Hematologic, prostaglandin F2α -metabolite, serum amyloid A, and serum iron changes in horses with experimentally induced endotoxemia.

BACKGROUND: Endotoxemia is a common and severe disease of horses. Most previous studies have monitored changes caused by a bolus dose of endotoxin over short time periods. OBJECTIVES: We aimed to describe inflammatory responses to endotoxin with inflammatory and hematologic markers monitored over a longer time than has been performed in the past using more prolonged endotoxin exposures. METHODS: Escherichia coli O55:B5 endotoxin was administered as a 6-hour continuous intravenous infusion of lipopolysaccharide (LPS) to eight horses. Blood cell counts, and prostaglandin F2α -metabolite (PGM), serum amyloid A (SAA), and serum total iron concentrations were monitored for up to 3 or 6 days. RESULTS: An immediate and severe decrease in neutrophils and monocytes occurred in all horses, which subsequently changed to a moderate to strong neutrophilia and monocytosis that persisted for more than 78 hours postinfusion (PI) of LPS. Lymphocyte and eosinophil numbers decreased gradually and then normalized after 66- and 78-hours PI, respectively. Mild to moderate, biphasic thrombocytopenia occurred. A pronounced, transient increase in PGM occurred between 1 and 7 hours, peaking at 2 hours. Serum amyloid A began to increase after 6 hours PI and remained elevated after 72 hours PI. Serum iron was decreased between 6 and 48 hours. The clinical signs were most prominent during the first 24 hours PI and subsided within 48 hours PI. CONCLUSIONS: Neutrophilia, monocytoses, and high SAA concentrations were present in horses even after the clinical signs had subsided. Serum iron normalized before SAA. Knowledge of these findings is imperative when interpreting laboratory results in horses with possible endotoxin exposure.

PGF(2α), LH, testosterone, oestrone sulphate, and cortisol plasma concentrations around sexual stimulation in jackass.

Many hormones are involved in the regulation of male reproductive functions, controlling sexual behavior, and influencing sexual arousal, the onset of erection and ejaculation, and the post-ejaculatory detumescence. The aims of this study were to analyze the plasma concentrations of 15-ketodihydro-PGF(2α) (PGFM), LH, testosterone (T), oestrone sulphate (OS), and cortisol (C) in relation to sexual stimulation and to evaluate the possible correlations among circulating hormones and between hormones and semen characteristics in the donkey stallion. Thirteen sexually experienced Martina Franca jackass of proven fertility were enrolled and semen was collected through an artificial vagina. Plasma samples were collected at 12, 9, 6 and 3 min before oestrous jenny exposure, at the first erection in the mating arena in the presence of an oestrous jenny, during ejaculation, at dismounting, 3, 6, 9 and 12 min after ejaculation in box, and then every 10 min during the following 50 min. PGFM showed an increasing trend with significant differences between the pre-ejaculatory and post-ejaculatory period, suggesting a role of this hormone in the control of ejaculation. LH showed a significantly higher concentration at ejaculation compared to last samples, while T showed significantly higher levels at erection, ejaculation and dismounting, probably for its influence on these processes and on sexual behavior. Finally, OS did not show any difference in the period of observation, while C presented a significant increase only 22 minutes after erection. The only hormonal correlation found was a positive one between LH and T at erection and dismounting, while T and OS were positively correlated with total and progressive motility, respectively.

Peripartal plasma concentrations of 15-ketodihydro-PGF2α, cortisol, progesterone and 17-ß-estradiol in Martina Franca jennies.

The transition from intra- to extrauterine environment represents a very delicate phase, in which the successful coordination of maturation is strictly connected with several hormonal changes during the last weeks of gestation and at parturition. While the peripartal endocrinology in the mare has been deeply investigated, the peripartal hormonal changes in the jenny need further evaluation. The aim of this study is to evaluate the mean 15-ketodihydro-PGF(2α) (PGFM), cortisol (C), progesterone (P4), and 17ß-estradiol (E2) levels during the peripartal period in this species. Ten Martina Franca jennies, with normal gestational length and parturition, were enrolled. From each jenny, blood was collected twice a day from 10 d before to 7 d after parturition and from the plasma obtained PGFM, C, P4 and E2 were analyzed by RIA. Higher, constant PGFM concentrations were observed in the pre-foaling days compared to the decreasing levels detected the days after delivery, as previously observed in the mare. During the whole period of observation no significant differences in plasma C levels were detected. In contrast to the mare, P4 has always been detectable and the highest level found at -2.5 days was significantly different compared to samples obtained between -10 and -4.5 days and between 1.5 and 7 days after foaling. Finally, E2 showed higher concentrations before foaling, with the highest values between -3 and -1.5 days, decreasing only one day before foaling. A positive correlation was found between PGFM and P4, during the last 4 days of gestation, while a positive correlation between PGFM and E2 was observed during the prepartum. Despite some similarities with the mare exist, differences have been found in P4 and E2 profiles, underlining once more the differences in the physiology of this two species.

Canine placenta: a source of prepartal prostaglandins during normal and antiprogestin-induced parturition.

Expression of cyclooxygenase 2 (COX2, now known as PTGS2), prostaglandin E2 synthase (PTGES, PGES), and prostaglandin F2alpha synthase (PGFS), of the respective receptors PTGFR (FP), PTGER2 (EP2), and PTGER4 (EP4) and of the progesterone receptor (PGR, PR) was assessed by real-time PCR, immunohistochemistry (IHC), or in situ hybridization (ISH) in utero/placental tissue samples collected from three to five bitches on days 8-12 (pre-implantation), 18-25 (post-implantation), and 35-40 (mid-gestation) of pregnancy and during the prepartal luteolysis. Additionally, ten mid-pregnant bitches were treated with the antiprogestin aglepristone (10 mg/kg bw (2x/24 h)); ovariohysterectomy was 24 and 72 h after the second treatment. Plasma progesterone and 15-ketodihydro-PGF2alpha (PGFM) concentrations were determined by RIA. Expression of the PGR was highest before implantation and primarily located to the endometrium; expression in the placenta was restricted to the decidual cells. PTGS2 was constantly low expressed until mid-gestation; a strong upregulation occurred at prepartal luteolysis concomitant with an increase in PGFM. PGFS was upregulated after implantation and significantly elevated through early and mid-gestation. PTGES showed a gradual increase and a strong prepartal upregulation. PTGFR, PTGER2, and PTGER4 were downregulated after implantation; a gradual upregulation of PTGFR and PTGER2 occurred towards parturition. ISH and IHC co-localized PGFS, PTGFR, PTGES, and PTGS2 in the trophoblast and endometrium. The changes following application of aglepristone were in the same direction as those observed from mid-gestation to prepartal luteolysis. These data suggest that the prepartal increase of PGF2alpha results from a strong upregulation of PTGS2 in the fetal trophoblast with the withdrawal of progesterone having a signalling function and the decidual cells playing a key role in the underlying cell-to-cell crosstalk.

Steroid hormone receptors ERalpha and PR characterised by immunohistochemistry in the mare adrenal gland.

BACKGROUND: Sex steroid hormone receptors have been identified in the adrenal gland of rat, sheep and rhesus monkey, indicating a direct effect of sex steroids on adrenal gland function. METHODS: In the present study, immunohistochemistry using two different mouse monoclonal antibodies was employed to determine the presence of oestrogen receptor alpha (ERalpha) and progesterone receptor (PR) in the mare adrenal gland. Adrenal glands from intact (n = 5) and ovariectomised (OVX) (n = 5) mares, as well as uterine tissue (n = 9), were collected after euthanasia. Three of the OVX mares were treated with a single intramuscular injection of oestradiol benzoate (2.5 mg) 18-22 hours prior to euthanasia and tissue collection (OVX+Oe). Uterine tissue was used as a positive control and showed positive staining for both ERalpha and PR. RESULTS: ERalpha staining was detected in the adrenal zona glomerulosa, fasciculata and reticularis of all mare groups. Ovariectomy increased cortical ERalpha staining intensity. In OVX mares and one intact mare, positive ERalpha staining was also detected in adrenal medullary cells. PR staining of weak intensity was present in a low proportion of cells in the zona fasciculata and reticularis of all mare groups. Weak PR staining was also found in a high proportion of adrenal medullary cells. In contrast to staining in the adrenal cortex, which was always located within the cell nuclei, medullary staining for both ERalpha and PR was observed only in the cell cytoplasm. CONCLUSION: The present results show the presence of ERalpha in the adrenal cortex, indicating oestradiol may have a direct effect on mare adrenal function. However, further studies are needed to confirm the presence of PR as staining in the present study was only weak and/or minor. Also, any possible effect of oestradiol treatment on the levels of steroid receptors cannot be determined by the present study, as treatment time was of a too short duration.

Energy balance, leptin, NEFA and IGF-I plasma concentrations and resumption of post partum ovarian activity in Swedish Red and White breed cows.

In the purpose to provide further information in respect of the relationship between metabolism and post partum (PP) ovarian activity resumption in dairy cows, the aim of the present study was to characterize the energy balance (EB) and leptin, NEFA and IGF-I plasma levels in Swedish Red and White (SRW) cows with and without ovarian activity re-initiation within 7 weeks PP. The study was conducted on 12 primiparous SRW cows fed the same diet as total mixed ration for ad libitum intake. The EB was calculated weekly from parturition until seven weeks PP. Blood samples were collected weekly from one week before until 7 weeks after calving for leptin, NEFA and IGF-I analysis. For progesterone (P4) analysis, blood samples were collected two times per week from parturition until the end of the study. P4 profile was used in addition to the clinical examination to detect cows with and without ovarian activity resumption. The clinical and ultrasonographic examination, coupled with P4 profile analysis showed the resumption of ovarian activity within 7 weeks after calving in 8 (group A) and no ovarian resumption in 4 cows (group B). No significant differences were detected in the whole period of observation in the amount of milk production between the two groups, while the mean milk protein content was significantly lower in group B at the third week PP. The calculated EB was negative in both groups in the first three weeks after calving, but more marked in group B. NEFA and Leptin plasma levels did not show significant differences between the two groups. In conclusion, the results of the present study showed that, when low milk producing primiparous cows are concerned, no significant differences in BW loss, milk yield, EB and leptin and NEFA plasma levels between the cows with and without resumption of ovarian activity within 7 weeks post partum were seen. However, significantly higher IGF-I levels in the first two weeks after calving were found in cows with post partum ovarian activity resumption, highlighting the important role of IGF-I as sensitive signal between metabolism and reproduction.

Plasma concentrations of cortisol and PGF2alpha metabolite in Danish sows during mating, and intrauterine and conventional insemination.

BACKGROUND: The aims of the present work was to study whether there are any relationships between cortisol and PG-metabolite in mated sows or inseminated with the intrauterine technique and compare these to changes occurring in conventionally inseminated sow. METHODS: Thirty three crossbred sows (Danish Landrace x Danish Large White) were fitted with jugular vein catheters through vena auricularis from one of the ears. The sows were randomly divided into three groups (Boar-, IUI- and AI-group) and blood samples were collected before, during and after service. In a final evaluation only 25 sows that became pregnant and farrowed piglets at full term were used. RESULTS: Cortisol concentrations increased in all groups but Boar-group (n = 8) had a significantly higher cortisol during 10 to 20 min after service than sows in AI-group (n = 8). In mated sows cortisol concentrations peaked at 15 minutes after service. The Boar-group (n = 8) showed no ascending PG-metabolite levels during the whole experiment, while both IUI- and AI-groups (n = 9 and n = 8, respectively) had a 2.5-fold increase in PG-metabolite 15 minutes after service. CONCLUSION: In conclusion, mating of sows by a boar results in a greater increase of cortisol than AI and without an elevation of PG-metabolite levels, which was seen in both the inseminated groups. It was also demonstrated that IUI-group had an earlier significant increase of PG-metabolite levels than sows inseminated conventionally. Further investigation using different semen extenders or even different type of insemination catheters might be helpful in understanding the reason for an immediate increase of PG-metabolite after insemination but not after mating.

Longitudinal observation on reproductive and lactation performances of smallholder crossbred dairy cattle in Fitche, Oromia region, central Ethiopia.

A two-year longitudinal study was conducted to assess the reproductive and lactation performances of smallholder crossbred dairy cattle in Fitche, central Ethiopia. Twenty-four smallholder dairy farms were monitored and data on reproductive, breeding, lactation and management aspects of crossbred dairy cows (n=69) were collected and analysed. Moreover, milk samples were collected and analysed for progesterone. The overall Least-squares means for calving interval (CI), calving to conception interval (CCI) and first observed oestrus after calving were 516, 253 and 141 days, respectively. Suckling significantly prolonged these intervals. The mean first onset of luteal activity (OLA) after calving was 52 days, while 67.4% n=43) had a delayed (>55 days) return to cyclicity after calving. Suckling and parity number significantly (p < 0.05) influenced the OLA. The mean lactation length was 54.4 weeks. The overall daily mean milk yield for the first 43 weeks of lactation after calving was 11.7 L/day. The estimated daily milk yield increased slowly and reached peak (13.8 L/day) around the 11th week post partum and declined gradually and steadily. Suckling status, season of calving and parity number significantly influenced the estimated daily milk yield. In conclusion, the present study indicated that the smallholder crossbred dairy cows in the study area had prolonged intervals to first oestrus after calving, to conception and to the next calving, and thus their reproductive performance is unsatisfactory. Delayed first onset of luteal activity (postpartum anoestrus) contributed to these extended intervals. Further detailed investigation is suggested to examine the effects of other relevant factors on the reproductive and lactation performances of smallholder crossbred dairy cows for appropriate intervention.

Clinical features and hormonal profiles of cloprostenol-induced early abortions in heifers monitored by ultrasonography.

BACKGROUND: The present study describes the clinical features and plasma profiles of bovine pregnancy-associated glycoprotein 1 (bPAG1), the main metabolite of prostaglandin F2alpha (PG metabolite) and progesterone (P4) in heifers in which early abortions were induced. METHODS: Early abortions were induced in four heifers with cloprostenol and monitored by ultrasonography. Blood samples were collected and the plasma were analyzed for bPAG 1, P4 and PG metabolite. RESULTS: The foetal heartbeat rates varied from 170-186 beats per minute for all foetuses up to the date of cloprostenol treatment. Foetal death was confirmed within two days after cloprostenol treatment. Prior to cloprostenol injection, blood plasma concentrations of bPAG1, PG metabolite and P4 varied from 8.4-40.0 ng/mL, 158-275 pmol/L and 20.7-46.9 nmol/L, respectively. After the foetus expelled, the plasma level of bPAG1 began to decrease but the decrease was small and gradual. The estimated half-life of bPAG1 was 1.8-6.6 days. The plasma level of the PG metabolite started to have short lasting peaks (above 300 pmol/L) within three hours after cloprostenol treatment. The plasma concentrations of P4 dropped sharply to less than 4 nmol/L after 24 hours of cloprostenol injection. CONCLUSION: The current findings indicated that after early closprostenol-induced foetal death, the plasma concentration of bPAG1 decreased gradually and showed a tendency of variation with the stages of pregnancy.

A preliminary study on the induction of dioestrous ovulation in the mare--a possible method for inducing prolonged luteal phase.

BACKGROUND: Strong oestrous symptoms in the mare can cause problems with racing, training and handling. Since long-acting progesterone treatment is not permitted in mares at competition (e.g. according to FEI rules), there is a need for methods to suppress unwanted cyclicity. Spontaneous dioestrous ovulations in the late luteal phase may cause a prolongation of the luteal phase in mares. METHODS: In this preliminary study, in an attempt to induce ovulation during the luteal phase, human chorionic gonadotropin (hCG) (3000 IU) was injected intramuscularly in four mares (experimental group) in the luteal phase when a dioestrous follicle > or = 30 mm was detected. A fifth mare included in this group was not treated due to no detectable dioestrous follicles > or = 30 mm. Four control mares were similarly injected with saline. The mares were followed with ultrasound for 72 hours post injection or until ovulation. Blood samples for progesterone analysis were obtained twice weekly for one month and thereafter once weekly for another two to four months. RESULTS: Three of the hCG-treated mares ovulated within 72 hours after treatment and developed prolonged luteal phases of 58, 68 and 82 days respectively. One treated mare never ovulated after the hCG injection and progesterone levels fell below 3 nmol/l nine days post treatment. Progesterone levels in the control mares were below 3 nmol/l within nine days after saline injection, except for one mare, which developed a spontaneously prolonged luteal phase of 72 days. CONCLUSION: HCG treatment may be a method to induce prolonged luteal phases in the mare provided there is a dioestrous follicle > or = 30 mm that ovulates post-treatment. However, the method needs to be tested on a larger number of mares to be able to draw conclusions regarding its effectiveness.

Ultrasonographic appearance of the conceptus, fetal heart rate and profiles of pregnancy-associated glycoproteins (PAG) and prostaglandin F2alpha-metabolite (PGF2alpha-metabolite) after induction of fetal death with aglepristone during early gestation in cattle.

A higher incidence of fetal losses, especially after the use of artificial reproduction techniques, asks for more intensive monitoring of bovine pregnancies. In this study, a model for fetal death (FD) was created by administering the antiprogesterone aglepristone twice, at Day 47 and 48 of gestation (n=5). Control heifers received the solvent (n=5). The temporal relationships between changes in ultrasonographic appearance of fetal fluids and membranes, fetal heart rate (FHR) and peripheral plasma levels of pregnancy-associated glycoprotein (PAG) and PGF2alpha-metabolite as determined by radioimmunoassay associated with FD were monitored at eight hour intervals around treatment. For the analysis of plasma levels the period under study was divided into five epochs (T1: before injection of aglepristone/solvent; T2: from first to second injection; T3: from second injection to FD; T4: from diagnosis of FD to 56 h later; T5: from 56 h to 104 h after diagnosis of FD). Control heifers produced healthy calves at term, but in treated heifers, FD occurred on average at 58 (range 48-80) h after first injection of aglepristone. Fetal death was always preceded by a visible reduction of the amount of allantoic fluid and by segregation of the allantochorionic membrane from the endometrium. FHR remained rather constant in both groups, but a (non-significant) drop in FHR around 8h before FD was diagnosed in four of five treated animals. All fetuses were expulsed after FD. Levels of PAG remained constant or even slightly increased in controls, but decreased in treated animals from T2 onward: levels during T4 and T5 significantly differed from those during T1 and from values in controls during T4 and T5 (P<0.01). PGF2alpha-metabolite levels did not change in the controls, but in the treated group they were significantly higher during T3 when compared to T1 (P<0.05). After this increase, a sharp decrease in PGF2alpha-metabolite level occurred, reaching a significantly lower level at T5 when compared to control animals (P=0.01). It is concluded, that FD induced by aglepristone is preceded by ultrasonographic visible changes in fetal membranes and fluids and a rise in PGF2alpha-metabolite and is followed by a drop in PAG and PGF2alpha-metabolite.

Effect of dexcloprostenol on endogenous prostaglandin F2alpha release in dairy heifers.

Cloprostenol was previously believed to be unable to release endogenous prostaglandin F2alpha (PGF2alpha) when administered during early bovine diestrus. A prostaglandin release is, however, seen in late diestrus. The aim of this study is to find out whether dexcloprostoenol (containing the only biologically active isomer, d-isomer, of cloprostenol) induces endogenous PGF2alpha release during early and late diestrus. Twelve heifers of the Finnish Ayrshire breed were allocated into two equal groups. Their estrous cycles were synchronized with dexcloprostenol. A further luteolysis was induced with 0.15 mg of dexcloprostenol either on Day 7 (group D7 or early diestrus) or on Day 14 (group D14 or late diestrus) after ovulation. Blood for progesterone and the PGF2alpha metabolite 15-ketodihydro-PGF2alpha determinations was collected immediately before dexcloprostenol treatment and thereafter every second hour for 48 h. Five of the six heifers in both groups showed significantly increased blood levels of 15-ketodihydro-PGF2alpha at some time during the 48-h experimental period. The intervals from treatment to the first significant increases of the PGF2alpha metabolite were 32.8+/-2.3 h (min. 30 h, max. 36 h) and 20.0+/-4.2 h (min. 14 h, max. 24 h) in groups D7 and D14, respectively (P < 0.01). We have concluded that dexcloprostenol induced endogenous PGF2alpha release in most cases, regardless the time of its administration (early or late diestrus). This release, however, differs from that observed during spontaneous luteolysis.

Estrous cycle characteristics, luteal function, secretion of oxytocin (OT) and plasma concentrations of 15-keto-13,14-dihydro-PGF2alpha (PGF2alpha-metabolite) after administration of low doses of prostaglandin F2alpha (PGF2alpha) in pony mares.

In the present study, the kinetics of the prostaglandin F2alpha (PGF2alpha)-metabolite 15-keto-13,14-dihydro-PGF2alpha after a single intramuscular application of various doses of the natural PGF2alpha dinoprost at Day 7 of the cycle in the mare were investigated. Effects of low doses on estrous cycle length and life span of corpus luteum were examined, because release of PGF2alpha is still under discussion to have detrimental influence on success rates of transcervical transfer of equine embryos. Eight Shetland pony mares were each randomly assigned to each of four treatments: (a) 0.8 mg/100 kg (group T1), (b) 0.4 mg/100 kg (group T2), (c) 0.2 mg/100 kg BM dinoprost i.m. (group T3), and (d) 1 ml physiological saline i.m. (group CO). Treatments were administered as single doses on Day 7 of the estrous cycle. Administration of dinoprost caused dose-dependent rises of plasma concentrations of PGF2alpha-metabolite, although values of individual mares showed great variation within groups. Prostaglandin treatments resulted in a distinct decrease of plasma progesterone concentrations to values between 1.6 and 7.9 ng/ml within 24 h. Treatment groups had significantly lower progesterone area under the curve (AUC: T1 942.8+/-175.9, T2 1050+/-181.2 and T3 1117+/-179.8 ng/ml/h) when compared with controls (CO 1601.9+/-227.6; t-test, P<0.05 ). There was a small, but significant negative correlation between AUC of progesterone and of PGF2alpha-metabolite ( R=-0.4; P=0.05 ). Administration of PGF2alpha caused secretion of oxytocin in three (T1, T2) and two (T3) mares out of eight ranging from 19.3 to 63.1 pg/ml. The AUC of oxytocin was positively correlated with AUC of PGF2alpha-metabolite ( R=0.4, P<0.05) and negatively correlated with AUC of progesterone ( R=-0.4, P<0.05). Administration of dinoprost yielded significantly shorter intervals from treatment to estrus and ovulation (values in parentheses), respectively, when compared with controls: T1 3.9+/-0.7 days ( 12.1+/-0.7 days), T2 4.5+/-0.6 ( 12.3+/-0.6 ), T3 4.9+/-0.5 ( 12.3+/-0.6 ), and CO 8.9+/-0.6 days ( 16.5+/-0.8 days) (t-test, P<0.01 ) (Fig. 2). Different doses of PGF2alpha caused similar effects. Data suggest that progesterone concentrations at applications influence efficacy of treatments more than doses administered, as demonstrated by their high correlation with estrous cycle patterns. It is important to note that differences we achieved are gradual and that all mares responded to treatment by luteolysis and premature estrus, regardless of doses applied.

The impact of induced stress during days 13 and 14 of pregnancy on the composition of allantoic fluid and conceptus development in sows.

Stress due to regrouping of breeding females is difficult to avoid completely in loose-housing systems. The effects of stress during the maternal recognition of pregnancy on fetal development and survival at Day 30 of pregnancy was, therefore, studied in 17 sows allocated into one control (C-) group, one group deprived of food during Days 13 and 14 (FD-), and one group (A-), which was treated with ACTH (0.01 mg/kg body weight of Synacthen Depot) every sixth hour during the same period. Total number of fetuses, fetal survival rate, volume of allantoic fluid, and the weight and length of total fetal unit, placentas, allantochorion and fetuses were determined. The concentrations of progesterone (P4), PGFM, PGF2, PGE, estrone-sulfate, and estradiol-17beta in the allantoic fluid were analyzed. No significant differences between groups were found for any parameter measured except for P4. Food deprivation increased P4 concentration in the allantoic fluid, and there was a positive correlation between the P4 concentration and the weight of the placenta. It is, therefore, suggested that P4 influences the placenta size among food-deprived sows.

A long-term study of Neospora caninum infection in a Swedish dairy herd.

A longitudinal study was performed in a Swedish dairy herd where Neospora caninum had been isolated from a stillborn calf. Starting in autumn 1994, blood samples from all female animals in the herd were collected once yearly until 1999. The sera were analysed for presence of IgG1 antibodies to N. caninum by the iscom ELISA, and by an avidity ELISA to establish the timing of infection. In addition, data on reproductive performance were compiled. During the study the percentage of seropositive female animals increased from 63% to 87%. In 1994 a large number of young animals tested seropositive although their dams were seronegative, indicating that a transmission of the parasite other than the vertical had recently occurred. Low avidity values supported this assumption. The annual abortion rate increased from a mean of 2% before the initiation of the study to 9% in 1994-1998. During the same time, as judged by the avidity data, a large proportion of the animals shifted from being recently to being chronically infected. The source of the external infection in the herd could not be identified.

Effect of exogenous melatonin on in vivo and in vitro prostaglandin secretion in Rasa Aragonesa ewes.

The effect of exogenous melatonin on prostaglandin secretion was measured on Rasa Aragonesa ewes. Fourteen ewes received an 18 mg melatonin implant (M+) on 10 April and were compared with 13 control animals (without implants M-). Twenty days later, intravaginal pessaries were inserted in all animals to induce a synchronized oestrus (day 0). On day 14, ewes were injected, i.v., with 0.5 IU oxytocin. Plasma 15-ketodihydro-PGF(2alpha) (PGFM) concentrations were measured to assess uterine secretory responsiveness to oxytocin. After euthanasia, pieces of endometrium were collected to determine progesterone content and PGE(2) and PGF(2alpha) secretion in vitro, in the presence or absence of either 20 microg/ml recombinant ovine interferon-tau (roIFNt) or 1 nmol/l oxytocin in the medium. Endometrial progesterone content was similar in the two treatments (M+: 50.25+/-17.34 ng/mg tissue, M-: 43.08+/-11.21 ng/mg tissue). M+ ewes that responded to oxytocin had significantly higher plasma PGFM concentrations between 10 and 80 min after oxytocin administration, a higher mean PGFM peak (P<0.001), higher plasma PGFM levels after the challenge (P<0.05) and higher plasma progesterone concentrations (P<0.01) than control ewes. In the in vitro experiment, M+ and M- control samples secreted similar amounts of PGE(2). The presence of roIFNtau and oxytocin only stimulated PGE(2) production (P<0.05) in M- tissues. Control M+ tissues secreted higher amounts of PGF(2alpha) (P=0.07) and PGF(2alpha) secretion was significantly (P<0.01) stimulated by roIFNtau. Oxytocin produced this effect only in M- samples (P<0.01). In conclusion, although previous studies have demonstrated a positive effect of melatonin on lamb production, PGF(2alpha) secretion is higher in vitro and the PGE(2):PGF(2alpha) ratio is unfavourable in response to IFNtau, which could affect embryo survival. Whether or not these mechanisms are similar in pregnant ewes remains to be elucidated.

Premature prostaglandin F2alpha secretion causes luteal regression in GnRH-induced short estrous cycles in cyclic dairy heifers.

This study aimed to confirm that the luteolysis in normal-cycling dairy heifers seen during short estrous cycles induced with cloprostenol (Clp) and GnRH administered 24h apart is caused by a premature release of prostaglandin F(2alpha) (PGF(2alpha)). A further aim was to study the PGF(2alpha) release pattern more closely to determine whether it resembles the spontaneous release occurring during normal regression of the corpus luteum (CL) or whether PGF(2alpha) is continuously secreted after the induced ovulations, leading to short estrous cycles. Twenty-four Ayrshire heifers were allotted to four equally sized groups. After estrus synchronization with 0.5mg of Clp, a new luteolysis was induced with 0.5mg of Clp on Day 6 (groups T-d6 and C-d6) or Day 7 (groups T-d7 and C-d7) after ovulation. Gonadorelin (0.1mg i.m.) was given to groups T-d6 and T-d7 to induce premature ovulation 24h later. Groups C-d6 and C-d7 served as controls. Ovaries were examined daily by transrectal ultrasonography, while blood samples (for progesterone and 15-ketodihydro-PGF(2alpha) analyses) were obtained via a jugular catheter every 3h, starting from the second Clp treatment and continuing for 9 days postovulation. Unresponsiveness to Clp or anovulation resulted in 4 C-d6 heifers being excluded. Four heifers in group T-d6 and three in group T-d7 had a short estrous cycle of 8-12 days, while all others had a cycle of normal length. Significant elevations in 15-ketodihydro-PGF(2alpha) concentrations with recurrent high peaks coincided with a decrease in progesterone concentration and were detected in all heifers that showed a short estrous cycle, but not in any heifers with normal estrous cycles in groups T and C. In conclusion, a premature release of PGF(2alpha), which closely resembles its release during spontaneous luteolysis, causes luteal regression in these short cycles.

Secretion patterns of oxytocin and PGF2alpha-metabolite in response to cervical dilatation in cyclic mares.

We conducted the present study to establish a standardized method for cervical stimulation without affecting the endometrium, and to investigate the effect on estrous cycle pattern and concentrations of progesterone, oxytocin and PGF2alpha-metabolite of cervical dilatation in the mare. Six healthy Haflinger mares underwent three different treatments (control, insertion, dilatation) on Days 5 and 7 of the cycles in different orders according to a Latin square design. During dilatation, the balloon of the catheter was inflated stepwise every 30s with warm physiological saline to a maximum of 50 ml. At this stage the size of the balloon was 4.5 cm in diameter and 6 cm length. Estrous cycle length was significantly shortened by dilatation when compared to controls (control: 22.8+/-1.7, insertion: 21.8+/-2.5, dilatation: 20.0+/-1.3 days; P<0.05). Concentrations of progesterone at Days 10, 12 and 14 after ovulation were significantly lower in dilatation cycles. Calculation of the area under the curve (AUC) for progesterone secretion from Day 7 to Day 12 also revealed a significant decrease in progesterone secretion in the dilatation group (dilatation: 34.1+/-7.3, insertion: 35.6+/-7.8, control: 39.1+/-5.9 ng/ml; P<0.05). Cervical insertion and dilatation caused a rapid and pronounced increase in plasma concentrations of oxytocin from basal levels (1.0-6.1 pg/ml) to maximum peaks (insertion: 125.5 pg/ml and dilatation: 305.2 pg/ml). The AUC for oxytocin was significantly higher after insertion (Day 5: 858.4+/-469.9; Day 7: 411.9+/-213 pg/ml/h) and dilatation (Day 5: 1697+/-1725; Day 7: 1078.5+/-764 pg/ml/h) when compared to controls (Day 5: 186+/-98; Day 7: 156+/-23.5 pg/ml/h; P<0.05). Manipulations did not cause considerable changes in plasma PGF2alpha-metabolite concentrations. Because cervical dilatation up to a diameter of 4.5 cm did not cause any immediate PGF2alpha release, the luteolytic pathway is unlikely to be responsible for shortening the length of diestrus and the estrous cycle. The present data suggest an involvement of oxytocin in the shortening of the luteal phase in response to cervical manipulation.