Bromocriptine-induced premature oestrus is associated with changes in the pulsatile secretion pattern of follicle-stimulating hormone in beagle bitches.
(9/254)
The secretory profiles of LH and FSH were investigated before and during the administration of bromocriptine in six beagle bitches. Plasma samples were obtained via jugular venepuncture at 10 min intervals for 6 h every 2 weeks until the next ovulation. Bromocriptine treatment was started 100 days after ovulation. Both before and after bromocriptine treatment, LH and FSH pulses occurred together. The mean duration of the FSH pulse (120 min) was significantly longer than that of the LH pulse (80 min). The interoestrous interval in the bitches treated with bromocriptine was significantly shorter than that of the preceding cycle (160 +/- 3 versus 206 +/- 24 days). The mean basal plasma FSH concentration (7.4 +/- 0.6 versus 6.1 +/- 0.7 iu l-1) and the mean area under the curve for FSH (46.6 +/- 4.7 versus 40.4 +/- 4.4 iu l-1 in 6 h) increased significantly after the start of the bromocriptine treatment. In contrast, the differences in mean basal plasma LH concentration (2.1 +/- 0.2 versus 2.0 +/- 0.2 micrograms l-1) and the mean area under the curve for LH (19.0 +/- 3.1 versus 19.5 +/- 2.5 micrograms l-1 in 6 h) between the day before and 14 days after the start of the bromocriptine treatment were not significant. Bromocriptine administration also lowered the mean amplitude of the FSH pulse and shortened the mean duration of the FSH pulse, without influencing the LH pulse. In addition to demonstrating the concurrent pulsatile secretion of LH and FSH, the results of the present study demonstrate that the bromocriptine-induced shortening of the interoestrous interval in the bitch is associated with an increase in plasma FSH concentration without a concomitant increase in plasma LH concentration. This finding indicates that treatment with the dopamine agonist bromocriptine increase plasma FSH to a concentration that results in the enhancement of follicle development. (+info)
Duration of the seasonal anestrus in sheep selected for fertility in a fall-lambing system.
(10/254)
Crossbred ewes (1/2 Dorset, 1/4 Rambouillet, and 1/4 Finnsheep) from a flock being selected for spring fertility, defined as ability to lamb following ram exposure in May and June in Virginia (37 degrees N latitude), were used to study the duration of the seasonal anestrus. In the first 3 yr of the study (1992, 1993, and 1995), mature ewes were divergently selected based on EBV for fertility, and the duration of anestrus was measured by continuously exposing the ewes to vasectomized rams equipped with marking harnesses from mid-January until approximately August 1. Only ewes that had lambed in the previous fall were used to ensure that ewes were in a comparable physiological state, and the same rams remained with the ewes in each year to avoid induction of estrus by introduction of novel rams. The duration of anestrus in high-fertility ewes (n = 26; mean fertility EBV of 12.6%) was 28.4 d, which was significantly less than the 70.2 d of anestrus observed for low-fertility ewes (n = 15; mean fertility EBV of .3%). Five high-fertility ewes did not exhibit a period of anestrus. The regression of number of days of anestrus on fertility EBV was -2.15 +/- .72 d/%. In yr 4 (1997), 11 high-fertility and two low-fertility ewes were evaluated. None of these ewes exhibited a clear seasonal anestrus; six unequivocally cycled continuously. Between January 23 and July 31, the mean duration of anestrus for these ewes was only approximately 11 d. The duration of anestrus for high-fertility ewes seems to be the shortest reported for temperate sheep breeds. (+info)
Photoperiodic versus metabolic signals as determinants of seasonal anestrus in the mare.
(11/254)
The objectives of this study were to compare the timing and mechanisms controlling the onset of anestrus in young and mature mares treated either continuously with melatonin and in those that remained untreated. Changes in body weight, subcutaneous body fat measured to provide an estimate of total body fat, and circulating concentrations of leptin were compared throughout the 1-yr experimental period. The results demonstrate that in young mares the timing of anestrus occurs significantly earlier in the year than in mature mares and that mature mares are more likely to exhibit continuous reproductive activity during the nonbreeding season. The propensity of mature mares to exhibit this phenomenon is not modified by continuous treatment with melatonin but is associated with higher mean circulating concentrations of leptin, body weight, and estimated percent of body fat. In both young and mature mares, body weight, percent of body fat, and circulating concentrations of leptin are higher during summer than winter months. We conclude that, in the mare, the reproductive response to a decrease in photoperiod or a presumptive inhibitory melatonin signal is modified by energy availability, which may be signaled to the hypothalamus-pituitary axis via a change in the circulating concentration of leptin. An additional observation confirmed that the prolactin axis is responsive to continuous treatment with melatonin but that a suppression of prolactin secretion is limited to the spring months. (+info)
Pulsatile secretion pattern of growth hormone during the luteal phase and mid-anoestrus in beagle bitches.
(12/254)
The pulsatile secretion pattern of growth hormone was investigated during four stages of the luteal phase and during mid-anoestrus in six cyclic beagle bitches. Plasma samples were obtained via jugular venepuncture at 10 min intervals for 12 h at 19 +/- 2 (mean +/- SEM; luteal phase 1), 38 +/- 2 (luteal phase 2), 57 +/- 2 (luteal phase 3), 78 +/- 2 (luteal phase 4) and 142 +/- 4 days (mid-anoestrus) after ovulation. During all stages, growth hormone was secreted in a pulsatile fashion. The mean basal plasma growth hormone concentration during luteal phase 1 (2.2 +/- 0.3 microgram l(-1)) was significantly higher than that during luteal phase 4 (1.5 +/- 0.1 microgram l(-1)) and mid-anoestrus (1.4 +/- 0.2 microgram l(-1)). The mean area under the curve (AUC) above zero during luteal phase 1 (27.3 +/- 2.7 microgram l(-1) in 12 h) tended to be higher than that during luteal phase 4 (20.8 +/- 1.8 microgram l(-1) in 12 h) and mid-anoestrus (19.2 +/- 2.5 microgram l(-1) in 12 h). In contrast, the mean AUCs above the baseline during luteal phase 1 (1.1 +/- 0.5 microgram l(-1) in 12 h) and luteal phase 2 (1.2 +/- 0.5 microgram l(-1) in 12 h) were significantly lower than that during luteal phase 4 (2.8 +/- 0.5 microgram l(-1) in 12 h). In conclusion, the pulsatile secretion pattern of growth hormone changes during the luteal phase in healthy cyclic bitches: basal growth hormone secretion is higher and less growth hormone is secreted in pulses during stages in which the plasma progesterone concentration is high. It is hypothesized that this change is caused by a partial suppression of pituitary growth hormone release by progesterone-induced growth hormone production in the mammary gland. The progesterone-induced production of growth hormone in the mammary gland may promote the physiological proliferation and differentiation of mammary gland tissue during the luteal phase of the bitch by local autocrine-paracrine effects. In addition, progesterone-induced mammary growth hormone production may exert endocrine effects, such as hyperplastic changes in the uterine epithelium and insulin resistance. (+info)
Characterization and distribution of gonadotrophs in the pars distalis and pars tuberalis of the equine pituitary gland during the estrous cycle and seasonal anestrus.
(13/254)
Little is known about the neuroendocrine control of fertility in the horse. In this species, unusual features characterize the normal estrous cycle such as a prolonged preovulatory LH surge during the follicular phase and a distinctive FSH surge during the midluteal phase. This study investigated the distribution and hormonal identity of gonadotrophs in the pars distalis (PD) and pars tuberalis (PT) of the equine pituitary gland as possible morphological bases for the referred unusual endocrine characteristics. In addition, the proportion of gonadotrophs in relation to other pituitary cell types during both the estrous cycle and anestrus were investigated. Pituitary glands were collected from sexually active (n = 5) and seasonally anestrous (n = 5) mares in November, and single or double immunofluorescent staining was carried out on 6-microm sections using monoclonal antibodies to the LHbeta or FSHbeta subunits and a polyclonal antibody to ovine LHbeta. Gonadotrophs were densely distributed around the pars intermedia in the PD and in the caudal ventral region of the PT. In addition to isolated cells, clusters of gonadotrophs were found surrounding the capillaries. No significant differences were detected in the number of gonadotrophs between sexually active and anestrous mares in either the PD or PT. In the PD, gonadotrophs represented 22.7 +/- 5. 8% and 19.1 +/- 2.1% of the total cell density in sexually active and anestrous animals, respectively (P: > 0.05). However, in the PT, gonadotrophs accounted for a higher proportion of the total cell population in sexually active (6 +/- 0.1%) than in anestrous (1.2 +/- 0.05%) mares (P: < 0.02). Double immunofluorescence revealed that the majority of gonadotrophs were bihormonal (i.e., positive for LH and FSH); however, in the sexually active mare, a larger proportion of gonadotrophs (22.5 +/- 3.6%) were monohormonal for either LH or FSH, when compared to anestrous animals (9.7 +/- 1.2%; P: < 0.02). Based on these findings we conclude that: 1) although the relative distribution of gonadotrophs is similar to those reported for other species, a significantly larger proportion of gonadotroph cells is present in the equine pituitary gland; 2) gonadotroph density does not appear to differ between sexually active and anestrous mares in the PD; 3) a larger proportion of gonadotrophs is apparent in the PT of sexually active animals; and 4) although a large incidence of bihormonal gonadotrophs is present in the horse, specific LH or FSH cells differentiate predominantly during the sexually active phase. (+info)
Effects of recent sexual experience and melatonin treatment of rams on plasma testosterone concentration, sexual behaviour and ability to induce ovulation in seasonally anoestrous ewes.
(14/254)
The aim of this study was to determine whether advancing the seasonal changes associated with rams by treatment with exogenous melatonin and allowing the rams previous sexual experience would increase the proportion of anoestrous ewes ovulating in early July. North Country Mule ewes (n = 225) were grouped by live body weight and body condition score and allocated randomly to the following treatments: (i) isolated from rams (control; n = 25); (ii) introduced to rams (treatment 2); (iii) introduced to rams that had mated with ewes during the previous 2 days (treatment 3); (iv) introduced to rams implanted with melatonin (treatment 4); and (v) introduced to rams that were implanted with melatonin and had mated with ewes during the previous 2 days (treatment 5). Treatments 2-5 were replicated (2 x 25 ewes) and two rams were introduced to each replicate group. Introductions began on 4 July and were completed by 11 July. The rams were withdrawn from the ewes after 8 days. Melatonin was administered as a subcutaneous implant (Regulin((R))) on 22 May and again on 20 June. Blood samples were taken from all rams to determine plasma melatonin and testosterone concentrations (19 samples in 6 h). The behaviour of the sheep was videotaped continuously during the first 3 h after the ram was introduced. Ovulation was detected by an increase in plasma progesterone concentrations from < 0.5 ng ml(-1) to > 0.5 ng ml(-1). Mean +/- SE plasma melatonin concentrations were 649.7 +/- 281.4 and 18.3 +/- 2.4 pg ml(-1) in rams with and without melatonin implants, respectively (P < 0.001). Melatonin implants also increased plasma testosterone concentrations from 4.30 +/- 1.88 to 10.10 +/- 1.10 ng ml(-1) (P < 0.01), the libido of the rams and the proportion of ewes that ovulated in response to the rams (43 and 56% (treatments 4 and 5) versus 24% (treatments 2 and 3)). In conclusion, implanting rams with melatonin before introducing them to seasonally anoestrous ewes increases the proportion of ewes that ovulate in response to introduction of a ram, but previous sexual experience of rams appears to have little or no effect. (+info)
Calf removal improves conception rates to the Ovsynch and CO-Synch protocols.
(15/254)
Beef cows (n = 473) from two locations were stratified by breed, postpartum interval, age, and AI sire and were randomly allotted to one of four treatments for synchronization of ovulation. Ovulation synchronization protocols included the Ovsynch protocol with (n = 114) or without (n = 123) 48-h calf removal from d 7 to 9 (d 0 = 1st GnRH injection) or the CO-Synch protocol with (n = 119) or without (n = 117) 48-h calf removal from d 7 to 9. The Ovsynch protocol included administration of GnRH (100 microg; i.m.) on d 0, PGF2alpha (25 mg; i.m.) on d 7, GnRH (100 microg; i.m.) on d 9, and timed insemination on d 10. The CO-Synch protocol included administration of GnRH (100 microg; i.m.) on d 0, PGF2alpha (25 mg; i.m.) on d 7, and GnRH (100 microg; i.m.) with timed insemination on d 9. Blood samples were collected from all cows on d -10 and d 0 for analysis of serum progesterone. Cows with at least one serum progesterone concentration greater than 1 ng/mL were considered to be cyclic at the time of treatment. Conception rates of cows that received the CO-Synch + calf removal, Ovsynch + calf removal, CO-Synch, or Ovsynch protocol (63, 61, 54, and 52%, respectively) were not different (P = 0.50). Conception rates were not different (P = 0.80) among CO-Synch- and Ovsynch-treated cows; however, both estrual status and 48-h calf removal affected conception rates. Conception rates of cyclic cows (66%) were greater (P = 0.01) than those of anestrous cows (53%), regardless of which synchronization protocol was used. When data were pooled across synchronization protocol, conception rates of cows with 48-h calf removal (62%) were greater (P = 0.09) than conception rates of cows without calf removal (53%). The CO-Synch + calf removal protocol induces a fertile ovulation in cyclic and anestrous cows, requires handling cattle just three times, results in high conception rates from timed insemination, and should be a useful program for synchronization of ovulation in beef cows. (+info)
Reproductive seasonality in domestic sows kept outdoors without boars.
(16/254)
Plasma progesterone, LH and prolactin concentrations were measured twice a week in mature sows kept outdoors without boars in two experiments to examine whether perception of daylength change underlies seasonal infertility in domestic pigs. In Expt 1, melatonin implants inserted on 12 April or 22 May to block perception of the increasing daylength did not affect the oestrous cycle significantly, since only two untreated control sows became seasonally anoestrous. In Expt 2, all control sows became anoestrous for 131 +/- 42.5 days (n = 11). Melatonin implants inserted at the spring equinox (n = 9) prevented seasonal anoestrus (P < 0.001), but timed daily oral melatonin administration was less effective (P < 0.05): 5 of 11 sows became anoestrous for 132 +/- 45.6 days. In both experiments, there were significant low-amplitude seasonal rhythms in mean plasma prolactin and LH concentrations. Prolactin reached maximum concentrations 2-4 weeks before the summer solstice, whereas LH reached a nadir 4-6 weeks after the summer solstice. Neither anoestrus nor melatonin administration altered these patterns consistently. Endogenous plasma melatonin was higher (P < 0.001) during darkness (12.5 ng l(-1)) than during daytime (8.9 ng l(-1)) in untreated sows, but only clearly so during spring and summer. Melatonin implants increased mean daily plasma melatonin to 146 ng l(-1), whereas melatonin fed at 15:00 h increased values to 40-60 ng l(-1) 2-4 h after administration, but daytime concentrations were unchanged. Melatonin administration, despite decreasing seasonal anoestrus, did not prevent the seasonal increase in plasma prolactin and had no significant effect on plasma LH; therefore, its role in regulating seasonal changes in the reproduction of domestic sows remains uncertain. (+info)