Superovulatory response of Murciana goats to treatments based on PMSG/Anti-PMSG or combined FSH/PMSG administration

Superovulation in goats is frequently restricted by the cost of gonadotropin or the handling requirements. In this situation PMSG has the advantage of a lower cost and single dose protocol, but the variability of response obtained restricts its use. Thus, 2 alternative treatments with the advantages of PMSG were tested. In Experiment 1, we compared the ovulatory response of does treated with PMSG in combination or not with anti-PMSG antibodies at the onset of estrus, during season and out of season. In Experiment 2, we explored the effect of a partial substitution of FSH by PMSG at the end of treatment, comparing this treatment with a standard FSH protocol. Our results showed a significant (P < 0.01) seasonal effect on the incidence of corpora lutea (CL) regression in both experiments. The mean of viable embryos collected from does treated with anti-PMSG antibodies (mean = 5.75) was significantly higher than in the control PMSG-treated group (mean = 2.74) during spring (P < 0.05). Response during the fall was significantly lower regardless of treatment, and administration of antibody did not provide any significant improvement in superovulatory response (2.14 vs 1.77). In Experiment 2, the partial substitution of 3 doses of FSH by a single administration of PMSG did not reduce the number of CL or viable embryos, and no seasonal differences were observed, confirming that FSH provides a less variable response. From our results, it can be concluded that the use of PMSG antibodies for super-ovulating goats is an efficacious treatment which increases the number of viable embryos collected. However, partial replacement of FSH with PMSG at the end of treatment also did not compromise the number of embryos collected. Both approaches can be considered a valid alternative to treatments based on FSH.     

Comparative studies on the superovulatory effect of PMSG and FSH in water buffalo (Bubalus bubalis )

A total of thirty-eight lactating water buffalo cows were treated in four experiments simultaneously either with FSH (first group) or PMSG(second group). To the first group (half of the animals), a total dose of 40 mg FSH-P at 12-hr intervals was given i.m. within a 4-day period. The second group was treated i.m. with 3000 IU PMSG (Gestyl). Forty-eight hours after initiation of the superovulatory treatment all buffaloes were given 500 ug Cloprostenol. Fi seen buffaloes from the FSH-treated group (78.9%) and 17 from the second group (89.5%) came into heat at average PGF 2 alpha/standing heat intervals of 42.8+/-1.48 and 44.8+/-2.31, respectively. Superovulatory treatment resulted in meath number of 4.3+/-0.87 and 1.9+/-0.50 CL and 0.5+/-0.24 and 2.2+/-0.82 follicles for the first and second group. Twenty-five eggs were recovered after non-surgical flushing from 8 of 13 flushes in the first group and all except one were fertilized and classified as good embryos. Twelve eggs were recovered from 4 of 11 flushes in the second group and 11 of the eggs were fertilized and 10 of them classified as good ones.     

Endocrine and superovulatory responses in heifers pretreated with FSH or bovine follicular fluid

This study examined the effects of altered serum FSH concentration on subsequent ovarian response to superovulation. Synchronized heifers were assigned randomly on Day 1 of the cycle (estrus = Day 0) to three pretreatment groups that consisted of 6-d of saline (7ml, s.c., b.i.d.; Group I), FSH-P (0.5 mg, i.m., b.i.d.; Group II) or charcoal-extracted bovine follicular fluid (BFF; 7 ml, s.c., b.i.d.; Group III) injections. Superovulation was initiated on Day 7 and consisted of FSH-P in decreasing dosages over 4 d (4,3,2,1 mg; i.m., b.i.d.), with cloprostenol (500 mug) on the morning of the third day. A second replicate with 14 heifers was conducted using the same protocol but twice the pretreatment dosage of FSH-P (1 mg) and BFF (14 ml). Endogenous plasma FSH decreased during BFF and FSH-P pretreatments compared to controls (P < 0.02). Endogenous FSH concentrations in both primed groups (II and III) were similar to control values (Group I) 12 h after the start of superovulation. Basal LH concentrations were not different between pretreatment groups. The interval from cloprostenol treatment to the preovulatory LH surge in Group III was 21.3 and 23.9 h longer (P < 0.0001) than it was in Groups I and II. The postovulation progesterone rise was delayed in Group III. The number of corpora lutea (CL) was lowest in the BFF-primed group (4.2 +/- 0.8) compared with the FSH-primed (7.4 +/- 1.3) and the control (12.0 +/- 1.8; P < 0.003) groups. In the FSH-primed group (0.68 +/- 0.06 cm(3)), CL volumes were larger than in the control group (0.45 +/- 0.03 cm(3)), whereas in the BFF-primed group (0.27 +/- 0.02 cm(3)) CL volumes were smaller compared with the control group (P < 0.0001). Mean FSH concentrations for 48 h preceding superovulation and the number of CL per cow were positively correlated (r = 0.55; P < 0.004; n = 26). We concluded that both FSH-P and BFF pretreatments decreased the superovulatory response of heifers to FSH-P. The mechanism for this would appear to be associated with reduced endogenous FSH prior to the start of superovulation.     

Influence of maternal environment on the number of transferable embryos obtained in response to superovulatory FSH treatments in ewes

In a first experiment, embryo viability was estimated after recovery in the uterus or the oviduct of 70 Manchega ewes following a treatment of superovulation with decreasing doses of OVAGEN. Fewer viable embryos (5.6 +/- 0.9 vs. 8.3 +/- 0.8, P < 0.05) and more degenerative embryos (31.3% vs. 6.8%, P < 0.005) were obtained from the uterus than from the oviduct respectively. In a second experiment performed on 14 ewes, embryo viability was analyzed in relation to the follicular population estimated by ultrasonography (follicles > or = 2 mm) at the first FSH administration. Progesterone (P4) and oestradiol 17beta (E2) concentrations were also determined from the beginning of the superovulation treatment to the recovery of the embryos. The number of viable embryos (4.3 +/- 1.4) was positively correlated (r = 0.824) with of 2-4 mm diameter follicles (P < 0.05), and with E2 concentrations at -12 h (r = 0.891, P < 0.01) , 0 h (r = 0.943, P < 0.0001) and +24 h (r = 0.948, P < 0.05) from estrus detection. Prolonged high levels of E2 up to 72 h with low levels of P4 on days 3 and 4 after estrus had a negative (P < 0.05) effect on embryo viability. These results indicate that ovarian response to superovulatory protocols is related to the individual variations in the number of follicles of 2-4 mm at the start of FSH treatment, and that embryo viability is conditioned by the steroid patterns during the time spent in the genital tract of the super-ovulated ewes.     

Plasma concentrations of progesterone, 17beta-estradiol and androstenedione and superovulatory response of Nelore cows (Bos indicus) treated with FSH

Progesterone (P(4)), 17beta- estradiol (E(2)) and androstenedione (A(4)) plasma concentrations were correlated with palpated corpora lutea (CL), recovered embryos and viable embryos in 13 Nelore cows induced to superovulate with FSH, starting on Day 10 of the estrous cycle. Administration of FSH increased the number of ovulations and recovered embryos. Plasma P(4), E(2) and A(4) levels on Day 0 and of P(4) on Days 10 and 11 of the cycle were not correlated with the superovulatory response. Determination of CL by palpation per rectum was used to estimate the number of recovered embryos. Plasma P(4) levels higher than 1 ng/ml on the induced estrus day (Day 14) had an adverse effect on the embryo viability rate. Plasma E(2) concentrations on Day 14 were positively correlated with the number of viable embryos collected, a correlation that has not been previously reported. The present data indicate that plasma P(4) and E(2) concentrations in FSH-PGF2alpha-treated Nelore cows are useful for the identification of 2 different populations of Nelore donors and are correlated with superovulatory response and, particularly, with the number of viable embryos.     

Induced ovulation in mature mice and developmental capacity of the embryos in vitro.

Embryos from gonadotrophin-treated mature mice were cultured from the two-cell to the early implantation stage. Their developmental capacity was very similar to that of spontaneously ovulated eggs.     

Timing of multiple ovulations in the ewe after treatment with FSH or PMSG with and without GnRH

Ovulation rate, median time to first ovulation, median time of all ovulations and median time from first to last ovulation were studied by repeated laparoscopy in Merino ewes. Treatments with FSH or PMSG significantly affected ovulation rate (8.4 +/- 0.81 and 7.3 +/- 1.21 respectively, P less than 0.05) and in median time of all ovulations (60 and 54 h respectively after progestagen sponge removal, P less than 0.05). Differences in the median time to first ovulation (60 and 48 h) and median time from first to last ovulation (6 and 6 h) for the respective treatments were not significant. The synchrony of ovulation after both treatments was adversely affected by (1) the occurrence of premature ovulations before the onset of superovulation, (2) variability in the time of commencement of superovulation, and (3) variability in the time from first to last ovulation. Administration of GnRH synchronized the timing of ovulation with both gonadotrophin treatments. This synchrony was due to a reduction in the period during which superovulation began and in the interval from first to last ovulation. The median time of all ovulations was significantly less with FSH + GnRH than with PMSG + GnRH (45 and 48 h after progestagen sponge removal, respectively, P less than 0.05). Administration of GnRH at 16, 20 or 24 h after progestagen sponge removal significantly affected all traits examined except ovulation rate. Administration at 20 and 24 h produced an equally good synchrony of ovulation which was better than that obtained at 16 h. We suggest that the use of GnRH in embryo collection programmes appears justified and is likely to improve embryo yields due to improved rates of fertilization.     

Measurement of inhibin A and follicular status predict the response of ewes to superovulatory FSH treatments

Variability in superovulatory response to FSH stimulation is common to most mammals and imposes practical problems for assisted reproduction. In sheep, we have studied if this response is related to the ovarian follicular population and activity before the stimulation. During the breeding season, 30 ewes were treated with 40 mg FGA sponges for 14 days and 125 microg cloprostenol injection on Day 12, considering Day 0 as the day of progestagen insertion. Superovulatory response was induced with two different FSH regimes using the same total dose (8.8 mg), administered twice daily from 60 h before to 24 h after progestagen withdrawal. At the first FSH injection, all follicles > or = 2 mm were observed by transrectal ultrasonography and plasma FSH and inhibin A levels were determined. The number of corpora lutea and the number of and viability of recovered embryos in response to the treatment were determined on Day 7 after sponge withdrawal. No significant differences were found between treatments. The total mean number of corpora lutea (11.5 +/- 1.2) and recovered embryos (7.9 +/- 1.1) were positively correlated (P < 0.05 and <0.01, respectively) with the number of small antral follicles (2-3 mm: 9.2 +/- 0.7) and inhibin A concentration (240 +/- 18 pg/ml; P < 0.05 for corpora lutea and P < 0.005 for recovered embryos) observed at the onset of the superovulatory treatment, which was also positively correlated with the number of viable embryos (5.8 +/- 0.9, P < 0.005). In 18 ewes with follicles > or = 6 mm prior to FSH treatment, the ovulation rate was unaffected but the number of embryos (6.1 +/- 0.9 versus 11.6 +/- 2; P < 0.05) and their viability (4.5 +/- 0.8 versus 8.5 +/- 2; P < 0.05) was reduced. The lower number of embryos produced when a large follicle is present suggest that a proportion of the smaller follicles are in early stages of atresia and the developmental competence of their oocyte is compromised.     

Follicular dynamics and superovulatory response in Holstein cows treated with FSH-P in different endocrine states

The effect of follicular and/or endocrine environments on superovulatory response was tested. Eighteen nonlactating Holstein cows were superovulated with 32 mg FSH-P given in decreasing doses at 12-h intervals plus two injections of prostaglandin F2-alpha (25 mg each) on the third day of treatment. Cows were assigned randomly to treatments: T1, superovulatory treatment initiated on estrous cycle Day 10.5; T2, CIDR (intravaginal device containing 1.9 g of progesterone) inserted from Days 3 to 9 and superovulation initiated on Day 6.5; T3, identical to T2 but Buserelin (GnRH agonist) was injected (8 mug, i.m.) on Day 3 at the time of CIDR insertion. Embryos were recovered on Day 7 after the superovulatory estrus. Cows were examined daily by ultrasonography and blood was collected for progesterone and estradiol determinations. Mean diameter of the dominant follicle (frequency of first-wave dominant follicle) at the beginning of FSH injections was 13.7 mm (4 6 ), 11.2 mm (6 6 ) and 8.7 mm (6 6 ) (P<0.01) for T1, T2 and T3, respectively. Following initiation of superovulation, follicles moved into larger follicle classes (Class I, <3 mm; Class II, 3 to 4 mm; Class III, 5 to 9 mm; Class IV >9 mm) earliest in T1 (P<0.01). Cumulative follicular diameter and plasma concentrations of estradiol at Day 4 of superovulation were higher (P<0.01) in T1 (200 mm, 82 pg/ml) compared with T2 (123 mm, 24 pg/ml) and T3 (130 mm, 18 pg/ml). Proportion of cows in estrus prior to 12 h vs 12 to 24 h differed (P<0.05) between groups (T1: 5 vs 1; T2: 2 vs 4; T3: 1 vs 5). Mean number of follicles on the last day of superovulation treatment, number of CL and number of embryos plus unfertilized ova recovered were 17.5, 12.2 and 13.3; 13.8, 10 and 8.2 (P<0.1) and 8.7, 4.5 and 2.3 (P<0.05) for T1, T2 and T3, respectively. The developmental stage of the dominant follicle was associated with not only the number of ovulations, but also the size and periestrous concentrations of plasma estradiol associated with the recruited follicles.     

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

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

Effects of FSH commercial preparation and follicular status on follicular growth and superovulatory response in Spanish Merino ewes

Ovarian follicular development was characterized in 24 Spanish Merino ewes to study effects of the follicular status and the FSH commercial product used on follicular growth and subsequent superovulatory response. Estrus was synchronized using 40 mg fluorogestone acetate sponges. The superovulatory treatment consisted in 2 daily i.m. injections of FSH from 48 h before to 12 h after sponge removal. Sheep were assigned randomly to 2 groups treated with 6 decreasing doses (4, 4, 3, 3, 2, 2 mg) of FSH-P or with 6 doses of 1.25 mL of OVAGEN. Growth and regression of all follicles > or = 2 mm were observed by transrectal ultrasonography, and recorded daily from Day 6 before sponge insertion to the first FSH injection, and then twice daily until estrus was detected with vasectomized rams. Differences were detected in follicular development from the first FSH injection to detection of estrus (-48 to 36 h from sponge removal) between groups. Administration of FSH-P increased the appearance of new follicles with respect to OVAGEN (6.3 +/- 0.7 vs 4.8 +/- 0.4; P < 0.05), and the mean number of medium (4 to 5 mm) follicles (8.9 +/- 1.2 vs 6.6 +/- 0.9; P < 0.05). However, the mean number of follicles that regressed in size after sponge removal (5.9 +/- 0.4 vs 3.3 +/- 0.4) and the number of preovulatory sized follicles that did not ovulate (60 vs 42.4%) were also higher in FSH-P treated ewes (P < 0.05). So, finally, there were no differences in ovulation rate, as determined by laparoscopy on Day 7 after sponge removal, between ewes treated with FSH-P or OVAGEN (6.3 +/- 1.9 vs 7.0 +/- 1.7 CL). In all the ewes, the ovulatory response was related (P < 0.05) both to the number of small follicles (2 to 3 mm in diameter) present in the ovaries at the start of treatment with exogenous FSH and to the number of follicles that reached > or = 4 mm in size at estrus, despite differences in the pattern of follicular development when using different commercial products.     

Enhanced antibody response in retrovirus-infected mice treated with endotoxin or nontoxic polysaccharide derivative

Friend leukemia virus (FLV) is a retrovirus which causes marked suppression of the immune response of genetically susceptible mice. In the present study the depressed antibody response to sheep erythrocytes by spleen cells from FLV-infected mice was partially reversed by injection of either a bacterial endotoxin or a nontoxic polysaccharide derivative directly into infected mice or by addition to spleen cell cultures from these mice immunized in vitro with sheep red blood cells (SRBC). The endotoxin and PS in a dose-related manner markedly increased the antibody responsiveness of the spleen cells to SRBC. Thus these results indicate that the nontoxic polysaccharide derivative has properties equivalent to the toxic endotoxin in enhancing the antibody responsiveness of FLV-suppressed spleen cells to a T-cell-dependent antigen like SRBC.     

小鼠电激活孤雌胚胎早期体内外发育能力的比较

目的探讨小鼠电激活孤雌胚胎的早期体内、外发育能力。方法 利用不同电脉冲参数和激活液对小鼠卵母细胞进行活化,观察激活后的小鼠孤雌胚体外发育状况和移植后的发育能力。结果非电解质激活液优于电解质液,脉冲强度、脉冲宽度和脉冲次数3个参数各自处于某一范围内时,他们之间存在某种相关性,降低其中1个参数可通过升高另外2个参数得到补偿,经筛选较适宜的电脉冲参数为：1.0 kV/cm、40μs、2 p,或者1.5kV/cm、30/μs、2 p,分别为74.65%和71.19%,体外囊胚发育率分别为43.40%和47.62%。电激活孤雌胚体外发育时序比正常胚胎慢,但囊胚细胞数与对照组差异不显著。它们经胚胎移植后,其中的一部分能够着床,但着床率仅为3.6%,极显著低于对照组（67%,P〈0.01）。结论电刺激能够较好地模拟正常受精过程激活小鼠卵母细胞,但激活后的多数小鼠孤雌胚胎着床能力较低,不能够顺利着床。     

Effect of low dose of FSH given at the beginning of the estrous cycle and subsequent superovulatory response in Holstein cows

A total of 47 superovulations were conducted on forty non-lactating cows to evaluate two different schemes using follicle stimulating hormone (FSH) for superovulating cattle. Cows randomly assigned to treatment A (26 collections) were superovulated beginning on days 9 to 13 of the estrous cycle by giving FSH at decreasing doses of 6, 6, 5, 5, 3, 3, and 2, 2 mg for 4 consecutive days at 12-h intervals while those in treatment B (21 collections) also received 2.5 mg of FSH on days 3 and 4 of the estrous cycle. Animals in both treatments were each given 12.5 mg of prostaglandin F(2alpha) (PGF(2alpha)) at 60 and 72 h after the initiation of superovulatory treatment. Cows were artificially inseminated at 0, 12, and 24 h after the onset of estrus. Embryos were recovered nonsurgically on d 6 and morphologically evaluated. Ovaries of the cows were palpated at the end of flushings to assess the number of corpora lutea (CL). The mean interval from PGF(2alpha) to the onset of estrus was not different (P>0.05) for treatments A (56.6 h) and B (50.0 h). Also, mean duration of standing estrus was not different for either treatment (13.4 h vs 12.8 h). The mean number of CL palpated (7.3 vs 12.9) and ova recovered (5.5 vs 14.2) were significantly greater (P<0.05) for treatment B. The mean number of excellent and good embryos recovered was lower for treatment A animals, but not significant (P>0.05). Therefore, low doses of FSH given at the beginning of the cycle increased ovulation rate and embryo recovery in non-lactating cows.     

Differential mRNA expression in in vivo produced pre-implantation embryos of dairy heifers and mature cows

Decreasing fertility with increasing parity is considered to be a major constraint in the reproductive management of dairy cows. Even though pregnancy rates (PR) in mature cows have declined drastically in the last 50 years, it has remained constant in heifers. Early embryonic loss is a major cause for the loss of pregnancy in cows. Expression of developmentally important genes is vital for the function and survival of embryos. Hence, in this study, we compared the mRNA abundance of GLUT5, INFτ, HSP70, Na/K-ATPase, BAX, and BCL2 genes in the pre-implantation embryos of dairy heifers and mature cows. Heifers (n = 25) and cows (n = 20) were superovulated and artificially inseminated on the day of estrus. On day 7, the embryos were flushed and morphologically graded and RT-PCR was performed. HSP70 was expressed more in the grade I embryos in heifers than in cows, and in the grade I embryos of heifers than in grade II embryos of heifers. In pooled embryos (both grades I and II) of heifers and cows, expression for INFτ was greater in heifers than in cows. Grade I embryos had a higher expression of GLUT5 and Na/K-ATPase than the grade II embryos of cows. From this study, we conclude that there is differential expression of some developmentally important genes between embryos of heifers versus cows and between grades I and II embryos regardless of the embryo source. Future research will be necessary to elucidate any potential cause and effect between these genes and reduced PR observed in dairy cows. Mol. Reprod. Dev. 76: 1165–1172, 2009. © 2009 Wiley-Liss, Inc.     

The effects of previous ovarian status on ovulation rate and early embryo development in response to superovulatory FSH treatments in sheep

A total of 64 ewes was used to determine if the changes in superovulatory yields related to the ovarian status at the start of superovulatory treatment are due to differences in the population of gonadotrophin-responsive follicles, alterations in the processes of ovulation or transport of embryos from oviduct to uterus and/or developmental competence of the oocyte/embryo. Ovarian status at the start of a superovulatory FSH step-down treatment, administered coincidentally with a progestagen, was assessed by ultrasonography. On Day 4 after progestagen withdrawal, embryos were recovered from oviduct and their viability was determined by assessing development in vitro culture (IVC) until the hatched blastocyst stage. In all the ewes, the ovulation rate was related positively to the number of 2-3 mm follicles at first FSH injection (P<0.005). However, the total number of embryos and their viability were related to the more limited category of 3 mm follicles (P<0.05), whereas a higher degeneration rate was related to the number of 2mm follicles. The presence of a corpus luteum (CL) at the start of superovulatory treatment exerted a protective effect on embryonic viability, decreasing the degeneration of embryos. On the other hand, the presence of a dominant follicle at first FSH dose affected the mean size of the pool of follicles responding to the superovulation treatment, because ovulation arose from 3 to 5 mm follicles in absence of large follicles (P<0.05), but from 2 to 3 mm follicles when large follicles were present (P<0.005), indicating atresia in medium sized follicles in the presence of a large follicle.     

Fertilization in vitro with spermatozoa from different mice increased variation in the developmental potential of embryos compared to artificial parthenogenetic activation

Although successful embryo development is dependent upon genetic and epigenetic contributions from both the male and female, the male potential to adversely affect embryo development has been scarcely studied. It is unclear whether the sperm variation among different males would affect the outcome of oocyte evaluation by embryo development following fertilization. In the present study, variation in the developmental potential of mouse embryos was first compared between in vitro fertilization with epididymal spermatozoa from different males and Sr(2+) parthenogenetic activation using oocytes of different qualities, and then the effect of male on fertilization and embryo development was examined using randomly chosen oocytes and spermatozoa from cauda epididymidis, vas deferens or electro-ejaculates. Rates of fertilization and blastocyst formation were significantly higher with spermatozoa from cauda epididymidis or vas deferens than with ejaculated spermatozoa. Rates of embryonic development differed significantly between different males, but not between different ejaculates of the same male. Analysis of standard errors of means and coefficients of variance indicated that as long as multiple males were involved, the variation in oocyte fertilization/activation and blastocyst formation was always higher after fertilization than after Sr(2+) parthenogenetic activation whether spermatozoa were collected from epididymidis, vas deferens or ejaculates and regardless of oocyte qualities. It is concluded that (1) epididymal mouse spermatozoa fertilize more oocytes than ejaculated spermatozoa under identical experimental conditions; (2) like farm animals, the mice also show a remarkable male effect on the developmental potential of in vitro produced embryos although they are supposed to be less genetically diverse; (3) parthenogenetic activation is recommended for assessment of oocyte quality to exclude the effect of male.     

Sex-related differences in developmental rates of bovine embryos produced and cultured in vitro.

The classical concept of sex determination in mammals is that a Y chromosomal gene controls the development of the indifferent gonad into a testis. Subsequent divergence of sexual phenotypes is secondary to this gonadal determination. The most likely candidate gene is SRY (sex-determining region Y) in humans, and Sry in mouse. However, several lines of evidence indicate that sexual dimorphism occurs even before the indifferent gonad appears. Here we present evidence that bovine male embryos generally develop to more advanced stages than do females during the first 8 days after insemination in vitro. Corresponding relationships between both cell numbers and mitotic indices and sex were also seen. Although it is not clear whether this phenomenon involves factors originating before or after fertilization, these findings suggest that sex-related gene expression affects the development of embryos soon after activation of the embryonic genome and well before gonadal differentiation.