Fecundity Gene Research Articles

Effect of pre-mating nutrition on reproductive performance of Booroola Merino × South Australian Merino ewes

To investigate the effect of pre-mating nutritional status on the reproductive performance of ewes carrying the Booroola ( Fec B ) gene, Booroola Merino × South Australian Merino ewes heterozygous for the high fecundity gene ( Fec B Fec + ), were exposed to varying levels of nutrition 11 weeks before and 6 weeks during mating, and the reproductive performance and productivity were assessed. Liveweight varied from 44.0 to 55.2 kg for five nutritional treatments and mean ovulation rates varied from 2.62 to 3.01. The positive response of ovulation rate to improved nutrition was reflected in increases in litter size at days 40 and 80 of pregnancy, and at birth ( P < 0.05). There were no statistically significant differences between nutritional treatments for either the proportion of pregnant ewes of ewes mated or lamb survival. Differences between nutritional treatments for ovulation rate and litter size were not reflected in net reproductive efficiency (lambs weaned per ewe exposed). Lamb growth was not affected by varying the level of pre-mating nutrition of the ewe, although ewe fleece weight and wool quality (tenderness) were compromised.

Effect of castration on plasma concentrations of luteinizing hormone and follicle-stimulating hormone in adult Merino rams which were homozygous carriers or non-carriers of the Booroola fecundity gene

Before castration, the mean plasma concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) did not differ between FF and ++ Booroola rams. After castration, mean LH and FSH concentrations increased after 8 h, and for the next 14 days the rate of increase in FSH, but not LH, secretion was significantly faster in FF than in ++ rams (P less than 0.05). Mean FSH concentrations over this period were significantly higher in FF than in ++ rams (P less than 0.05). In both genotypes, the ranked FSH values did not significantly change their order over time, i.e. a significant within-ram effect was noted (P less than 0.05). Repeated-measures analysis of variance indicated a significant effect of genotype on mean FSH secretion (P less than 0.05) and a significant effect of sire in the FF (P less than 0.05), but not the ++ (P = 0.76), genotype. From Day 28 to Day 58 after castration, FSH and LH concentrations were variable and no overall increases in concentrations were observed. The mean concentrations of both hormones over this period were not related to genotype. There were no gene-specific differences in pulsatile LH secretion 14 weeks after castration. However, the mean LH, but not FSH, response to a bolus injection of 25 micrograms of gonadotrophin-releasing hormone (GnRH) was significantly higher in FF than in ++ rams (P less than 0.05) and this was not significantly affected by sire. These studies support the hypothesis that the F gene is expressed in adult rams, in terms of pituitary responsiveness to an injection of GnRH and to the removal of the testes, but it is not clear from this study whether the influence of sire is related to or independent of the apparent gene-specific differences.

Inhibin production in vitro by granulosa cells from Booroola ewes which were either homozygous or non-carriers of a fecundity gene influencing their ovulation rate

The production of inhibin by granulosa cells was studied in vitro using cells from follicles of various sizes and health. Follicles were recovered on Days 10-13 of the oestrous cycle, from Booroola x Romney ewes which were homozygous (FF) carriers or non-carriers (++) of the fecundity (F) gene. Inhibin was measured using a bioassay based on the suppression of follicle-stimulating hormone (FSH) output by cultured pituitary cells from ovariectomized Romney ewes and, in some instances, for comparative purposes, by radioimmunoassay also. Geometric mean inhibin production by granulosa cells from nonatretic follicles increased with increasing follicle diameter, during the first 24 h of culture, for both genotypes. The geometric mean production of inhibin by cells from nonatretic 3-4.5 mm diameter FF follicles (the largest follicles found in FF ewes), was significantly higher (P less than 0.05) than that by cells from non-atretic 3-4.5 mm diameter ++ follicles, but similar to that of cells from non-atretic greater than or equal to 5 mm diameter ++ follicles. The production of oestradiol-17 beta by cells cultured in the presence of testosterone (1 microgram/ml) followed a pattern similar to cellular inhibin production. There was a positive linear correlation between inhibin and oestradiol-17 beta production during the first 24 h of culture, for both genotypes. In addition to acting as a substrate for oestradiol-17 beta synthesis, testosterone generally had a slight, stimulatory effect on inhibin production.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma LH, FSH and testosterone concentrations in adult rams which were homozygous carriers or non-carriers of the Booroola fecundity gene

No gene-specific differences were found with respect to LH or testosterone pulsatile secretion (over 12 h), or in 12 hourly mean FSH concentrations in adult Booroola FF and ++ rams. Also, no differences between genotypes in the LH response to an injection of testosterone propionate, the FSH response to an infusion of bovine follicular fluid, or the testosterone response to injections of PMSG were noted. However, during the phase of seasonal testicular development, mean testosterone pulse amplitude (over 12 h) and the FSH response to 25 micrograms GnRH were higher in FF than in ++ rams (P less than 0.05); there were also significant effects of sire (P less than 0.05 in FF genotype only) and litter size (P less than 0.05) on testosterone pulse amplitude and GnRH-stimulated FSH release, respectively. During the breeding season, mean LH, but not FSH, concentrations were higher in FF than in ++ rams, after an injection of 0.5 micrograms GnRH; LH release was not affected by sire or litter size (P greater than 0.05). Long-term studies revealed that the FF rams were born in significantly larger litters, they weighed significantly less than ++ rams (P less than 0.05), and that bodyweight was significantly correlated (P less than 0.05) with litter size. There were no differences in testis size, and testis size was not significantly correlated with bodyweight. There was a strong tendency (P = 0.056) for overall mean FSH concentrations, measured weekly for 9 months, to be highest more often in FF than in ++ rams.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary Binding Sites for Gonadotrophin‐Releasing Hormone in Booroola Merino Ewes which were Non‐Carriers or Homozygotes of the Fecundity Gene F

Abstract Pituitary binding sites for gonadotrophin-releasing hormone (GnRH) were examined in Booroola ewes on Days 4 and 12 of the oestrous cycle and more than 12 months after ovariectomy. No significant differences were observed in the affinity of the binding sites for [(125) I]D Ala6, des Gly(10) GnRH ethylamide, in non-carriers (++) or homozygotes of the fecundity gene (FF), in intact or ovariectomized animals (overall K(a)= (1.8 +/- 0.1) x 10(9) M(-1); mean +/- SEM, n = 67). In ++ ewes, the number of GnRH binding sites on Day 4 of the oestrous cycle (0.199 +/- 0.025 fmol/mg pituitary, n = 8) was significantly greater (P<0.05) than on Day 12 (0.107 +/- 0.012 fmol/mg pituitary, n = 12). In contrast in FF ewes the number of binding sites on Days 4 and 12 were similar (Day 4: 0.119 +/- 0.030, n = 8; Day 12: 0.092 +/- 0.014, n = 10). On Day 4, but not Day 12, the binding site numbers were significantly higher in ++ compared with FF pituitaries (P<0.05). Likewise on Day 4, but not Day 12, the plasma concentrations of follicle-stimulating hormone were significantly higher (P<0.005) in FF (1.60 +/- 0.15 ng/ml) than ++ ewes (0.96 +/- 0.10 ng/ml). After ovariectomy, no gene-specific differences in binding site numbers were noted despite significantly higher plasma follicle-stimulating hormone concentrations in FF animals. No gene-specific differences in plasma luteinizing hormone concentrations were observed in these animals on Days 4 or 12, or after ovariectomy. Moreover, luteal phase plasma progesterone concentrations were also similar between ++ and FF ewes. We conclude that the gene-specific differences in pituitary responsiveness to GnRH and in pituitary gonadotrophin output are unlikely to be due to differences in GnRH receptor binding affinities.

Effects of oestradiol-17 , progesterone or bovine follicular fluid on the plasma concentrations of FSH and LH in ovariectomized Booroola ewes which were homozygous carriers or non-carriers of a fecundity gene

The plasma concentrations of FSH and LH were measured in ovariectomized Booroola FF and ++ ewes before and after treatment with subcutaneous implants of oestradiol-17 beta (0, 2 or 8 cm Silastic capsules; 5 ewes/genotype per dose) or progesterone (0, 1 or 3 Silastic envelopes; 5 ewes/genotype per dose) or subcutaneous injections of steroid-free bovine follicular fluid (bFF; 0, 0.5, 1.0, 2.5 or 5 ml; 4 ewes/genotype per dose). During the first 50 h after implantation of oestradiol or progesterone, or the first 24 h after bFF treatment, the FSH and LH concentrations in plasma were not different between the genotypes although there were significant effects of the steriods and bFF with respect to dose (P less than 0.05). At 6 days after steroid implantation, no gene-specific effects were noted for the plasma concentrations of FSH although significant effects of dose of oestradiol (P less than 0.01) but not progesterone were noted. Also at 6 days after steroid implantation, no gene-specific differences in the pulsatile patterns (i.e. peak frequency or amplitude) of plasma LH concentrations were noted although there were significant effects of steriod dose (P less than 0.05) on frequency and/or amplitude. It is concluded that the higher ovulation-rate in FF than ++ Booroola ewes is unlikely to be due to gene-specific differences in the sensitivity of the hypothalamic-pituitary axis to ovarian hormones.

Secretion of bioactive inhibin by the ovary of the Booroola Merino ewe with or without a copy of the fecundity (F) gene.

The secretion rates of bioactive inhibin, oestradiol and progesterone were measured during the mid-luteal phase and at various times during the follicular phase of the cycle by a sensitive bioassay using sheep pituitary cells in culture in 12 Booroola ewes with and without copies of the Fecundity (F) gene in which the left ovary had been auto-transplanted to the neck. Inhibin secretion was high during the luteal phase and fell in the early follicular phase in all genotypes (P less than 0.01). In Booroola ewes with a F/- genotype, inhibin secretion then increased again, towards luteal rates, in the mid and late follicular phases. In Booroola ewes without a copy of the F gene (+/+) inhibin secretion remained low at all three sampling times in the follicular phase. The secretion rate of inhibin at 36 h (P less than 0.1) and 48 h (P less than 0.01) were significantly lower in ewes from the +/+ (no copy of the gene) ewes than in F/- (one copy of the gene) ewes. Oestradiol secretion was low during the luteal phase and increased steadily during the early (24 h) to a plateau in the mid (36 h; P less than 0.01) and late (48 h; P less than 0.05) follicular phase. Progesterone secretion was high during the luteal phase, and decreased to a very low rate by 24 h after prostaglandin (PG) treatment (P less than 0.001) and remained low. At 24 h after PG the concentration of FSH was significantly lower (P less than 0.01) than that during the luteal phase and remained suppressed until the onset of the LH surge.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics and experiences of Chios breed

Discussed are the reproductive and productive characteristics of the dairy and prolific Chios sheep breed, originating from the homonymous Greek island. Besides the island, the breed is also raised in the Greek mainland, the westcoast of Turkey and in Cyprus. It is early maturing, with long reproductive reason and lambing period, extending from October to March. Inspite its high ovulation rate, repeatability estimates do not suggest the presence of fecundity genes. The average prolificacy ratio ranges between 1.80 and 2.0, with triplets and quadruplets not uncommon. The average exploitable milk yield varies between 180 and 200 kg, with occasionally reported productions of up to 400 and 500 kg. Repeatabilities of prolificacy and milk production based on island data were found 0.15 and 0.40, respectively. Heritability of milk yield from the island was 0.31 and 0.40, respectively, for second and third lactations. Recent estimates from Cyprus report values of 0.30 and 0.39 for 90-day milk and total milk yield, respectively. Other parameters and information on udder (mechanical milking), growth, and carcass characteristics as well as on crossbreeding trials are also reported. Some considerations are given with regard to potential and valorization of this highly productive sheep breed.

Induction of ovulation in chronically hypophysectomized Booroola ewes.

Booroola Merino ewes, with (F+; N = 17) and without (++; N = 13) a copy of the fecundity gene were hypophysectomized and 6 weeks later were given an i.m. injection of PMSG (high, medium or low dose) followed by hCG. The induced ovulation rates were observed laparoscopically. Ovulation rates were significantly higher (P less than 0.01) in Booroola F+ ewes than in ++ ewes (8.00 +/- 1.66 s.e.m. vs 3.62 +/- 1.10 respectively). This suggests that the high fecundity of the Booroola ewe may be due primarily to ovarian rather than pituitary factors.

Immunoassay of gonadotrophin-releasing hormone in brain tissue of Booroola Merino ewes.

The presence of a fecundity gene (F) in Booroola Merino ewes increases the ovulation rate. To test how F gene expression affects the gonadotrophin-releasing hormone (GnRH) concentration in hypothalamic or extrahypothalamic regions of the brain, GnRH was measured by radioimmunoassay in acetic acid extracts of various brain tissues from Booroola ewes which were homozygous (FF), heterozygous (F+) or non-carriers (++) of the F gene. The GnRH concentration in brain tissues from FF, F+ and ++ animals which had been ovariectomized 5 months previously was also evaluated. No significant F gene-specific differences were noted in any of the brain areas tested, in intact or ovariectomized animals. However, in ovariectomized ewes, the concentrations of GnRH increased about 2-fold in the median eminence of the hypothalamus, remained unchanged in the medial basal hypothalamus and dropped to less than 10% of the values in intact ++ animals in the preoptic area. These studies suggest that the changed pituitary sensitivity and increased gonadotrophin release in Booroolas carrying the F gene(s) is not attributable to increased hypothalamic GnRH concentrations in these animals.

Differences in gonadotrophin-stimulated cyclic AMP production by granulosa cells from Booroola x Merino ewes which were homozygous, heterozygous or non-carriers of a fecundity gene influencing their ovulation rate

Granulosa cells from follicles of different sizes from Booroola x Merino ewes which were homozygous (FF), heterozygous (F+) or non-carriers(++) of a fecundity gene were obtained 0-48 h after cloprostenol injection on Day 10 of the oestrous cycle. The highest mean amounts of cAMP produced by the cells did not differ between the genotypes. However, in the ++ ewes it was attained by cells from follicles greater than or equal to 5 mm in diameter, whereas in F+ and FF ewes it was attained by cells from follicles 3-4.5 mm in diameter. Cells from 1-2.5-mm diameter follicles of FF ewes were more sensitive to FSH and LH than were corresponding cells from F+ or ++ ewes. Granulosa cells from greater than or equal to 5 mm diameter follicles of ++ ewes 12-24 h after injection of cloprostenol had a lower mean response to FSH and LH than did cells obtained 0-6 or 36-48 h after cloprostenol. No such effect of time was evident for cells from any size of follicles obtained from F+ or FF ewes. In 1-2.5-mm diameter follicles, the mean aromatase activity of granulosa cells from ++ and F+ ewes was similar, but significantly lower than that of cells from FF ewes. In 3-4.5 mm diameter follicles, the mean aromatase activity of cells from F+ and FF ewes was similar, and significantly higher than that of cells from ++ ewes. For all 3 genotypes, there was a significant positive relationship between FSH or LH stimulation of granulosa cell cAMP production and cellular aromatase activity.

Natural and induced ovulation rate in prolific and non-prolific breeds of sheep in Ireland, Morocco and New Zealand

Ovulation rate, in mixed-age groups of prolific and non-prolific ewe breed types, after administration of a range of doses of PMSG (0, 375, 750 and 1500 i.u.) during the follicular phase of the oestrous cycle, were compared in Ireland, Morocco and New Zealand. The ewes in Ireland and Morocco were from the Finnish Landrace and Galway, and D'Man and Timhadite breeds, respectively. In New Zealand Booroola Merino x Romney ewes which had been previously identified as heterozygous carriers (F+) of the Booroola high fecundity gene and purebred Romneys were used to represent the prolific and non-prolific genotypes respectively; in addition a group of Booroola Merino x Romney non-carriers (++) of the major gene were also included for comparison. Ovulation rate at the oestrus which preceded stimulation with PMSG was also measured in all animals. In all 3 locations the ewes of the prolific genotype had a greater ovulation rate after PMSG stimulation than did the non-prolific controls. However, this association between prolificacy and response to PMSG was removed when ovulation rate after PMSG was transformed by dividing by the ovulation rate observed before PMSG administration. Despite the differences in the genetic basis of their high prolificacy the pattern of response to PMSG over the range of dosages used was similar in Finnish Landrace, D'Man and Booroola Merino x Romney (F+) ewes and all breeds had means of about 10 ovulations in response to 1500 i.u. PMSG. Amongst the non-prolific breeds, the Timhadite was the most responsive to PMSG although it had the lowest natural ovulation rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian follicular activity in Booroola lambs with and without a fecundity gene.

The ovaries of 3-month-old Booroola lambs which were heterozygous carriers of a major gene (F) influencing the ovulation rate in mature ewes (i.e. F + lambs) were compared to those ofsimilarly-aged Booroola lambs which were non-carriers of the F-gene (i.e. ++ lambs). The ovaries of the F + Booroola lambs were significantly lighter (P less than 0.01) than those of ++ lambs even though the mean +/- s.e.m. number of follicles (greater than or equal to 1 mm diam.) in the F + lambs was greater than that in the ++ lambs (i.e. F + lambs, 30.2 +/- 2.5 follicles; ++ lambs, 18.4 +/- 1.2 follicles; P less than 0.01). In granulosa cells from non-atretic follicles (greater than or equal to 1 mm diam.) from F + and ++ Booroola lambs, FSH (NIAMDD-FSH-S16) doses of 100 and 1000 ng/ml caused significant stepwise increases (P less than 0.05) in cyclic adenosine 3',5'-monophosphate (cAMP) production compared to that achieved at FSH doses of 0 and 1 ng/ml or at any FSH dose in cells from atretic follicles. However, no significant differences in FSH-induced cAMP production were noted with regard to Booroola genotype or follicular diameter. None of the granulosa cell preparations from non-atretic follicles of 1-2.5 mm diameter from F + lambs (N = 13) or from non-atretic follicles of 1-4.5 mm diameter from ++ lambs (N = 16) responded to LH (NIAMDD-LH-S24; 10 or 1000 ng/ml) to produce significantly more cAMP than did the controls. In contrast, the granulosa cell preparations from non-atretic follicles of 3-4.5 mm diameter from F + lambs (N = 4) and from non-atretic follicles of greater than or equal to 5 mm diameter of ++ lambs (N = 4) produced significantly more cAMP (P less than 0.05) in response to LH (1000 and/or 10 ng/ml) relative to that in the controls. The theca interna from follicles of lambs of both genotypes had functional LH receptors as judged by the androstenedione responses to exogenous LH although no genotypic differences were noted. In F + lambs, the follicular fluid concentrations of testosterone but not oestradiol (i.e. in 1-4.5 mm diam. follicles) and granulosa cell aromatase activity (i.e. in 3-3.5 mm diam. follicles) were significantly higher (both P less than 0.05) than in corresponding follicles or cells from ++ lambs. Collectively the results suggest that the Booroola F-gene influences the composition and function of sheep ovaries before puberty.

125I-labelled hCG binding characteristics in theca interna and other tissues from Romney ewes and from Booroola x Romney ewes with and without a major gene influencing their ovulation rate.

Specific receptors for 125I-labelled hCG in ovarian follicle wall were located in the theca interna. No specific binding of 125I-labelled hCG was found in theca externa and/or stromal tissue. The kinetics of 125I-labelled hCG binding to theca interna followed second order kinetics with calculated association rate constants (ka +/- s.d.) of 1.57 +/- 0.16 X 10(6) and 0.57 +/- 0.02 X 10(6) litres mol-1 sec-1 at 37 degrees C and 22 degrees C respectively. Dissociation of specifically bound 125I-labelled hCG from theca interna was minimal at 37 degrees C and 22 degrees C. The binding of 125I-labelled hCG to theca interna could be displaced with PMSG, FSH-P and sheep LH but other sheep pituitary hormones and LH-releasing hormone showed little or no cross-reaction. The calculated binding capacities (Bmax) and equilibrium dissociation constants (Kd) for 125I-labelled hCG binding to theca interna did not differ between Romney ewes and Booroola x Romney ewes with and without the fecundity (F) gene on Day 10 of the oestrous cycle, during anoestrus or at 36 h after an injection of cloprostenol on Day 10 of the oestrous cycle. When the data for Day 10 and anoestrus were pooled, the median (range) Bmax and Kd values in non-atretic follicles (greater than or equal to 3 mm diameter) were 12.0 (5.1-23.5) fmol/mg protein and 0.10 (0.05-0.16) nM respectively. At 36 h after cloprostenol injection the respective median (range) Bmax and Kd values in non-atretic follicles (greater than or equal to 3 mm diam.) increased to 46.9 (28.4-70.3) fmol/mg protein and 0.23 (0.13-0.65) nM respectively. In corpora lutea the hCG binding characteristics were similar in all the above breeds/genotypes. On Day 10 of the cycle, the mean Bmax but not the mean Kd value was significantly higher (P less than 0.01) than the corresponding value at 36 h after cloprostenol injection. In granulosa cells, from follicles of greater than or equal to 5 mm diameter of Romney and Booroola x Romney (++) ewes and from follicles of greater than or equal to 3 mm diameter of Booroola x Romney (F+) ewes, the hCG binding characteristics were similar. In granulosa cells from smaller sized follicles from the above breeds/genotypes, no specific hCG binding was noted.

Adenosine cyclic 3',5'-monophosphate and steroid production by small ovarian follicles from Booroola ewes with and without a fecundity gene.

The tissue contents of adenosine cyclic 3',5'-monophosphate (cAMP) in freshly dissected follicles (0.13-1.00 mm diam.) were significantly higher in Booroola ewes containing a major fecundity gene (FF and F+ ewes) compared to those values in Booroolas with no copy of the gene (++ animals; P less than 0.025). After a 1 h incubation with LH + FSH, the respective proportions of follicles with a diameter of 0.13-0.52 mm (n = 288) and 0.53-1.00 mm (n = 271) that had synthesized greater than or equal to 0.6 pmol cAMP and greater than or equal to 1.0 pmol cAMP were significantly influenced by genotype (Booroola ewes homozygous for the F-gene, FF greater than heterozygous, F+ greater than ++; P less than 0.01 for both follicle size ranges). The contents of progesterone, androstenedione, testosterone and oestradiol-17 beta in minced ethanolic extracts of freshly dissected follicles (n = 188) were undetectable regardless of Booroola genotype. However, when follicles of 0.53-1.00 mm but not 0.13-0.52 mm diameter were cultured for 48 h with LH + FSH under 70 kPa of a 50% O2, 45% N2 and 5% CO2 gas mixture, the proportions that synthesized high levels of progesterone (greater than or equal to 4.0 ng), androstenedione (greater than or equal to 3 ng), and oestradiol (greater than or equal to 0.8 ng) were significantly influenced by genotype (FF greater than F+ greater than or equal to ++; P less than 0.05 for each steroid). No significant genotypic differences were noted for testosterone synthesis. Collectively, these results show that the Booroola F-gene has an influence on the maturation of ovarian follicles from an early stage of growth.

Gonadotrophin-stimulated cyclic AMP production by granulosa cells from Booroola x Romney ewes with and without a fecundity gene.

The influence of follicular size and health on FSH and LH stimulation of cAMP production by granulosa cells in vitro was studied in cells from Booroola X Romney ewes, with (F+) and without (++) a fecundity gene. The granulosa cells were obtained 0-48 h after the initiation of luteolysis on Day 10 of the oestrous cycle by cloprostenol. The highest mean amounts of cAMP produced by granulosa cells challenged with FSH or LH were not significantly different between the genotypes. However, they were achieved using granulosa cells from follicles greater than 3-4 mm in diameter in F+ ewes but from follicles greater than 4 mm in diameter in ++ ewes. Follicles may thus attain ovulatory maturity at a smaller diameter in F+ ewes than in ++ ewes. Granulosa cells from most atretic follicles gave a poor cAMP response to FSH or LH, compared to cells from non-atretic follicles. Granulosa cell responsiveness to FSH was independent of the time the cells were recovered after cloprostenol treatment in F+ ewes, but not in ++ ewes. Cellular responsiveness to LH was independent of time for sheep of both genotypes. There was a significant positive relationship for sheep of both genotypes between the level of aromatase activity in granulosa cells and cellular responsiveness to FSH and LH.