Alternatives to improve a prostaglandin-based protocol for timed artificial insemination in sheep

The objective was to improve the reproductive performance of a prostaglandin (PG) F_2α-based protocol for timed artificial insemination (TAI) in sheep (Synchrovine®: two doses of 160 μg of delprostenate 7 d apart, with TAI 42 h after second dose). Three experiments were performed: Experiment 1) two doses of a PGF_2α analogue (delprostenate 80 or 160 μg) given 7 d apart; Experiment 2) two PGF_2α treatment intervals (7 or 8 d apart) and two times of TAI (42 or 48 h); and Experiment 3) insemination 12 h after estrus detection or TAI with concurrent GnRH. Experiments involved 1131 ewes that received cervical insemination with fresh semen during the breeding season (32/34 °S–58 °W). Estrous behaviour, conception rate, prolificacy, and fecundity (ultrasonography 30–40 d), were assessed. In Experiment 1, ewes showing estrus between 25 and 48 h or at 72 h after the second PGF_2α did not differ between 80 and 160 μg of delprostenate (73 vs 86%, P = 0.07; and 92 vs 95%, P = NS, respectively). Conception rate and fecundity were lower (P < 0.05) using 80 vs 160 μg (0.24 vs 0.42, and 0.27 vs 0.47, respectively). In Experiment 2, giving PGF_2α 7 d apart resulted in higher (P < 0.05) rates of conception (0.45 and 0.51) and fecundity (0.49 and 0.53) than treatments 8 d apart (conception: 0.33 and 0.29; fecundity: 0.33 and 0.34) for TAI at 42 and 48 h, respectively. In Experiment 3, rates of conception, prolificacy and fecundity were similar (NS) between Synchrovine® with TAI at 42 h (0.50, 1.13, and 0.56) and AI 12 h after estrus detection (0.47, 1.18, and 0.55), and Synchrovine® plus GnRH at TAI (0.38, 1.28, and 0.49). However, all TAI treatments had lower (P < 0.05) prolificacy and fecundity compared to AI following detection of spontaneous estrus (1.39 and 0.83, respectively). In conclusion, the Synchrovine® protocol was: a) more successful using 160 vs 80 μg delprostenate; b) more successful with a 7 d than 8 d PGF_2α interval; c) similarly effective for TAI versus AI 12 h after estrus detection; and d) not improved by giving GnRH at TAI.     

Cervical dilation, conception rate, and concentrations of progesterone and estradiol-17B in postpartum ewes treated with porcine relaxin

Experiments were conducted to determine the effects of porcine relaxin (pRLX) on cervical dilation and conception rates in postpartum ewes. In Experiment 1, ewes received medroxyprogesterone acetate (MAP) sponge on day 16 (day 0 = lambing) and 750 IU pregnant mare serum gonadotropin (PMSG) at sponge removal on day 30. Control ewes received saline and relaxin-treated (RLX) ewes received 0.5 mg pRLX (>/= 3000 U/mg) i.m. at 24 h and 1.0 mg pRLX at 36 h after PMSG. All ewes were inseminated (Al) at 55 h after PMSG with 0.4 ml fresh semen. The proportion of RLX treated ewes (6 6 ) in which the cervix was penetrated was greater (P < 0.05) than in Control ewes (0 5 ). However, ova recovery rate was lower (P < 0.05) for RLX ewes (1 6 ) than for control ewes (5 5 ). In Experiment 2, ewes between Days 90 to 120 post partum received MAP sponges for a period of 8 d and 750 IU PMSG at sponge removal. Control ewes (n = 9) received saline; RLX-1 ewes (n = 8) received 0.5 mg pRLX at 24 h and an additional 0.5 mg pRLX at 36 h after PMSG; and RLX-1.5 ewes (n = 9) received 0.5 mg pRLX at 24 h and an additional 1.0 mg pRLX at 36 h after PMSG. Ewes were mated to rams at estrus, and cervical dilation was checked at 55 h after PMSG. The cervix could not be penetrated in any of the ewes. Conception rates on Day 26 were 66, 56 and 63% for control, RLX-1 and RLX-1.5 groups, respectively. These results demonstrate that the effect of relaxin on cervical dilation and conception rate is dependent upon the postpartum stage of the ewes.     

Ovarian follicular development and oocyte quality in anestrous ewes treated with melatonin, a controlled internal drug release (CIDR) device and follicle stimulating hormone

The objective of the current study was to determine the effects of hormonal treatments on ovarian follicular development and oocyte quality in anestrous ewes. Multiparous crossbred (RambouilletxTarghee) ewes were given melatonin implants (MEL) and/or controlled internal drug release (CIDR) devices in conjunction with follicle stimulating hormone (FSH) during anestrus (March-May). In Experiment 1, ewes (n=25) were assigned randomly to four groups (n=4-7/group) in a 2x2 factorial arrangement [+/-MEL and +/-CIDR], resulting in Control (no treatment), CIDR, MEL, and MEL/CIDR groups, respectively. Ewes received an implant containing 18 mg of melatonin (Melovine) on Day 42 and/or a CIDR from Days 7 to 2 (Day 0: oocyte collection). In Experiment 2, ewes (n=12) were assigned randomly to two groups (n=6/group; 1CIDR or 2CIDR) and received the same type of melatonin implant on Day 60. All ewes received a CIDR device from Days -22 to -17 and 2CIDR ewes received an additional CIDR device from Days -10 to -2. In both experiments, ewes were given FSH im twice daily (morning and evening) on Days -2 and -1 (Day -2: 5 units/injection; Day -1: 4 units/injection). On the morning of Day 0, ovaries were removed, follicles>or=1 mm were counted, and oocytes were collected. Thereafter oocytes were matured and fertilized in vitro. In Experiment 1, the number of visible follicles and the rates of oocyte recovery and in vitro maturation were similar (P>0.10) for Control, CIDR, MEL and MEL/CIDR (overall 29.7+/-2.9%, 89.9+/-7.1% and 95.0+/-2.0%, respectively). The rates of in vitro fertilization (IVF) were lower (P<0.01) for CIDR and MEL/CIDR than for Control and MEL groups (10.3% and 10.1% versus 20.0% and 18.5%, respectively). In Experiment 2, the number of visible follicles, and the rates of oocyte recovery and in vitro maturation were similar (P>0.10) for 1CIDR and 2CIDR groups (overall 27.3+/-3.2%, 92.1+/-2.7% and 90.2+/-1.9%, respectively). However, the rates of IVF were lower (P<0.01) for 2CIDR than 1CIDR group (30.2% versus 58.0%, respectively). In summary, when treatment with P4 commenced only 2 d before oocyte collection, rates of IVF were reduced in both experiments. Therefore, progestin treatment protocols used in ovine IVF programs should be carefully designed to minimize adverse effects on fertilization rates. In addition, melatonin treatment did not affect follicular development and oocyte quality for anestrous ewes.     

Short-term nutritional treatments grazing legumes or feeding concentrates increase prolificacy in Corriedale ewes

We tested whether short periods of increased nutrition will improve ovulation rate and prolificacy, irrespective of the method used to synchronise the cycles of the ewes. In Experiment 1, we used 138 Corriedale ewes to evaluate two factors: synchronization treatment (sponges versus a single injection of prostaglandin) and type of pasture (native versus improved with Lotus corniculatus). Ewes were mated at the end of the grazing period and prolificacy was evaluated at lambing. Grazing Lotus corniculatus for 12 days tended to increase the number of twin lambs born (P=0.09). The percentage of ewes showing oestrus during a 9-day period was similar among synchronization treatments. Animals in Experiments 2 (n=282) and 3 (n=288) were allocated to a control group or a group fed a supplement of corn grain and soybean meal for 7 days. Ewes received 2 prostaglandin injections and the supplement was fed from Days 11 to 17 after the second prostaglandin. Ovulation rate was measured in 65 (Experiment 2) and 61 (Experiment 3) ewes that were confirmed to have consumed the supplement and showed oestrus in a 4-day period. The supplement increased ovulation rate by 14% in both experiments (P<0.05). We conclude that Corriedale ewes can respond with increases in prolificacy to a 12-day period grazing Lotus corniculatus and in ovulation rate to 7 days feeding with a supplement rich in energy and protein. Moreover, in these studies, prostaglandin was as effective as sponges for synchronising oestrus, an important factor in future decisions about hormonal management of fertility.     

Administration of 6-methoxybenzoxazolinone (MBOA) does not augment ovulatory responses in St. Croix White ewes superovulated with PMSG

The objective of this investigation was to examine the effects of 6-methoxy-benzoxazolinone (MBOA), a plant compound that resembles melatonin and alters ovarian function in rodents, in combination with PMSG on superovulatory responses in the cycling ewe. In Experiment I, St. Croix White ewes (n = 44) were synchronized (intra-vaginal progestin sponge) for 14days followed by hCG (750 IU) at 1 day after sponge removal (day 0). Ewes were assigned to one of six treatments administered on day -1: Control (no PMSG or MBOA; n = 7); PMSG (1000 IU i.m.; n = 7); Low MBOA (0.43 mg/kg i.m.; n = 7); High MBOA (1.15 mg/kg i.m.; n = 7); Low MBOA + PMSG (n = 8); High MBOA + PMSG (n = 8). In Experiment II, St. Croix White ewes (n = 24) were synchronized (progestin CIDR) for 14 days followed by hCG on day 1 after CIDR removal (day 0). Ewes were assigned to one of three treatments administered on day -1: Control (n = 8); PMSG (n = 8); Low MBOA+PMSG (n = 8). Laparoscopy was performed on day 9 to assess numbers of corpora lutea (CL) and visible follicles on each ovary. Blood samples were collected on day -13, -1, 0, 1, and days 6 or 7-12 for analysis of serum progesterone (P4) by RIA. Treatment groups receiving PMSG (alone or with MBOA) exhibited greater (P < 0.05) serum concentrations of P4 post-synchrony than Control and MBOA-only groups. Ovulation rate was lower (P < 0.05) for Control and MBOA-only treated ewes than ewes receiving PMSG. Ovulation rate in ewes treated with MBOA alone was similar (P > 0.10) to Controls, and PMSG treatment alone did not differ (P > 0.10) from MBOA + PMSG treatment. Ewes treated with PMSG alone did not differ (P > 0.10) in follicle number from High MBOA + PMSG treated ewes, however, Low MBOA + PMSG treated ewes had greater numbers of follicles at day 9 (P < 0.05) than the PMSG or High MBOA + PMSG groups in Experiment I; although, this was not replicated in Experiment II with numbers of follicles in the Low MBOA + PMSG group being similar (P > 0.10) to PMSG alone. In summary, the addition of MBOA in combination with PMSG as part of a synchronization-superovuation protocol in the ewe did not increase ovulation rate.     

Effect of GnRH administration, combined with the ram effect, on the occurrence of ovulation and pregnancy during the transition period from anoestrus in crossbred ewes

The effect of a GnRH analogue (buserelin) combined with the ram effect on the reproductive efficiency of ewes was investigated in 105 cross-bred fat tailed ewes, during the transition period from anoestrus to the natural breeding season. Plasma progesterone concentration was used in the assessment with regard to ovulation and pregnancy. Ewes were maintained on natural pastures composed of medium to low quality forages, and received supplementation (40% alfalfa hay: 60% wheat straw) ad libitum, plus 100–300 g barley grain per head per day. Ewes were isolated from the rams for at least two months and then kept in close proximity of the rams for one week, before the introduction of the rams. The ewes were randomly divided into three equal groups (n = 35 per group). With the introduction of the rams into the flock (day 1) one group was considered as the control and the other two groups were treated with 4.2 μg (low dose) and 8.4 μg (high dose) buserelin on days 5 and 19, respectively. Blood samples were collected on days 5, 12, 26 and 120 after ram introduction for determining the plasma progesterone levels. On day 12 (one week after treatment) the high dose GnRH group recorded significantly lower plasma P4 concentrations (P < 0.05), compared with the control group (1.0 ± 0.1 ng/ml versus 2.4 ± 0.4 ng/ml). On the same day the low GnRH dose group recorded intermediate P4 concentrations, recording no significant differences with the other two groups. The high dose group recorded a significantly (P < 0.05) higher proportion of non-ovulated ewes (61.8%), compared to the control (32.3%) and low dose (31.4%) groups on day 12 of the study. At days 5 and 26 these differences were not significant, but the proportion of non-ovulated ewes was higher in the high dose buserelin treatment group. The percentage of pregnant (plasma P4 > 2.5 ng/ml) and non-pregnant (plasma P4 ≤ 2.5 ng/ml) ewes at day 120 of the study was not statistically different between the treatment groups. The pregnancy rate was highest in the control group (97.1%), when compared to the treated ewes (94.3% and 88.6% in low dose and high dose treatment groups, respectively). Treatment with buserelin combined with the male effect during the breeding season negatively affected the plasma P₄ concentration, reducing the reproductive performance of the ewe treatment groups.     

Minor FSH surge,minor follicular wave,and resurgence of preovulatory follicle several days before ovulation in heifers

Blood samples were collected and follicle diameters were determined daily beginning on Day 12 (Day 0 = ovulation) in 35 interovulatory intervals (IOIs) in heifers. A minor follicular wave with maximal diameter (6.0 ± 0.3 mm) on Day −4 was detected in six of seven IOIs that were scanned for follicles 4 mm or greater. The number of IOIs with a CV-identified minor FSH surge toward the end of the IOI was greater (P < 0.03) in two-wave IOIs (10/17) than in three-wave IOIs (4/18). The 17 two-wave IOIs were used for study of the temporal relationships among preovulatory follicle, FSH, LH, and estradiol. Daily growth rate of the preovulatory follicle was maximum on Days −11 to −7, minimum (P < 0.05) on Days −7 to −4, and increased (resurged, P < 0.05) on Days −4 to −3. A transient increase in FSH was maximum on mean Day −4, and the peak of a minor FSH surge occurred on Day −4.5 ± 0.2. Concentration of LH and estradiol increased between Days −5 and −4. Results demonstrated resurgence of the preovulatory follicle apparently for the first time in any species. Resurgence seemed more related temporally to the minor FSH surge than to the LH increase, but further study is needed. Results supported the novel hypotheses that a minor FSH surge near the end of the IOI is temporally associated with (1) the emergence of a minor follicular wave and (2) the resurgence in growth rate of the preovulatory follicle.     

Ultrasonographic study of ovarian function during early pregnancy and after parturition in the ewe

Transrectal ultrasonography of ovaries was performed in 11 ewes from Days 10 to 26 and on Day 30 of pregnancy to record the number, size, and position of ovarian follicles > or = 3 mm in diameter and corpora lutea (CL). Transrectal and/or transabdominal ultrasonography of the uterus was performed on Days 10 to 26, 30, 35, 40, 45 and 50 of gestation to ascertain the number and position of the conceptuses. In a second experiment, ultrasonography was conducted in 15 ewes on Days 10, 25, 30, 45 and 50 of pregnancy and from Days 13 to 29 after parturition. Ovarian data were classified into ovaries without CL (Group 1), ovaries with the CL in 1 ovary (Group 2), and ovaries with the CL in both ovaries during pregnancy (Group 3). In early pregnant ewes, the total number of follicles and the diameter of all follicles > or = 3 mm were smaller (P < 0.05) in the CL-bearing ovaries (both Group 2, n = 7 and Group 3, n = 8) than in the non-CL-bearing ovaries (Group 1, n = 7), while the largest follicle diameter was significantly smaller in Group 3 than in Group 1 or 2 ovaries. The number of 3-mm follicles in Group 2 ovaries was lower (P < 0.05) than in Group 1 or 3 ovaries, but the mean number of follicles > or = 5 mm in diameter was significantly lower in Group 3 than in Group 1. The total luteal volume per ovary was higher (P < 0.001) in Group 2 than in Group 3 ovaries of early pregnant ewes. The total follicle diameter and the number of follicles growing from 3 to > or = 5 mm in diameter was lower (P < 0.05) for Group 2 ovaries of ewes that carried twins (n = 3) compared with Group 2 ovaries from ewes with singletons (n = 4). There were no differences in follicular dynamics between Group 3 ovaries and the ovaries of Group 2 in ewes that carried twins. No follicles > 3 mm were seen in the ovaries of postpartum ewes that contained CL during gestation, until Days 21 and 25 postpartum for Groups 2 (n = 10) and 3 (n = 8), respectively, and follicles reaching > or = 5 mm in diameter were detected in only 2 ovaries (Group 2), on Days 27 and 28 postpartum, respectively. We conclude that during early pregnancy in ewes there is a suppression of antral follicle growth which appears to be exerted primarily by the developing conceptus but remains confined to CL-bearing ovaries. Residual local inhibition of follicular development extends into the postpartum period.     

Progestagen synchronisation in the absence of a corpus luteum results in the ovulation of a persistent follicle in cyclic ewe lambs

Progestagens are widely used to synchronise oestrous in sheep but the effects on follicular dynamics are not clear. We tested the hypothesis that when luteolysis occurs early during progestagen synchronisation prolonged growth of the ovulatory follicle will occur. Cyclic ewe lambs (40.0+/-0.3 kg) were divided into three groups: eight ewes (Long group) received a progestagen sponge (60 mg medroxyprogesterone acetate) from Days 5 to 19 after oestrous and eight ewes (Short group) received a progestagen sponge on Day 5 which was replaced on Day 10 and again on Day 15, and removed on Day 19 after oestrous. On Days 6 and 7, ewes in both groups received prostaglandin. A third group (n=5, Control) did not receive any treatment. The growth and development of follicles > or =2 mm in diameter were characterised using daily transrectal ultrasonography. On Day 18, blood samples were collected every 12 min for 8 h from five ewes in the Long and Short groups. Data were analysed by ANOVA. The maximum diameter and age (emergence to ovulation) of the ovulatory follicle was greater (P<0.01) in ewes in the Long group (7. 4+/-0.2 mm and 12.1+/-0.6 days) than in ewes in the Short group (6. 3+/-0.2 mm and 5.1+/-0.5 days) and Control group (6.3+/-0.4 mm and 6. 8+/-0.6 days). On Day 18 of the cycle, LH pulse frequency and oestradiol concentrations were greater (P<0.05) in ewes in the Long group (3.2+/-1.1 pulse per 8 h and 1.15+/-0.09 pg ml(-1)) than the Short group (0.8+/-0.4 pulses per 8 h and 0.54+/-0.08 pg ml(-1)).We suggest that the negative feedback efficacy of a long-term progestagen sponge decreased with time and led to an increase in LH pulse frequency and prolonged growth of the ovulatory follicle. We conclude that, in the absence of luteal progesterone, synchronisation with a single progestagen sponge for 14 days resulted in higher LH pulse frequency and ovulation of a persistent follicle with a larger maximum diameter, compared with controls.     

Two-way coupling between FSH and the dominant follicle in heifers

Follicular Wave 1 and 2 and the associated FSH Surge 1 and 2 were used to designate the first two waves and surges of the interovulatory interval in two experiments in heifers. In experiment 1, a group with early (group E, N = 9) and late (group L, N = 5) development of the dominant follicle of Wave 1 were used as natural models to study FSH/follicle coupling. The day of wave emergence and the day of deviation in diameters between the two largest follicles were not different between groups. Emergence of Wave 2 and maximal FSH concentration in Surge 2 was approximately 1 day later (P < 0.03) in group L. Diameter of the dominant follicle of wave 1 (13.8 ± 0.3 mm vs. 12.0 ± 0.3 mm) and FSH concentrations in Surge 2 (0.29 ± 0.02 ng/mL vs. 0.21 ± 0.03 ng/mL) were first greater (P < 0.05) in group E than in group L at 4 and 5 days, respectively, after wave emergence. In experiment 2, treatment with estradiol (N = 8) when the dominant follicle of Wave 1 was ≥11 mm (Hour 0) resulted in a decrease (P < 0.02) in FSH and slower (P < 0.05) growth rate of the follicle between Hours 0 and 4. Results supported the following hypotheses: (1) the FSH surge that stimulates emergence of a follicular wave is associated with final growth of the dominant follicle of the previous anovulatory wave; and (2) suppression of FSH Surge 2 when the dominant follicle of Wave 1 is ≥11 mm is associated with a decrease in diameter. It is concluded for the first time that two-way FSH/follicle coupling in heifers continues during final growth of the dominant follicle of Wave 1 and that Surge 2 is the FSH source.     

Effect of monensin and progesterone priming on ram-induced reproductive performance of boutsiko mountain breed ewes

The effects of monensin and progesterone priming on reproductive performance (estrous response, lambing rate and prolificacy) of grazing Boutsiko mountain breed adult and 18-mo.-old ewes at the end of seasonal anestrus were investigated. In Experiment 1 the feed supplement with or without monensin was offered for 21 d after introduction of vasectomized rams (Day 0). Progesterone was administered to the ewes in the respective groups as a single injection at Day -3. Ewes of both age groups were assigned randomly to 1 of 4 treatments: C, C+P, C+M and C+M+P. In Experiment 2 the supplement C or M was offered from Day -26 to Day 21. The treatments consisted of C, C+P and C+M+P. Blood samples were taken 50 h after ram introduction for determination of plasma concentrations of P and insulin-like growth factor-I (IGF-I). There was a greater increase in estrous response at Days 17 to 19 and at Days 0 to 19 when supplementation was offered before rather than after ram introduction in both age groups. In the adult group ewes synchronization of estrus at Days 17 to 19 was significantly increased by administration of monensin (P<0.05) and progesterone (P<0.01) compared with the control group in the first but not the second experiment. The incidence of estrus at Days 17 to 19 or at Days 0 to 19 was highest in the adult groups treated with monensin and progesterone in both experiments. In 18-mo.-old ewes progesterone was effective in synchronizing estrus only in Experiment 2. Mean plasma IGF-I concentrations were increased by monensin treatment (P<0.05) in adult ewes that were at the periovulatory stage at blood sampling time. Correlation coefficients between IGF-I and progesterone concentrations in monensin plus progesterone group adults were -0.715 (P<0.02) and -0.516 (P<0.01), respectively across all treatments. The results suggest that monensin and progesterone priming improved reproductive performance, and the monensin-induced increase in plasma IGF-I levels at the periovulatory stage may be causally related to the ability of ovulatory follicles to develop into functional corpora lutea (CL).     

Exercise affects both ovarian follicular dynamics and hormone concentrations in mares

The objectives were to evaluate the effects of exercise on ovarian folliculogenesis and related hormones in mares. Mares (n = 11) were randomly assigned into a control (non-exercised) or treatment (exercised) group. Treatment mares (n = 5) were moderately exercised for 30 min, 6 d/wk. All mares underwent daily transrectal ultrasonographic examinations and ovarian follicles > 6 mm were measured. Blood samples were collected during the first (Cycle 1) and last (Cycle 4) cycle, and serum concentrations of cortisol, LH, and FSH were determined. Mean cortisol concentrations were elevated (P < 0.05) in exercised mares, 6.29 ± 0.22 compared with 5.62 ± 0.16 ng/dL (mean ± SEM), 30 min post exercise. There were no significant differences between groups in mean FSH concentrations; however, exercised mares had lower (17.3 ± 6.4 vs 41.1 ± 5.5 ng/mL; P < 0.05) peak LH concentrations. Furthermore, exercised mares experienced a longer (24.7 ± 0.8 vs 22.2 ± 0.8 d; P < 0.05) mean interovulatory interval for all cycles combined, fewer (P < 0.05) follicles 6 to 20 mm in diameter, and an increased (P < 0.05) number of follicles >20 mm following deviation. The dominant and largest subordinate follicle in exercised mares had a greater (P < 0.05) mean diameter on the day of deviation, suggesting delayed deviation. Exercised mares also tended (P = 0.06) to have an increased number of cycles with at least two dominant follicles compared to control (62 vs 36%, respectively), indicating a decreased ability of the largest follicle to assert dominance. Under the conditions of this study, moderately exercising mares induced higher cortisol concentrations, lowered peak LH concentrations, and altered ovarian follicular dynamics.     

Effects of level of food intake on ovarian follicle number,size and steroidogenic capacity in the ewe

The effect of high (H) or low (L) levels of food intake, during the preceding 4 weeks, on ovarian follicle numbers and steroidogenic capacity were investigated in groups of 12 adult Scottish Blackface ewes. Ewes of the two treatments had similar levels of body condition at the time of study but there was a twofold difference in levels of food intake. Ovaries were surgically removed on day 11 or 12 of the oestrous cycle (luteal phase; n=6 per nutritional treatment) or at 30 h after injection (i.m.) of prostaglandin F_2α analogue on day 11 or 12 of the cycle (follicular phase; n=6 per nutritional treatment). Ovarian follicles >1 mm diameter were dissected out and incubated individually for 2 h at 37°C, in 1 ml of medium 199 which was then assayed to determine concentrations of oestradiol and testosterone. There were significantly more small follicles (1–2.5 mm diameter) in (H) than (L) ewes (P<0.05) but no treatment difference in the numbers of large follicles (>2.5 mm diameter) during either phase of the cycle and no difference in the mean diameters (mm) of the two largest follicles in each animal. However, although there were higher rates of synthesis of both oestrogen (P<0.05) and testosterone (P<0.01) in the large follicles of (L) ewes as compared with (H) ewes, there was a lower oestrogen/testosterone ratio in (L) than (H) follicles which may indicate a lower level of aromatase activity in (L) follicles. It is concluded that the effects of level of food intake on ovulation rate are expressed through differences in late stages of follicle development, probably through effects on the intrafollicular steroid milieux.     

Ovulation rate, embryo mortality and intrauterine growth retardation in obese swine with gene polymorphisms for leptin and melanocortin receptors

The Mediterranean Iberian pigs are obese genotypes, due to a leptin resistance syndrome related to leptin receptor gene polymorphisms. The Iberian pig is affected by a lower prolificacy when compared to lean breeds, and thus may constitute a good animal model for adverse effects of obesity in reproductive performance. The present study determined possible differences in rates of ovulation and embryo implantation and later incidence of embryo mortality and intrauterine growth retardation (IUGR) in sows of Iberian breed (n = 23) and highly-prolific lean commercial crosses (Large White × Landrace, n = 17) at two critical periods of swine pregnancy: Day 21 (just after achievement of trophoblast attachment) and Day 35 (just after completion of the transition from late embryo to early foetal stage). Two different reproductive performances were identified in the Iberian breed; 58.3% of the females had lower ovulation rates than LWxL (13.2 ± 2.3 vs 22.5 ± 1.6, P < 0.05), but 41.7% had a similar number of ovulations (18.2 ± 3.9). However, those Iberian sows having high ovulatory rates showed a high incidence of regression of corpora lutea and embryo losses between Days 21 and 35, which was not found in Iberian females with low ovulation rates; therefore, the number of viable embryos was similar in both Iberian groups (8.2 ± 1.0 and 8.4 ± 1.0) and lower that in highly-prolific LWxL (14.8 ± 1.8, P < 0.05). At Day 35, a total of 167 conceptuses (73 LWxL and 94 IB) were evaluated for IUGR. The LWxL conceptuses were longer and wider than Iberian (69.5 ± 0.1 and 64.4 ± 0.1 vs 49.9 ± 0.1 and 41.9 ± 0.1 mm, P < 0.0001). However, Iberian conceptuses were heavier than LWxL (107.4 ± 6.6 vs 68.6 ± 2.4 g) due to a lower quantity of fluids and a higher development of the placental tissues in comparison to the embryo itself. In conclusion, current study indicates a bimodal effect of obese genotypes on reproductive performances, either by lowering ovulation rate or by increased embryo losses in the first third of pregnancy.     

The reproductive performance of Thoroughbred mares treated with intravaginal progesterone at the start of the breeding season

The objective of this study was to investigate the effects of intravaginal progesterone on the reproductive performance of transitional Thoroughbred mares on commercial stud farms. Two hundred twenty-seven (227) non-lactating transitional Thoroughbred mares aged between 4 and 18 y (mean 9.4 ± 3.2 y) located on three stud farms in the Waikato region of New Zealand were used in the study performed during four consecutive breeding seasons (2007-10). Mares were age-matched in pairs and either treated with an intravaginal progesterone releasing device (Cue-Mare, 1.72 g progesterone, 10% w/w) for up to 10 d (Treated; n = 126) or left untreated (Control; n = 101). In both groups, 1,667 iu of hCG was given IV when an ovarian follicle ≥35 mm was detected (in conjunction with estrous behavior) and each mare was bred by natural service. Treated mares were served earlier in the breeding season (mean ± SD interval to first service was 13.9 ± 3.0 vs 26.7 ± 13.2 d for Treated and Control groups, respectively; P < 0.001). In the Treated and Control groups, 95.2 and 42.6% of mares were served within the first 21 d of the season (P < 0.001). Treated mares conceived earlier in the breeding season (mean number of days to conception 37.5 ± 14.2 vs 50.8 ± 21.3 d, P = 0.01). There was no difference between groups in the first service pregnancy rates (53.9 and 50.5% for Treated and Control mares, P = 0.89). Treatment with an intravaginal device increased the number of mares conceiving by the end of the breeding season (91.3 vs 82.3% for Treated and Control groups, P = 0.04). Therefore, this treatment protocol appeared to offer a convenient, economical and reliable method for managing transitional mares on commercial Thoroughbred stud farms.     

Reproductive performance of prepubertal Bos indicus heifers after progesterone-based treatments

The objective was to evaluate the effects of exogenous progesterone (P4) on reproductive performance of prepubertal Bos indicus heifers. Prepubertal Nelore heifers (n = 589; 24.0 ± 1.13 mo; 298.0 ± 1.89 kg; body condition score of 3.2 ± 0.26; mean ± SEM) were randomly assigned to receive, between experimental Days −12 and 0: no treatments (CIDR0; n = 113); a new intravaginal insert (CIDR) containing 1.9 g of P4 (CIDR1; n = 237); or a similar insert previously used three times, with each use occurring for 9 d (CIDR4; n = 239). An additional treatment group was pubertal heifers given 12.5 mg dinoprost tromethamine im on Day 0 (PGF; n = 346), and used as controls for evaluation of conception rates. On Day 0, transrectal palpation was done for uterine score evaluation (UtS; 1-3 scale), blood samples were taken for serum P4 concentrations, and follicle diameter (FD) was measured. The breeding season started on Day 1 and consisted of AI after detection of estrus between Days 1 and 45, and exposure to bulls between Days 46 and 90. There were effects of treatment (P < 0.05) on serum concentrations of P4 on Day 0 (0.37 ± 0.16, 2.31 ± 0.11, and 1.20 ± 0.11 ng/mL for CIDR0, CIDR1, and CIDR4, respectively; mean ± SEM), FD on Day 0 (9.45 ± 0.24, 9.72 ± 0.17, and 11.42 ± 0.16 mm), UtS on Day 0 (1.49 ± 0.06, 1.88 ± 0.04, and 2.24 ± 0.04), estrus detection rates at 7 d (19.5, 42.6, and 38.3%) and 45 d (52.2, 72.1, and 75.3%) of the breeding season, and on pregnancy rates at 7 d (5.3, 14.3, and 18.4%), 45 d (27.4, 39.2, and 47.7%) and 90 d (72.6, 83.5, and 83.7%) of the breeding season. Conception rate 7 d after the start of the breeding season was greater (P < 0.05) in heifers from the CIDR4 (46.8%) and PGF (43.8%) groups than in the CIDR0 (27.3%) and CIDR1 (33.7%) groups. In conclusion, exogenous P4 hastened puberty and improved pregnancy rates at the beginning of the breeding season in prepubertal Bos indicus heifers. Furthermore, previously used CIDR inserts were better than new inserts.     

Effect of progesterone concentrations,follicle diameter,timing of artificial insemination,and ovulatory stimulus on pregnancy rate to synchronized artificial insemination in postpubertal Nellore heifers

Two experiments were designed to evaluate the effects of treatments with low versus high serum progesterone (P₄) concentrations on factors associated with pregnancy success in postpubertal Nellore heifers submitted to either conventional or fixed timed artificial insemination (FTAI). Heifers were synchronized with a new controlled internal drug release device (CIDR; 1.9 g of P₄ [CIDR1]) or a CIDR previously used for 18 days (CIDR3) plus 2 mg of estradiol (E₂) benzoate on Day 0 and 12.5 mg of prostaglandin F2α on Day 7. In experiment 1 (n = 723), CIDR were removed on Day 7 or 9 and heifers were inseminated after estrus detection. In experiment 2 (n = 1083), CIDR were all removed on Day 9 and FTAI was performed either 48 hours later in heifers that received E₂ cypionate (ECP) on Day 9 (0.5 mg; E48) or 54 or 72 hours later in conjunction with administration of GnRH (100 μg; G54 or G72). Synchronization with CIDR1 resulted in greater serum P₄ concentrations and smaller follicle diameters on Days 7 and 9 in both experiments. In experiment 1, treatment with CIDR for 9 days decreased the interval from CIDR removal to estrus (Day 7, 3.76 ± 0.08 days vs. Day 9, 2.90 ± 0.07; P < 0.01) and improved conception (Day 7, 57.1% vs. Day 9, 65.8%; P = 0.05) and pregnancy rates (Day 7, 37.6% vs. Day 9, 45.3%; P = 0.04). In experiment 2, treatment with ECP improved (P < 0.01) the proportion of heifers in estrus (E48, 40.9%^a; G54, 17.1%^c; and G72, 32.0%^b), but the pregnancy rate was not affected (P = 0.64) by treatments (E48, 38.8%; G54, 35.5%; G72, 37.5%). Synchronization with CIDR3 increased follicle diameter at FTAI (CIDR1, 11.07 ± 0.10 vs. CIDR3, 11.61 ± 0.10 mm; P < 0.01), ovulation rate (CIDR1, 82.8% vs. CIDR3, 88.0%; P < 0.01) and did not affect conception (CIDR1, 42.2 vs. CIDR3, 45.1%; P = 0.38) or pregnancy rates (CIDR1, 34.7 vs. CIDR3, 39.4%; P = 0.11). In conclusion, length of treatment with P₄ affected the fertility of heifers bred based on estrus detection. When the heifers were submitted to FTAI protocol, follicle diameter at FTAI (≤10.7 mm, 23.6%; 10.8–15.7 mm, 51.5%; ≥15.8 mm, 30.0%; P < 0.01) was the main factor that affected conception and pregnancy rates.     

Maternal periconceptional undernutrition in Merinos d'Arles sheep: 1. Effects on pregnancy and reproduction results of dams and offspring growth performances

Maternal undernutrition during gestation can condition offspring adult health, with the periconceptional period pointed out as a key period. The aim of this study was to evaluate the effects of maternal periconceptional undernutrition on pregnancy and offspring growth performance in sheep.52 Merinos d'Arles ewes were fed to requirements (control group, C), whereas 64 ewes received 50% of their dietary needs from −15 to +30 days post-conception (restricted group, R). Thereafter, both groups were fed according to needs. Maternal body weight (BW), body condition score (BCS) and Non Esterified Fatty Acids (NEFA), progesterone, leptin and cortisol plasma concentrations were monitored weekly during the restriction period and the following month, then monthly until weaning. Lambs were weighed weekly until weaning at 22 kg BW, then monthly. Plasma leptin was monitored monthly in lambs.The BW, BCS, and leptin concentrations were significantly decreased, whereas NEFA and cortisol concentrations were increased in R dams. Maximum progesterone concentration was higher in R ewes that had a high (10-25%) vs. low (0-10%) BW loss during restriction (27.9 ± 2.59 vs. 20.8 ± 2.00 ng/mL, P < 0.05). Overall, gestation was significantly longer in the R group (151.0 ± 0.3 vs. 149.4 ± 0.4 days, P < 0.001). There was no difference between groups for pregnancy rates, prolificacy, birth weight and lamb mortality, but the proportion of male lambs was significantly higher in the R group, only for singletons (16/26 vs. 9/26, P < 0.05). Lamb growth was not significantly modified by treatment. Leptin concentrations at birth were significantly lower in R vs. C males (6.15 ± 0.13 ng/mL vs. 7.42 ± 0.36 ng/mL, P < 0.05), whereas in females, leptin concentrations were significantly higher in R vs. C lambs at 4 mo of age (7.31 ± 0.27 ng/mL vs. 6.41 ± 0.29 ng/mL, P < 0.05).These results indicate that maternal periconceptional undernutrition in a hardy breed does not significantly affect lamb birth weight and growth rates, in contrast to previous reports in other breeds, suggesting that caution must be taken when extrapolating programming data between breeds and breeding conditions.     

Lack of effect of transrectal ultrasonography with restraint on lambing rate and prolificacy in ewes

The objective was to determine if transrectal ultrasonography for determination of pregnancy in restrained ewes increases embryonic/fetal death or loss of pregnancy. Ten flocks (N=873 ewes) bred in either the estrous or anestrous season were randomized, into control (C) or examined (E) groups within flock. Examined ewes were placed in a tilting squeeze chute and scanned by one of three operators for pregnancy by transrectal ultrasonography once between Days 25 and 100 post-breeding. Control ewes were not subjected to handling in the squeeze chute or pregnancy diagnosis. Two operators counted embryos in E ewes in six flocks. There were no differences between E and C ewes in percent ewes lambing or lambing rate on a per flock basis. Prolificacy per flock was greater in E ewes (P=0.05; 1.53 versus 1.60, C and E, respectively) than in C ewes. Eighty-five percent of exposed ewes lambed in the estrous season, while only 62% of ewes lambed in the anestrous season (P=0.05). Overall prolificacy did not differ with season (1.60 versus 1.53), and there was no season by treatment interaction for any variable tested. Losses averaged 0.02 per E ewe exposed in the estrous season and 0.20 in the anestrous season (P<0.05). Examined ewes in this study had similar pregnancy and lambing rates to C ewes in the same flocks and prolificacy was slightly greater. Based on these data, the combination of transrectal ultrasonography with restraint is safe for pregnancy diagnosis in ewes.     

Genetic basis of variation in reproductive performance. I. Ewe lambs treated with fluorogestone acetate and PMSG in a controlled environment

This study involved records on fertility, prolificacy, multiple birth, fecundity, body weight and age at breeding of 2380 ewe lambs from 432 sires of three synthetic strains developed at the Animal Research Centre, Ottawa, Canada. Ewes were divided into two equal flocks which were bred to lamb alternately at 4-month intervals under an 8-month breeding cycle. Lambs were housed indoors, in a controlled environment, on expanded metal mesh floors in windowless barns and were bred in January, May and September at the end of a period of short days. Ewes that lambed were generally heavier and slightly older at breeding as were ewes that lambed to mating at the synchronised estrus. Though not significant, trends demonstrating seasonal differences in the heritabilities of all reproductive traits were observed. Paternal half-sib estimates showed fertility, prolificacy, multiple births and fecundity were non-heritable in ewes lambing to matings at the synchronized estrus. Heritability estimates for prolificacy and multiple birth were 0.22 and 0.13, respectively, in ewes lambing to matings at the synchronized plus follow-up estrus, suggesting that slow genetic progress can be achieved in these traits from selection. Heritability estimates ranged from 0.03 to 0.22 for body weight and from 0.28 to 0.54 for age at breeding. Ewes that lambed showed lower values than all ewes exposed. Phenotypic correlations between reproductive traits and either body weight or age at breeding were low and ranged from 0.04 to 0.09. There were higher estimates of genetic correlation of prolificacy (and multiple birth) with either body weight or age at breeding in ewes lambing to matings at the combined estruses. Indirect selection of ewe lambs based on age and body weight at breeding may be an effective alternative to direct selection for genetic improvement of prolificacy and multiple birth.