Interoestrous Interval Research Articles

Effect of ovarian follicular wave pattern and endocrine characteristics on pregnancy outcome in cows.

The effect of two (2W) versus three (3W) wave patterns of follicular dynamics and concurrent endocrine milieu of follicle-stimulating hormone (FSH), luteinizing hormone (LH), oestradiol 17-β (E2) and progesterone (P4) were investigated during one interoestrous interval (IEI) before insemination, on ensuing pregnancy, in 70 lactating Jersey crossbred cows. The findings were evaluated for between [included all (overall) 2W-O and 3W-O cows] and within [after separating pregnant (P) and non-pregnant (NP) cows in 2W and 3W] wave patterns. The propensity of two (58.6%, n=41) and three (41.4%, n=29) wave patterns was similar (p=.15). The IEI, shorter by 2.6days for 2W-O versus 3W-O (p<.0009), predicted wave pattern as 100% 2W-O cows had IEI of ≤21days, present only in 27.6% 3W-O cows (p<.0001). The ovulatory follicle persisted for a significantly shorter duration for 3W-O versus 2W-O cows. The average FSH, LH, E2 and P4 concentrations during the IEI did not differ for between and within the wave patterns. Pregnancy rate (%) of 58.6 versus 41.4 (p=.15) for 2W-O versus 3W-O and 56.1-P versus 43.9-NP (p=.44) for within 2W was similar, but tended to differ for within the 3W pattern (69.0-P versus 31.0-NP, p=.06). The pregnancy outcome was influenced by the age of ovulatory follicle for between the wave patterns and by follicular count as well as FSH surge concentration for within the wave patterns. A shorter luteal phase reduced the pregnancy outcome, a novel finding of the present study.

Comparison of milk production of dairy cows vaccinated with a live double deleted BVDV vaccine and non-vaccinated dairy cows cohabitating in commercial herds endemically infected with BVD virus.

Daily milk production and reproductive performance of cows vaccinated with a live double-deleted Bovine Viral Diarrhoea Virus (BVDV) vaccine were compared to those of non-vaccinated cows, cohabitating in endemic BVDV herds. All animals in the treatment group were vaccinated on study day 0 irrespective of lactation or gestation status, while control animals did not receive any treatment. 1463 animals were enrolled in the study from four different farms in three different countries (UK, Italy, France). Endemic presence of BVDV in study herds was demonstrated by the detection of BVDV in the bulk tank milk, and seroconversion was evaluated at the beginning of the study. For individual animals, the day of calving was taken to be the start of lactation for the calculation of days in milk (DIM). The standard lactation period of 305 days was divided into three periods: early lactation (EL, from DIM 8 to DIM 102), mid lactation (ML, from DIM 103 to DIM 204 and late lactation (LL, from DIM 205 to DIM 305). For each farm and each lactation period, a mixed model statistical analysis was performed with daily milk production as response, and group, day as well as the interaction between those two factors as fixed factors. Chi-square test was used to compare abortion rate and prolonged inter-oestrous interval rate between treatment and control groups. A significant increase in milk production in the vaccinated group was observed in farms 1 (1.023 L/day) and 3 (0.611 L/day) during EL (p<0.001) and in farm 2 (1.799 L/day) during ML (P<0.001). In addition, at farm 2, vaccinated cows produced more milk than non-vaccinated cows starting from 80 DIM. No differences were found between groups in abortion rates or prolonged inter-oestrous interval rates. Data demonstrate that cows in herds endemically infected with BVDV and vaccinated with live double-deleted BVDV vaccine produce more milk; the difference in milk production occurs during early lactation.

Manipulation of the oestrous cycle of the bitch-what works… for now.

Manipulation of the oestrous cycle of the bitch is a common request of pet owners for different reasons. On one side, clients may be interested in temporally preventing oestrus until the bitch has finished the performance career, or to manage the kennel in the presence of a stud dog and to avoid undesirable breeding. Additionally, clients with no interest to use their animal for breeding, may, for ethical reasons, prefer to avoid elective surgery such as ovariectomy, to control reproduction. On the other side, clients may want to induce oestrus to better control the time of birth, to use a male with limited availability during a specific time, or to reduce the duration of the interoestrous interval in bitches with a long oestrous cycle (>8months). Both these options for oestrous manipulation are based on hormonal treatments. For oestrous prevention, synthetic progesterone has been used since the 1960s. Induction of oestrus has been established with reliable results using dopamine agonists in the late 1980s and more recently using GnRH agonists. This review is focusing on the current and recently available treatments to manipulate the oestrous cycle in the bitch.

Effect of dietary zearalenone on the performance, reproduction tract and serum biochemistry in young rats

ABSTRACTThe present study was conducted to determine the toxic dose response of a chronic dietary Zearalenone (ZEA) in weaned young rats. Sixty, 21-day-old, Sprague Dawley female rats were randomly allocated to five groups of four replicate cages containing three rats. Rats were fed diets with increasing amounts of ZEA (0, 0.5, 0.9, 1.8 and 3.6 mg/kg) for 4 weeks. Daily feed intake was reduced (P < .05) by feeding the ZEA diets with 0.9 and 3.6 mg ZEA/kg feed. Rats fed the diet containing 1.8 mg ZEA/kg increased (P < .05) the body weight gain (BWG) and reduced (P < .05) feed conversion rate (FCR) as compared to the control group. The two highest levels of dietary ZEA also increased (P < .05) the weight of the uterus. However, ovaries’ weight, timing of vaginal opening and the inter-oestrous interval were not affected by increasing the doses of dietary ZEA (P > .05). Similarly, serum concentrations of total protein, follicle-stimulating hormone and alanine aminotransferase, aspartate aminotransferase and alkaline phosphate activities were not altered by the ZEA treatments. In conclusion, our results indicated that a chronic dietary consumption of ZEA at concentrations of 1.8 mg ZEA/kg increases the BWG and the uterus weight of weaning female rats.

Supplementation of Slow-Release Melatonin Improves Recovery of Ovarian Cyclicity and Conception in Summer Anoestrous Buffaloes (Bubalus bubalis).

The role of melatonin as a protective neurohormone against restoring cyclicity in summer anoestrous animals in photoperiod species has gained wider acceptance. This study was designed to uncover the evidence the slow-release melatonin (MLT) has on initiation of ovarian cyclicity and conception rate (CR) in summer anoestrous buffaloes. Thus, buffaloes diagnosed as summer anoestrous (absence of overt signs of oestrus, concurrent rectal examination and radioimmunoassay for serum progesterone at 10 days interval) were grouped as untreated (Group I, sterilized corn oil, n = 8) and treated (Group II, single subcutaneous injection of MLT @18 mg/50 kg bwt in sterilized corn oil, n = 20). Animals treated and detected in oestrus were artificially inseminated (AI) followed by division into Group III (second dose of MLT on 5th day post-AI, n = 8) and Group IV (no melatonin administration, n = 10). Blood samples were collected at 4 days interval for estimation of serum MLT, progesterone and oestrogen using radioimmunoassay kit. Mean oestrous induction rate (OIR), oestrous induction interval (OII), interoestrous interval (IOI) and CR were estimated. Compared to control, concentration of melatonin was significantly (p < 0.05) higher in treated group ranging from 14.34 ± 1.72 to 412.31 ± 14.47 pg/ml whereas other two hormones did not show any concentration difference. Melatonin-administered buffaloes showed significantly (p < 0.05) higher (90%) OIR with OII of 18.06 ± 1.57 days. Results showed improvement in conception rate in buffaloes administered with post-insemination melatonin. It can be concluded from the study that slow-release melatonin supplementation restored cyclicity in summer anoestrous animals resulting in improvement in conception rate in buffaloes.

Sequential ovulation and fertility of polyoestrus in American black bears (Ursus americanus).

American black bears (Ursus americanus) are seasonally polyoestrous and exhibit delayed implantation, which may allow equal and independent fertility of recurrent oestruses of a mating season. We postulated that the luteal inactivity during delayed implantation allows bears to have sequential ovulation during a polyoestrous mating season such that each oestrus of a polyoestrous female will have equivalent fertility, and pregnancy would not preclude subsequent ovulation and superfetation. Controlled mating experiments were conducted on semi-free-ranging female American black bears during three mating seasons, wherein females were bred by different male cohorts in each oestrus. Behavioural observation, vulva score ranking, genetic paternity analysis, gross morphology of ovaries and microscopic morphology of diapaused embryos were used to evaluate the fertility of each subsequent oestrus in polyoestrous females. Oestrus duration, number of successful mounts and median vulva scores were similar between first and subsequent oestruses of the season. Polyoestrus occurred in 81.3% of oestrous females, with a 9.7 ± 5.5 day (mean ± SD) inter-oestrous interval. Sequential ovulation was documented in three polyoestrous females, including one that possessed both a corpus haemorrhagicum and a developed corpus luteum. Among polyoestrous dams, four of nine embryos were conceived in the first oestrus and five of nine in the second oestrus. These results indicate that each oestrus of polyoestrous females is capable of fertility, even if the female is already pregnant from a prior oestrus. Although superfetation was not directly observed in the present study, our results strongly suggest the potential of superfetation in the American black bear and provide novel insight into the complex behavioural and physiological breeding mechanisms of bears. Given that most endangered bear species share similar reproductive traits with American black bears, captive breeding programmes could take advantage of superfetation by mating females with different males at each subsequent oestrus of the season in order to increase the genetic diversity of captive endangered bears.

Suppression of fertility in adult cats.

Cats are animals with highly efficient reproduction, clearly pointing to a need for suppression of fertility. Although surgical contraception is highly effective, it is not always the method of choice. This is predominantly because it is cost-intensive, time-consuming and irreversible, with the latter being of major importance for cat breeders. This article reviews the use of progestins, scleroting agents, immunocontraception, melatonin, GnRH antagonists and finally, GnRH agonists, in adult male and female cats in detail, according to the present state of the art. By now, various scientific and clinical options are available for the suppression of fertility in adult cats and the decision as to which should be chosen - independent of the legal registration of any state - depends on different facts: (i) feral or privately owned animal? (ii) temporary or permanent suppression of fertility wanted/needed? (iii) sex of the animal? New effective and available methods for hormonal contraception include melatonin implants for short-term post ponement of oestrus in adult queens and slow-release GnRH-agonist implants containing deslorelin (Suprelorin(®) ) for short- and long-term contraception in male and female companion and breeding cats.

Double Cloprostenol Administration During mid Luteal Phase of Oestrous Cycle does not Modify the Interoestrous Interval in Gilts

The present study was undertaken to test the effect of two vulva injections of D-cloprostenol on day 7, 9 and 10 of oestrous cycle on the duration of the interestrous interval in gilts. Following a pre-treatment oestrous cycle, 87 gilts were assigned to receive vulva injections of 75 μg D-cloprostenol at 08:00 and 14:00 h on day 7 (D7; n=30), day 9 (D9; n=29) or day 10 (D10; n=28) of their second observed oestrous cycle. Across the treatments, the duration of the oestrous cycle with D-cloprostenol treatment (19.1±0.1 d) was not different from that of the previous oestrous cycle (20.1±0.4 days). Plasma progesterone concentrations were evaluated 6 h before and 24 and 72 h after D-cloprostenol treatment in the D9 group. Compared to pretreatment levels (9.6±0.4 ng/mL), plasma progesterone concentrations were reduced (P<0.05) at 24 h (6.3±1.0 ng/mL) and 72 h after treatment but complete luteolysis did not occur. These data indicate that in gilts double vulva administration of D-cloprostenol is not able to induce a complete luteolisys and hence the duration of the oestrous cycle is not modified.

Serum Progesterone in Pregnant Bitches Supplemented with Progestin Because of Expected or Suspected Luteal Insufficiency

Progesterone profiles of individual bitches may vary considerably both between and within individuals during pregnancy and non-pregnancy. Suspected luteal deficiency is commonly purported but is difficult to evaluate in clinical cases when progesterone is supplemented because this masks the underlying hormone changes. Therefore, in this study, suspected cases of luteal deficiency (six pregnancies from five bitches) were supplemented with oral medroxyprogesterone acetate (MPA), allowing measurement of endogenous progesterone using conventional assay. MPA (0.1 mg/kg) treatment commenced between days 30 and 36 after estimated ovulation and was continued for 18-28 days. Endogenous progesterone was measured throughout treatment, and blood was additionally analysed for prolactin (PRL) and relaxin (RLN) as well as MPA. The latter revealed delayed MPA clearance in two bitches, in which Caesarean operation had to be performed because of a low foetal heart rate. In two cases with confirmed basal concentrations of both P(4) and MPA at term, spontaneous parturition occurred. Low endogenous progesterone during pregnancy was not apparent in three bitches that had previously had a short inter-oestrous interval of which two had previously had confirmed short luteal phase. However, in the remaining two cases, there had been previous pregnancy failure, but in only one of these, a premature decrease in endogenous progesterone to <2 ng/ml was detected. The latter had also low concentrations of PRL and RLN. The results of this preliminary clinical study suggest that abnormal progesterone profiles in pregnancy may be uncommon in bitches even when there has been previously documented short inter-oestrous interval. However, luteal deficiency may be suspected in bitches with a history of repeated pregnancy failure or abortion. MPA supplementation appears to be efficacious for management of suspected luteal deficiency and verification of the ovarian dysfunction, but care should be taken regarding the timing of MPA withdrawal and prolongation of pregnancy because of delayed elimination of MPA from blood circulation.

Effects of the 3β-hydroxysteroid dehydrogenase inhibitor trilostane on luteal progesterone production in the dog

Interference with the pregnancy-maintaining influence of progesterone is the basis of most methods for termination of unwanted pregnancy in dogs. The currently available methods are based on induction of luteolysis or blocking of the progesterone receptor. Inhibition of progesterone synthesis using a competitive inhibitor of 3β-hydroxysteroid dehydrogenase (3β-HSD) could be another strategy to terminate unwanted pregnancies.In this study we investigated the effects of the 3β-HSD inhibitor trilostane on corpus luteum function in non-pregnant bitches. Trilostane was administered orally for seven consecutive days in either the pituitary-independent part of the luteal phase (PIP, start of treatment on D11 after ovulation, n = 6) or the pituitary-dependent part (PDP, start of treatment on D31 after ovulation, n = 6), in an oral dose of about 4.5 mg/kg bw, twice daily. Results were compared with those obtained in control bitches (n = 6). ACTH stimulation tests were performed to assess adrenocortical reserve capacity.Trilostane caused no apparent side effects and ACTH stimulation tests revealed good suppression of cortisol secretion. Trilostane also caused a significant decrease in plasma progesterone concentration. When it was stopped during PIP, progesterone secretion was completely restored and there was no difference in the length of the luteal phase between those dogs and control dogs (99 days, range 70–138 d and 99 d, range 60–112 d, respectively). When trilostane was stopped during PDP there was no post-treatment recovery of progesterone secretion and although the luteal phase tended to be shorter (66 d, range 41–101 d) the difference was not significant (P = 0.09). Plasma prolactin concentration did not increase after the trilostane-induced decrease in plasma progesterone. The interoestrous interval in dogs treated during PIP (234 d, range 175–269 d) or PDP (198 d, range 120–287 d) was not significantly shorter than the control interval (247 d, range 176–313 d).In conclusion, trilostane treatment was effective in decreasing plasma progesterone concentration in bitches during the luteal phase, but the dose regimen used in this study produced less clear-cut inhibition of ovarian steroidogenesis than have other strategies to decrease plasma progesterone concentration. Further studies are warranted to determine whether trilostane can be used to terminate unwanted pregnancy in the bitch without inducing adrenocortical insufficiency.

Reproduction control in cats: new developments in non-surgical methods.

Reproduction control is an area of feline medicine that is assuming increasing importance in companion animal practice. Signs of oestrus such as increased vocalisation, rolling on the ground and a very short interoestrous interval may negatively influence the relationship between cat and owner, and prompt the owner to seek a method of reproduction control. In breeding catteries, control of reproduction may be needed as part of a planned breeding programme. Surgical contraception is not always the owner's wish - especially when a cat may be intended for future breeding. Besides, ethical principles and animal welfare legislation in an increasing number of countries are imposing restrictions on this 'classical approach' to reproduction control. Progestins are routinely used as non-surgical alternatives in cases where fertility is to be preserved, but the associated risks of uterine disease, mammary tumours, fibroadenomatosis or diabetes mellitus have to be taken into account - especially in predisposed animals. Modern, effective pharmacological alternatives are available for managing oestrous suppression and unwanted pregnancy. Detailed knowledge of the physiology of the oestrous cycle in the cat is necessary to ensure that the appropriate treatment is chosen for the individual animal and its owner. This article presents an update for small animal practitioners on these alternative methods; specifically, the use of slow-release GnRH agonists or melatonin implants for hormonal contraception, and the antiprogestin aglepristone for pregnancy termination. Several studies have documented the mode of action and risk of side effects of the traditional alternative to surgical castration - treatment with progestins. Evidence underpinning the safety and efficacy of GnRH agonists and melatonin implants for suppression of fertility in queens and toms is reviewed.

Clinical and Subclinical Endometritis in the Mare: Both Threats to Fertility

Endometritis, a major cause of mare infertility arising from failure to remove bacteria, spermatozoa and inflammatory exudate post-breeding, is often undiagnosed. Defects in genital anatomy, myometrial contractions, lymphatic drainage, mucociliary clearance, cervical function, plus vascular degeneration and inflamm-ageing underlie susceptibility to endometritis. Diagnosis is made through detecting uterine fluid, vaginitis, vaginal discharge, short inter-oestrous intervals, inflammatory uterine cytology and positive uterine culture. However, these signs may be absent in subclinical cases. Hypersecretion of an irritating, watery, neutrophilic exudate underlies classic, easy-to-detect streptococcal endometritis. In contrast, biofilm production, tenacious exudate and focal infection may characterize subclinical endometritis, commonly caused by Gram-negative organisms, fungi and staphylococci. Signs of subclinical endometritis include excessive oedema post-mating and a white line between endometrial folds on ultrasound. In addition, cultures of uterine biopsy tissue or of small volume uterine lavage are twice as sensitive as guarded swabs in detecting Gram-negative organisms, while uterine cytology is twice as sensitive as culture in detecting endometritis. Uterine biopsy may detect deep inflammatory and degenerative changes, such as disruption of the elastic fibres of uterine vessels (elastosis), while endoscopy reveals focal lesions invisible on ultrasound. Mares with subclinical endometritis require careful monitoring by ultrasound post-breeding. Treatments that may be added to traditional therapies, such as post-breeding uterine lavage, oxytocin and intrauterine antibiotics, include lavage 1-h before mating, carbetocin, cloprostenol, cervical dilators, systemic antibiotics, intrauterine chelators (EDTA-Tris), mucolytics (DMSO, kerosene, N-acetylcysteine), corticosteroids (prednisolone, dexamethasone) and immunomodulators (cell wall extracts of Mycobacterium phlei and Propionibacterium acnes).

Ovarian function in ewes after treatment with mifepristone early during the oestrous cycle

The aim of this study was to determine whether endogenous progesterone regulates synthesis and secretion of luteal oxytocin. In Expt 1, mature ewes (n = 5 per group) were assigned randomly to control or mifepristone (RU486) treatment groups. Ewes were injected s.c. twice a day with vehicle or 10 mg RU486 on days 5-7 of the oestrous cycle (oestrus = day 0). On day 8, after an i.v. injection with prostaglandin F(2alpha) (250 microg cloprostenol), venous blood samples were collected at frequent intervals to determine plasma oxytocin concentrations. Plasma oxytocin concentrations of RU486-treated ewes were not significantly different from those of control ewes. In Expt 2, ewes were injected s.c. each day with vehicle or 175 mg RU486 on days 2-5 of the oestrous cycle followed by administration of prostaglandin F(2alpha) on day 6. Four of five RU486-treated ewes showed 'split-oestrus' (oestrous behaviour for 36 h and then again at 84-108 h after the onset of initial oestrus). There was no significant difference in mean plasma oxytocin or progesterone concentrations between treatment groups. The mean masses of mature corpora lutea from control and RU486-treated ewes on day 6 of the oestrous cycle did not differ significantly (394.8 +/- 28.8 versus 319.5 +/- 48.3 mg). RU486-treated ewes contained mature corpora lutea, new corpora lutea (two of four ewes) and preovulatory follicles (>or= 10 mm, two of four ewes). The average interoestrous interval for RU486-treated ewes was 9 days more than that for control animals (26.2 +/- 2.9 versus 17 +/- 0.5 days; P < 0.025).

Ovarian function in ewes after treatment with mifepristone early during the oestrous cycle

The aim of this study was to determine whether endogenous progesterone regulates synthesis and secretion of luteal oxytocin. In Expt 1, mature ewes (n = 5 per group) were assigned randomly to control or mifepristone (RU486) treatment groups. Ewes were injected s.c. twice a day with vehicle or 10 mg RU486 on days 5-7 of the oestrous cycle (oestrus = day 0). On day 8, after an i.v. injection with prostaglandin F(2alpha) (250 microg cloprostenol), venous blood samples were collected at frequent intervals to determine plasma oxytocin concentrations. Plasma oxytocin concentrations of RU486-treated ewes were not significantly different from those of control ewes. In Expt 2, ewes were injected s.c. each day with vehicle or 175 mg RU486 on days 2-5 of the oestrous cycle followed by administration of prostaglandin F(2alpha) on day 6. Four of five RU486-treated ewes showed 'split-oestrus' (oestrous behaviour for 36 h and then again at 84-108 h after the onset of initial oestrus). There was no significant difference in mean plasma oxytocin or progesterone concentrations between treatment groups. The mean masses of mature corpora lutea from control and RU486-treated ewes on day 6 of the oestrous cycle did not differ significantly (394.8 +/- 28.8 versus 319.5 +/- 48.3 mg). RU486-treated ewes contained mature corpora lutea, new corpora lutea (two of four ewes) and preovulatory follicles (>or= 10 mm, two of four ewes). The average interoestrous interval for RU486-treated ewes was 9 days more than that for control animals (26.2 +/- 2.9 versus 17 +/- 0.5 days; P < 0.025).

Non-invasive assessment of oestrous cycles and evaluation of reproductive seasonality in the female wild black rhinoceros (Diceros bicornis minor).

Female wild black rhinoceroses in Zimbabwe were monitored non-invasively using faecal progesterone metabolite analysis and observation of reproductive behaviour. A postpartum period of reproductive inactivity of at least 4 months, followed by a period of 4-7 months of oestrous cyclicity, was detected in six multiparous females. Three-quarters of the oestrous cycles (n = 21) had a total duration (mean +/- SEM) of 26.8 +/- 1 days. Other types of cycle were characterized either by an extended luteal phase, lasting on average twice as long as the normal cycle, or by an extended follicular phase. These extended cycles may have resulted from early embryo loss and heat stress. Female rhinoceroses did not conceive before 8 months after giving birth and some females (n = 2) most likely aborted after 3.0-3.5 months of gestation. The detected period of cyclic oestrus occurred between May and March in females (n = 9), and there was a 3 month extended interoestrous interval in nulliparous females during the period of decreasing daylengths that can be presumed to be the period of poorest fertility for the black rhinoceros under tropical latitudes. In contrast, the period of optimum fertility in the Southern hemisphere coincided with the late spring and early summer, and corresponded to the early rainy season. As a result, a higher incidence of births was detected in the late rainy season, providing the lactating female with the most suitable environment in terms of nutritional requirements.

A retrospective study on some reproductive parameters of German shepherd bitches in Kenya.

Data relating to reproductive parameters of German shepherd bitches were collected from registered German shepherd dog (GSD) breeders with information kept over a 15-year period (1982-1997). The information obtained was verified using the East African Kennel Club records. A total of 594 bitches from 280 breeders were recorded. From these, 798 heats were observed, 594 of which were used for breeding, resulting in 3592 puppies. The mean age at puberty was 519.0 +/- 41 days. Heats occurred throughout the year, although significantly (P < 0.05) higher and lower incidences were observed in October and April respectively Pregnancy significantly (P < 0.01) increased interoestrous interval, which was 247.8 +/- 99.6 and 183 +/- 52 days among bred/pregnant and non-bred bitches respectively. Most bitches in oestrus (73.7%) were bred, and breeding was carried out throughout the year, with a distribution closely related to that of heat incidence. Subsequently, whelping occurred throughout the year, and 95.5% of the bitches that were mated whelped. A mean gestation period of 60.6 +/- 5.1 days was observed. The mean litter size was 6.4 +/- 0.4 puppies, and did not differ significantly between months. The preweaning losses were low, with 2.3% stillbirths, 0.9% culls and 11.4% mortalities.

Bromocriptine-induced premature oestrus is associated with changes in the pulsatile secretion pattern of follicle-stimulating hormone in beagle bitches.

The secretory profiles of LH and FSH were investigated before and during the administration of bromocriptine in six beagle bitches. Plasma samples were obtained via jugular venepuncture at 10 min intervals for 6 h every 2 weeks until the next ovulation. Bromocriptine treatment was started 100 days after ovulation. Both before and after bromocriptine treatment, LH and FSH pulses occurred together. The mean duration of the FSH pulse (120 min) was significantly longer than that of the LH pulse (80 min). The interoestrous interval in the bitches treated with bromocriptine was significantly shorter than that of the preceding cycle (160 +/- 3 versus 206 +/- 24 days). The mean basal plasma FSH concentration (7.4 +/- 0.6 versus 6.1 +/- 0.7 iu l-1) and the mean area under the curve for FSH (46.6 +/- 4.7 versus 40.4 +/- 4.4 iu l-1 in 6 h) increased significantly after the start of the bromocriptine treatment. In contrast, the differences in mean basal plasma LH concentration (2.1 +/- 0.2 versus 2.0 +/- 0.2 micrograms l-1) and the mean area under the curve for LH (19.0 +/- 3.1 versus 19.5 +/- 2.5 micrograms l-1 in 6 h) between the day before and 14 days after the start of the bromocriptine treatment were not significant. Bromocriptine administration also lowered the mean amplitude of the FSH pulse and shortened the mean duration of the FSH pulse, without influencing the LH pulse. In addition to demonstrating the concurrent pulsatile secretion of LH and FSH, the results of the present study demonstrate that the bromocriptine-induced shortening of the interoestrous interval in the bitch is associated with an increase in plasma FSH concentration without a concomitant increase in plasma LH concentration. This finding indicates that treatment with the dopamine agonist bromocriptine increase plasma FSH to a concentration that results in the enhancement of follicle development.

Treating cattle with progesterone as well as a GnRH analogue affects oestrous cycle length and fertility

Initiating the chronic administration of progesterone to cattle during metoestrus will produce shortened oestrous cycles containing one or two wave-like sequences of ovarian follicle development. Conception rates are reduced to inseminations at the oestrus preceding these shortened cycles. In contrast, a single injection of the GnRH analogue, buserelin, around mid-dioestrus can lengthen the oestrous cycle by increasing the proportion of cycles with three waves of follicular development and may also increase conception rates. A series of trials was conducted to test the hypothesis that the adverse effects of progesterone on oestrous cycle length and conception rate could be prevented with a strategic injection of GnRH. In Trial 1, progesterone was administered per vaginum to heifers for 10 days from Day 2 or 3 (Oestrus = Day 0) and with (n = 42) or without (n = 46) an injection of a GnRH analogue (10 microg buserelin) on Day 12 or 13. Other heifers (n = 44) served as an untreated control group. The average inter-oestrous interval (IOI) for those heifers treated only with progesterone was 17.0 days and was less (p<0.05) than the average intervals for those also receiving GnRH (20.2 days) or in the control group (20.0 days). In Trial 2, 45 heifers were inseminated following a synchronised oestrus. Progesterone was administered as in Trial 1 to 22 of the heifers. Their conception rate was 45.4% and this was less (p<0.05) than the 73.9% obtained with their 23 untreated contemporaries. Trial 3 was completed using 530 cows in commercial dairyherds. The 259 cows receiving progesterone and GnRH (buserelin) after their first inseminations had a conception rate of 68.3% compared to 56.1% for their 271 untreated herdmates (p<0.05%). Heifer calves born to treated cows had heavier birthweights (33.4 vs. 31.1 kg; p<0.05), but birthweights of bull calves were unaffected (35.5 vs. 35.8 kg). Gestation lengths for cows conceiving to first inseminations were similar for treated and control groups (280.9 vs. 280.5 days). The results of these trials confirmed the hypothesis that a strategic injection of the GnRH analogue, buserelin, could prevent the reductions in oestrous cycle length and conception rate associated with the chronic metoestrous administration of progesterone.

Practical use of a combination of a dopamine agonist and a synthetic prostaglandin analogue to terminate unwanted pregnancy in dogs.

The combination of a dopamine agonist, cabergoline, and a synthetic analogue of prostaglandin F2 alpha, cloprostenol, was used to induce termination of pregnancy from day 25 after the estimated luteinising hormone surge (day 27 +/- 4 after the first mating) in five mature beagle bitches. Cabergoline was administered orally at 5 micrograms/kg daily and cloprostenol was injected subcutaneously at 1 microgram/kg every other day. Treatment efficacy, in terms of pregnancy termination, was 100 per cent. Termination always took place by resorption of the fetuses. No side effects were observed. A mean of three injections of cloprostenol and nine days of cabergoline treatment was necessary to eliminate all signs of gestation. Termination was in each case accompanied by a decline in plasma progesterone (to less than 1 ng/ml) within 72 hours of initiation of treatment. In a control group of five, untreated bitches, plasma progesterone remained elevated throughout a corresponding period (from day 25 to day 50 after the estimated luteinising hormone surge). In the treated group, interoestrous intervals (98 +/- 41 days) were reduced, compared with previous cycles (194 +/- 9 days) or with those of the control animals (205 +/- 37 days). It is concluded that the combination treatment with the anti-prolactinic agent, cabergoline (5 micrograms/kg/day), and the synthetic prostaglandin F2 alpha, cloprostenol (1 microgram/kg/two days), is an easy, practical, reliable and safe method to terminate pregnancy near and before mid-gestation in dogs.

Intrauterine transfer of bovine trophoblast vesicles during dioestrus after breeding to increase pregnancy rates in dairy cows

Early embryonic mortality postbreeding is a major contributing factor to impaired reproductive performance in the dairy cow and is a limiting factor in maintaining a compact calving period in the dairy herd. The objectives of these experiments were (1) to measure the effect of intrauterine transfer of bovine trophoblast vesicles (bTV) during dioestrus on luteal function in dairy cows and (2) to identify if there was an effect of postpartum interval in dairy cows on the pregnancy rate response to bTV transfer between 5 and 7 days after artificial insemination (Al). In Experiment 1, 36 dairy cows were allocated for transfer of three bTV ( n = 18) or carrier medium ( n = 18) to the ipsilateral uterine horn on Day 7 of the oestrous cycle. In Experiment 11, 410 cows calved ⩽ 55 days were allocated at random for transfer of three bTV ( n = 205) or carrier vehicle ( n = 205) to the ipsilateral uterine horn on Day 5–7 after AI. In Experiment III, 410 cows calved > 55 days were allocated at random to receive three bTV ( n = 205) or carrier vehicle ( n = 205) as in Experiment II. In Experiment I, the mean interoestrous interval was 21.4 ± 0.63 days for cows receiving bTV and not different ( P > 0.10) from 21.1 ± 0.66 days for controls. Similarly, serum progesterone concentrations during the oestrous cycle were not affected ( P > 0.10) by bTV transfer. In Experiment II, the pregnancy rate for cows receiving bTV was 43.4% (89/205) and was greater ( P < 0.05) than 30.7% (63/205) for controls. In Experiment III, the pregnancy rate for cows receiving bTV was 54.6% (112/205) and was not different ( P > 0.10) than 51.7% (105/205) for controls. In summary, the transfer of bTV to the ipsilateral uterine horn during dioestrus did not extend the interoestrous interval, increased pregnancy rates in cows bred during the early postpartum period, but not in cows bred beyond 55 days postpartum.