Effects of treatment with GnRH from 4 to 8 weeks of age on the attainment of sexual maturity in bull calves

In bull calves an early transient increase in circulating concentrations of LH occurs between 6 and 20 weeks of age. This has been shown to influence reproductive development and performance later in life. In an attempt to hasten the onset of sexual maturity, bull calves (Hereford x Charolais) were treated (im) with 120 ng/kg of GnRH (n=6) twice every day from 4 to 8 weeks of age; control calves received saline (n=6). Injection of GnRH resulted in an LH pulse in all animals. GnRH treated bulls displayed more rapid testicular growth rates between 22 and 44 weeks of age. Sexual maturity (SC>or=28 cm) was achieved earlier in GnRH treated bulls compared to saline treated bulls (41.7+/-2.22 and 47.0+/-0.45 weeks of age, respectively) and this was confirmed by age of sexual maturity based on ejaculate characteristics (>50 million spermatozoa, >10% motility; 45.0+/-0.86 and 49.0+/-1.13 weeks of age for GnRH and control treated bull calves, respectively; P<0.05). We concluded that treatment with GnRH, twice daily, from 4 to 8 weeks of age, prior to the endogenous early increase in plasma LH concentrations, could increase in plasma LH concentrations, advance testicular development and reduce age at puberty in beef bull calves. This may provide the basis for a simple regimen to hasten sexual development in the bull calf.

Does injection of prostaglandin F2α (PGF2α) cause ovulation in anestrous Western White Face ewes?

In a previous study in our laboratory, treatment of non-prolific Western White Face (WWF) ewes with PGF(2 alpha) and intravaginal sponges containing medroxyprogesterone acetate (MAP) on approximately Day 8 of a cycle (Day 0 = first ovulation of the interovulatory interval) resulted in ovulations during the subsequent 6 days when MAP sponges were in place. Two experiments were performed on WWF ewes during anestrus to allow us to independently examine if such ovulations were due to the direct effects of PGF(2 alpha) on the ovary or to the effects of a rapid decrease in serum concentrations of progesterone at PGF(2 alpha)-induced luteolysis. Experiment 1: ewes fitted with MAP sponges for 6 days (n = 12) were injected with PGF(2 alpha) (n = 6; 15 mg im), or saline (n = 6) on the day of sponge insertion. Experiment 2: ewes received progesterone-releasing subcutaneous implants (n = 6) or empty implants (n = 5) for 5 days. Six hours prior to implant removal, all ewes received a MAP sponge, which remained in place for 6 days. Ewes from both experiments underwent ovarian ultrasonography and blood sampling once daily for 6 days before and twice daily for 6 days after sponge insertion. Additional blood samples were collected every 4 h during sponge treatment. Experiment 1: 4-6 (67%) PGF(2 alpha)-treated ewes ovulated approximately 1.5 days after PGF(2 alpha) injection; these ovulations were not preceded by estrus or a preovulatory surge release of LH, and resulted in transient corpora hemorrhagica (CH). The growth phase was longer (P < 0.05) and the growth rate slower (P < 0.05) in ovulating versus non-ovulating follicles in PGF(2 alpha)-treated ewes. Experiment 2: in ewes given progesterone implants, serum progesterone concentrations reached a peak (1.7 2 ng/mL; P < 0.001) on the day of implant removal and decreased to basal concentrations (<0.17 ng/mL; P < 0.001) within 24 h of implant removal. No ovulations occurred in either the treated or the control ewes. We concluded that ovulations occurring after PGF(2 alpha) injection, in the presence of a MAP sponge, could be due to a direct effect of PGF(2 alpha) at the ovarian level, rather than a sudden decline in circulating progesterone concentrations.

Patterns of expression of steroidogenic enzymes during the first wave of the ovine estrous cycle as compared to the preovulatory follicle

The expression patterns of steroidogenic enzymes in ovarian antral follicles at various stages of growth in a follicular wave have not been reported for sheep. Ovaries were collected from ewes (n=4-5 per group) when the largest follicle(s) of the first wave of the cycle, as determined by ultrasonography, reached (i) 3 mm, (ii) 4 mm, (iii) > or =5 mm in diameter or when there was a single (iv) preovulatory follicle in the last wave of the cycle, 12h after estrus detection. The expression pattern of steroidogenic enzymes was quantified using immunohistochemistry and grey-scale densitometry. The expression of CYP19 in the granulosa and 3beta-HSD and CYP17 in the theca increased (P<0.01) progressively from 3 to > or =5 mm follicles in the first wave of the cycle and was lower (P<0.01) in the preovulatory follicle compared to > or =5 mm follicles. However, the expression of 3beta-HSD in the granulosa increased (P<0.05) from 3 to > or =5 mm follicles and was maintained (P<0.05) at a high level in the preovulatory follicles. The amount of CYP19 in the granulosa of the growing follicles correlated positively (r=0.5; P<0.03) with the concurrent serum estradiol concentrations. We concluded that the expression pattern of steroidogenic enzymes in theca and granulosa of follicles growing in each wave in the ewe, paralleled with serum estradiol concentrations, with the exception that concentrations of 3beta-HSD in granulosa increased continuously from follicles 3mm in diameter to the preovulatory follicle.

The temporal relationship between patterns of LH and FSH secretion, and development of ovulatory-sized follicles during the mid- to late-luteal phase of sheep

The aim of the present study was to investigate the temporal relationship between the secretory pattern of serum LH and FSH concentrations and waves of ovarian antral follicles during the luteal phase of the estrous cycle in sheep. The growth pattern of ovarian antral follicles and CL were monitored by transrectal ultrasonography and gonadotropin concentrations were measured in blood samples collected every 12 min for 6 h/d from 7 to 14 d after ovulation. There were two follicular waves (penultimate and final waves of the cycle) emerging and growing during the period of intensive blood sampling. Mean and basal LH concentrations and LH pulse frequency increased (P < 0.001) with decreasing progesterone concentration at the end of the cycle. Mean and basal FSH concentrations reached a peak (P < 0.01) on the day of follicular wave emergence before declining to a nadir by 2 d after emergence. None of the parameters of pulsatile LH secretion varied significantly with either the emergence of the final follicular wave or with the end of the growth phase of the largest follicle of the penultimate wave of the cycle. However, mean and basal LH concentrations did increase (P < 0.05) after the end of the growth phase of the largest follicle of the final follicular wave of the cycle. Furthermore, the end of the growth phase of the largest follicle of the final wave coincided with functional luteolysis. In summary, there was no abrupt or short-term change in pulsatile LH secretion in association with the emergence or growth of the largest follicle of a wave. We concluded that the emergence and growth of ovarian antral follicles in follicular waves do not require changes in LH secretion, but may involve changes in sensitivity of ovarian follicles to serum LH concentrations.

The Effect of the Manipulation of Follicle-Stimulating Hormone (FSH)-Peak Characteristics on Follicular Wave Dynamics in Sheep: Does an Ovarian-Independent Endogenous Rhythm in FSH Secretion Exist?1

We designed three experiments to investigate the relationship between FSH peaks and ovarian follicular waves and to examine whether an endogenous rhythm of FSH peaks exists in sheep. In experiment 1, anestrous ewes were treated with ovine FSH (oFSH) or vehicle (6 ewes per group) at the expected time of an endogenous FSH peak, to double the FSH-peak amplitude in treated ewes. In experiment 2, anestrous ewes were treated with either oFSH or vehicle (6 ewes per group) at the expected time of two consecutive interpeak nadirs, such that the treated ewes had 5 FSH peaks in the time frame of 3 FSH peaks in control ewes. In experiment 3, to measure FSH concentrations, daily blood samples were collected from 5 cyclic ewes for a control period during the estrous cycle and then for three 17-day periods after ovariectomy. Daily blood samples were collected from another group of 8 ovariectomized ewes that were treated with estradiol-releasing implants and intravaginal progestogen sponges. Doubling the FSH-peak amplitude did not alter the characteristics of the following follicular wave. Increasing the frequency of FSH peaks stimulated the emergence of additional follicular waves, but did not alter the rhythmic occurrence of FSH peaks and follicular wave emergence. Endogenous follicular waves in oFSH-treated ewes emerged and grew in the presence of the growing largest follicle of the induced follicular waves. Finally, based on the observation of serum FSH concentrations in ovariectomized ewes, it appears that there exists an endogenous rhythm for peaks in daily serum FSH concentrations, which is, at least in part, independent of regulation by ovarian follicular growth patterns.

Effects of treatment with LH or FSH from 4 to 8 weeks of age on the attainment of puberty in bull calves

A transient increase in gonadotropin secretion between 6 and 20 weeks of age is critical for the onset of puberty in bull calves. To try and hasten the onset of puberty, bull calves were treated (s.c.) with 3 mg of bLH (n = 6) or 4 mg of bFSH (n = 6) once every 2 days, from 4 to 8 weeks after birth; control calves received saline (n = 6). At 4 and 8 weeks of age, mean LH concentrations were higher (P < 0.05) in bLH-treated (2.3 +/- 0.04 ng/ml and 1.20 +/- 0.04 ng/ml) as compared to control calves (0.50 +/- 0.1 ng/ml and 0.70 +/- 0.10 ng/ml). Mean serum FSH concentrations at 4 and 8 weeks of age, were higher (P < 0.05) in bFSH-treated (1.60 +/- 0.20 ng/ml and 1.10 +/- 0.2 ng/ml) as compared to control calves (0.38 +/- 0.07 ng/ml and 0.35 +/- 0.07 ng/ml). The age at which scrotal circumference (SC) first reached > or = 28 cm, occurred earlier (P < 0.05) in bFSH-treated calves as compared to saline-treated calves (39.3 +/- 1.3 and 44.8 +/- 1.3 weeks of age, respectively). Based on testicular histology at 56 weeks of age, treatment with bFSH resulted in greater (P < 0.05) numbers of Sertoli cells (5 +/- 0.2, 6 +/- 0.3 and 5 +/- 0.3 in bLH-, bFSH- and saline-treated calves, respectively); elongated spermatids (42 +/- 2, 57 +/- 8 and 38 +/- 5 in bLH-, bFSH- and saline-treated calves, respectively) and spermatocytes (31 +/- 3, 38 +/- 3 and 29 +/- 2 in bLH-, bFSH- and saline-treated calves, respectively) per seminiferous tubule. We concluded that treatment of bull calves with bFSH from 4 to 8 weeks of age increased testicular growth (SC); hastened onset of puberty (SC > or = 28 cm); and enhanced spermatogenesis.

Patterns of Antral Follicular Wave Dynamics and Accompanying Endocrine Changes in Cyclic and Seasonally Anestrous Ewes Treated with Exogenous Ovine Follicle-Stimulating Hormone During the Inter-Wave Interval1

In the ewe, ovarian follicular waves emerge every 4 to 5 days and are preceded by a peak in FSH secretion. It is unclear whether large antral follicle(s) in a wave suppress the growth of other smaller follicles during the inter-wave interval, as is seen in cattle. In this study, anestrous (n = 6; experiment 1) and cyclic (n = 5; experiment 2) Western white face ewes were given ovine FSH (oFSH) (0.5 microg/kg; two s.c. injections, 8 h apart) during the growth phase (based on ultrasonography) of a follicular wave (wave 1). Control ewes (n = 5 and 6, respectively) received vehicle. In oFSH-treated ewes, serum FSH concentrations reached a peak (P < 0.05) by 12 h after oFSH treatment, and this induced FSH peak did not differ (P > 0.05) from the endogenous FSH peaks. In all ewes, emergence of follicular waves 1 and 2 was seen (P > 0.05). However, in oFSH-treated ewes, an additional follicular wave emerged approximately 0.5 days after treatment: during the interwave interval of waves 1 and 2 without delaying the emergence of wave 2. The growth characteristics and serum estradiol concentrations did not differ (P > 0.05) between oFSH-induced waves and waves induced by endogenous FSH peaks. We concluded that, unlike in cattle, the largest follicle of a wave in sheep has limited direct effect on the growth of other follicles induced by exogenous oFSH. In addition, the largest follicle of a wave may possibly not influence the rhythmicity of follicular wave emergence, as it does in cattle.

Use of high-resolution transrectal ultrasonography to assess changes in numbers of small ovarian antral follicles and their relationships to the emergence of follicular waves in cyclic ewes

Transrectal ovarian ultrasonographic studies have shown that, in cattle, follicular wave emergence is associated with a large increase in the number of small antral follicles (4-6mm in diameter); an analogous association has not been found for small follicles (2-3mm in diameter) in the ewe. In previous studies in ewes, accurate assessment of the number of follicles has been limited to follicles > or =2 or 3mm in size. Newer, high-resolution equipment allowed us to identify follicles > or =0.4mm and to quantify all antral follicles > or =1mm in diameter in seven cyclic Western White Face ewes. This allowed us to expand the small follicle pool examined, from 1 to 4 follicles/day (2-3.5mm in diameter) in earlier studies, to 8-18 follicles/day (1-3mm in diameter). Total number of small follicles (> or =1 and < or =3mm in diameter) increased between Days -1 and 0 (Day 0=day of ovulation), and declined between Days 1 and 3 (P<0.05). There were no significant changes in the number of small or medium (4mm in diameter) follicles around days of follicle wave emergence (+/-2 days). The 1-3 follicles in the 2-3mm size range, which constituted a follicle wave (i.e. grew to > or =5mm in size before regression or ovulation), were the only small follicles to emerge in an orderly succession during the estrous cycle, approximately every 3-5 days. Thus, unlike in cattle, there is no apparent increase in numbers of small follicles at follicle wave emergence in cyclic sheep, and little evidence for selection of recruited follicles and follicular dominance.

Luteogenesis in cyclic ewes: echotextural, histological, and functional correlates

To date, it has not been possible to detect corpus luteum (CL) by ultrasonography, immediately following ovulation, in the ewe. Early CL detection is essential to be able to relate luteal outcome to the developmental pattern of the ovulated follicle and to confirm ovulation. Image analysis of the CL may be useful in providing a noninvasive picture of CL differentiation and function. The present study was designed to use high-resolution ultrasonography to monitor and to correlate the echotextural, histological, and functional attributes of the developing ovine CL from Days 1 to 3 after ovulation. Ten ewes underwent twice-daily transrectal ultrasonography and blood sampling from the day of synchronized estrus. Ewes were ovariectomized at 12-24, 36-48, and 60-72 h after ovulation. Ovaries collected were scanned in a water bath before processing for histology. Ultrasonographic images of CL were analyzed for echotexture. Histological sections were analyzed for the percentage area of the CL occupied by blood clot or luteal tissue. Serum samples were analyzed for progesterone concentration. Numerical pixel value, heterogeneity, and percentage of the CL occupied by blood clot declined (P<0.05) from 12-24 to 60-72 h after ovulation. Luteal area and serum progesterone concentration increased (P<0.05) from 12-24 to 60-72 h. The results indicated that it was possible to visualize developing CL as early as 12-24 h after ovulation in the ewe. Echotexture of the CL was closely associated with its morphological and functional characteristics; image analysis holds promise for noninvasive monitoring of CL differentiation and growth.