig cell nuclear diameters and populations were also significantly (P = 0.000) reduced. Relative volume of seminiferous tubules in the testis, testicular sperm production/mg testis and per testis and peripheral testosterone concentrations were all higher (P < 0.05) in breeding than non-breeding testis. The ducts in the epididymal region also saw significant (P < 0.05) reductions in luminal diameters in non-breeding birds. Significant regression in anatomical and histological structures of the guinea cock reproductive tract occurred during the non-breeding season, and lower peripheral testosterone concentrations may be responsible for this phenomenon.

Ovarian function and FSH receptor characteristics during canine anoestrus.

Ovaries of bitches are relatively inactive during anoestrus despite apparently adequate circulating FSH concentrations. Alternative FSH receptor (FSH-R) transcripts in bitches might hinder the follicular response to gonadotrophins, which may account for anoestrus. The expression of the full length FSH-R and novel isoforms in bitches was examined using in situ hybridization and RT-PCR analysis. Various PCR primers to the FSH-R were used and its expression was assessed in ovarian tissue at different stages of the oestrous cycle. RT-PCR amplification of the extracellular domain (exon 1-10) was generally successful, indicating that cFSH-R expression (> 90%) occurs throughout the oestrous cycle. Two FSH-R isoforms were sequenced, but there were no clear differences in the pattern of expression between anoestrus and other stages of the oestrous cycle, except that isoform expression was less frequent (30% occurrence) in prepubertal bitches. Data from in situ hybridization showed clear expression of the FSH-R in secondary and antral follicles, and corpora lutea. It was concluded that there is no evidence of a change in the expression of the FSH-R specific to anoestrus.

Measurement of plasma oestradiol after an injection of a gonadotrophin as a test for neutered bitches.

Twenty-eight bitches with unknown reproductive histories were injected intravenously with either human chorionic gonadotrophin (hCG) or equine chorionic gonadotrophin (eCG) (pregnant mare's serum gonadotrophin) and their oestradiol responses were measured at the time of the injection and 90 minutes later. They were at various stages of the oestrous cycle as determined by histology and a progesterone assay for luteal function. Twenty-six of them were considered to be entire because they showed either an increase in plasma oestradiol over preinjection values or steady high values. The ovaries were removed from 25 of these animals and the other probably had a remnant of ovary because it came into oestrus some weeks later. In two remaining bitches no oestradiol could be detected either before or after the injection of gonadotrophin and they were predicted to have been neutered, which was confirmed at laparotomy. In the entire bitches, the highest plasma oestradiol concentration was measured during metoestrus and the lowest during anoestrus.

Formation of a secondary corpus luteum after ultrasound-guided follicular aspiration in cows.

This paper reports the observed formation of a secondary corpus luteum (CL) in the presence of the cyclic corpus luteum, on the ovaries of a cow after ultrasound-guided follicular aspiration for oocyte recovery. The secondary structure, although smaller and lighter (4.97 g vs. 6.02 g) than the natural one, had the typical macroscopic appearance of a corpus luteum. Histological examination of the structure using electron microscopy revealed typical structural features of a natural CL. Mean tissue progesterone concentration was significantly lower in the secondary CL (31.15 +/- 3.11 compared with 58.29 +/- 6.32 micrograms/g tissue of the cyclic CL) and oestradiol-17 beta significantly higher than in the natural CL (108 +/- 11.6 compared with 74.2 +/- 7.81 pg/g tissue). P450scc and P450(17 alpha) mRNA was detected in both structures while P450arom and full-length mRNA FSH receptor were detected only in the secondary structure.

Plasma estradiol FSH and LH concentration after dominant follicle aspiration in the cow.

This work investigates the estrogenic role of the dominant follicle with regard to regulation of plasma FSH and LH concentration. Eight Holstein-Friesian cows were used for aspiration of the dominant follicle using ultrasound guidance during the early, mid and late stages of the luteal phase. Blood samples were collected at 15-min intervals from 4 h before until 7 h after aspiration. Plasma progesterone concentration increased from 0.7 to 7.2 ng mL-1 from early to mid luteal phase and then fell slightly to 5.9 ng mL-1 in the late luteal phase, but remained unaffected by follicle puncture. The follicular aspirate contained a thousandfold higher estradiol, than plasma concentration but its estradiol:progesterone ratio remained at around 2 at each stage of the luteal phase. Aspiration caused plasma estradiol concentration to fall from 1.4 to 0.7, 1.8 to 1.0 and 1.7 to 0.8 pg mL-1 in the early, mid and late stages of the luteal phase, respectively (P < 0.05). At the same time, mean plasma FSH concentration was increased from 1.1 to 1.8, 1.7 to 2.9 and 0.8 to 1.9 ng mL-1 (P < 0.05), respectively. The results suggest that estradiol secreted from dominant follicles selectively regulates gonadotropin secretion, since aspiration of the dominant follicle at any stage of the cycle affected circulating FSH but did not appear to influence the mean LH concentration.

Effect of experimental infection with Trypanosoma congolense and scrotal insulation on Leydig cell steroidogenesis in the ram.

Testicular steroid content and Leydig cell steroidogenesis in vitro were investigated in rams on Days 28 and 58 after Trypanosoma congolense infection and were compared with those of rams in which testicular temperature had been raised artificially by insulation of the scrotum for 58 d. Testicular testosterone content increased significantly on Day 28 after infection but was lower than that of controls on Day 58 while it increased in scrotal-insulated rams compared with that of controls by Day 58. Testicular progesterone was undetectable in the control and trypanosome-infected groups throughout the experiment, but it increased in the insulated rams by day 58. Basal (unstimulated) Leydig cell testosterone production in the infected rams was similar to that of control rams on Day 28 but was significantly lower on Day 58. Stimulation of Leydig cell testosterone production with hCG or 22R-hydroxycholesterol (22ROHC) significantly reduced in infected rams at both 28 and 58 d after infection as well as in scrotal-insulated rams on Day 58. It is concluded that the increase in testicular testosterone content in the infected and scrotal-insulated rams on Days 28 and 58, respectively, was induced by elevation of testicular temperature by trypanosome infection, perhaps through an effect on testicular blood flow. Reduced testosterone production by Leydig cells from infected and scrotal-insulated rams in response to hCG and 22ROHC suggests that trypanosome-induced pyrexia might be involved in reducing Leydig cell steroidogenesis and subsequent plasma testosterone levels, possibly by affecting enzymes involved in steroid biosynthesis.

Urinary LH, plasma LH and progesterone and their clinical correlates in the periovulatory period of domestic bitches.

Ten bitches were examined daily from pro-oestrus until metoestrus to correlate endocrine, vaginoscopic and cytological assessments of stage of the oestrous cycle. It was considered that oocytes were fertile by 4 days after the LH peak assuming a 2 day lag before ovulation and a further 2 days for oocyte maturation. Eight bitches showed a plasma LH peak and five bitches showed a peak in urinary LH, which corresponded to the plasma LH peak. Plasma concentration of progesterone increased in all bitches. Initially, this coincided with the preovulatory LH peak and reached values of 7.7 +/- 0.6 ng ml-1 4 days later. The peak in number of a nuclear vaginal epithelial cells and the onset and peak of vaginal mucosal shrinkage with angulation occurred on average 2.4 +/- 1.5, 2.1 +/- 2.4, and 6.1 +/- 1.1 days after the plasma LH peak, respectively, giving sufficient precision to be of practical value in estimating the fertile period. However, the onset of vulval softening, changes in rectal temperature and colour of the vulval discharge varied considerably. Nine of the bitches were mated at the time of highest percentage of a nuclear cells, coinciding with the onset of the period of vaginal mucosal shrinkage with angulation. Eight became pregnant. Selected clinical parameters are therefore useful in predicting the optimal mating time of bitches, as is detection of plasma progesterone concentration higher than about 8 ng ml-1, but the latter appears to be the most reliable method. Detection of the urinary LH peak was more difficult and as yet offers no practical advantages except from the point of view of easy sample collection.

Use of the polymerase chain reaction to sex the bovine fetus using cells recovered by ultrasound-guided fetal fluid aspiration.

The aim of this study was to carry out first trimester fetal sex diagnosis using the polymerase chain reaction (PCR) to amplify DNA from bovine fetal cells recovered by transvaginal ultrasound-guided uterine puncture and fetal fluid aspiration. For sex determination, a nested, allele-specific, PCR amplification of the bovine zfx and zfy gene fragments was utilised. The PCR assay was validated using fetal fluids recovered from uteri post mortem. Cells were harvested from the fetal fluids, genomic DNA extracted and the PCR assay applied. A technique which was developed for transvaginal ultrasound-guided follicle aspiration was modified to recover fetal fluid from live animals. Small volumes of fetal fluid (0.5-5 ml) were recovered between days 61-97 of gestation and the PCR assay applied. The gender determined by PCR of fetal fluid cells was in all cases confirmed by visual inspection (n = 15 abattoir specimens) or ultrasound scanning (n = 7 live animals). Fetal death, attributed to the introduction of intrauterine infection, occurred in 4/4 cows in the first series of aspirations but in only 1/3 heifers in the second series of aspirations.

Effects of castration on luteinizing hormone secretion and response to gonadotrophin-releasing hormone in sheep infected with Trypanosoma congolense.

The effects of trypanosomiasis on the endocrine function of the hypothalamo-pituitary-gonadal axis were investigated before and after castration of Scottish Blackface rams infected with Trypanosoma congolense and uninfected controls. Blood samples were collected at 15-min intervals for 6 h before and at 10, 20, 40, 60, 80, 100 and 120 min after injection of synthetic gonadotrophin-releasing hormone (GnRH, 20 micrograms iv) 2 days before infection and 26 and 54 days after infection, with castration being performed 28 days after infection. Mean luteinizing hormone (LH) pulse amplitude was higher (3.3 +/- 0.2 vs 2.6 +/- 0.3 ng/ml) and mean plasma testosterone concentration was lower (4.1 +/- 0.6 vs 7.6 +/- 1.2 nmol/l) in infected vs control rams 26 days after infection (p < 0.05). Mean plasma LH concentration and pulse amplitude increased in both groups after castration but both were significantly lower in infected compared to control rams (6.6 +/- 1.5 and 13.0 +/- 2.2 ng/ml, p < 0.01; 7.7 +/- 0.9 and 11.6 +/- 0.9 ng/ml, p < 0.001), respectively. However, LH responses to exogenous GnRH were similar in infected and control rams at each stage of the experiment, suggesting that the smaller increase in plasma LH after castration in infected rams was not caused by reduced responsiveness of the pituitary to GnRH but by alterations in GnRH secretion by the hypothalamus or its transport to the adenohypophysis. These results also demonstrate that impairment of testosterone secretion within 4 weeks of T. congolense infection in sheep may be due to testicular rather than pituitary effects.

An ultrasonographic study of bovine cystic ovarian disease and its treatment.

This study assessed the value of ultrasonography in characterising bovine cystic ovaries and monitoring their responses to different treatments. Thirteen cows were diagnosed by ultrasonography as having luteinised ovarian cysts and seven were diagnosed as having follicular ovarian cysts. Six of the former were treated with prostaglandin, four with a progesterone intravaginal device (PRID) and three with gonadotrophin-releasing hormone (Gn-RH); five of the latter were treated with Gn-RH and two with a PRID. All the animals were re-examined by ultrasound and blood was collected for the measurement of plasma progesterone concentration at intervals until oestrus. The treatment of the luteinised cysts with prostaglandin caused marked decreases in size and plasma progesterone concentration and altered their echotexture within two to four days; oestrus occurred within three to four days. In two of the cows treated with a PRID the cysts regressed within one to two weeks but the other two cows required supplementary treatment with prostaglandin; oestrus and ovulation were observed only after the cysts collapsed. Gn-RH stimulated oestrus and ovulation within three to four days but the cysts did not collapse until much later. The treatment of the follicular cysts with Gn-RH or a PRID caused fresh ovulation and the formation of a corpus luteum but had little immediate effect upon the cyst. The plasma progesterone concentrations in some of the cows with either follicular or luteal cysts were similar on the day of treatment and were therefore of little value in differentiating the types of cyst.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Trypanosoma congolense on pituitary and adrenocortical function in sheep: changes in the adrenal gland and cortisol secretion.

The effect of trypanosomiasis on adrenal function was studied in 10 pubertal Scottish blackface rams infected with Trypanosoma congolense and nine uninfected controls. Plasma cortisol concentration was measured by radioimmunoassay in samples obtained twice a week for three weeks before infection and three times a week for 79 days after infection. There was a significant (P < 0.001) increase in cortisol concentration in all the infected rams after the onset of parasitaemia nine to 16 days after infection. This was followed by a transient non-significant decrease in cortisol levels between 19 and 41 days and a variable and parasitaemia-dependent increase in cortisol levels between 44 and 79 days after infection. Marked hypertrophy of the zona fasciculata-reticularis, infiltration of mononuclear cells into the cortical and medullary zones, hyperaemia and focal coagulative necrosis were evident in the adrenal glands of infected rams killed at the end of the study. Trypanosome infection induced a low grade persistent pyrexia, marked anaemia, reduced growth rates and general loss of body condition. These results demonstrate that T congolense infection in sheep causes marked pathological changes in the adrenal cortex and changes in the secretion of cortisol.

Effects of Trypanosoma congolense on pituitary and adrenocortical function in sheep: responses to exogenous corticotrophin-releasing hormone.

To investigate whether the aberrations in adrenocortical and gonadal activity observed in trypanosomiasis may be induced by the refractoriness of the pituitary to hypothalamic liberins, the responses of the pituitary and adrenal glands and the testes to stimulation with ovine corticotrophin-releasing hormone (oCRH) were studied in rams 23 days (acute phase) and 65 days (chronic phase) after they were infected with Trypanosoma congolense. On both occasions a peak of plasma ACTH was observed within 20 minutes of the injection of CRH but the rate of increase in ACTH and the mean peak values in the infected rams were significantly lower (P < 0.001) on day 23 but higher (P < 0.05) on day 65 than in the uninfected control rams. Plasma cortisol concentration increased in all the rams after the injection of CRH. The rate of increase in plasma cortisol and the mean peak values were not significantly different between the control and infected rams on day 23 but were significantly (P < 0.001) higher in the infected rams on day 65. However, the post peak concentrations of ACTH declined more rapidly in the infected rams than in the controls on both days 23 and 65. The plasma concentration of luteinising hormone (LH) did not change after the injection of CRH, whereas the testosterone levels showed a delayed response and its concentration increased when plasma ACTH and cortisol concentrations declined in both groups. On day 23, there was a greater increase in testosterone in the infected than in the control rams.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Trypanosoma congolense infection in rams on the pulsatile secretion of LH and testosterone and responses to injection of GnRH.

Changes in pulsatile secretion of LH and testosterone and responses to exogenous GnRH were assessed at different stages of Trypanosoma congolense infection in rams. Jugular blood samples were collected every 15 min for 6 h followed by immediate injection of GnRH (20 micrograms i.v.) and further sample collection after 10, 20, 40, 60, 80, 100 and 120 min. This sampling and injection regimen was performed 5 days before infection (day -5) and 23 and 52 days after infection. T. congolense infection increased (P < 0.05) the mean plasma LH concentration over 6 h on day 23 (3.2 +/- 0.2 ng ml-1) and decreased (P < 0.05) the mean LH concentration on day 52 (1.2 +/- 0.2 ng ml-1, P < 0.05) compared with day -5 values (2.0 +/- 0.2 ng ml-1). Trypanosome infection induced a rapid decline in plasma testosterone concentration from a mean of 7.5 +/- 1.4 nmol l-1 on day -5 over 6 h to 3.6 +/- 0.4 nmol l-1 (P < 0.05) on day 23 and 1.7 +/- 0.3 nmol l-1 (P < 0.001) on day 52. The observed decline in plasma LH concentration in infected rams was not associated with reduced sensitivity of the pituitary to GnRH or its ability to release LH, as the LH response to exogenous GnRH was not impaired throughout the period of infection. However, the testosterone response to GnRH-induced LH stimulation was depressed on both days 23 and 52 after infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal Leydig cell development at puberty in the androgen-resistant Tfm mouse.

Leydig cells are the major source of androgens in the male, and it is likely that these cells are also targets for androgen action. The role of androgen action in regulating the development of Leydig cell function has been determined using the testicular feminized (Tfm/Y) mouse, which lacks androgen receptors. In Tfm mice, the testes fail to descend at the normal time (25 days), and testicular descent was, therefore, surgically prevented in control (+/Y) animals. The activity of 3 beta-hydroxysteroid dehydrogenase increased during development from 5-40 days in control and Tfm mice, with no significant difference between the groups. In control animals, 17 alpha-hydroxylase activity was low from 5-25 days, at which time there was a 26-fold increase up to 40 days. In the Tfm group, 17 alpha-hydroxylase activity was 4-fold higher than that in controls on day 5, but showed no change in activity after 25 days and remained at neonatal levels up to 40 days. The activity of 17-ketosteroid reductase in the control animals showed a developmental pattern similar to that of 17 alpha-hydroxylase, with a marked increase in activity after 25 days. In the Tfm group, 17-ketosteroid reductase was normal on day 5, but failed to show any significant change thereafter and remained at neonatal levels on day 40. Serum LH levels in control animals increased from 5 days to a peak at 30 days. In Tfm mice, LH levels were significantly increased on days 20 and 40, but did not differ from controls on days 5, 25, and 30. In control +/Y animals, in which normal testicular descent was allowed to proceed at 25 days, the pattern of development was similar to that in the cryptorchid +/Y animals, although the increase in 17 alpha-hydroxylase activity at 30 and 40 days was significantly greater. The results show 1) that fetal Leydig cell steroidogenesis is enhanced in the absence of androgen receptors, but 2) that adult Leydig cells require receptor-mediated androgen activity around day 25 for normal functional development. In addition, 3) the lack of testicular descent at 25 days reduces the pubertal rise in 17 alpha-hydroxylase activity.

A critical evaluation of ultrasonic monitoring of superovulation in cattle.

This study evaluated real time B-mode ultrasonic monitoring for scanning ovaries of cows superovulated using eCG (1500 or 3000 i.u.). Follicular growth was monitored after stimulation and follicles categorized according to size. Numbers of large (> or = 10 mm) follicles correlated weakly (r = 0.31) with numbers of luteal structures formed subsequently. Timing of ovulation was confirmed by comparison with peak LH and plasma progesterone concentrations. Ovulation was visible on scanning but quantitation of corpora haemorrhagica was not accurate in superovulated ovaries. Luteal structures counted at scanning correlated significantly with findings at post mortem (r = 0.75; P < 0.01) but enumeration of structures was inaccurate. Scanning consistently underestimated luteal structures. Numbers of observed luteal structures correlated weakly with embryo recovery (r = 0.36). It was concluded that the presence of luteinized follicles greatly reduced the accuracy of identification of structures in superovulated ovaries.

Endocrinology of anoestrous bitches.

Plasma luteinizing hormone (LH), prolactin and oestradiol concentrations and responses to a standard challenge with a gonadotrophin-releasing hormone (GnRH) analogue were measured at defined stages of consecutive oestrous cycles in beagle bitches. In each of 35 sampling sequences blood samples were collected every 20 min for 6 h followed immediately by injection of a GnRH analogue (GnRH-A) and collection of further samples after 10, 20, 40 and 60 min. Cycle stages were based on progesterone profiles and the day of the preovulatory LH peak. Sampling sequences were obtained during the luteal phase (n = 5), transition to anoestrus (n = 10), anoestrus (n = 17) and pro-oestrus (n = 3), which were 154-71, 114-44, 85-11 and 7-1 days before the preovulatory LH peak, respectively. Pulsatile LH secretion occurred spontaneously at all stages of the cycle and there was no effect of cycle stage on mean LH concentration or variability. In contrast, oestradiol was undetectable in most samples from early and mid-anoestrus until approximately 1 month before the preovulatory LH peak, after which average oestradiol concentrations and between-sample variability appeared to increase. Mean (+/- SEM) oestradiol concentrations for all preinjection samples collected from 100-75, 74-50, 49-25, 24-10 and 9-1 days before the LH peak was 1.4 +/- 0.1, 1.3 +/- 0.1, 2.4 +/- 0.3, 11.0 +/- 1.4 and 36.0 +/- 3.2 pg ml-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of the periparturient egg rise in sheep: a possible role for IgA.

The relationship between anti-parasite IgA antibody levels in plasma and the periparturient egg rise in sheep was investigated. Ostertagia circumcincta larvae (5000 third stage larvae three times weekly) were administered to three groups of seven adult immune ewes from 12 weeks before until three weeks after lambing (group 1) or from six (group 2) or 14 (group 3) weeks before until three weeks before lambing. Seven additional ewes were not challenged (group 4 controls). Ewes in groups 1, 2 and 4 received anthelmintics 14 weeks before lambing. Challenge of the pregnant ewes with O circumcincta larvae resulted in substantial increases in faecal egg counts only during the periparturient period regardless of the larval dosing regimen. Furthermore, the periparturient rise in faecal egg counts was closely associated with a significant increase in anti-parasite IgA antibody levels in plasma. This rise in IgA antibody levels occurred at a time when IgA is transported from the gut to milk during early lactation. It is postulated that this may lead to a temporary reduction in abomasal antibody levels of ewes and hence permit the establishment of larvae and, or, the emergence and development of inhibited larvae and thereby lead to the periparturient rise in faecal egg count.

Concentrations of luteinizing hormone and oestradiol in plasma and response to injection of gonadotrophin-releasing hormone analogue at selected stages of anoestrus in domestic bitches.

Concentration of plasma luteinizing hormone (LH) and oestradiol concentrations and responses to a standard challenge with a gonadotrophin-releasing hormone (GnRH) analogue were measured at certain stages of anoestrus during consecutive cycles in five beagle bitches. Blood samples were collected every 20 min for 6h followed immediately by injection of GnRH analogue (0.16 micrograms i.v.) and collection of further samples after 10, 20, 40 and 60 min. Five, 10, 17 and three such sampling sequences were obtained during the luteal phase, transition to anoestrus, anoestrus and pro-oestrus respectively (i.e. 154-71, 114-44, 85-11 and 7-1 days before the preovulatory LH peak, respectively). Pulsatile LH secretion occurred spontaneously at all stages of the luteal phase and anoestrus and there was no effect of cycle stage on mean LH concentration or variability. In contrast, oestradiol could not be detected in most samples from early and mid-anoestrus until approximately one month before the preovulatory LH peak, after which average oestradiol concentration and between sample variability appeared to increase. Mean (+/- SEM) oestradiol concentration for all samples collected from 100-75, 74-50, 49-25, 24-10 and 9-1 days before LH peak was 1.4 +/- 0.1, 1.3 +/- 0.1, 2.4 +/- 0.3, 11.0 +/- 1.4 and 36.0 +/- 3.2 pg ml-1, respectively. Plasma LH concentration increased in all bitches after GnRH analogue injection (2.7 +/- 0.7 ng ml-1 at t = 0, 12.5 +/- 1.0 ng ml-1 at t = 10 min, mean +/- SEM, n = 35) regardless of cycle stage.(ABSTRACT TRUNCATED AT 250 WORDS)