Effect of rumen degradable bolus containing melatonin or progestagen pessary plus pregnant mare serum gonadotropin on estrus response and lambing rate in ewes

Two practical regimens designed to induce estrus and ovulation in ewes in late anestrus were compared. Forty ewes were given a soluble glass rumen bolus containing 150 mg melatonin on July 9 and were joined with two vasectomized rams on July 23 and with three fertile rams on August 6. A second group of 40 ewes was treated with an intravaginal progestagen pessary (60mg medroxy-progesterone acetate) on July 23. Following pessary removal after 12 d, ewes were given 750 IU of pregnant mare serum gonadotropin (PMSG). Five fertile rams were joined with these ewes 48 h after progestagen removal. Melatonin concentrations were determined in single blood samples collected in early afternoon of July 21. Mating dates, lambing dates and litter sizes were recorded. Date of mating was significantly later in ewes treated with melatonin compared with those treated with progestagen plus PMSG (P<0.0001). All ewes given melatonin were mated within 4 wk, and those on progestagen plus PMSG treatment within one day of fertile ram introduction. Thirty-four ewes (85%) allocated to melatonin treatment and 36 (90%) allocated to progestagen plus PMSG treatment lambed (P>0.05). Mean (+/-SEM) lambing date was later in melatonin-treated ewes (January 17+/-1.2 d) compared to those given progestagen plus PMSG (December 30+/-0.6 d; P<0.0001). Mean litter size was lower in melatonin-treated ewes (1.5+/-0.1) compared with those given progestagen plus PMSG (2.0+/-0.1; P<0.001). Plasma melatonin concentrations indicated that 9 of 40 ewes treated with melatonin had circulating melatonin concentrations of less than 16 pg/ml. It is concluded that under conditions that existed in this experiment, treatment with progestagen plus PMSG in late anestrus resulted in more synchronous mating and lambing and a higher litter size than that following administration of a soluble glass rumen-degradable bolus containing melatonin.     

Ovarian response, ova recovery and fertility in merino ewes superovulated either during the luteal phase of their oestrous cycle or after intravaginal progestagen treatment

Five groups of merino ewes were treated with 1000 i.u. of pregnant mare serum gonadotropin (PMSG) as a single injection per ewe. Three of these groups received treatment on days 7,9 and 11 of their oestrous cycle. Oestrus was synchronized with 125 mg of prostaglandin F2(alpha) (PG) given two days after PMSG. Oestrus in the other two groups was synchronized by intravaginal progesterone sponges inserted for 14 days. In one group, the sponges were inserted nine days after oestrus onset. In the other group the stage of the oestrous cycle was unknown. In both these groups, PMSG was given a day prior to sponge removal. No significant differences were recorded for either the mean numbers of corpora lutea, unovulated follicles or ova recovery between the five groups. However, progestagen synchronized ewes yielded significantly more fertilized ova (p < 0.05) than PG synchronized ewes.     

Effect of anti-oestradiol-17B antibodies on the reproductive response of ewes superovulated with PMSG

A field experiment was conducted to examine the effect of anti-oestradiol-17B antibody titre on the oestrous and ovulatory responses of ewes to low (600 i.u.) or high (1200 i.u.) doses of pregnant mare's serum gonadotrophin (PMSG). Merino ewes were treated with intravaginal sponges and were subsequently used as vehicle-treated controls or were immunized to produce reciprocal anti-oestradiol-17B antibody titres less than 1000 or greater than 1000. Ewes were then treated with PMSG and the incidence of oestrus and ovulation, ovulation rate, and yield of embryos recorded. Treatment of immune ewes with 1200 i.u. PMSG resulted in both a higher proportion of ewes ovulating and a higher ovulation rate than in immune ewes treated with 600 i.u. (86% v. 67% and 13.4 v. 6.0 respectively). As anti-oestradiol-17B titres increased there was a reduction in the proportion of ewes exhibiting oestrus. The proportion of ewes ovulating decreased as antibody increased in ewes treated with 600 i.u. PMSG but not in those treated with 1200 i.u., suggesting an increased positive feedback of oestradiol with high PMSG doses. Fertilization rates were highest at the lower PMSG dose (68% v. 42%) and increased with increasing titre. Overall, there was no increase in ovulation rate or in yield of embryos over control values from either low (less than 1000) or high (greater than 1000) antibody titres.     

Natural and induced ovulation rate in prolific and non-prolific breeds of sheep in Ireland, Morocco and New Zealand

Ovulation rate, in mixed-age groups of prolific and non-prolific ewe breed types, after administration of a range of doses of PMSG (0, 375, 750 and 1500 i.u.) during the follicular phase of the oestrous cycle, were compared in Ireland, Morocco and New Zealand. The ewes in Ireland and Morocco were from the Finnish Landrace and Galway, and D'Man and Timhadite breeds, respectively. In New Zealand Booroola Merino x Romney ewes which had been previously identified as heterozygous carriers (F+) of the Booroola high fecundity gene and purebred Romneys were used to represent the prolific and non-prolific genotypes respectively; in addition a group of Booroola Merino x Romney non-carriers (++) of the major gene were also included for comparison. Ovulation rate at the oestrus which preceded stimulation with PMSG was also measured in all animals. In all 3 locations the ewes of the prolific genotype had a greater ovulation rate after PMSG stimulation than did the non-prolific controls. However, this association between prolificacy and response to PMSG was removed when ovulation rate after PMSG was transformed by dividing by the ovulation rate observed before PMSG administration. Despite the differences in the genetic basis of their high prolificacy the pattern of response to PMSG over the range of dosages used was similar in Finnish Landrace, D'Man and Booroola Merino x Romney (F+) ewes and all breeds had means of about 10 ovulations in response to 1500 i.u. PMSG. Amongst the non-prolific breeds, the Timhadite was the most responsive to PMSG although it had the lowest natural ovulation rate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Superovulatory response of Chios sheep to PMSG during spring and autumn

To study the superovulatory response of Chios sheep to pregnant mares' serum gonadotrophin (PMSG), two experiments were carried out; one in spring and one in autumn. Four doses of PMSG (1500 IU, Group 1; 1000 IU, Group 2; 750 IU, Group 3; 500 IU, Group 4; controls, Group 5) were tested on 46 ewes. Oestrus was synchronised by means of MAP intravaginal sponges and PMSG was injected i.m. at the time of sponge withdrawal. When in oestrus, ewes were naturally mated. On Day 7 after sponge removal, mid-ventral laparotomy was performed and the uterine horns and/or oviducts were flushed with 20–40 ml Dulbecco's phosphate-buffered saline supplemented with 15% foetal bovine serum (FBS). The embryos were examined under a dissecting microscope and were evaluated according to morphological criteria.The interval from sponge removal to the onset of oestrus was significantly (P < 0.001) shorter in autumn than in spring in all groups. No significant differences regarding superovulatory response, collection and fertilisation rate or numbers of ova and embryos collected were found between spring and autumn. The clinical signs of oestrus started earlier (P < 0.001) in all PMSG treated animals than in the controls, both in spring and in autumn. The highest ovulation rate was recorded in Group 2 (5.9 ± 1.0), followed by Groups 1 (5.0±0.9), 3 (3.9±0.5), 4 (26±0.4) and 5 (1.3±0.1). The increase observed in total ovarian response (corpora lutea + large anovulated follicles) parallelled the increase of PMSG dose (10.7 ± 1.6, 7.7 ± 0.9, 4.5 ± 0.6, 3.4 ± 0.5 and 1.8 ± 0.2 for Groups 1, 2, 3, 4 and 5, respectively). The highest mean number of ova was collected from Group 3 (3.4±0.5), followed by Groups 2 (2.6 ± 0.4), 4 (2.2 ± 0.3), 1 (1.6 ± 0.5) and 5 (1.1 ± 0.1). The higher doses of PMSG (1500 and 1000 IU) significantly increased the mean number of anovulated follicles and significantly decreased recovery rate. Mean number of high viability embryos collected per ewe treated (0.9 ± 0.6, 1.5 ± 0.4, 2.2 ± 0.5, 1.5 ± 0.4, 0.9 ± 0.1 for Groups 1, 2, 3, 4 and 5, respectively) was not improved by PMSG dose.It is concluded that Chios sheep can be superovulated in autumn and in spring with similar results. Clinical signs of oestrus are initiated earlier in autumn than in spring. PMSG treatment shortens the interval from sponge removal to the onset of oestrus. Although PMSG does not seem to be the most suitable hormone for the induction of superovulation in Chios sheep, a dose of 750–1000 IU PMSG gives satisfactory results; higher doses are associated with side effects in a significant number of animals (many anovulated follicles, low recovery rate).     

Follicular activity and ovulation regulated by exogenous progestagen and PMSG in anestrous ewes

Follicular dynamics and ovulation were compared in 3 groups of anestrous ewes: those treated with medroxyprogesterone acetate (MAP) sponges for 12 d, then with 750 IU PMSG at the time of sponge removal (P4 + PMSG, n = 6), or PMSG alone (n = 6) and untreated controls (n = 6). Waves of follicular activity were observed in all the animals. In the P4 + PMSG treatment group, MAP priming permitted more ovulatory follicles (P < 0.001) to be recruited without changing follicle growth rate; MAP priming also delayed the time of ovulation (P < 0.001) and the time of the LH surge (P < 0.01), which allowed for an increase in the size of ovulatory follicles (P < 0.05). Ovulation also resulted in normal luteal function after P4 + PMSG (P < 0.01) but not after PMSG alone, since premature luteal regression occurred in 80% of the cases and was related to the presence of follicles > 4 mm when P4 levels were < 1 ng/mL on the day following ovulation. The results showed that MAP priming increased the ovulation rate by increasing the number of follicles that responded to PMSG.     

Factors affecting pregnancy rates following laparoscopic insemination of 28,447 Merino ewes under commercial conditions: a survey

The results of laparoscopic insemination of 28,447 Australian Merino ewes with semen from 468 rams were used to study factors influencing pregnancy. The overall pregnancy rate was 71.7% (20,423/28,447). Pregnancy rates varied with type of progestagen implant, type and dosage of PMSG, fresh or frozen semen, wool type and number of ewes inseminated per hour. The pregnancy rate (64.6%) obtained with Medroxy-progesterone acetate (MAP) sponges, was significantly (P < 0.01) lower than with Fluorogestone acetate 30 mg (FGA 30; 74.7%) sponges, Fluorogestone acetate 40 mg (FGA 40; 72.1%) sponges, and Controlled Internal Drug Release (CIDR-G; 71.7%) implants. A PMSG dose of 200 IU resulted in significantly (P < 0.05) lower pregnancy rates (62.4%) compared with 250 IU (72.9%), 300 IU (79.1%) and > or = 375 IU (69.4%). The mean pregnancy rate for ewes administered Folligon PMSG was 71.9%, which was significantly higher (P < 0.001) than that of ewes treated with Pregnecol PMSG (65.8%). The use of Pregnecol PMSG and MAP sponges was associated, and thus their conditional effects could not be calculated. Ewes inseminated with fresh semen were significantly (P < 0.001) more likely to become pregnant (82.2%) than those inseminated with semen frozen in pellets (69.5%) or straws (71.6%). Ewes inseminated during the months of March, April or May (fall, 71.5%) were just as likely to become pregnant as those ewes inseminated in November, December, January or February (69.6%). Significantly (P < 0.05) fewer strong wool ewes become pregnant to laparoscopic AI, (67.6%) than fine (71.7%), fine medium (73%) or medium wool ewes. Significantly (P < 0.0001) more pregnancies (77.6%) were achieved when more than 55 ewes were inseminated per hour compared with fewer than 35 ewes per hour (63.4%).     

Ovulation response to pregnant mares' serum gonadotrophin in prepubertal ewe lambs of different Booroola genotypes

Ovulation rates following treatment with PMSG were measured in prepubertal ewe lambs of known Booroola genotype to evaluate the technique as a method of early identification of Booroola genotypes. Two experiments were conducted with homozygous (FF), heterozygous (F+) and non-carrier (++) interbred $\text{1}\text{2}$ Merino $\text{1}\text{2}$ Romney breed type ewe lambs and a third experiment compared first cross F+ $\text{1}\text{2}$ Merino $\text{1}\text{2}$ Coopworth breed type with contemporary Coopworths (++). The ewe lambs aged 5–6 months were injected with 400 or 600 i.u. PMSG. The percentage of ewe lambs ovulating following treatment with PMSG was similar in all experiments (75–77%) but in Experiment 1 the FF and F+ lambs had a significantly higher proportion ovulating than the ++ lambs (P<0.05). The mean ovulation rate of FF ewe lambs treated with PMSG was 1.03 (Expt 1) and 1.69 (Expt 2) higher than ++ lambs (P<0.05). In Experiment 1 the mean ovulation rate of F+ ewe lambs was 0.33 higher than ++ ewe lambs but this difference was not significant. However, in Experiments 2 and 3 the mean ovulation rate of F+ ewe lambs treated with 600 i.u. PMSG was 1.06 and 0.45 higher than ++ ewe lambs respectively (P< 0.05). These results show that PMSG treatment is a promising technique for identifying the Booroola genotype of ewe lambs at an early age but further experiments with different dose rates of PMSG and different ages and liveweights of lambs are required to determine optimum dose rates and time of treatment.     

Ovarian response in ewes following horse anterior pituitary extract and progestagen treatment

Sixty adult ewes were treated intravaginally for 12 days with one of three progestagen treatments: (1) 500 mg progesterone pessary, (2) 30 mg flurogestone acetate pessary, (3) 12% (w/w) progesterone in a Controlled Internal Drug Release (CIDR) device. On days 10, 11 and 12 of progestagen treatment ewes received either 60, 45 and 30 mg; 45, 45 and 45 mg or 30, 45 and 60 mg of horse anterior pituitary extract (HAP), respectively. Progestagen treatment was terminated on day 12 at the time of the last HAP treatment. Ewes were bred by artificial insemination at 8- and 16-h intervals during oestrus, which was checked by using vasectomized rams. Ovarian response and fertility were determined at laparotomy 8 days after progestagen withdrawal. Progestagen treatment significantly increased (P<0.05) ovulation rate, with a mean of 9.1, 12.0 and 6.6 ovulations from treatments (1), (2) and (3), respectively. The method of HAP administration had no significant effect on ovulation rate, with a mean of 9.8, 10.0 and 7.8 after either decreasing, constant or increasing levels during treatment. There was no difference in the fertilization rate following flurogestone acetate (45.7%) or CIDR (47.0%), but a lower rate resulted after the progesterone pessary (30.0%) (P<0.025). More eggs were recovered following local than following general anaesthesia (P<0.05). Results indicate that cervical insemination does not give a satisfactory yield of fertilized eggs following hormonal inductions of superovulation.     

Ram-induced oestrus and ovulation in lactating and weaned Corriedale ewes

Two experiments were conducted in consecutive years in which recently (Experiment 1) or temporarily (Experiment 2) weaned ewes and matched post-partum non-lactating flockmates (DRY) were exposed to a stimulus group of rams and oestrous ewes (10 and 20 in Experiment 1, 20 and 20 in Experiment 2) for 28 days in spring. Lactating ewes (n = 130) in Experiment 1 were isolated from their lambs 4 (W-4), 2 (W-2), 1 (W-1) or 0 (W-0) days in advance and exposed along with a group of 32 DRY flockmates. Lactating ewes in Experiment 2 (n = 230) were allocated to an unreplicated factorial of two levels of temporary weaning before stimulation (B0: control; B24: lambs removed 24 h before stimulation) by four levels of ewe-lamb contact imposed at the start of the stimulation (A0: control; A12, A24 and A36: lamb-ewe separation during the initial 12, 24 or 36 h of exposure); DRY ewes (n = 54) acted as an augmented factorial control. Oestrus (rump marks) and ovulation (laparoscopy on day 5 and on day 28 (Experiment 1) or day 32 (Experiment 2)) were recorded. Ovulation and oestrous responses in Experiment 1 were similar for DRY (90.6% and 55.2%, respectively) and recently weaned ewes (83.8% and 53.7%, respectively). Amongst recently weaned ewes, the immediate ovulation response to the rams and the proportion of ewes still cycling by day 28 tended to be lower (P = 0.065 and P = 0.011) in ewes weaned on the day of ram exposure (71.9% and 54.8% v. 87.8% and 80.0%, respectively). Ovulation rate was lower (P < 0.003) in W-2 ewes (1.3 ± 0.10) than in the other recently weaned groups. In Experiment 2, ovulation (83.3%) and oestrous (68.9%) responses in DRY ewes were higher (P = 0.022 and P = 0.053, respectively) than in lactating ewes (66.2% and 51.0%, respectively). More ewes ovulated (P = 0.036) in B24 (70.5%) than in B0 (61.8%). Ewes having their lambs returned 12 h after the onset of stimulation (A12) had poorer ovulation responses (54.9%) than control ewes (A0, 72.9%, P < 0.05); this was probably associated to lamb restitution after the sunset. Main conclusions were that (i) the presence of the lambs is a depressing factor of both ovulation and oestrous responses to the ram effect in lactating ewes, (ii) the ovulation response of lactating ewes will probably benefit from removing lambs for a period of 24 h before the onset of stimulation, (iii) until additional information becomes available, temporary weaning protocols should be designed avoiding lamb restitution during the night.     

Plasma progesterone concentration in relation to ovulation rate and embryo yield in Chios ewes superovulated with PMSG

The main purpose of this work was to investigate the relationship between plasma progesterone concentration and the number of ovulations and/or the number of embryos collected from Chios ewes induced to superovulate with various doses of PMSG.The oestrous cycles of the animals were synchronized by means of MAP intravaginal sponges for 14 days and PMSG was injected i.m. (1500 IU, Group 1; 1000 IU, Group 2; 750 IU, Group 3; 500 IU, Group 4; 0 IU, Group 5) at the time of sponge withdrawal. Seven days after sponge removal and 5 days after mating, mid-ventral laparotomy was performed and the uterine horns and/or oviducts were flushed. The number and diameter of corpora lutea (CL), the number of large (diameter > 0.5 cm) anovulated follicles and the total ovarian response (TOR = CL + large anovulated follicles) were recorded. The embryos were examined under a dissecting microscope and evaluated according to morphological criteria. Blood samples were collected once daily for 4 days starting on the day of sponge withdrawal. One more sample was taken on the day of embryo collection. Progesterone concentration was determined using a conventional ELISA.A significant positive correlation was found between plasma progesterone concentration and number of corpora lutea (r = 0.61, P < 0.001), total diameter of corpora lutea (r = 0.63, P < 0.001), total ovarian response (r = 0.63, P < 0.001), number of eggs (r = 0.51, P < 0.001), number of embryos (r = 0.43, P < 0.001) and number of transferable embryos (r = 0.36, P < 0.01) collected per ewe treated. A negative relation between progesterone concentration (≥ 2 ng ml⁻¹) at the beginning of oestrus and number of corpora lutea (CL) was observed. The investigation of the relationship between ovulation rate and plasma progesterone concentration on the day of embryo collection resulted in the calculation of a formula for the prediction of the response of Chios sheep after superovulation with the specific hormonal regimen.     

Early cycle FSH-p priming as a prelude to superovulating gonadotropin administration in ewes and heifers

The effect of an exogenous FSH treatment in the periovulatory, post-LH surge period on superovulatory response in the subsequent cycle of ewes and heifers was investigated. Thirty-five ewes were synchronized with progestagen pessaries and pregnant mares serum gonadotropin. The day following the onset of estrus (Day 1) 17 ewes received one intramuscular injection of 5 mg follicle stimulating hormone of porcine origin (FSH-p). All 35 ewes received another progestagen pessary on Day 1 and were superovulated with horse anterior pituitary extract (HAP). The ewes were bred and embryos collected 6 days following the onset of estrus. Early cycle FSH-p administration did not increase the subsequent ovulation rate (6.5 vs. 8.4 for controls, n.s.). Recovery rate for the FSH-p treated animals was higher (78.5% vs. 49.3%; P<0.05) as was fertilization rate (100% vs. 62.4%; P<0.05). The final result was a mean of 4.4 transferable embryos per ewe treated among the FSH-p boosted ewes and 2.6 transferable embryos per ewe treated among the control ewes.Twenty-nine heifers were brought into estrus with one 500-μg injection of prostaglandin F_2α (PG). Twelve of the 29 heifers were given one intramuscular injection of 10 mg FSH-p on either Day 2 or 3 (Day 1 is the day following the onset of estrus). All heifers were superovulated starting on Day 11–16, over a 4-day period using a decreasing dosage of FSH-p. Prostaglandin was administered at the time of the fifth superovulatory FSH-p injection and the heifers were bred by artificial insemination. Ova were recovered between 2 and 4.5 days following the onset of estrus. There was no effect on ovulation rate due to the interval from FSH-p priming to the day of superovulatory FSH-p initiation. The proportion of heifers that ovulated when given a FSH-p injection early in the cycle was higher than in the control group (94% vs. 68%; P<0.05). The primed heifers had a higher number of ovulations than did the control heifers (16.3 vs. 6.2; P<0.01). The effect of higher ovulation rate carried through all parameters measured, so that the FSH-p primed heifers also had a higher number of fertilized ova than the controls (10.7 vs. 3.9; P<0.05), indicating that there was no significant deterioration in ovum quality due to the FSH-p priming. The results show that FSH-p improved superovulatory efficiency in both sheep and cattle.     

Time of ovulation in the South Australian Merino ewe following synchronization of estrus. 1. Variation within and between flocks

Observations were made by repeated laparoscopy to determine the time of ovulation in seven flocks of South Australian Merino ewes treated with pregnant mare serum gonadotropin (PMSG, 400 IU per ewe) and an intravaginal pessary containing 60 mg medroxy-progesterone acetate (MAP). Ovulation most often commenced within 57 h of pessary removal and was completed in all flocks within 81 h. There was, however, significant variation in the time of onset of ovulation; it did not commence until 69 h in one of three observations of Flock 1 and in two of three observations of Flock 2. On the other hand, in a flock of two-year-old nulliparous ewes (Flock 7), ovulation commenced significantly (P < 0.001) earlier than in most observations of other flocks, with 18 39 ewes ovulating within 57 h of pessary removal. The effect of the progestagen (MAP vs flugestone acetate) and the gonadotropin preparation (Pregnecol vs Folligon) on the time of ovulation were observed in separate studies. The characteristic time of ovulation was not influenced in either comparison. However, ovulation occurred significantly (P < 0.001) earlier in ewes treated with progesterone released from a controlled internal drug release dispenser (CIDR). The implications of these findings to artificial insemination and embryo transfer are discussed.     

Induction of ovulation and fertilization in the 90-day-old ewe lamb.

The induction of ovulation and fertilization was studied in 50 sexually immature crossbred ewe lambs which received 500 or 1000 i.u. PMSG with or without pretreatment with progesterone. Pretreatment with progesterone did not significantly affect ovulation, fertilization or ova recovery rates. Also, progesterone pretreatment did not significantly affect weight of the ovaries, corpora lutea, follicular fluid or the reproductive tract. Lambs receiving 1000 i.u. PMSG had a significantly (P<.05) higher ovulation rate (13.2) than lambs receiving 500 i.u. PMSG (3.4). Weights of the ovaries, corpora lutea, follicular fluid and the reproductive tract were significantly (P<.05) higher in ewes receiving 1000 i.u. PMSG. None of the lambs exhibited estrus when checked daily following HCG injection. The low ova recovery rate (16 to 38 percent) was postulated to be due to failure of the fimbria of the influndibulum to surround the enlarged stimulated ovary and pick up released ova.     

Plasma follicle stimulating hormone,ovulation rate and fertility in Merino ewes treated with bovine follicular fluid

Charcoal-treated bovine follicular fluid (bFF) given as four 5-ml subcutaneous injections to 13 Merino-Border Leicester ewes around the time of natural luteolysis suppressed (P<0.01) plasma levels of follicle stimulating hormone (FSH) [from 1.08 ± 0.05 to 0.41 ± 0.03, mean ± s.e.m. of log_e (ng+ 1) /mlplasma]. This was followed (P < 0.01) by hypersecretion or a rebound of FSH (to 1.46 ± 0.11) lasting 32 h in 10 of the treated ewes, and then by a further fall (to 0.73 ± 0.03, P < 0.05) before the surge (1.21 ± 0.07, P < 0.05) associated with the preovulatory surge of luteinizing hormone (LH).Plasma FSH at 56–72 h before the LH surge (i.e., at the time of the FSH rebound) was correlated with the subsequent ovulation rate (n=13, r= + 0.73, P < 0.01). Fewer ewes treated with four injections of 2 or 5 ml of bFF than control ewes (injected with bovine plasma) became pregnant (28 of 41 vs. 38 of 41, χ² = 4.05, P < 0.05), although plasma progesterone was similar at Day 11 in treated and control ewes. It is concluded that plasma FSH during such a rebound influences the subsequent ovulation rate in sheep.     

Are differences in FSH concentrations involved in the control of ovulation rate in Romanov and Ile-de-France ewes?

Despite differences in FSH concentrations ranging from 1.5 ng/ml (Romanov ewes) to 4 ng/ml (Ile-de-France ewes) between the follicular and luteal phases, follicular growth (numbers of follicles growing, growth rates, maximum size reached) was morphologically similar between the two stages of the cycle. Injection of 750 i.u. hCG at Day 6 or 16 of the cycle triggered ovulation of 4.1 +/- 0.7 and 4.0 +/- 1.3 follicles in Romanov and 2.2 +/- 0.5 and 1.7 +/- 0.5 follicles in Ile-de-France ewes, respectively, demonstrating that functional differentiation was similar between the two stages of the cycle. As gonadotrophin environment differs between these two stages of the cycle, this suggests that there is a wide flexibility in the amount of gonadotrophins required to trigger terminal follicular growth and that ovarian requirements for gonadotrophins might work through thresholds. When Romanov and Ile-de-France ewes were given similar amounts of exogenous gonadotrophins (1250 i.u. PMSG, 750 i.u. hCG) after hypophysectomy, ovulation rates were close to the usual values (Romanov, 5.5 +/- 3.9; Ile-de-France, 1.4 +/- 0.5), demonstrating that differences in gonadotrophin concentrations during the follicular phase do not play a major role in the high ovulation of the Romanov compared to the Ile-de-France ewes.     

Time of ovulation in goats (Capra hircus) induced to superovulate with PMSG

The timing of ovulation in feral goats treated with 1200 i.u. PMSG +/- 50 micrograms GnRH was studied by repeated laparoscopy. Experiment 1 established that superovulation began as early as 30 h after withdrawal of progestagen-impregnated sponges and was not completed at 54 h if goats received PMSG alone. GnRH synchronized ovulation, leading to 91% of ovulations appearing between 36 and 48 h after sponges were withdrawn. Experiment 2 established that superovulation continued until up to 77 h in goats treated only with PMSG. The stress of repeated laparoscopy appeared to delay or abolish ovulation in some females. The mean (+/- s.e.) ovulation rate was greater in goats treated with GnRH (12.7 +/- 1.3) than in those that received PMSG only (9.7 +/- 1.1; P less than 0.05). Out of 47 of the females in Exp. 1, 43 had one or more corpora lutea at laparoscopy 24 h after withdrawal of progestagen. These early corpora lutea were associated with an increased concentration of plasma progesterone during the periovulatory period. Experiment 3 provided evidence that these corpora lutea arose before the withdrawal of progestagen-impregnated sponges.     

The effects of post-weaning progestagen treatment (Regumate) of early-weaned primiparous sows on subsequent reproductive performance

This study investigated the effects of feeding the orally active progestagen, altrenogest (Regumate) post-weaning on the subsequent reproductive performance of early weaned sows. Ninety (90) Large White/Landrace first parity sows were randomly assigned to three treatments. Treatment 1 (EW) and treatment 3 (CW) sows were weaned on day 12 and day 24 post-partum, respectively while treatment 2 sows (EW-R) were weaned on day 12 post-partum and received an individual daily dose of 20 mg of Regumate on days 13 to 24 post-partum inclusive. Each sow was mated naturally at least twice at the first post-weaning or post-treatment oestrus and slaughtered on days 25–28 of pregnancy to determine the number of corpora lutea and embryos. Regumate-to-oestrus and weaning-to-oestrus intervals were similar for EW-R and CW sows (6.2 vs. 5.6 days). However, both intervals were significantly shorter (P<0.01) than the weaning-to-oestrus interval of EW sows (7.3 days). An excellent synchronization of oestrus was achieved with Regumate treatment with 97% of treated sows in oestrus within 7 days of Regumate withdrawal compared with 64% for EW sows (P<0.01) and 87% for CW sows (P>0.05). Treatment with Regumate resulted in a significant increase in ovulation rate (16.9 vs. 15.4 and 14.9 for treatments EW-R, EW and CW, respectively; P<0.05) and a non-significant increase in early embryonic survival (77% vs. 68% vs. 68% for treatments EW-R, EW and CW, respectively; P>0.05). These results indicate that Regumate feeding is a potential management tool to alleviate the diminished reproductive performance associated with early weaning regimes since it leads to successful control of oestrus, higher ovulation and embryo survival rates and thus a greater potential litter size.     

Endocrine responses of goats after induction of superovulation with PMSG and FSH

Goats in Group A were pretreated for 9 days with a synthetic progestagen, administered via intravaginal sponge, and 1000 i.u. PMSG s.c. on Day 12 of the oestrous cycle. Goats in Group B had the same PMSG treatment, but not the progestagen pretreatment. Group C goats received a s.c. twice daily injection of a porcine FSH preparation (8 mg on Day 12, 4 mg Day 13, 2 mg Day 14 and 1 mg Day 15). Oestrus was synchronized in all animals by 50 micrograms cloprostenol, 2 days after the start of gonadotrophin treatment. The vaginal progestagen sponges were removed from Group A at the same time. Mean ovulation rate was slightly higher in FSH-treated than in the PMSG-treated animals, whereas the incidence of large follicles that failed to ovulate was significantly elevated in PMSG-treated animals in Group B. More goats in Groups A and B than in Group C exhibited premature luteal failure. Progestagen pretreatment appeared to suppress both follicular and luteal activity, as indicated by numbers of large non-ovulating follicles and by the magnitude and duration of elevated plasma oestradiol levels following PMSG stimulation, and by decreased plasma progesterone levels before and after PMSG treatment. Oestrogenic response to FSH was considerably less than that to PMSG, as indicated both by a considerably shorter duration of elevation of circulating oestradiol levels during the peri-ovulatory period, and by lower maximal oestradiol levels. Differences in the ovarian responses to PMSG and FSH may be attributed primarily to differences in the biological half-life of each preparation.     

Corpus luteum function following single and double ovulation during estrous cycle in Sanjabi ewes

This study compared the effect of double and single ovulation on serum progesterone concentrations and luteal characteristics in Sanjabi ewes at different days of the estrous cycle. The estrous cycles of 197 Sanjabi ewes were synchronized by a 12-day treatment with intravaginal sponges (Chronogest^®). Estrus was detected in 144 ewes 27–39 h after sponge removal. Daily blood samples were taken every morning and analyzed for serum progesterone (P4). Ewes were then transported to a local abattoir, where nine ewes were slaughtered on each experimental day (days 1–16 after estrus) for ovary collection. The ovarian follicles were measured and categorized by size (very small <2 mm; small 2–3.5 mm; medium 3.5–5 mm; large >5 mm). On each slaughter day, the number of corpora lutea per ewe was classified as single and double ovulation. The results show that the effect of dominant follicles was less during the mid-luteal phase. Ovulation rate of right, left and both ovaries were (54.9%), (23.6%) and (21.5%), respectively. The incidence of double ovulations was 40.2%. In the case of ewes exhibiting double ovulation, 46.6% occurred unilateral (ewes exhibited both ovulations on the right ovary); whereas 53.4% occurred bilateral (ewes exhibited ovulations on the right and left ovaries). Unilateral double ovulation was not observed in the left ovary. The right ovary appeared to play a significantly greater role in ewes showing single and double ovulations than the left ovary (P < 0.05). Serum progesterone concentration showed minimum and maximum levels of 0.29 ± 0.15 and 5.51 ± 0.75 ng/ml on days 16 and 11 post-estrous, respectively (P < 0.001). The mean volume of individual corpus lutea in ewes with single ovulations was significantly higher than in ewes with double ovulations (P < 0.01). However, the total volume of corpus lutea in ewes with single ovulation was significantly lower than in ewes with double ovulations in some days of estrous cycle (P < 0.01). The serum progesterone concentration was significantly higher in double than single ovulating animals on days 1–16 of the estrous cycle (P < 0.001). These results indicated a relatively high incidence of double ovulation in ewes associated with increasing total luteal volume and high circulating concentrations of progesterone.