Effect of exogenous gonadotropins on the weaning-to-estrus interval in sows

The efficacy of PG 600 (400 IU PMSG and 200 IU hCG) for accelerating the onset of estrus was determined for sows weaned during the summer. Yorkshire sows (average parity = 4.6), nursing 8.6 +/- 0.2 pigs (mean +/- SEM) were weaned after 27.7 +/- 0.4 d of lactation and were treated intramuscularly with either PG 600 (n = 35) or with 0.9% saline (n = 35). Sows were checked for estrus once daily in the presence of a mature boar. Treatment with PG 600 increased (P < 0.05) the percentage of sows in estrus within 7 d after weaning (97.1 vs 82.9%). Relative to controls, sows given PG 600 expressed estrus sooner (3.8 +/- 0.1 d vs 4.5 +/- 0.1 d; P < 0.01). Sows exhibiting estrus within 7 d after treatments were artificially inseminated 0 and 24 h after first exhibiting estrus. The percentage of inseminated sows that farrowed tended to be higher (P < 0.07) for control than for PG 600-treated sows (96.6 vs 82.3%). The number of pigs born live was similar (P > 0.1) for sows treated with PG 600 and with saline, and was 12.7 +/- 0.6 and 11.7 +/- 0.7, respectively. Pigs farrowed by saline-treated sows, however, tended to be heavier (P < 0.09) than pigs farrowed by sows treated with PG 600 (1.49 +/- 0.06 kg vs 1.34 +/- 0.06 kg). In summary, PG 600 accelerated the onset of estrus in sows weaned during the summer. Sows mated during the induced estrus, however, tended to have a lower farrowing rate and farrowed lighter pigs than control sows inseminated during a natural estrus occurring within 7 d after weaning.     

Response of anestrous ewes to the ram effect after follicular wave synchronization with a single dose of estradiol-17beta

Anestrous ewes respond to the introduction of rams with either an ovulation within 2-3 days that may be followed by luteal phases of normal or short length, with delayed ovulations (5-6 days later), or with the luteinization of follicles. The aim of this work was to study the relationship between the growth status of the largest follicle present when rams are introduced and the type of ovarian response in non-treated ewes and in ewes treated with estradiol-17beta before ram introduction. Thirteen anestrous Corriedale ewes were divided into 2 groups: E2 (n = 7) and C (n = 6). The E2 ewes received a single dose of 50 microg estradiol-17beta 5 days before the introduction of the rams to synchronize the onset of their follicle waves, while C ewes remained untreated. When the rams were introduced, all E2 ewes had the largest follicle in a growing stage in contrast with the C ewes (3 out of 6; P < 0.05). Five C and 4 E2 ewes ovulated after the introduction of the rams (Day 3.4 +/- 0.4 for C vs. 4.8 +/- 0.3 for E2 ewes, respectively, P < 0.05). Only one ewe from each group developed a normal luteal phase: 4 C and 3 E2 ewes had short luteal phases. One C ewe and 2 E2 ewes had short luteal phases originating from follicles that did not ovulate. After the first luteal phase, all ewes returned to anesirus without a second ovulation or luteal phase. The remaining E2 ewe did not ovulate or show any changes in progesterone serum concentrations. We conclude that the growth status of the largest follicle alone does not determine the ovarian responding pattern of anestrous ewes to the ram effect.     

The influence of breeding intensity on above- and below-average sexual performance rams in single- and multiple-sire breeding environments

Two studies were conducted to evaluate the relationship between serving capacity scores and breeding performance of rams. The first study was conducted to determine whether rams with above or below mean serving capacity scores could perform equally in greater and lesser breeding intensity, single-sire mating schemes. The second study was conducted to determine whether rams with above and below mean serving capacity scores could perform equally well when only one or two ewes were in estrus daily in a multiple-sire breeding scheme (two rams/pen). Rams (n=68) were ranked according to average number of ejaculations recorded in serving capacity tests. Sixteen rams with the greatest scores (above-average) and 16 rams with least scores (below-average) were identified for breeding. Half of above-average and half of below-average rams were used in the two studies. For study 1, each ram was individually introduced to 23 estrus-synchronized ewes for 9 d to simulate high breeding intensity. Rams were given a 5-d rest before they were individually introduced to 23-24 naturally cyclic ewes for 17 d (low breeding intensity). For study 2, 16 rams were paired across ram types, and each pair competed for 20 ewes for 18 d (8 pens). For study 1, ewe fertility (ewes lambing/ewes present at lambing) and number of lambs born were greater (P<0.001) for above-average (0.67+/-0.03 and 27.6+/-1.2, respectively) than for below-average rams (0.39+/-0.07 and 15.3+/-2.7) with greater breeding intensity. Ewe fertility and lambs born did not differ for above-average (0.91+/-0.03 and 37.8+/-1.9, respectively) and below-average rams (0.86+/-0.03 and 39.0+/-1.9) with less breeding intensity. For study 2, number of ewes lambing (99+/-8.0 compared with 72+/-13.6; P=0.12) and number of lambs sired (149+/-18.5 compared with 101+/-22.8; P=0.14) did not differ between above- and below-average rams, respectively, in direct competition. Sexual classifications based on serving capacity tests are related to breeding performance of rams in certain breeding environments. When breeding intensity is greater, above-average rams impregnate more ewes and sire more lambs than below-average rams. When only a small number of ewes are in estrus daily, below-average rams for serving capacity scores perform as well as above-average rams in multiple-sire and single-sire breeding environments. We suggest that above-average rams should be used to reduce number of rams required when breeding intensity is greater.     

Breeding ewes out-of-season using melengestrol acetate, one injection of progesterone, or a controlled internal drug releasing device

A series of studies was designed to identify methods of improving out-of-season breeding success in ewes. In Experiment 1, 190 mature ewes were assigned to receive in April, either: (A) a control ration of 0.3 kg corn twice daily for 8 d before ram introduction (control ewes n=49), (B) the control ration containing 0.125 mg of melengestrol acetate (MGA) in 0.3 kg corn (MGA8a ewes n=46), (C) the control ration or 7.5 d followed by 1 feeding of 0.5 mg MGA in 0.3 kg corn (MGA1 ewes n=48), or (D) the control ration plus a 20 mg i.m. injection of progesterone on D 8 (P ewes n=47). Ewes were exposed to rams for 21 d. A greater percentage of MGA8a and P ewes lambed than did control ewes (P < 0.04). The lambing rate was greatest among MGA8a (P < 0.02 vs. control), intermediate among P ewes (P < 0.19 vs. control) and least among MGA1 and control ewes (P > 0.79). In Experiment 2, 70 mature ewes were assigned to receive in June, either: (A) a control ration of 0.3 kg of corn twice daily for 8 d before to ram introduction (control ewes n=25), (B) the control ration containing 0.125 mg of MGA per 0.3 kg corn (MGA8b ewes n=21), or (C) the control ration and simultaneous treatment of ewes with a progesterone-containing controlled internal-drug releasing device (CIDR ewes n=24). Ewes were exposed to rams for 21 d. Both CIDR and MGA8b ewes exhibited estrus earlier than did control ewes (P < 0.01). The CIDR ewes exhibited estrus earlier than did the MGA8b ewes (P < 0.05). A greater percentage of ewes treated with CIDR or MGA8b lambed than did control ewes (P < 0.01), with more CIDR ewes lambing than MGA8b ewes (P < 0.01). The lambing rate was greater in CIDR ewes than in control ewes (P < 0.04). These data provide evidence that several options exist to improve pregnancy success in ewes bred out of season and that success varies with method of treatment.     

Induction of ovulation in the acyclic postpartum ewe following continuous, low-dose subcutaneous infusion of GnRH

Pituitary and ovarian responses to subcutaneous infusion of GnRH were investigated in acyclic, lactating Mule ewes during the breeding season. Thirty postpartum ewes were split into 3 equal groups; Group G received GnRH (250 ng/h) for 96 h; Group P + G was primed with progestagen for 10 d then received GnRH (250 ng/h) for 96 h; and Group P received progestagen priming and saline vehicle only. The infusions were delivered via osmotic minipumps inserted 26.6 +/- 0.45 d post partum (Day 0 of the study). Blood samples were collected for LH analysis every 15 min from 12 h before until 8 h after minipump insertion, then every 2 h for a further 112 h. Daily blood samples were collected for progesterone analysis on Days 1 to 10 following minipump insertion, then every third day for a further 25 d. In addition, the reproductive tract was examined by laparoscopy on Day -5 and Day +7 and estrous behavior was monitored between Day -4 and Day +7. Progestagen priming suppressed (P < 0.05) plasma LH levels (0.27 +/- 0.03 vs 0.46 +/- 0.06 ng/ml) during the preinfusion period, but the GnRH-induced LH release was similar for Group G and Group P + G. The LH surge began significantly (P < 0.05) earlier (32.0 +/- 3.0 vs 56.3 +/- 4.1 h) and was of greater magnitude (32.15 +/- 3.56 vs 18.84 +/- 4.13 ng/ml) in the unprimed than the primed ewes. None of the ewes infused with saline produced a preovulatory LH surge. The GnRH infusion induced ovulation in 10/10 unprimed and 7/9 progestagen-primed ewes, with no significant difference in ovulation rate (1.78 +/- 0.15 and 1.33 +/- 0.21, respectively). Ovulation was followed by normal luteal function in 4/10 Group-G ewes, while the remaining 6 ewes had short luteal phases. In contrast, each of the 7 Group-P + G ewes that ovulated secreted progesterone for at least 10 d, although elevated plasma progesterone levels were maintained in 3/7 unmated ewes for >35 d. Throughout the study only 2 ewes (both from Group P + G) displayed estrus. These data demonstrate that although a low dose, continuous infusion of GnRH can increase tonic LH concentrations sufficient to promote a preovulatory LH surge and induce ovulation, behavioral estrus and normal luteal function do not consistently follow ovulation in the progestagen-primed, postpartum ewe.     

Behavioral and endocrine responses of hair sheep ewes exposed to different mating stimuli around estrus

Hair sheep ewes were used to evaluate the influence of various levels of mating stimuli on the duration and timing of estrus and LH concentrations around estrus. Ewes were treated with PGF2alpha (15 mg, im) 10 d apart. At the time of the second PGF2alpha treatment (Day 0) ewes were placed in groups and exposed to different types of mating stimuli. One group of ewes (n = 16) was exposed to an epididymectomized ram (RAM), a second group of ewes (n = 16) was exposed to an epididymectomized ram wearing an apron to prevent intromission (APRON) and a third group of ewes (n = 17) was exposed to an androgenized ovariectomized ewe (T-EWE). Jugular blood samples were collected from ewes at 6-h intervals through Day 5. Plasma was harvested and LH concentration was determined by RIA. The ewes were observed at 6-h intervals to detect estrus. A ewe was considered to be out of estrus when she no longer stood to be mounted by the teaser animal. There was no difference (P > 0.10) in the proportion of ewes expressing estrus (79.6%) or having an LH surge (85.7%) among the treatments. Neither the time to estrus nor the duration of estrus were different (P > 0.10) among APRON, RAM or T-EWE groups (41.6+/-3.8 vs 43.6+/-3.6 vs 46.1+/-3.6 h, respectively, and 26.5+/-2.2 vs 24.8+/-2.3 vs 30.5+/-2.2 h, respectively). The time to LH surge was similar (P > 0.10) among APRON, RAM and T-EWE groups (51.2+/-4.5 vs 51.2+/-4.7 vs 52.7+/-4.5 h, respectively). The magnitude of the LH surge was similar (P > 0.10) in the T-EWE, APRON and RAM ewes (99.7+/-4.9 vs 87.2+/-4.9 vs 85.8+/-5.0 ng/mL, respectively). The time from estrus to the LH surge was not different (P > 0.10) among APRON, RAM or T-EWE ewes (10.1+/-2.2 vs 9.8+/-2.3 vs 11.6+/-2.3 h, respectively). These results show that the expression and duration of estrus are not influenced by different types of mating stimuli in hair sheep ewes. In addition, the timing and the magnitude of LH release does not appear to be influenced by mating stimuli around the time of estrus.     

Use of progestagen-gonadotrophin treatments in estrus synchronization of sheep

The main objective of this study was to investigate the effectiveness of certain progestagen-gonadotrophin treatments on synchronization of estrus in sheep. In Experiment I, 30 Chios ewes were treated at the beginning of the breeding season with medroxyprogesterone acetate (MAP) intravaginal sponges for 12 days and a single i.m. treatment of either FSH (Group 1,10 IU, n = 8; Group 2, 5 IU, n = 8; Group 3, 2.5 IU, n = 8) or eCG (Group 4, 400 IU, n = 6) at the time of sponge removal. Ten days after sponge removal laparotomy was performed to record ovarian response. Clinical estrus was observed in more (though not at a significant level) FSH treated than eCG treated sheep (62.5% versus 33.3%). Administration of 400 IU eCG resulted in the highest mean number of CL perewe ovulating (2.8 +/- 0.2), with administration of 10 IU FSH producing the next best results (2.1 +/- 0.3). Statistically significant differences in the mean number of CL per ewe ovulating were found only between ewes in Group 3 (1.7 +/- 0.4) and Group 4 (2.8 +/- 0.2) (P < 0.05). In Experiment II, 53 Chios and 30 Berrichon ewes were treated during the mid-breeding season with MAP intravaginal sponges for 12 days and a single i.m. treatment of either 10 IU FSH (27 Chios and 16 Berrichon ewes) or 400 IU eCG (26 Chios and 14 Berrichon ewes), at the time of sponge removal. Ewes that were in estrus on Days 2-4 and 19-23 after sponge removal were mated to fertile rams. No significant differences were recorded between treatment or breed groups in the proportions of ewes observed in estrus after treatment. In the Berrichon breed, FSH administration resulted in higher lambing rates (93.8% versus 57.1%, P < 0.05) and higher mean number of lambs born per ewe exposed to rams (1.4 +/- 0.2 versus 0.8 +/- 0.2, P < 0.05) than that of eCG. After treatment with eCG, the mean number of lambs born per ewe exposed to rams was higher in the Chios than the Berrichon breed (1.4 +/- 0.2 versus 0.8 +/- 0.2, P < 0.05). After treatment with FSH, the lambing rate was higher in the Berrichon than the Chios breed (93.8% versus 63.0%, P < 0.05). In conclusion, a single FSH treatment (5 or 10 IU) at the end of progestagen treatment appears to be more effective than eCG for the induction of synchronized estrus in sheep at the beginning of the breeding season, with no cases of abnormal ovarian response observed. During the mid-breeding season FSH (10 IU) appears to be equally as effective as eCG (400 IU) in respect of lambing rate and mean number of lambs born per ewe.     

Ovarian function in ewes during the transition from breeding season to anoestrus

Transrectal ovarian ultrasonography was conducted in six Western white-faced ewes for 35 days from the last oestrus of the breeding season, to record the number and size of all ovarian follicles > or = 3 mm in diameter and luteal structures. Blood samples were collected once a day for estimation of serum concentrations of follicle-stimulating hormone (FSH), oestradiol and progesterone. Each ewe had five follicular waves (follicles growing from 3 to > or = 5 mm in diameter) over the scanning period. The duration of the growth phase of the largest ovarian follicles did not differ (P > 0.05) between waves, but follicular static and regressing phases decreased significantly (P < 0.05) after the decline in serum progesterone concentrations at the end of the last luteal phase of the breeding season. The intervals between the five follicular waves were: 9.2+/-0.4, 5.2+/-0.7, 8.3+/-0.8 and 5.8+/-0.7 days; the two shorter intervals differed (P < 0.05) from the two longer intervals. Using the cycle-detection program, rhythmic increases in serum FSH concentrations were detected in all ewes; the amplitude, duration and periodicity of FSH fluctuations did not vary (P > 0.05) throughout the period of study. The number of identified FSH peaks (7.8+/-0.5 peaks per ewe, per scanning period) was greater (P < 0.05) than the number of emerging follicular waves. Serum concentrations of oestradiol remained low (< or = 1 pg/ml) on most days, in five out of the six ewes studied, and sporadic elevations in oestradiol secretion above the non-detectable level were not associated with the emergence of follicular waves. The ovulation rate was lower than that seen during the middle portion of the breeding season (November-December) in white-faced ewes but the transitional ewes had larger corpora lutea (CL). Maximal serum concentrations of progesterone appeared to be lower and the plateau phase of progesterone secretion appeared to be shorter during the last luteal phase of the ovulatory season in comparison to the mid-breeding season of Western white-faced ewes. During the transition into anoestrus in ewes, the endogenous rhythm of FSH release is remarkably robust but the pattern of emergence of sequential follicular waves is dissociated from FSH and oestradiol secretion. Luteal progesterone secretion is suppressed because of fewer ovulations and diminished total luteal volume, but it may also result from diminished gonadotropic support. These season-related alterations in the normal pattern of ovine ovarian cycles appear to be due to reduction in ovarian responsiveness to gonadotropins and/or attenuation in secretion of luteinizing hormone (LH) occurring at the onset of the anovulatory season in ewes.     

The relationship between ram breeding capacity and flock fertility

The effect of breeding capacity of rams on flock fertility was studied by exposing each of 15 rams to 1 of 15 flocks of 200 naturally-cycling ewes for 17 days. Five of the rams were arbitrarily designated as being of high breeding capacity (mean+/-SEM = 14.7+/-0.5 services in 2 3-hour pen breeding tests); five rams were designated as being of medium capacity (7.3 +/- 0.2); and the remaining five were designated as being of low breeding capacity (1.7 +/- 0.5). Breeding capacity was shown to be positively correlated with the number of services during flock mating, to the number of ewes mated and to insemination success. Breeding capacity as measured in a pen test of shorter duration (1 hour) was shown to be similarly related to flock fertility. Further, the number of services during flock mating was also positively correlated with the number of ewes mated and impregnated, as well as to the number of fetuses conceived and to insemination success. Breeding frequency of the ram is, therefore, closely related to flock fertility, but breeding capacity, as measured in the present study, is only a moderately accurate indicator of breeding frequency.     

Effects of melatonin and undernutrition on the viability of ovine embryos during anestrus and the breeding season

This study examined the effects of melatonin and level of nutrition on embryo yield during anestrous and breeding season. Adult Rasa Aragonesa ewes were assigned randomly to one of the four treatment groups in two experiments using a 2x2x2 factorial design. Individuals were treated (+MEL) or not treated (-MEL) with a subcutaneous implant of melatonin for 42d (Melovine, CEVA) and fed 1.5 (control, C) or 0.5 (low, L) times the daily maintenance requirements for 20d. Ewes were mated at oestrus (Day=0) and embryos were recovered on Day 5. Level of nutrition and melatonin supplements did not have a significant effect on ovulation rate or the number of recovered ova per ewe in the Reproductive Season (RS) and the Anestrous Season (AS). During the RS, undernutrition reduced the number of viable embryos per ewe (C: 1.1+/-0.2; L: 0.6+/-0.2; P<0.05); however, the number of viable embryos per ewe in the L+MEL group (0.2+/-0.15) was significantly lower than it was in the L, C+MEL and C groups (0.9+/-0.3, 1.2+/-0.3, 1.0+/-0.4, respectively; P<0.05). In the AS, nutrition did not have a significant effect on the number of viable embryos per ewe, although melatonin supplements might have improved rates slightly. Embryo viability rate (% viable embryos/embryos recovered) was unaffected by melatonin supplements or level of nutrition in the RS and the AS. Season had a strong effect on the number of viable embryos per functional corpus luteum among ewes in the L+MEL group, only (RS: 0.2+/-0.1; AS: 0.6+/-0.2; P<0.05). In conclusion, undernutrition impaired the viability of sheep embryos in the RS, particularly among ewes that were given melatonin supplements subcutaneously, but melatonin appeared to improve embryo quality in the AS, which suggests that the mechanisms involved in the interactive effects of melatonin and nutrition on embryo development are influenced by season.     

The effect of the infusion of insulin during the luteal phase of the estrous cycle on the ovulation rate and on plasma concentrations of LH, FSH and glucose in ewes

The role of insulin in mediating pituitary responses to nutrition was investigated in 30 mature Border Leicester X Merino ewes. The ewes were infused with saline (n = 15) or bovine insulin at 0.4 IU/kg/d (n = 15) for 72 h during the luteal phase of the estrous cycle The ewes were housed in individual pens and were fed, ad libitum, a diet of low quality straw. Their estrous cycles were synchronized with prostaglandin (PG), with infusions given over Days 9 to 11 of the estrous cycle. A further injection of PG was given at the end of the infusion, and the subsequent ovulation rate was determined by endoscopy 12 d later. Blood samples were collected every 4 h from Day 8 until 52 h after the final PG injection for the determination of plasma FSH, insulin and glucose concentrations. On Day 11 blood samples were also taken every 20 min for 24 h for the determination of LH pulse characteristics. During the infusion of insulin, its concentration rose 4-fold and remained elevated until the end of infusion, when it fell to pretreatment concentrations. Glucose concentrations were significantly reduced during the insulin infusion and rose to pretreatment concentrations after infusion. In control ewes glucose and insulin concentrations did not change. Ovulation rate of treated ewes was not affected by the insulin (1.9 +/- 0.07) compared with that of control ewes (2.0 +/- 0.10). Neither were FSH concentrations affected by treatment with insulin, although a significant interaction of treatment with time was observed in the 36 h after infusion. The pre-ovulatory decline in FSH concentrations was delayed by about 8 h in the insulin treated ewes. The mean (+/- SEM) LH pulse frequency (4.3 +/- 0.4 vs 1.8 +/- 0.3 pulses per 24 h) and the mean (+/- SEM) concentration of LH (0.48 +/- 0.04 vs 0.32 +/- 0.03 ng/ml) were both significantly reduced by insulin. These results indicate that insulin-induced hypoglycaemia inhibits LH secretion in cyclic ewes and implicates insulin as a mediator of normal hypothalamo-pituitary function.     

The introduction of rams induces an increase in pulsatile LH secretion in cyclic ewes during the breeding season

Application of the ram effect during the breeding season has been previously disregarded because the ewe reproductive axis is powerfully inhibited by luteal phase progesterone concentrations. However, anovulatory ewes treated with exogenous progestagens respond to ram introduction with an increase in LH concentrations. We therefore tested whether cyclic ewes would respond to ram introduction with an increase in pulsatile LH secretion at all stages of the estrous cycle. We did two experiments using genotypes native to temperate or Mediterranean regions. In Experiment 1 (UK), 12 randomly cycling, North of England Mule ewes were introduced to rams midway through a frequent blood-sampling regime. Ewes in the early (EL; n=3) [corrected] and late luteal (LL; n=6) phase responded to ram introduction with an increase in LH pulse frequency and mean and basal concentration [corrected] of LH (at least P<0.05). In Experiment 2 (Australia), the cycles of 32 Merino ewes were synchronised using intravaginal progestagen pessaries. Pessary insertion was staggered to produce eight ewes at each stage of the estrous cycle: follicular (F), early luteal (EL), mid-luteal (ML) and late luteal (LL). In all stages of the cycle, ewes responded to ram introduction with an increase in LH pulse frequency (P<0.01); EL, ML and LL ewes also had an increase in mean LH concentration (P<0.05). In conclusion, ram introduction to cyclic ewes stimulated an increase in pulsatile LH secretion, independent of ewe genotype or stage of the estrous cycle.     

Effect of insulin on feed intake and reproductive performance of well-nourished nulliparous ewes

Eighty-four nulliparous ewes were used to examine the effect of short-term insulin treatment on feed intake and reproductive performance. Following estrus synchronization, ewes were observed for estrus (= Day 0) and were penned individually beginning on Day 7. Ewes were fed twice daily and feed intake was recorded. On Days 9 through 13, ewes were treated s.c. with 1 IU/kg BW insulin (n = 44) or an equivalent volume of saline (n = 40). On Day 14, ewes were placed with fertile rams and number of ewes in estrus (bred) was recorded. Thirty days post-breeding, ewes were checked for pregnancy via ultrasonography. Feed intake and percentage of ewes in estrus did not differ between saline- and insulin-treated ewes. Similarly, neither pregnancy rate (69 +/- 8.7% vs. 80 +/- 8.1%, respectively) nor lambing rate (61 +/- 8.9% vs. 78 +/- 8.4%, respectively) differed between treatments. The number of lambs born per ewe was, however influenced by a breed-group effect (P < 0.0002). Romanov ewes had more (P < 0.001) lambs than the other breed groups in the study. Therefore, treating well-nourished, nulliparous ewe lambs with insulin did not increase reproductive efficiency, possibly because the ewes were already at a maximal nutritional and/or reproductive state.     

Melatonin-improved reproductive performance in sheep bred out of season

The effects of melatonin implants on out-of-season breeding in New Zealand Romney composite ewes, was determined by comparison of reproductive performance in ewes treated with progesterone+equine chorionic gonadotrophin (eCG) (control; n=107), melatonin+progesterone+eCG (n=97) or melatonin+progesterone (n=96). Conception rates in melatonin+progesterone+eCG-treated ewes (67%) were higher than in the control ewes (P<0.01; 47%). Pregnancy rates were higher in melatonin+progesterone+eCG-treated ewes (55%; P<0.001) compared with the control ewes (40%). Fewer melatonin+progesterone-treated ewes displayed oestrus (14%; P<0.001) and subsequently became pregnant (6%). Oestrus rates in melatonin+progesterone-treated ewes (14%) were lower than both the melatonin+progesterone+eCG-treated (82%) and control ewes (86%; P<0.001), which were similar to each other. The number of foetuses per pregnant ewe was similar in all three treatment groups. Serum melatonin concentrations at Day -9 were higher in the ewes treated with melatonin and there was a large variation between individual ewes, but concentrations were similar for pregnant and nonpregnant ewes. The combination of higher conception rate and the trend for more lambs per pregnant ewes resulted in more lambs being born per ewe treated in melatonin+progesterone+eCG-treated ewes compared to the other two treatment groups. These results suggest that melatonin implants, in conjunction with administration of progesterone and eCG, may be suitable as a means of increasing the number of lambs born per ewe treated in an out-of-season breeding program in New Zealand sheep flocks while melatonin and progesterone is not.     

Short-term treatment with a controlled internal drug releasing (CIDR) device and FSH to induce fertile estrus and increase prolificacy in anestrous ewes

The objectives were to evaluate, in anestrous ewes, the effectiveness of a CIDR-G device (0.3 g progesterone) administered for 5 d to induce estrus; and FSH (Folltropin; 55 mg NIH-FSH-P1 equivalent) in saline:propylene glycol (1:4) 24 h before insert removal (Day 0), to increase ovulation rate and prolificacy. Ewes of mixed breeding were assigned at random to 3 treatments: control (C; n = 125), 5 d progesterone (P5; n = 257) and 5 d progesterone plus FSH (P5F; n = 271). Intact rams were joined at insert removal and ewes were observed every 24 h for 3 d. On Day 14, the ovulation rates of all ewes detected in estrus in the treated groups were determined using transrectal ultrasonography. Rams were removed on Day 26 to 31. Ewes were examined for pregnancy then, and again 20 to 25 d later to detect ewes that conceived to the second service period. Percentage of ewes marked by rams was higher in progesterone-treated (77%) than in C (20%; P < 0.01), but did not differ between P5 and P5F. The ovulation rate (1.95+/-0.04) did not differ due to FSH. Conception (68%) and pregnancy (52%) rates were higher in progesterone-treated (P < 0.01) than in C (0%) ewes. Estrous response varied quadratically with time after ram introduction, and the conception rate varied quadratically with the time of observation of onset of estrus. Over two service periods more progesterone-treated than C ewes lambed (65 vs 45%; P < 0.01). Lambs born per ewe exposed (0.7+/-0.1, 1.0+/-0.1, and 1.1+/-0.1 for C, P5 and P5F, respectively) was increased by progesterone (P < 0.05). Litter size to the first service period (1.59+/-0.04) and overall (1.54+/-0.03) did not differ among treatment groups. FSH-treated ewes tended to have more lambs (1.67+/-0.1) than did ewes receiving progesterone alone (1.5+/-0.1; P = 0.06) and than did ewes lambing to the second service period (1.5+/-0.1; P = 0.06). In summary, a 5-d progesterone pre-treatment of anestrous ewes induced estrous cycles and increased the pregnancy rates. A single injection of FSH only tended to increase litter size.     

Changes in gonadotrophin secretion and ovarian antral follicular activity in seasonally breeding sheep throughout the year

Overall, significantly more antral follicles greater than or equal to 1 mm diameter were present in Romney ewes during anoestrus than in the breeding season (anoestrus, 35 +/- 3 (mean +/- s.e.m.) follicles per ewe, 23 sheep; Day 9-10 of oestrous cycle, 24 +/- 1 follicles per ewe, 22 sheep; P less than 0.01), although the mean numbers of preovulatory-sized follicles (greater than or equal to 5 mm diam.) were similar (anoestrus, 1.3 +/- 0.2 per ewe; oestrous cycle, 1.0 +/- 0.1 per ewe). The ability of ovarian follicles to synthesize oestradiol did not differ between anoestrus and the breeding season as assessed from the levels of extant aromatase enzyme activity in granulosa cells and steroid concentrations in follicular fluid. Although the mean plasma concentration of LH did not differ between anoestrus and the luteal phase of the breeding season, the pattern of LH secretion differed markedly; on Day 9-10 of the oestrous cycle there were significantly more (P less than 0.001) high-amplitude LH peaks (i.e. greater than or equal to 1 ng/ml) in plasma and significantly fewer (P less than 0.001) low amplitude peaks (less than 1 ng/ml) than in anoestrous ewes. Moreover, the mean concentrations of FSH and prolactin were significantly lower during the luteal phase of the cycle than during anoestrus (FSH, P less than 0.05, prolactin, P less than 0.001). It is concluded that, in Romney ewes, the levels of antral follicular activity change throughout the year in synchrony with the circannual patterns of prolactin and day-length. Also, these data support the notion that anovulation during seasonal anoestrus is due to a reduced frequency of high-amplitude LH discharges from the pituitary gland.     

Synchronization of follicular wave emergence in the seasonally anestrous ewe: the effects of estradiol with or without medroxyprogesterone acetate

Fertility is often lower in anestrous compared to cyclic ewes, after conventional estrus synchronization. We hypothesized that synchronization of ovarian follicular waves and ovulation could improve fertility at controlled breeding in anestrous ewes. Estradiol-17beta synchronizes follicular waves in cattle. The objectives of the present experiments were to study the effect of an estradiol injection, with or without a 12-d medroxyprogesterone acetate (MAP) sponge treatment, on synchronization of follicular waves and ovulation in anestrous ewes. Twenty ewes received sesame oil (n=8) or estradiol-17beta (350 microg; n=12). Eleven ewes received MAP sponges for 12d and were treated with oil (n=5) or estradiol-17beta (n=6) 6d before sponge removal. Saline (n=6) or eCG (n=6) was subsequently given to separate groups of ewes at sponge removal in the MAP/estradiol-17beta protocol. Estradiol treatment alone produced a peak in serum FSH concentrations (4.73+/-0.53 vs. 2.36+/-0.39 ng/mL for treatment vs. control; mean+/-S.E.M.) after a short-lived (6 h) suppression. Six of twelve ewes given estradiol missed a follicular wave around the time of estradiol injection. Medroxyprogesterone acetate-treated ewes given estradiol had more prolonged suppression of serum FSH concentrations (6-18 h) and a delay in the induced FSH peak (32.3+/-3.3 vs. 17.5+/-0.5 h). Wave emergence was delayed (5.7+/-0.3 vs. 1.4+/-0.7d from the time of estradiol injection), synchronized, and occurred at a predictable time (5-7 vs. 0-4d) compared to ewes given MAP alone. All ewes given eCG ovulated 3-4d after injection; this predictable time of ovulation may be efficacious for AI and embryo transfer.     

The effect of subluteal levels of exogenous progesterone on follicular dynamics and endocrine patterns during early luteal phase of the ewe

Nineteen Corriedale ewes were treated with an im dose of a PGF2alpha during the luteal phase to synchronize estrus. After ovulation had been detected by using ultrasonography (Day 0); the ewes were randomly assigned to 2 different groups. In 11 ewes a CIDR, which had previously been used for 10 d, was inserted on the fourth day after ovulation. The ewes then received a dose of PGF2alpha on Day 5 to induce luteolysis. The CIDR remained in place until the end of the experiment (Day 9). Control ewes (n = 8) received no treatment. Blood samples were taken daily for estradiol, progesterone and FSH determinations. In the untreated ewes, 2 follicular waves were detected in all of the animals throughout the monitoring period, with a mean wave interval of 4.5 d. The total number of follicles which were > or =2 mm decreased from Day 0 to Day 4 (8.8+/-1.0 to 5.3+/-0.6; P< or =0.05) and then increased at Day 7 (7.5+/-0.9; P< or =0.05). The growth profiles of both the largest and the second largest follicles of Wave 1 showed significant divergence, while no divergence was observed in Wave 2. Serum estradiol concentrations decreased significantly from the day before to the day of ovulation and then increased again during the growing phase of the largest follicle of Wave 1. Concentrations of FSH were high on the day of emergence of both waves, but while a significant decline was observed after emergence in Wave 1, the levels remained high in Wave 2. In 8 of the 11 treated ewes, the largest follicle of Wave 1 was still present on the ninth day after ovulation (persistent follicle). In the other 3 ewes, the largest follicle of Wave 1 was already regressing on the day that the treatment was administered, and the largest follicle that was present on Day 9 originated from Wave 2 (nonpersistent follicle). In persistent follicle ewes, the largest follicle of Wave 1 prolonged its lifespan significantly, attaining the maximum diameter (Day 8.1+/-0.8) later than in untreated (Day 3.0+/-0.4) and nonpersisted follicle ewes (Day 2.0+/-0.6). The total number of follicles decreased in persistent follicle ewes between Day 0 and Day 4 (7.9+/-1.5 to 4.5+/-0.5, respectively; P< or =0.05) and remained low until the end of the experiment. Progesterone concentrations (nmol/L) between Days 6 and 9 were significantly different between untreated and persistent follicle ewes (12.8+/-1.0 vs. 9.4+/-1.0, P< or =0.02). The present study confirms that the largest follicle of Wave 1 is dominant in the ewe and that subluteal progesterone concentrations can prolong its lifespan and extend this dominance.     

Ultrasonographic study of the effects of the corpus luteum on antral follicular development in unilaterally ovulating western white-faced ewes

The objective of this study was to examine the local effects of the corpus luteum (CL) on ovarian antral follicle development by looking at follicle populations and dynamics in ovaries with or without CL, in unilaterally ovulating ewes, using a retrospective analysis of daily ultrasonographic records. The present report summarises the data from the first luteal phase of the breeding season (August-October; n = 4), a luteal phase in the mid-breeding season (November-December; n = 5), the last luteal phase of the breeding season (January-March; n = 5), and the luteal phase after GnRH-induced ovulations in mid-anoestrus (May-June; n = 4) of western white-faced ewes. Mean daily numbers of 3mm follicles that did not grow any larger were significantly reduced in the CL-containing ovaries of ewes at all periods of study except for the transition to anoestrus. With all scanning periods combined, daily numbers of 3mm follicles not growing further increased (P<0.05) between day 6 and 15 after ovulation in the CL-containing ovaries. Based on mean data for the whole periods of observation, the non-CL-bearing ovaries of ewes in the transition to anoestrus had fewer (P<0.05) follicles growing from 3 to > or =5mm in size before regression compared with the mid-breeding season and mid-anoestrus. The lifespan of follicles reaching > or =5mm in diameter was shorter (P < 0.05) in the CL- compared with non-CL-containing ovaries of anoestrous ewes induced to ovulate with GnRH ((6.5+/- 1.3) and (9.0+/- 1.0) days, respectively). Circulating concentrations of progesterone were lower during both transitional periods (into and out of anoestrus) and mid-anoestrus than during the mid-breeding season (P < 0.001), and were less during anoestrus than during both transitional periods (P < 0.05). It was concluded that CL/luteal structures locally suppressed the growth of ovarian antral follicles to the 3mm size-range except during the transition to anoestrus, but that there was no inhibitory effect of the CL on the growth of ovarian follicles to larger diameters. The presence of CL/luteal structures did not affect the length of the lifespan of follicles reaching > or =5mm in diameter nor the number of ovulations per ovary in cyclic ewes, but shortened large follicle lifespan in anoestrous ewes. Variations in peripheral concentrations of progesterone across the breeding season and between the breeding season and anoestrus did not alter the lifespan of large antral follicles. In the transition to anoestrus and during mid-anoestrus, the presence of the CL in an ovary appeared to maintain follicle development to ovulatory sizes and to increase the rate of turnover of large antral follicles, respectively.     

Receptors for prostaglandins F2 alpha and E2 in ovine corpora lutea during maternal recognition of pregnancy.

Plasma membrane receptors for prostaglandins (PG) F2 alpha and E2 were quantified in ovine corpora lutea obtained from nonpregnant and pregnant ewes on Days 10, 13, and 15 post-estrus, and from additional ewes on Days 25 and 40 of pregnancy. Regardless of reproductive status or day post-estrus, concentrations of luteal receptors for PGF2 alpha were 7- to 10-fold greater than those for PGE2. In pregnant ewes the concentration of receptors for PGF2 alpha was highest on Day 10 (35.4 +/- 2.8 fmol/mg) and lowest on Day 25 (22.3 +/- 2.5 fmol/mg). A difference in the concentration of luteal receptors for PGF2 alpha between pregnant and nonpregnant ewes was apparent only on Day 15 post-estrus, at which time the concentration of receptors for PGF2 alpha was higher in pregnant ewes than in nonpregnant ewes (27.1 +/- 2.7 vs. 17.7 +/- 2.7 fmol/mg). Concentrations of receptors for PGE2 in pregnant ewes were similar (p > 0.05; 2.8 +/- 0.3 to 3.7 +/- 0.2 fmol/mg) between Days 13 and 40 but were higher (p < 0.05) than in corpora lutea obtained from nonpregnant ewes on Days 10 (5.0 +/- 0.4 vs. 4.1 +/- 0.2 fmol/mg) and 15 (3.7 +/- 0.2 vs. 2.0 +/- 0.4 fmol/mg) post-estrus. Although concentrations of receptors for both PGF2 alpha and PGE2 were lowest in corpora lutea obtained from nonpregnant ewes on Day 15, this was not due to luteal regression since the weights and concentrations of progesterone in corpora lutea on Day 15 were not lower than those for corpora lutea obtained on Days 10 and 13.(ABSTRACT TRUNCATED AT 250 WORDS)