Serum concentrations of LH, FSH, oestradiol and cortisol were measured in control gilts not exposed to a boar and in gilts with fence-line exposure to a boar that allowed full muzzle contact. All gilts were between 134 and 200 days of age. Control gilts showed first oestrus at 193 ± 7 days of age (n = 5). Twelve of the gilts exposed to the boar showed first oestrus at 169 ± 5 days of age and five had not shown oestrus by 200 days of age. Introduction of a boar produced a transient increase in LH pulse frequency lasting no longer than 20 days (P < 0.001) in gilts responding to the boar with oestrus. Basal and mean serum LH concentrations were also increased (P < 0.05) in the gilts that responded to a boar with oestrus, but only in the 6 h after introducing the boar. Mean serum concentrations of FSH were lower in gilts exposed to a boar compared with the controls at 10 days after introduction of the boar, but by 20 days only gilts responding to the boar with oestrus had lower FSH concentrations (P < 0.05). Serum concentrations of cortisol decreased over the day the boar was introduced in all groups of gilts (P < 0.05) and were always highest in gilts exposed to a boar but not showing oestrus by 200 days of age (P < 0.05). There were no significant trends in serum concentrations of oestradiol but oestradiol concentrations varied over a wide range in gilts that did not respond to the boar with oestrus. These data suggest that the presence of an intact male stimulates an increase in LH pulse frequency over 10 days in prepubertal gilts, and that this increase may stimulate some gilts to become cyclic before 200 days of age. It was of interest that high cortisol concentrations were measured in the gilts that did not respond to the boar with oestrus. An increase in cortisol secretion would not appear to mediate the ability of a boar to induce oestrus in gilts.
D. L. Kingsbury and N. C. Rawlings
N. C. Rawlings and W. R. Ward
Summary. In 7 ewes during late pregnancy, peripheral plasma concentrations of oestrogens were correlated with uterine activity (P < 0·01; r=+0·47).
In myometrial tissue, the concentration of progesterone was similar to that in plasma; it rose to a plateau from Days 115 to 130 of pregnancy and then fell, but was still detectable during parturition. Myometrial oestrogen concentration was much higher than in plasma; from a peak at Days 100–115 it decreased, but rose sharply just before parturition.
N. C. Rawlings and W. R. Ward
Summary. In 4 Clun Forest ewes maternal peripheral plasma concentrations of progesterone were still elevated at the onset of parturient uterine activity. Fetal and maternal plasma concentrations of oestrogen started to rise before parturition and concentrations in maternal plasma were positively correlated with parturient uterine activity (P < 0·05; r = +0·42). Fetal plasma concentrations of corticosteroids were positively correlated with fetal plasma concentrations of oestrogen (P < 0·01; r = +0·65), but negatively correlated with maternal peripheral plasma progesterone concentrations (P < 0·05; r = −0·50). Before parturition plasma concentrations of PGF rose but stayed high only in maternal peripheral plasma. Maternal peripheral plasma concentrations of PGF were positively correlated with uterine activity (P < 0·05; r = +0·79) and plasma concentrations of oestrogen (P < 0·05; r = +0· 79), but negatively correlated with plasma concentrations of progesterone (P < 0·01; r = −0·54).
J. P. Ravindra and N. C. Rawlings
Daily transrectal ovarian ultrasonography was performed in ten ewes for 5 consecutive days, once in early July, once in late July (anoestrus) and then continuously until from mid-August until ewes had completed one ovulatory cycle. During anoestrus the size range and numbers of ovarian antral follicles were similar to those seen during the breeding season. However, numbers of small antral follicles (2–3 mm in diameter) decreased during late anoestrus, and maximum follicle diameter increased just before the short period of progesterone secretion preceding the first observed ovulation. The ovarian antral follicles that ovulated first and second in the breeding season grew from 2 mm in diameter to 5.7 ± 0.3 mm and 6.2 ± 0.3 mm diameter over 4.7 ± 0.3 days and 4.6 ± 0.3 days, respectively, and the interovulatory interval was 16.6 ± 0.2 days. During the first ovulatory cycle, follicles emerged to grow from the 2 mm size class on 11 of the 17 days, but peaks of emergence were seen on days 2 and 11. The first observed ovulation was preceded by a transient increase in serum concentrations of progesterone (6 days duration), with a peak concentration of 1.30 ± 0.22 nmol l−1. With ultrasonography, no evidence of ovulation was seen before the increase in progesterone secretion and no luteal structure was detected during the small increase in progesterone secretion; however, luteal structures are normally detected by ultrasonography only from 3 to 5 days after ovulation. An LH surge similar to a preovulatory LH surge preceded the first increase in progesterone secretion in five ewes. Oestrus occurred consistently with ovulation only at the second observed ovulation of the breeding season, after a normal luteal phase. LH pulse frequency and mean and basal serum concentrations of LH all increased in late anoestrus, but no major trends in serum concentrations of FSH and oestradiol were seen during this period. It was concluded that at the end of anoestrus there is no major change in ovarian antral follicle dynamics. At this time, increased LH secretion was seen as was a reduction in numbers of small antral follicles and a greater maximum diameter of follicles. A surge release of LH resulted in a short-lived secretion of progesterone, the source of which was unclear; this was followed by the first observed ovulation and the first ovulatory cycle of the breeding season. Oestrus occurred consistently only at the second observed ovulation of the season and the peak concentration of progesterone at each period of progesterone secretion increased to at least the second ovulatory cycle.
W. D. Currie and N. C. Rawlings
Summary. In ewes in the mid-luteal phase, LH pulse frequency (P < 0·01) and amplitude (P < 0·05) increased during a 24 h infusion of naloxone (0·5 mg/kg/h) compared to a 24 h infusion of vehicle (mean ± s.e.m.; 0·25 ± 0·03 vs 0·14 ± 0·01 pulses/h and 0·84 ± 0·08 vs 0·55 ± 0·08 ng/ml serum, respectively). The increase in pulse amplitude was immediate, but was less (P < 0·05) during the second 12h, compared to the first 12 h, of naloxone infusion (0·52 ± 0·14 vs 0·98 ± 0·08 ng/ml serum). Oestradiol concentrations were higher (P < 0·01) during naloxone than during control infusion (5·63 ± 0·26 vs 4·13 ± 0·15 pg/ml serum). In ovariectomized ewes in the breeding season, LH pulse frequency was lower (P < 0·01) during a 24 h infusion of morphine (0·5 mg/kg/h) than during a 24 h infusion of vehicle (mean ± s.e.m.; 1·17 ± 0·08 vs 1·71 ± 0·06 pulses/h). We conclude that long-term infusion of naloxone results in a sustained increase in LH pulse frequency but only a transient elevation in pulse amplitude. No effects on FSH secretion were noted. LH secretion was sensitive to morphine in the absence of ovarian steroids, suggesting that ovarian steroids are not required for the presence of functional opioid receptors capable of modulating LH release.
Keywords: LH; FSH; ewe; morphine; naloxone
N. C. Rawlings and I. J. Churchill
Summary. Spring-born crossbred ewe lambs were raised in a natural photoperiod and saline (N = 6) or naloxone (1 mg/kg) in saline (N = 6) was injected (i.m.) every 2 h for 6 h at 5, 10 and 15 weeks of age and for 8 h at 20,25 and 30 weeks of age. Blood samples were taken every 12 min during treatment periods.
Naloxone had no effect on time to first oestrus (controls 235 ± 6 days, naloxone 242 ± 7 days). Mean serum LH concentrations and LH pulse frequency were elevated by naloxone in ewe lambs at 20, 25, and 30 weeks of age (P < 0·05). The only FSH response to naloxone was a depression of mean serum concentrations at 30 weeks of age (P < 0·05). LH pulse amplitude was elevated at 5 weeks of age in all ewe lambs and declined thereafter to a nadir at 30 weeks of age in control, but not in naloxone-treated animals (P < 0·05). LH pulse frequency was elevated at 10 weeks of age in control ewe lambs and in all animals at 30 weeks of age (P < 0·05). FSH pulse frequency declined from 5 weeks of age in control ewe lambs (P < 0·05), with very few pulses noted in 25- and 30-week-old animals. We conclude that (1) opioidergic suppression of LH, but not FSH, secretion developed at 20 weeks of age in the growing ewe lambs used in the present study, with no obvious change in suppression before the onset of first oestrus: (2) pulsatile FSH secretion occurred in the young ewe lamb but was lost as the lamb matured: (3) attainment of sexual maturity was preceded by an elevation in LH pulse frequency.
Keywords: ewe lamb; naloxone; LH; FSH; sexual maturation
N. C. Rawlings and W. R. Ward
Summary. Fetal hypophysectomy performed between 97 and 130 days of gestation caused a significant (P < 0·005) prolongation of pregnancy in 5 goats in which every fetus was treated. Three of these goats gave birth spontaneously. Sham surgery or hypophysectomy of one fetus of twins had no effect on gestation length. Hypophysectomized kids, delivered after prolonged pregnancy, were significantly heavier than normal term kids (P < 0·005) and had lighter adrenals (P < 0·025). Measurements of maternal peripheral plasma concentrations of progesterone and total unconjugated oestrogens showed that the changes in goats carrying hypophysectomized fetuses were similar to those of normal pregnancy except that the prepartum oestrogen peak was absent, whether or not parturition occurred spontaneously.
A. P. Beard and N. C. Rawlings
The mammalian reproductive system is sensitive to exposure to endocrine disrupting chemicals, particularly during sexual maturation. The purpose of this study was to examine reproductive function in second and third generation male and female mink exposed to pesticides from conception to maturity. The mink were fed untreated feed or feed treated with Lindane (1 mg kg−1 day−1), Carbofuran (0.05 mg kg−1 day−1 or Pentachlorophenol (1 mg kg−1 day−1) from the time they were weaned. The second generation mink had also been exposed to the pesticides in utero and from their mother's milk as their mothers were similarly fed pesticides, from 3 weeks before breeding. The third generation mink were the offspring of mink (second generation females) who had themselves undergone long-term exposure to pesticides from conception onwards. Blood samples and endocrine tissues were obtained at necropsy from both generations of mink. No overt signs of toxicity were seen. The pesticides did not affect the percentage of mink mated. Lindane treatment reduced the proportion of mated mink that subsequently whelped (P < 0.1) and the litter size of mink that whelped (P <0.05). Testis size was reduced in the Lindane-treated, third generation males (P < 0.05). Serum concentrations of cortisol, testosterone and oestradiol were not affected by any pesticide treatment; however, thyroxine concentration was reduced by Pentachlorophenol (P < 0.05). In conclusion, exposure of mink to Lindane from conception resulted in a decrease in reproductive efficiency when they were subsequently mated, leading to a 60% reduction in the number of kits born.
R. K. Chandolia, A. C. O. Evans, and N. C. Rawlings
In bull calves serum concentrations of LH, FSH, and to a lesser extent testosterone, are increased transiently, between 6 and 20 weeks of age. The function of gonadotrophin and testosterone secretion in this period of growth and development was tested by injecting five Hereford bull calves with a GnRH agonist (15 mg Leuprolide acetate) i.m. at 6, 10 and 14 weeks of age; five vehicle treated calves acted as controls. On the basis of blood samples taken every 15 min for 10 h, at 12 weeks of age, mean serum concentrations of LH, FSH and testosterone and LH and FSH pulse frequency and amplitude were decreased (P < 0.05) by Leuprolide acetate. At 24 weeks of age, mean serum concentrations of LH, and LH and FSH pulse frequency in Leuprolide acetate treated calves exceeded (P < 0.05) that seen in control calves. On the basis of blood samples taken every other week, treatment with Leuprolide acetate decreased mean serum concentrations of FSH and testosterone at 14, 16 and 18 weeks of age compared with control calves and delayed the peak of the early increase in LH secretion from 20 to 24 weeks of age (P < 0.05). Scrotal circumference between 22 and 50 weeks of age, pixel units from ultrasound images of the testes, testis mass at castration at 50 weeks of age, and numbers of spermatids and pachytene spermatocytes were all lower in Leuprolide treated calves than in controls. A transient increase in secretion of LH, FSH and testosterone in young bull calves before 20 weeks of age may, therefore, be a critical step in the initiation and timing of testicular development in bull calves.
A. C. O. Evans, G. P. Adams, and N. C. Rawling
The aim of this study was to characterize changes in ovarian follicle dynamics in relation to changes in hormone secretion in heifer calves from birth to 8 months of age. The position and diameter of ovarian follicles ≥4 mm in diameter were recorded, the number of ovarian follicles ≥2 mm in diameter counted, and blood samples collected daily for periods of 18 days, starting at 2, 8, 14, 24 and 34 weeks of age in ten heifers. The mean age at first ovulation was 52.8 ± 1.6 weeks. At all ages ovarian follicular development occurred in a wave-like manner, as in mature cattle. The maximum diameter of the dominant and the largest subordinate follicles increased between 2 and 34 weeks of age (P < 0.05); however, the greatest increase occurred between 2 and 8 weeks of age. There was a similar increase in the numbers of small and large ovarian follicles (P < 0.05). The duration of detection of dominant follicles (number of days visible at a diameter of ≥4 mm) also increased between 2 and 34 weeks of age (P < 0.05). The emergence of waves of follicular development was preceded by peaks in plasma FSH concentrations (P < 0.05) at 2 weeks of age but this was less clear at other ages. There was a rise in circulating concentrations of gonadotrophins between 4 and 14 weeks of age. We concluded that in heifer calves as young as 2 weeks of age ovarian follicles grew in a wave-like fashion, similar to those of adult cattle. We speculate that the early rise in gonadotrophin secretion stimulated the increase in numbers of follicles and follicle diameters observed, indicating an early critical step in reproductive development.