Prolonged Duration of Fertility of Dog Ova

The fertile period for natural mating in dogs extends from before ovulation until day 5 post ovulation (PO) and involves a delay in oocyte maturation until 2–3 days PO and viability of secondary oocytes for 48–60 h or more. Spermatozoa do not enter the uterus after vaginal insemination in late oestrus. Cervical closure appears to occur on average 5 days PO, but conception may occur following intrauterine artificial insemination (IUAI) up to 8 days PO. Therefore, the present study was conducted to clarify the duration of fertility of canine ova. Using IUAI at 6, 7, 8 and 9 days PO (n = 5 bitches each) conception rates were 100%, 71.4%, 37.5% and 0%, respectively, with an average litter resorption rate of 30.8%, and with mean litter sizes and times to delivery PO being 4.3 ± 1.6 and 64.3 ± 0.3 days, 4.0 ± 1.4 and 66.3 ± 0.4 days, and 2.5 and 68 days for IUAI at 6, 7 and 8 days, respectively. The high pregnancy rates with IUAI at 6 and 7 days PO confirm that many canine oocytes are fertile at 4–5 days after maturation. The high rate of resorption was presumably because of aging of ova or asynchrony between embryonic development and the intrauterine environment.     

Temporal Relationships and Repeatability of Follicle Diameters and Hormone Concentrations within Individuals in Mares

Data were collected daily from 23 mares during two consecutive interovulatory intervals (IOIs). Several significant (p < 0.05) new observations on temporal relationships were made. The FSH increase that begins before ovulation temporarily plateaued on the day of discharge of follicular fluid into the peritoneal cavity in association with ovulation. During the declining portion of the pre-ovulatory oestradiol surge, an abrupt reduction in the rate of decrease occurred in synchrony with the peak of the LH surge and is consistent with a negative effect of LH on oestradiol. Repeatability within mares was based on the following positive and significant correlations between the two IOIs: (i) length of the interval between ovulations and between ovulation and the beginning of follicle deviation; (ii) diameter of the pre-ovulatory follicle on days -3 to -1; (iii) number of follicles in diameter classes of 2–5 mm (correlation for 22/23 days of the IOI), 5.1–10 mm (18/23 days), 10.1–15 mm (12/23 days) and 15.1–20 mm (12/23 days) and (iv) concentrations of FSH (18/23 days) and LH (22/23 days). The greatest repeatability for the follicle-diameter classes occurred in the 2–5 mm class, and thereafter the repeatability progressively decreased as the diameters for the classes increased. Results demonstrated measurable repeatability within mares for several end points between consecutive IOIs.     

Efficiency of Repeated In Vivo Oocyte and Embryo Recovery After rhFSH Treatment in Rabbits

This study aims to assess the efficiency of in vivo oocyte and embryo recovery after a recombinant human FSH (rhFSH) treatment in rabbit does. Females were distributed in two experimental groups: donor does were treated with rhFSH (superovulation group) for 3 days prior to artificial insemination (embryo recovery) or ovulation induction (oocyte recovery) and does without treatment remained as the control group. Mature oocytes or embryos were collected with the laparoscopy technique 16 h after ovulation induction (oocytes) or 72 h after artificial insemination (embryos). Up to four recoveries were performed with each doe. Recovery efficiencies differed significantly between embryos (84%) and oocytes (58%). Yet, the recovery rates for the superovulation and control groups did not differ. The rhFSH group was associated with a significant increase (p < 0.05) in the number of oocytes and embryos recovered in comparison with the control group (10.2 ± 1.0 and 14.3 ± 1.2 vs 6.0 ± 2.7 and 8.4 ± 2.3 for oocytes and embryos, respectively). Results from this study indicate that repeated in vivo oocyte and embryo recovery from rhFSH superovulated does maximizes the number of oocytes or embryos collected from the same female.     

Offspring from heterotopic transplantation of newborn mice ovaries

This study is aimed at investigating the developmental potential of the primordial follicles from ovaries of newborn mice after cryopreservation in liquid nitrogen for long-term storage, thawing, and heterografting into the kidney capsules of ovariectomized adult female mice. After stimulation of recipient mice with pregnant mare serum gonadotropin on day-19 after heterografting, the primordial follicles of the transplanted ovaries could develop into antral follicles. When the oocyte-cumulus cell complexes were retrieved from these antral follicles, they could mature after in vitro culture for 16–17 h. After in vitro fertilization, the rates of embryos derived from these oocytes that developed into the two-cell stage and the blastocyst stage after 16–17 h and after day-4, respectively, in the culture medium were 55.40% (55/107) and 9.09% (5/55), respectively. In the ovarian transplantation groups, no pups were derived from the 410 embryos that were transferred into 10 pseudopregnant mothers at the pronuclear stage. However, of the 10 surrogate mothers in whom 570 embryos were transferred at the two-cell stage, four achieved pregnancy and gave birth to 20 live offspring. These results demonstrated that primordial follicles in newborn mice ovaries were capable of sustaining their developmental potential after freezing and thawing. Once transplanted into the kidney capsules of ovariectomized adult female mice, these primordial follicles could develop and respond to gonadotropin stimulation and reach the antral stage; further, live offspring could be derived from these follicles.     

Control of Ovarian Activity in Llamas (Lama glama) with Medroxyprogesterone Acetate

Contents Progesterone and progestogens have proved to be effective in controlling follicle development and synchronization of ovarian activity in different species. In this study, vaginal sponges containing 120 mg medroxyprogesterone acetate were used to synchronize ovarian activity in llamas and to predict the time when a mature follicle will be present. Plasma concentrations of oestradiol-17β and progesterone were measured to determine follicle and corpus luteum development. The sponges were kept in the vagina for 9 days. Six days after sponge withdrawal, ovulation was induced by either GnRH injection (n = 4), mating with a vasectomized male (n = 8) or mating with an intact male (n = 10). Plasma progesterone concentrations varied between animals until day 6 after insertion of the sponges. Thereafter, progesterone levels remained close to the detection limit of the assay until ovulation was induced. The mean oestradiol-17β plasma concentration reached its lowest value 3–4 days after insertion of the sponges. Thereafter, concentrations increased and reached peak levels at day 6 after withdrawal of the sponges. All animals ovulated and developed a corpus luteum with a normal life span after the ovulatory stimulus. Blood samples were collected frequently after mating to evaluate the endocrine response to copulation. Plasma concentrations of PGF_2α metabolite and cortisol increased in parallel after copulation. The metabolite concentrations returned to basal levels 3–4 h after mating whereas the cortisol concentrations remained elevated for about 12 h after copulation The luteinizing hormone secretory pattern resembled that reported when llamas with a mature ovulatory follicle were mated. In conclusion, the protocol evaluated in this study was shown to be useful for the synchronization of ovarian activity and for predicting the time when an ovulatory follicle will be present in llamas.     

Effects of Follicular Fluid on the Transport of Porcine Oocytes into the Oviduct at Ovulation

Contents Three experiments were conducted to determine whether follicular fluid (FF) enters the oviduct and plays any role in the transport of oocytes into the oviduct. Experiment 1: Oestrus and ovulation were synchronized in cycling gilts (n = 21) over a 15 day period of feeding Regumate^® and injections of 1000 IU pregnant mare’s serum gonadotrophin (PMSG) 24 h after the last Regumate^® feed and 500 IU human chorionic gonadotrophin (hCG) 80 h after PMSG. Ipsi-lateral aspiration of FF and salpingectomy (group 1, n = 7), aspiration of FF without salpingectomy (group 2, n = 7) or ligation of the oviduct between the ampulla and infundibulum (group 3, n = 7) was performed endoscopically prior to ovulation (34–36 h after hCG). Ipsi-lateral (group 2 and 3) and contra-lateral salpingectomy was carried out in all gilts post ovulation, 42–44 h after hCG. The oviducts were flushed with 1 ml saline and the samples as well as the aspirated FF were analysed for progesterone and estradiol by RIA methods. In group 1 both progesterone and estradiol concentrations did not differ before and after ovulation. Withdrawal of FF from the ipsi-lateral ovary by aspiration (group 2) or ligation of the oviduct (group 3) did not influence the steroid content within the oviducts. Similarly low progesterone concentrations were measured in ipsi- and contra-lateral oviducts after ovulation (group 2: 0.29 ± 0.17 versus 0.24 ± 0.35 ng/ml and group 3: 0.22 ± 0.19 versus 0.21 ± 0.22 ng/ml). The high content of progesterone of FF (269.7 ± 67.9 and 389.6 ± 226.5 ng/ml in group 1 and 2, respectively) was not reflected in the oviductal fluid. Experiment 2: In five gilts 0.06 ml ³H-progesterone (30 000 dpm) were applied via a fine 27 G injection needle into the largest three follicles of the ipsi-lateral ovary prior to ovulation (34–36 h after hCG). The oviducts were flushed following ovario-salpingectomy 42–44 h after hCG. All follicles had ovulated. The oviductal flushings and oviductal and ovarian tissue were analysed for labelled progesterone. No differences were measured in the content of ³H-progesterone of oviductal flushings and of both oviductal and ovarian tissues between the ipsi-lateral injection and contra-lateral control sides. The main part of the counts detected was within the range of background dpm values. Only 2.4% of the initial counts were recovered from fluid and tissue samples. Experiment 3: In a subsequent study FF was cautiously aspirated by endoscopy from follicles of the ipsi-lateral ovary 34–36 h after hCG (n = 12 gilts). Postovulatory (58 h after hCG), both oviducts were flushed and the oocytes were recovered. To test the influence of follicle puncture alone on the process of ovulation (n = 8 gilts), the aspiration needle alone was pricked into the follicles of the ipsi-lateral ovary, without any fluid aspiration. Despite the cautious aspiration of FF from 89 follicles, 26 oocytes were recovered together with the FF. Eighty-six postovulatory follicles were observed on the ipsi-lateral ovary. Out of 57 oocytes able to reach the oviduct, 29 oocytes were flushed from the oviduct (50.4 ± 28.1%). From the contra-lateral control oviduct 71 oocytes out of 91 ovulations (69.0 ± 33.9%) were recaptured. Puncture of follicles without aspiration did not influence ovulation compared with the control (recovery rate 68.2 and 79.6%, respectively). Results indicate (1) on the basis of the low progesterone level within the oviductal fluid that only a small amount of FF seems to reach the oviduct at ovulation, and (2) FF does not appear to be a compulsory carrier of the porcine oocyte at ovulation.     

Follicular Dynamics, Ovulation and Conception Rates in Bitches

Real-time ultrasound imaging was used in a clinical study to estimate the number of follicles of different sizes, ovulation and conception rates, and to study follicle dynamics following oestrus-induction of bitches.
Follicles were identified during late anoestrus (between 100 and 60 days prior to the pre-ovulatory LH surge) and there appeared to be a shift in the population from small follicles (1–3 mm in diameter) to large follicles (>4 mm diameter) approximately 2 days prior to the LH surge. Corpora lutea could be reliably identified although the majority were cavitated. High ovulation rates (97–100%) and pregnant rates (86–100%) were detected, and although the conception rate was approximately 70% it varied between 8 and 92%. Within the narrow range of the clinical population studied there were trends relating age to reproduction performance. Oestrus induction with a gonadotrophin regime appeared to result in large numbers of small follicles that did not ovulate, whilst when using cabergoline the number of small and large follicels and the number of copora lutea were similar to those of control cycles.     

Patterns of Follicular Growth in Superovulated Sheep and Influence on Endocrine and Ovarian Response

Objectives of this study were to characterize patterns of follicular development in sheep superovulated with purified follicle stimulating hormone (FSH) (OVAGEN^TM, ICP, Auckland, New Zealand) and to determine its influence on preovulatory events (onset of the oestrus behaviour and timing of the preovulatory luteinizing hormone surge) and ovarian response (ovulation rate and embryo yield). Number and size of all ≥ 23 mm follicles from the first FSH injection to withdrawal of progestagen sponges was determined by transrectal ultrasonography just prior to every FSH injection in nine Manchega ewes superovulated with eight decreasing doses (ml) (1.5 × 3, 1.25 × 2 and 1 × 3) of OVAGEN injected twice daily from 60 h before to 24 h after the withdrawal of 40 mg fluorogestone acetate sponges. Oestrous detection and jugular blood sampling for LH radioimmunoassay were performed every 3 h from 14 to 53 h after sponge removal and ovulation rate and number of embryos were determined 4 days after progestagen withdrawal. Administration of OVAGEN induced a significant rise (p < 0.0005) in the number of follicles ≥ 4 mm in size because of an increased growth in size of follicles from the first FSH injection to sponge removal, an increase in the number of newly detected follicles from 12 to 36 h of the first FSH dose (p < 0.005) and a decrease in regression rate from 24 h (p < 0.001). The number of follicles 2–3 mm in size at first FSH dose (10.4 ± 1.5) was positively correlated with the number of ≥ 4 mm follicles at 0 h (19.0 ± 2.7, p < 0.01). A higher number of ≥ 4 mm follicles at 0 h was related with an earlier appearance of oestrus (31.5 ± 1.5 h, p = 0.08) and LH surge (45.0 ± 2.3 h, p < 0.005), and a higher ovulation rate (18.2 ± 3.8, p < 0.005). On the other hand, the rate of embryo recovery was decreased in ewes with earlier preovulatory LH peaks (p < 0.005), with a shorter interval between oestrus and LH peak (p < 0.05).     

Ovarian stimulation and ultrasound-guided oocyte retrieval in baboon (Papio Cynocephalus Anubis) during pituitary suppression with a GnRH agonist

The objective of this study was to investigate whether baboon females respond to an ovarian stimulation protocol incorporating pituitary suppression with a GnRH agonist (GnRHa) and either highly purified human FSH (hphFSH) or recombinant human FSH (rhFSH) with follicular development and oocyte maturation. A modified human ovulation induction protocol was applied to 5 adult female baboons with a history of regular menstrual cycles (33-34 days). A long-acting GnRHa implant containing goserelin acetate was placed subcutaneously (s.c.) on Days 22-24 of their menstrual cycle. Concentrations of serum oestradiol (E2), progesterone (P4) and human FSH were obtained by ELISA. Menses occurred approximately 10 days after GnRHa implantation. Daily hphFSH or rhFSH (75 IU i.m.) treatments were started approximately 10 days following menses. When the majority of follicles were > or = 5 mm in diameter and the E2 levels had reached a maximum, hCG (2000 IU i.m.) was administered to induce final maturation of oocytes and ovulation. Thirty to 34 h after hCG administration, transabdominal follicular aspiration was performed using a variable frequency transvaginal transducer with ultrasound. A total of 71 oocytes were collected from 4 animals (average: 17). The meiotic maturity of oocytes was evaluated 3 h after retrieval. Ninety-one percent of oocytes were in metaphase 2 and of grades I and II which are appropriate for in vitro insemination.     

Turnover of Dominant Follicles prior to First Ovulation and Subsequent Fertility in Postpartum Dairy Cows

Contents: The ovaries of 64 multiparous Holstein cows were scanned twice weekly by ultrasonographyfrom Day 6 postpartum until 60 days or return to normal estrous cycle, and turnover of dominant follicles in relation to subsequent fertility were determined. The mean (SD) number of days from parturition to detection of the first postpartum dominant follicle (10 mm) was 9.0 0.5, which was predominantly located in the ovary contralateral to previous pregnancy in 54/64 cows. The first postpartum dominant follicle ovulated in 34 cows, failed to ovulate in 18, became cystic in 10, and only 2 were diagnosed as ovarian quiescent which delayed the detection of dominant follicles until days 25 and 30 postpartum. Number of dominant follicles in cows with anovulated first dominant follicle was 2.8. 1.1 prior to first ovulation (range 2–5). Growth and regression of cystic follicles were observed 24 times in 6110 cows, and a total of 20 cystic follicles persisted 32.7 9.0 days (range 18–58 days) except one which persisted for 124 days. Conception rate was 89.5% and postpartum interval to conception within 180 d after calving was 96.7 days in cows detected with less than 3 dominant follicles before first ovulation compared with those of 42.9% and 141 days in cows detected with more than 4 dominant follicles. It is concluded that the number of dominant follicles detected prior to first ovulation varied from I to 5, which positively correlated with ovulation intervals, while only those cows which first ovulated less than 3 dominant follicles resulted in reasonable reproductive performance.     

Early Breeding and Pregnancy Diagnosis in Syrian Awassi Sheep Yearlings

Contents
Fifty-nine female yearlings of local Awassi sheep were randomly divided into two groups. Animals in group T (treated) were fitted with intravaginal sponges containing 60 mg of medroxyprogesterone acetate for 14 days followed by 400 IU of pregnant mare's serum gonadotrophin (PMSG) at sponge withdrawal, whereas group C (control) received no treatment. Oestrus rate was 92.7 and 11.2% for groups T and C, respectively. Lambing rate was 78 and 5.6% for groups T and C, respectively. Twinning rate was 31.3% in group T compared to zero in group C. Average birth weight for single born lambs (4.7 ± 0.6 kg) was significantly (p < 0.05) higher than twin born lambs (3.0 ± 0.5 kg) in group T. The average concentration of blood progesterone collected between days 17–19 after mating was 19.30 nmol/l and the accuracy of early pregnancy diagnosis was 100%. It was concluded that, it is possible to induce synchronized oestrus, and to increase the twinning rate in Syrian Awassi sheep yearlings outside the breeding season, using intravaginal sponges and PMSG. In addition, early pregnancy diagnosis could be successfully determined in female Awassi sheep yearlings between days 17–19 after mating.     

Development of One vs Multiple Ovulatory Follicles and Associated Systemic Hormone Concentrations in Mares

Ablation of follicles ≥  6 mm in diameter and treatment with PGF2α 10 days after ovulation were used to induce the development of ovulatory waves. Comparisons were made between induced waves with one (33 waves, 72%) and multiple (13 waves, 28%) ovulatory follicles. Diameter deviation was defined as the separation of follicles into dominant and subordinate categories. Multiple ovulatory follicles were preceded by more (p < 0.001) follicles ≥ 20 mm at the beginning of deviation, higher LH preceding deviation (approached significance, p < 0.08), lower (p < 0.05) concentrations of FSH on the day of deviation and thereafter, and higher (p < 0.0003) oestradiol by 2 days after deviation. During the peri-ovulatory period, systemic hormone concentrations for waves with multiple ovulations involved higher oestradiol before ovulation (approached significance, p < 0.07), lower FSH (p < 0.04) before and after ovulation, and both higher progesterone (p < 0.05) and lower LH (p < 0.05) beginning the day after ovulation. Results indicated that by the beginning of deviation there were more follicles ≥  20 mm and subsequently greater oestradiol production in waves that led to the development of multiple ovulatory follicles, and during the peri-ovulatory period differences between one and multiple ovulations were consistent with the negative effects of the ovarian hormones on the gonadotropins.     

Delayed feeding of first colostrum: are there prolonged effects on haematological, metabolic and endocrine parameters and on growth performance in calves?

To test the hypothesis that delaying first colostrum feeding of calves after birth exerts long-lasting effects on haematological, metabolic and endocrine traits and on growth performance, neonatal calves were fed first colostrum at 0–2 and 24–25 h after birth. Delayed feeding of first colostrum for 24–25 h after birth caused reduced plasma levels of total protein and globulin for up to 30 days and of insulin-like growth factor-I for up to 7 days, whereas concentrations of nonesterified fatty acids were elevated during the first day of life. There were no significant effects of delaying feeding for 24–25 h on leucocyte and erythrocyte number, packed cell volume and on haemoglobin levels and on plasma concentrations of albumin, urea, glucose, triglycerides, phospholipids, cholesterol, insulin, growth hormone, 3.5.3'-triiodothyronine and thyroxine and on growth performance. Thus, calves fed first colostrum with a delay of 24–25 h after birth were able to compensate rapidly for nutritional deficiencies on day 1 of life, i.e. there was no evidence for permanent imprinting of haematological, metabolic and of endocrine traits by starvation on the first day of life.     

Effects of mating behaviour and the ovarian follicular state of female alpacas on conception

OBJECTIVE: To determine relationships between mating behaviour, ovarian follicular state and successful conception in receptive female alpacas. PROCEDURE: Seventy pen matings were observed at a commercial alpaca stud in south-western Victoria. The behaviours observed included time taken to assume sternal recumbency, mating duration, and evidence of nonreceptive behaviour such as spitting, kicking and vocalisation. Ovarian follicular state was determined by ultrasonography, which was complemented by measuring plasma concentrations of oestradiol and progesterone. Pregnancies were confirmed by transabdominal ultrasonography between days 45 and 80 after mating. RESULTS: There were no significant differences between receptive females that conceived and those that failed to conceive in the time taken to adopt the copulation position of sternal recumbency, mating duration, or maximum follicle diameter. There was no significant relationship between time taken to assume sternal recumbency (log10) and maximum follicle diameter or plasma oestradiol (log10). However, there was a significant quadratic relationship between plasma oestradiol concentration (log10) and follicle diameter, and the probability of pregnancy increased as the plasma concentration of oestradiol (log10) at the time of mating increased. Females were sexually receptive most of the time in the absence of a corpus luteum, and regardless of size of the largest follicle or plasma concentration of oestradiol. Breed (Huacaya vs Suri), site of the dominant follicle (left or right ovary), lactation state, number of matings by the male (1 or 2), or interval between parturition and mating, did not affect pregnancy outcome. Follicles with a diameter less than 7 mm were able to ovulate in response to mating. This was smaller than previously reported. Thirty-four pregnancies (49% pregnancy rate) resulted in 30 (88%) births with a gestation length of 343 days (SEM +/- 2, range 316-367 days). There were 4 (12%) abortions between days 45 and 80 of gestation and full term. CONCLUSION: It was not possible to correlate mating behaviour and ovarian state with conception. To optimise pregnancy rates in receptive alpacas, matings need to occur in the presence of an oestrogenic follicle that is capable of ovulation in response to mating. A simple method of detecting alpacas with follicles in this state is not currently available and treatments that control ovarian follicular growth should therefore be investigated.     

家猫非繁殖季节诱导发情配种后排卵时间的确定

作者尝试在非繁殖季节应用外源促性腺激素对家猫进行人工诱导发情,并判断其较为准确的排卵时间。试验采用PMSG两次注射法对雌性家猫进行诱导发情,注射总剂量为150 IU,PMSG处理后的第6 d肌肉注射hCG（100 IU/只）并合笼配种。分别于合笼后的24、30、36 h手术法摘除家猫卵巢及输卵管部,观察记录卵巢排卵情况并对排卵侧的输卵管进行冲胚。试验结果显示,利用外源性促性腺激素可使家猫在非繁殖季节发情,且排卵时间范围为合笼配种后30 h左右。     

In vitro culture of mouse preantral follicles using membrane inserts and developmental competence of in vitro ovulated oocytes

To develop a reliable follicle culture system, mouse preantral follicles 150-200 microm in diameter were cultured individually for 5 or 6 days in membrane inserts or in droplets, and then induced to ovulate with hCG (Experiment 1). The nuclear maturation and developmental competence of the oocytes that ovulated from the follicles cultured in inserts were determined (Experiment 2). There was no significant difference between the two culture systems in the survival rate (83 and 77%). However, follicles cultured in inserts showed a higher ovulation rate (63%) than those cultured in droplets (39%, P<0.05). About 80% of the oocytes that ovulated from the follicles cultured in inserts were at the metaphase II stage. After in vitro fertilization, 75 and 48% of in vitro ovulated oocytes cleaved and developed into blastocysts, respectively. These results demonstrate that the insert culture system is superior to the droplet culture system in terms of follicular growth and ovulation, and can be used to investigate the growth and ovulation of follicles in vitro.     

Multi-systemic Trauma in a Ferret

A 5-year old, neutered, male, domestic sable ferret presented 24 hours after escaping outside and sustaining unknown trauma. Physical examination findings included tachycardia, tachypnea, and hind limb paresis in a laterally recumbent patient. Radiographs, laboratory evaluation, and abdominocentesis revealed the presence of hemoperitoneum, blunt hepatic trauma, pneumothorax, and a small abdominal hernia. The ferret was treated with resuscitative fluids, thoracocentesis, abdominal counterpressure, and blood transfusion. This is the first case report of multi-systemic trauma in a ferret. The ferret made a complete recovery and was discharged to the referring veterinarian three days after presentation. (Vet. Emerg. Crit. Care, 10:13–18, 2000)     

Effect of Suppression of FSH with a GnRH Antagonist (Acyline) Before and During Follicle Deviation in the Mare

A GnRH antagonist (Acyline) was used to study the role of FSH in early development of a follicular wave in 61 mares. In Experiment 1, a single dose of 3 mg per mare, compared with 0 and 1 mg, suppressed both the FSH and follicle responses to exogenous GnRH. In Experiment 2, high concentrations of FSH were induced by two successive ablations of all follicles ≥ 6 mm on days 10 and 13 (day 0 = ovulation). A single treatment with Acyline resulted in significantly greater suppression of plasma concentrations of FSH than a single treatment with charcoal-extracted follicular fluid (source of inhibin) or oestradiol. Suppression of FSH was not significantly different between the group treated with Acyline alone and a group treated with a combination of Acyline, inhibin and oestradiol. In Experiment 3, all follicles were ablated on day 10 to induce an FSH surge and a new follicular wave. Acyline treatment on day 10 resulted in an immediate decrease in FSH, without a significant effect on day of emergence of a new wave or growth of follicles from 7 to 11 mm on days 11–13. Treatment on day 15, a day before expected follicle deviation and after the peak of the wave-stimulating FSH surge, resulted in an immediate decrease in FSH and cessation of follicle growth. Results indicated that growth of follicles for about 2 days after wave emergence was independent of FSH. In contrast, during the decline in the wave-stimulating FSH surge and before follicle deviation, growth of follicles was dependent on FSH.     

Effect of GnRH Dose on Occurrence of Short Oestrous Cycles and LH Response in Cyclic Dairy Heifers

Prostaglandin F_2α (PGF_2α) and GnRH treatments given 24 h apart have been shown to result in short oestrous cycles (8–12 days) in some cows and heifers. The differences in responses may depend on the dose of GnRH. Therefore, the effect of the dose of GnRH on occurrence of short cycles and LH response was studied here. Oestrus was induced with dexcloprostenol (0.15 mg) in two groups of Ayrshire heifers. A second luteolysis was induced similarly on day 7 after ovulation; 24 h after PGF_2α treatment, the heifers were administered either a high (0.5 mg, n = 15, group T500) or low (0.1 mg, n = 10, group T100) dose of gonadorelin. Blood samples for progesterone analyses were collected daily from the second PGF_2α administration to the second ovulation after the PGF_2α injection. Beginning 24 h after the GnRH treatment, ovaries were examined by transrectal ultrasonography every 6 h until ovulation, and daily between day 4 and the next ovulation. Five heifers from both groups were sampled for LH analyses via a jugular catheter every 30 min from 1 h before to 6 h after the GnRH administration. Short oestrous cycles were detected in 7 of 10 cases in group T100 and in 12 of 15 cases in group T500. No significant differences in LH responses were detected between the groups. In group T500, the rise in LH concentration tended to be somewhat slower than in group T100. The dose of GnRH (0.1 vs 0.5 mg) did not affect the occurrence of short oestrous cycles and LH response.