A single dose of bovine somatotropin 5 days before the end of progestin-based estrous synchronization increases prolificacy in sheep

Bovine somatotropin (bST) enhances ovarian follicular and embryonic development in sheep and cattle. In the present study, the objective was to assess whether bST given 5 days before the end of progestin-based estrous synchronization improves prolificacy and lambing rate in sheep. Pelibuey ewes (n=92) exhibiting estrous cycles at regular intervals received an intravaginal sponge containing 45mg of FGA for 12 days. Five days before sponge withdrawal, ewes were treated with either 125mg of bST sc (bST group; n=47) or saline solution (control; n=45). After the sponge was removed, ewes were observed for estrus and subsequently mated twice. Lambing rate and prolificacy was determined at birth. Blood samples were taken from the time of treatment until day 15 after estrus in eight ewes from the bST group and nine from the control group. Concentrations of IGF-I were determined by immunoradiometric assay and progesterone by RIA. Treatment with bST increased (P<0.01) the proportion of ewes with more than one lamb (bST, 56% compared with control, 26%) and prolificacy (bST, 1.6 compared with control, 1.3). Treatment with bST increased (P<0.05) the lambing rate of multiparous (bST, 92% compared with control, 67%) but not in ewes at the first time they were mated (bST, 71% compared with control, 87%; P>0.05). IGF-I concentrations were greater (P<0.01) in ewes treated with bST than in control ewes from 2 days after treatment. Progesterone concentrations did not vary (P>0.05) between groups. It is concluded that a single dose of bST 5 days before progestin withdrawal increases lambing rate and prolificacy in sheep. These effects are associated with an increase in circulating concentrations of IGF-I.     

Effect of bovine somatotropin on reproductive function in lactating dairy cows

Several recent experiments have reported that chronic treatment with bovine somatotropin (bST) increased the number of days open without affecting the services per conception. The physiological basis for these effects was examined. Eleven lactating Holstein cows received daily injections of bST (40 mg) and 10 received daily injections of vehicle. Treatment was initiated between 32 and 85 d post partum and continued for up to 180 d. Eight of 11 bST-treated cows experienced at least one period of extended ovarian acyclicity during treatment. Only 3 of 10 control cows did so (P = 0.05). Concentrations of progesterone during luteal phases were lower in bST-treated cows than in controls (P = 0.06). Baseline concentrations of LH were suppressed in bST-treated cows compared with those of controls (P < 0.04). Neither the pulse frequency of LH nor the expression of estrous behavior was affected by bST (P > 0.30). These results indicate that chronic administration of a high dose of bST can reduce reproduction performance by promoting ovarian acyclicity.     

Bovine somatotropin increases embryonic development in superovulated cows and improves post-transfer pregnancy rates when given to lactating recipient cows

Previous studies indicated that the use of bovine somatotropin (bST) in concurrence with a timed artificial insemination (TAI) protocol increased pregnancy rates. However, the mechanisms for such a bST effect on fertility were not clear. Objectives of this study were to determine the effects of bST on fertilization and early embryonic development after cows received a superovulation treatment, test whether embryos recovered from bST-treated cows were more likely to survive after transfer to recipients, and evaluate whether treatment of recipient cows with bST affects pregnancy rates. Lactating (n = 8) and nonlactating (n = 4) Holstein donor cows were superovulated, inseminated at detected estrus and assigned to a nontreated control group or to a treatment group receiving a single injection of bST (500 mg, sc) at insemination. Embryos were nonsurgically flushed 7 days after AI and frozen in ethylene glycol for direct transfer. Embryos derived from bST-treated (bST-embryos) or control (control-embryos) donors were transferred to lactating Holstein recipient cows that received either bST treatment 1 day after estrus (500 mg, sc; bST-recipients) or were untreated controls (control-recipients). Thus, there were four treatment groups: control-embryos/control-recipients (n = 43), bST-embryos/control-recipients (n = 41), control-embryos/bST-recipients (n = 37), and bST-embryos/bST-recipients (n = 60). Pregnancy was determined by palpation per rectum 33-43 days after embryo transfer. Unfertilized ova per flush was less for bST than for control (1.0 +/- 0.9 < 3.7 +/- 0.9; P < 0.04). Percentage of transferable embryos was greater for bST than for control (77.2% > 56.4%; P < 0.01). Number of blastocysts per flush was greater for bST than for control (2.4 +/- 0.7 > 0.4 +/- 0.7; P < 0.04). Pregnancy rates following embryo transfer were 25.6% for control-recipient/control-embryo, 43.2% for bST-recipient/control-embryo, 56.1% for control-recipient/bST-embryo, and 43.3% for bST-recipient/bST-embryo. Transfer of bST-embryos increased pregnancy rates compared with transfer of control-embryos (P < 0.04). An interaction between embryo and recipient treatments (P < 0.05) indicated that treatment of recipient cows with bST increased pregnancy rates as compared to control-recipients that received a control-embryo. However, there was no additive effect when bST-recipients received a bST-embryo. Administration of bST at AI decreased the number of unfertilized ova, increased the percentage of transferable embryos, and stimulated embryonic development to the blastocyst stage. Moreover, bST affected both early embryonic development and recipient components to increase pregnancy rates following embryo transfer.     

The effect of bovine somatotropin (bST) administration on reproduction, progesterone concentration during lactation and LH secretion during estrus, in dairy ewes.

Twenty-two polytocous lactating Chios ewes were used to test the effects of bovine somatotropin (bST) on reproduction, progesterone concentration and LH secretion during estrus. Half of the ewes were injected every second week with 160 mg bST in a prolonged release vehicle, from the fifth day post partum until the end of lactation, while the remaining ones were used as controls. All animals were fed the same amount of ration. Supplementation with bST resulted in an increase of milk production (P<0.05) and an insignificant trend for delayed resumption of normal estrous cycles. Although there were no differences between groups, there was also a tendency for the bST group to display lower progesterone concentrations during the first three fortnights after the onset of normal estrous cycles and higher ones during the last three fortnights of the experiment, compared with the control group. Duration of the first normal luteal phase after delivery of the bST group was found to be shorter compared with the control group (P<0.05). After estrous synchronization the bST group showed a shorter estrus compared with the control group (P<0.05). Average and baseline LH concentrations during synchronized estrous in the bST group was lower (P<0.001) compared with the control group. Additionally, the conception rate did not differ between the two groups. This study supports the concept that the beneficial effects of bST treatment on milk production outweigh the potential deleterious effects on reproduction.     

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).     

Ovarian response to gonadotropin treatment initiated relative to wave emergence in ultrasonographically monitored ewes

Follicular recruitment and luteal response to superovulatory treatment initiated relative to the status of the first wave of the ovine estrous cycle (Wave 1) were studied. All ewes (n = 25) received an intravaginal progestagen sponge to synchronize estrous cycles, and ewes were monitored daily by transrectal ultrasonography. Multiple-dose FSH treatment (total dose = 100 mg NIH-FSH-P1) was initiated on the day of ovulation (Day 0 group) in 16 ewes. In the remaining 9 ewes, FSH treatment was started 3 d after emergence of the largest follicle of Wave 1 (Day 3 group). Ewes received PGF(2alpha) with the last 2 FSH treatments to induce luteolysis. Daily blood samples were taken to determine progesterone profiles and to evaluate the luteal response subsequent to superovulation. The ovulation rate was determined by ultrasonography and correlated with direct observation of the ovaries during laparotomy 5 to 6 d after superovulatory estrus when the uterus was flushed to collect embryos. Results confirmed that follicular recruitment was suppressed by the presence of a large, growing follicle. In the Day 0 and Day 3 groups, respectively, mean numbers (+/- SEM) of large follicles (>/= 4 mm) recruited were 6.4 +/- 0.6 and 2.7 +/- 0.7 (P < 0.01) at 48 h after the onset of treatment, and 6.7 +/- 0.5 and 5.1 +/- 0.6 (P = 0.08) at 72 h after the onset of treatment. Ovulation rates were 5.6 +/- 0.8 and 3.3 +/- 0.8 in the respective groups (P < 0.05). The number of transferable embryos was 1.8 +/- 0.5 and 0.3 +/- 0.2 in the respective groups (P < 0.05). Short luteal phases (相似文献   

The relationship between vaginal mucous impedance and serum concentrations of estradiol and progesterone throughout the sheep estrous cycle

The objective of this experiment was to assess the relationship between electrical resistance of the vaginal mucosa and serum concentrations of estradiol (E2) and progesterone (P4) during the estrous cycle in ewes. Vaginal impedance was recorded daily using a 2-electrode impedometer in 10 nonprolific Western white-faced and 7 prolific Finn ewes, during the mid-breeding season (October to December). Transrectal ultrasonography of ovaries was performed once a day to confirm ovulation and monitor follicle growth (follicles > or =3 mm in diameter) and development of corpora lutea (CL). Jugular blood samples were collected daily for radioimmunoassay (RIA) of estradiol and progesterone. In all ewes, a decline in vaginal impedance (to <40 ohms) was closely associated with the onset of behavioral estrus. In both breeds of sheep, there was no significant correlation between daily serum concentrations of estradiol and vaginal impedance throughout the estrous cycle. Daily serum concentrations of progesterone and the E2:P4 ratio were correlated with vaginal impedance during the period of luteolysis and follicular phase in both breeds (Western white-faced ewes: r = 0.62, P = 0.0002 and r = -0.56, P = 0.0002; Finn ewes: r = 0.61, P = 0.001 and r = -0.45, P = 0.03, respectively) and early in the cycle (Days 0 to 2, Day 0 = day of ovulation) in white-faced ewes (r = 0.61, P = 0.0003 and r = -0.36, P = 0.052, respectively) but not during the remaining portion of the luteal phase in either breed. In conclusion, vaginal mucous impedance appears to be primarily controlled by progesterone, but it also changes in response to shifts in the E2:P4 ratio when progesterone concentrations are low. Impedometric characteristics of the vaginal mucosa in cyclic ewes are an indicator of serum concentrations of progesterone and E2:P4 ratios during the terminal stage of the estrous cycle.     

Effect of somatotropin on adipose tissue net glucose-stimulated lipogenesis in young goats.

Net glucose-stimulated lipogenesis (NGSL: the rate of lipogenesis in the presence of glucose minus the rate of lipogenesis in the absence of glucose) in omental adipose tissue explants from young castrated male goats was evaluated in control animals (n = 3; placebo-treated) and in animals treated with the sustained release of recombinant bovine somatotropin (n = 4; bST; 100 mg at 7-day intervals in a 147 days lasting experiment). The rate of fatty acid synthesis was determined in acute incubations in both freshly prepared and chronically cultured explants. Adipose explants remained metabolically active and retained their ability to respond to hormones when maintained in a tissue culture medium. NGSL in explants cultured for 24 h in the presence of insulin alone or bST alone, was non-significantly increased (more in the controls) and decreased (more in bST-treated animals), respectively. However, cortisol alone decreased (P<0.05) NGSL in explants from both control and bST-treated animals. In tissues from bST-treated animals, cortisol acted synergistically with insulin to produce a higher rate of NGSL than that observed in cultures with insulin alone. bST inhibited insulin plus cortisol-stimulated lipogenesis significantly (P<0.05) in explants from bST-treated animals but non-significantly in control animals. The rates of NGSL were decreased (P<0.05) by catecholamines in explants from both control and bST-treated animals. Norepinephrine (NE) and isoprenaline (ISO) were equally effective in the controls, whereas isoprenaline was more effective than norepinephrine in bST-treated animals.     

An ultrasonographic study of luteal function in breeds of sheep with different ovulation rates

Development and demise of luteal structures were monitored using daily transrectal ultrasonography in 2 breeds of sheep differing in ovulation rates (nonprolific Western white-faced cross-bred, n = 12 and prolific pure-bred Finn sheep, n = 7), during 1 estrous cycle in the mid-breeding season. Jugular blood samples were collected once a day for radioimmunoassay (RIA) of progesterone. The mean diameter of ovulatory follicles was higher in Western white-faced than in Finn ewes (6.4 +/- 0.2 and 5.3 +/- 0.2 mm, respectively; P < 0.001). The mean volume of luteal structures was higher (P < 0.05) in Western white-faced compared with Finn sheep from Days 5 to 15 of the cycle (Day 0 = day of ovulation). This accounted for the higher (P < 0.05) total luteal volumes recorded in Western white-faced ewes on Day 7 and from Days 11 to 15, despite the higher ovulation rate in Finn ewes (2.7 +/- 0.3 and 1.7 +/- 0.2, respectively; P < 0.05). Mean serum progesterone concentrations were higher (P < 0.05) in Western white-faced than in Finn ewes from Days 4 to 14. Daily total luteal volumes were positively correlated with daily serum progesterone concentrations throughout the cycle in Finn sheep (r > or = 0.40, P < 0.02), and during luteal growth and regression (r > 0.60, P < or = 0.00001) but not during mid-cycle in white-faced ewes (r = 0.16; P = 0.22). During the growth of the corpora lutea (CL), luteal tissue volume increased faster (P < 0.05) than serum progesterone concentrations in both breeds of sheep. During luteolysis, the decrease in luteal volumes parallelled that in serum progesterone concentrations in Finn (P = 0.11) but not in Western white-faced ewes, where luteal volumes decreased more slowly (P = 0.02) in relation to progesterone secretion. Increased ovulation rate in prolific Finn ewes resulted in more but smaller CL, and lower serum progesterone levels compared with nonprolific Western white-faced ewes. We conclude that breed-specific mechanisms exist to control the formation of luteal tissue and progesterone secretion in cyclic ewes differing in prolificacy. The mechanisms may involve ovulation of Graafian follicles at different sizes and inhibitory paracrine effects of CL on co-existing CL.     

Effect of exogenous insulin and fasting on growth hormone receptor and IGF-I expression in the pre-ovulatory follicle of ewes

The aim of this study was to investigate the effect of fasting and exogenous insulin administration on the expression of growth hormone receptor (GHR) and IGF-I mRNA in the pre-ovulatory follicle of ewes. Fifteen ewes received an intravaginal progesterone releasing device that was removed 6 days later (day of removal = day 0). On day -2, the ewes were divided into three groups: (i) fasting group (n = 5) that was fasted from day -2 to day 2; (ii) control group (n = 5) that received a maintenance diet; and (iii) insulin group (n = 5) that received insulin injections (0.25 IU/kg) every 12 h from day -2 to day 2 under the same diet as the control group. Follicular samples were obtained on day 2. Fasting increased plasma non-esterified fatty acids concentrations from day -1 to day 2 (P < 0.001). There was no difference (P > 0.05) in the number of follicles, although there was a tendency for an increase in the pre-ovulatory follicle diameter for the insulin group in comparison to the control group (P = 0.12). Thecal GHR mRNA expression was very low and was considered insignificant. Moreover, granulosa cells GHR mRNA expression increased (P < 0.05) in the insulin group. Expression of IGF-I mRNA was not different among groups in both tissues. In conclusion, insulin administration increases GHR mRNA but not IGF-I mRNA expression in granulosa cells of the pre-ovulatory follicle. However, fasting did not change the pattern of GHR/IGF-I mRNA expression in the pre-ovulatory follicle.     

Transfer of superovulated sheep embryos obtained with different FSH-P

Embryo transfer is one way of accelerating genetic improvement in sheep. One of the main obstacles has been the production of good-quality embryos. The use of progestagens and the stimulation of ovulation with follicle stimulating hormone pituitary extract (FSH-P) has permitted the superovulation of donor and recipient ewes and the synchronization of their cycles. The injection of 16 mg FSH-P at the end of progestin treatment gave means of 9 +/- 1.5, 12 +/- 1.5, and 19.5 +/- 2.6 corpora lutea per ewes in the Préalpes, Lacaune, and Romanov x Préalpes breeds respectively (this last breed is particularly prolific). Twenty Préalpes donor ewes produced 133 embryos that were recovered surgically at Day 6 of gestation; of these, 99 morulae were transferable. Forty-five morulae transferred surgically into 24 Préalpes recipient ewes yielded 16 pregnant ewes and 27 lambs (1.7 per ewe). Twenty-two Lacaune ewes yielded 204 embryos, of which 152 morulae were transferable. Of 76 recipients, 58 became pregnant and gave birth to 97 lambs (1.7 per ewe). During anoestrus, the mean ovulation rate decreased from 11.2 to 8.4; 40.6% of the embryos recovered were of transferable quality versus 74.5% during the normal breeding season. An improved superovulation technique, based on the use of FSH-P with a known follicle stimulating hormone to luteinizing hormonal (FSH/LH) ratio, provided us with good-quality embryos. This treatment must be adapted to the season.     

Treatment with recombinant bovine somatotrophin enhances ovarian follicle development and increases the secretion of insulin-like growth factor-I by ovarian follicles in ewes

To investigate the effect of recombinant bovine somatotrophin (rGH) on ovarian folliculogenesis in sheep, 18 mature Scottish Blackface ewes were assigned randomly to two treatment groups. Starting from day 5 of the synchronised oestrous cycle, animals were injected daily with either vehicle (control group) or 12.5 mg rGH (rGH-treated group) for 7 days. Blood samples were collected once daily during the experimental period for the measurement of growth hormone (GH), insulin-like growth factor-I (IGF-I), insulin, follicle-stimulating hormone (FSH), luteinising hormone (LH) and progesterone. At the end of treatment animals were killed and ovaries collected. All follicles at least 1.0 mm in diameter were dissected out and diameters measured to assess follicular populations for individual animals. Five small follicles (1.0–3.4 mm in diameter) and all the large follicles (at least 3.5 mm) from each animal were incubated in 1 ml of Medium 199 for 1 h. Medium was then changed and incubation continued for a further hour. All medium samples were assayed for IGF-I, oestradiol, testosterone and progesterone.Treatment of ewes with rGH had no effect on the total number of follicles at least 1.0 mm in diameter (control, 34.4 ± 2.6; rGH-treated, 31.3 ± 1.4; P > 0.2). However, when follicles were further classified into different size categories (1.0–2.0, 2.1–3.0, 3.1–4.0, 4.1–5.0, 5.1–6.0 and over 6.0 mm in diameter), the population of follicles 2.1–3.0 mm in diameter was significantly increased by rGH treatment (control, 9.2 ± 0.7; rGH-treated, 13.8 ± 1.1; P = 0.02). The number of follicles of 3.1–4.0 mm diameter in the rGH-treated group tended to be increased (P = 0.09), whilst the population of follicles 1.0–2.0 mm in diameter was reduced (P = 0.07). Treatment of ewes with rGH significantly increased peripheral concentrations of GH (P < 0.01), IGF-I (P < 0.01), insulin (P < 0.01) and progesterone (P < 0.05). There was no effect of rGH treatment on circulating concentrations of FSH and LH. Both large and small follicles from rGH-treated ewes secreted significantly (P < 0.001) more IGF-I (37.8 ± 2.2 ng ml h⁻¹, n = 50) than follicles from the control group (26.7 ± 1.6 ng ml⁻¹ h⁻¹, n = 73). However, there was no significant effect of rGH treatment on the secretion of oestradiol, testosterone and progesterone by either large or small follicles.It is concluded that treatment of mature ewes with rGH can enhance the development of ovarian follicles to the gonadotrophin-dependent stages. Furthermore, rGH appears to act through increased secretion of ovarian IGF-I, as well as increased peripheral concentrations of IGF-I and insulin.     

Failure to maintain interspecific pregnancy after transfer of Dall's sheep embryos to domestic ewes

Over a 3-year period, 32 Dall's sheep (Ovis dalli dalli) embryos were transferred into 24 domestic sheep (O. aries) recipients and 4 were transferred into 2 Dall's sheep recipients. In the first year, none of the 10 O. aries recipients was diagnosed pregnant. In the following 2 years, 9 (37%) of the domestic sheep recipients were pregnant on Day 18, 8 (33%) on Day 40, 6 (25%) on Day 90 and 4 (16%) on Day 120; 1 aborted at Day 125 and another at Day 145. Pregnancies were established only in ewes that had previously been recipients of Dall's sheep embryos. The 2 remaining pregnant sheep were treated with progesterone from Day 125 until the fetuses were determined to be dead at Day 145. Both of the Dall's sheep recipients (Year 2) established pregnancies; 1 live Dall's sheep lamb was born 174 days after mating. No differences in serum progesterone, oestrone, prostaglandin F-2 alpha metabolites or cortisol concentrations could be detected during pregnancy between recipients carrying Dall's sheep embryos, recipients receiving progesterone treatment or domestic ewes carrying domestic sheep pregnancies. Six fetuses were necropsied (1 at Day 125 and 5 at Day 145-146): all fetuses were premature and had various degrees of hydranencephaly. No significant differences were found when cotyledon numbers were compared among domestic ewes carrying Dall's sheep lambs. Dall's sheep ewes lambing naturally and domestic ewes lambing naturally. These results demonstrate that the transfer of Dall's sheep embryos to domestic ewes results in the establishment but subsequent loss of pregnancy and that these losses occur throughout gestation.     

Ovine uterine gland knock-out model: effects of gland ablation on the estrous cycle

Ovine endometrial gland development is a postnatal event that can be inhibited epigenetically by chronic exposure of ewe lambs to a synthetic progestin from birth to puberty. As adults, these neonatally progestin-treated ewes lack endometrial glands and display a uterine gland knockout (UGKO) phenotype that is useful as a model for study of endometrial function. Here, objectives were to determine: 1) length of progestin exposure necessary from birth to produce the UGKO phenotype in ewes; 2) if UGKO ewes display normal estrous cycles; and 3) if UGKO ewes could establish and/or maintain pregnancy. Ewe lambs (n = 22) received a Norgestomet (Nor) implant at birth and every two weeks thereafter for 8 (Group I), 16 (Group II), or 32 (Groups III and IV) weeks. Control ewe lambs (n = 13) received no Nor treatment (Groups V and VI). Ewes in Groups I, II, III, and VI were hemihysterectomized (Hhx) at 16 weeks of age. After puberty, the remaining uterine horn in Hhx ewes was removed on either Day 9 or 15 of the estrous cycle (Day 0 = estrus). Histological analyses of uteri indicated that progestin exposure for 8, 16, or 32 weeks prevented endometrial adenogenesis and produced the UGKO phenotype in adult ewes. Three endometrial phenotypes were consistently observed in Nor-treated ewes: 1) no glands, 2) slight glandular invaginations into the stroma, and 3) limited numbers of cyst- or gland-like structures in the stroma. Overall patterns of uterine progesterone, estrogen, and oxytocin receptor expression were not different in uteri from adult cyclic control and UGKO ewes. However, receptor expression was variegated in the ruffled luminal epithelium of uteri from UGKO ewes. Intact UGKO ewes displayed altered estrous cycles with interestrous intervals of 17 to 43 days, and they responded to exogenous prostaglandin F(2 approximately ) (PGF) with luteolysis and behavioral estrus. During the estrous cycle, plasma concentrations of progesterone in intact control and UGKO ewes were not different during metestrus and diestrus, but levels did not decline in many UGKO ewes during late diestrus. Peak peripheral plasma concentrations of PGF metabolite, in response to an oxytocin challenge on Day 15, were threefold lower in UGKO compared to control ewes. Intact UGKO ewes bred repeatedly to intact rams did not display evidence of pregnancy based on results of ultrasound. Collectively, results indicate that 1) transient, progestin-induced disruption of ovine uterine development from birth alters both structural and functional integrity of the adult endometrium; 2) normal adult endometrial integrity, including uterine glands, is required to insure a luteolytic pattern of PGF production; and 3) the UGKO phenotype, characterized by the absence of endometrial glands and a compact, disorganized endometrial stroma, limits or inhibits the capacity of uterine tissues to support the establishment and/or maintenance of pregnancy.     

Ovarian follicular dynamics after cauterization of the dominant follicle in anestrous ewes

An experiment was conducted to ascertain if follicles could reach ovulatory size after the largest follicle (dominant) has been removed at different times during a progestin treatment in anestrous ewes, and secondly to determine if these new follicles could respond to an hCG-induced ovulation and have similar function as corpora lutea. Mature crossbred sheep (n=44) in anestrous were treated with an intravaginal sponge containing 40 mg of FGA (day 0=sponge insertion) for 9 days. Treatments consisted of cauterization of the largest follicle on the experimental day 3 (T1), day 6 (T2) and day 9 (T3); day 12 to ascertain the size of the largest follicle in control ewes. During laparotomies, the diameters of the largest follicle (DF), and those of the second and third largest follicles (SF1 and SF2, respectively) were determined. On day 12, a second laparotomy was performed for those ewes which had their DF cauterized on days 3, 6 and 9, a fourth group was left intact and only laparotomized on day 12. At this time, the size of the new DF, SF1 and SF2 were determined. Immediately after the laparotomy on day 12, all the ewes were treated with 1000 i.u. of hCG to induce ovulation. Blood samples were collected daily from day 0 to 50 and samples were analyzed for progesterone concentrations. The size of the DF at the time of sponge removal was smaller that those observed on day 3 or 6 of sponge suggesting that follicles in ewes treated with this progestin regress and a new wave of follicular development ensues between day 6 and the time of sponge removal. The size of the DF on day 12 was also smaller in ewes that have the largest follicle removed at the time of sponge removal reflecting that these follicles had a shorter period of growth; however, the rate of growth was greater for these follicles than for follicles arising after cauterization on day 3 or 6 after sponge insertion. There were no differences among treatments, in the number of ewes that formed a corpus luteum (CL) in response to hCG. Life span of the corpora lutea did not differ among ewes having their DF removed on day 6 or 9 or those that served as controls, however, ewes that had their DF removed on day 3 developed longer lived CL in a larger proportion of animals. Average progesterone concentration during the life span of the induced corpora lutea was greater in control ewes than in any other experimental group. These observations allow us to conclude that, (a) the follicular dynamics observed in anestrous ewes treated with a progestin intravaginal sponge resembles that observed during the normal estrous cycle in the ewe; (b) the effects of progesterone on life span of the corpus luteum could not be only related to direct effects at the follicle but also involve changes in other components of the uterine-ovarian-hypothalamic axis; (c) the mechanisms controlling luteal life span seem to be different to those mechanisms controlling the function of the induced corpus luteum.     

Donor and recipient ewe factors affecting in vitro development and post-transfer survival of cultured sheep embryos

Donor and recipient factors were assessed during development of embryos following superovulation, collection at the pronuclear and two-cell stage, culture in Synthetic Oviduct Fluid medium for 5 days and twin transfer into synchronised recipients to elucidate what factors affect embryo development and post-transfer survival. In particular, the administration of exogenous progesterone to recipients using an intravaginal CIDR^TM device immediately following embryo transfer was investigated.

From 138 embryos collected from 30 donor ewes, 75% (103) were of transferable quality following culture, of which 100 were transferred to 50 recipients. There was significant variation (P < 0.001) in embryo development to the blastocyst stage between different donor ewes, but this was not related to the donor ovulation rate. At ultrasound sonography (approximately Day 60 of pregnancy), 58% of recipients were pregnant and 42% embryos had survived. Donor ovulation rate was related to embryo survival (P < 0.05) after transfer; the survival rate of embryos from ewes with high ovulation rates was lower than that of embryos from ewes with low ovulation rates. Exogenous progesterone supplementation following transfer did not affect embryo survival, rate of embryo development or plasma progesterone levels. In general, the results from this study suggest that factors other than efficacy of embryo culture can affect the outcome of embryo survival following transfer and that, where possible, these factors should be considered and balanced in experimental designs.     

Superovulation of a low fecundity sheep breed using a porcine gonadotrophin extract with a defined LH content (Pluset)

The aim of this study was to determine the efficiency of a porcine pituitary gonadotrophin extract with a defined pLH content in the superovulation of sheep. Estrus was synchronized in 61 Polish Mountain ewes with intravaginal fluorogestone acetate sponges. Twenty-four hours before the sponges were removed, the ewes underwent different superovulatory treatments: Group I 250 IU of pFSH with 250 IU of pLH (n=19); Group II 500 IU of pFSH with 500 IU of pLH (n=19); and Group III 750 IU of pFSH and 750 IU of pLH (n=18). Gonadotrophine was administered intramuscularly twice a day over a 3-day period in decreasing dosages. A control group of ewes (n=5) was treated with saline. In most of the ewes estrus began about 20 hours after sponges were removed. All the ewes were bred naturally every 12 hours. Superovulation was confirmed in 75% of the treated animals. The ewes receiving 250 IU each of pFSH and pLH produced an average of 7.6 +/- 3.1 corpora lutea (CL), 6.3 +/- 2.4 ova and 4.3 +/- 4.1 transferable embryos. Group II (500 IU of pFSH and pLH) produced 8.5 +/- 4.0 CL, 7.6 +/- 4.1 ova, and 4.1 +/- 2.9 transferable embryos. Group III (750 IU each of pFSH and pLH) produced 8.3 +/- 5.2 CL, 7.5 +/- 5.5 ova and 5.2 +/- 5.1 transferable embryos. The mean embryo recovery rate was 87% for all three groups. Differences in superovulatory response and embryo recovery rate among the groups were not statistically significant (P>0.05).     

Effect of recombinant bovine somatotropin (bST) on follicular population and on in vitro buffalo embryo production

The objective of this study was to evaluate the effect of bovine somatotropin (bST) on ovarian follicular population in buffalo heifers and its influence on oocyte quality, recovery rates and in vitro embryo production. We tested the hypothesis that bST treatment in buffalo females submitted to an ovum pick-up (OPU) program would improve the number of follicles recruited, oocyte quality and in vitro embryo production. A total of 10 heifers were assigned into two treatment groups: group bST (n=5; receiving 500 mg of bST in regular intervals) and control group (n=5; without additional treatment). Both groups were subjected to OPU sessions twice a week (every 3 or 4 days), for a total of 10 sessions per female, although due to procedural problems, only the first five OPU sessions produced embryos. The number of follicles and the diameters were recorded at all OPU sessions. The harvested oocytes were counted and classified according to their quality as either A, B, C, D or E, with A and B considered good quality. Cleavage and blastocyst production rates were evaluated 2 and 7 days after in vitro fertilization, respectively. The bST treatment increased the total number of antral follicles (>3mm in diameter; 12.2 compared with 8.7; p<0.05) and of small antral follicles (<5mm; 9.1 compared with 6.5; p<0.05) per OPU session. The bST also tended to increase the number of oocytes recovered per session (5.2 compared with 4.1; p=0.07), and enhanced the percentage of good quality oocytes (48.8% compared with 40.6%; p=0.07). bST showed no effect on cleavage and blastocyst production rates (p>0.05). The significant effects of performing repeated OPU sessions were decreasing the follicular population (p<0.001) as well as the number of follicles aspirated (p<0.001), and oocytes recovered (p<0.02). In conclusion, bST treatment improves the follicular population, demonstrating its possible application in buffalo donors submitted to OPU programs.     

The ovine uterus as a host for in vitro-produced bovine embryos

A series of experiments were conducted to determine whether bovine blastocysts would develop beyond the blastocyst stage in the ovine uterine environment. In Experiment 1, in vitro matured, fertilized and cultured (IVM/IVF/IVC) expanded bovine blastocysts were transferred into uteri of ewes on Day 7 or 9 of the estrous cycle and collected on Day 14 or 15 to determine if the bovine blastocysts would elongate and form an embryonic disk. Springtime trials with ewes that were synchronized with a medroxyprogesterone acetate (MAP) sponge resulted in a 78% blastocyst recovery rate, and 68% of the recovered spherical or elongated embryos had embryonic disks. In Experiment 2, transfer of 4-cell bovine embryos to the oviducts of ewes at Day 3 resulted in a lower recovery (47 vs 80%) than the transfer of blastocysts at Day 7 when embryos were recovered at Day 14. However, the percentage of embryos containing embryonic disks was higher for embryos transferred at the 4-cell stage (71%) than for embryos transferred as blastocysts (50%). In Experiment 3, IVF embryos from super-ovulated cows or Day 8 in vitro produced embryos transferred to cows were collected at Day 14 and were found to be similar in size to those produced by transfer to ewes in Experiment 2. In Experiment 4, the transfer of bovine blastocysts to ewes did not prolong the ovine estrous cycle. In Experiment 5, extension of the ovine estrous cycle by administration of a MAP releasing intravaginal device allowed bovine embryos to elongate extensively and to become filamentous. In Experiment 6, uterine flushings on Day 14 or Day 16 contained elevated levels of interferon-tau when bovine blastocyst were transferred on Day 7. Transfer of bovine embryos to the reproductive tract of a ewe allows some embryos to develop normally to advanced perimplantation stages and may be a useful tool for studying critical stages of embryo development and the developmental capacity of experimental embryos.     

Concentrations of progesterone,follistatin, and follicle-stimulating hormone in peripheral plasma across the estrous cycle and pregnancy in merino ewes that are homozygous or noncarriers of the Booroola gene

The circulating concentrations of progesterone, FSH, and follistatin across the estrous cycle and gestation were compared in Australian merino sheep that were homozygous for the Booroola gene, FecB, or were noncarriers. The Booroola phenotype is due to a point mutation in the bone morphogenetic protein receptor 1B. Progesterone concentrations began to rise earlier and were higher in the Booroola ewes than in the noncarriers on most days of the luteal phase but not during the follicular phase of the cycle. Follistatin concentrations remained unchanged across the estrous cycle in both groups of ewes, with no differences between genotypes. FSH concentrations were higher in Booroola ewes than in noncarrier ewes on most days of the estrous cycle, with a significantly higher and broader peak of FSH around the time of estrus. Progesterone concentrations were significantly higher in early and midgestation in Booroola ewes but were lower toward the end of gestation than those in noncarriers. FSH declined in both groups across gestation, with lower concentrations of FSH in Booroola ewes during midgestation. Follistatin remained unchanged across gestation in Booroola ewes and noncarrier ewes with a twin pregnancy but declined across gestation in noncarrier ewes with a singleton pregnancy. These results suggest that follistatin concentration is not regulated by the FecB gene during the estrous cycle and pregnancy but is influenced by the number of fetuses. However, the FecB gene appears to positively affect both progesterone and FSH during the estrous cycle and across pregnancy, which suggests that bone morphogenetic proteins play an important role in the regulation of both hormones.