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Summary. Three experiments were carried out during seasonal anoestrus in Finnish Landrace and Scottish Blackface ewes, to establish whether the differences between the breeds in ovulation rate are functional during the non-breeding season and are therefore independent of the mechanism controlling ovulation.
In Expt 1, follicles ⩾2 mm in diameter were dissected from the ovaries of both breeds and incubated individually for 2 h to assess their ability to secrete oestradiol and testosterone. In both breeds, follicles producing ⩾500 pg oestrogen/ml/h (oestrogen-active) were readily identifiable from a population producing less (oestrogen-inactive). The number of oestrogen-active follicles in each breed was similar to the number of ovulations near the end of the breeding season. Oestrogen-active follicles also had more luteinizing hormone (LH) receptors and larger diameters than oestrogen-inactive follicles. There were, however, no significant differences between the two follicle types in follicular fluid or in-vitro testosterone concentrations.
In Expt 2, seasonally anoestrous Scottish Blackface ewes were unilaterally ovariectomized; the second ovary was removed 7 days later. Follicles from both ovaries were processed as described for Expt 1; oestrogen-active follicles were categorized according to their ability to produce >500 pg/ml/h. There were twice as many oestrogen-active follicles in the second ovary as in the first ovary; the number of oestrogen-active follicles in the second ovary was also similar to the total number of oestrogen-active follicles in both ovaries of the Scottish Blackface ewes in Expt 1. There were no significant differences between the first and second ovaries for any of the other parameters measured in oestrogen-active follicles. There were no significant changes in peripheral gonadotrophin concentrations measured 24 h after removal of the first ovary.
In Expt 3, seasonally anoestrous ewes of both breeds were challenged with an ovulatory dose of human chorionic gonadotrophin (hCG) (750 iu). There was a significant difference in the mean number of ovulations between the breeds and it was representative for the breed (Finnish Landrace 2·6 ± 0·2; Scottish Blackface 1·6 ± 0·2 mean ovulations per ewe). None of the saline-treated controls ovulated.
The results demonstrated that the mechanism controlling the number of mature, oestrogen-active follicles, and hence ovulation rate, is functional during seasonal anoestrus. This conclusion was confirmed by the observation that compensatory ovarian hypertrophy also occurs during seasonal anoestrus.
Keywords: sheep; follicle; ovulation rate; steroidogenesis; seasonal anoestrus
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Summary. Oxygen consumption and evaporation were measured in a single pregnant pipistrelle bat during labour and parturition of twins, using an open-flow respirometry system. During 233 min of measurements, three distinct phases were noted, which we suggest represent prelabour, labour and grooming or suckling the young.
On the basis of this hypothesis, during labour and parturition, oxygen consumption was a maximum of 8·9% of daily energy expenditure, evaporation was 2·7% of daily water turnover, and total water loss was 5·5% of daily water turnover in free-living bats in early lactation.
We estimated that, for the mother and young combined, oxygen consumption associated with grooming and suckling would be equivalent to 37·5% of daily energy expenditure of the mother, if carried out continuously. Similarly, evaporation due to grooming and suckling would be equivalent to 16·4% of daily water turnover.
In terms of daily energy expenditure and daily water turnover, labour and parturition are therefore cheap, but grooming and suckling (even ignoring costs in terms of losses in the milk) are expensive.
Keywords: bat; labour; parturition; oxygen consumption; evaporation
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The effects of recombinant bovine somatotrophin (BST) on the dynamics of ovarian follicular growth and development and peripheral insulin concentrations were investigated. Initially, studies were carried out in a population of Hereford × Friesian heifers to validate the ultrasound technique. In the first experiment, 12 heifers were injected daily with either 25 mg BST or vehicle for two oestrous cycles, and the effects on follicular dynamics and peripheral insulin were determined. In a second experiment, 12 heifers were given a single injection of 10 ml saline or 320 mg BST in a sustained-release formulation to examine the temporal relationships between growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin and the number of follicles. The validation studies demonstrated that small follicles (<5 mm in diameter) could be clearly detected by real-time ultrasound, and that 75% (9 of 12) of heifers showed three waves of dominant follicle development during the oestrous cycle, whereas the remainder had only two waves. The changes in the numbers of follicles of the three size categories (<5 mm, small; 5−10 mm, medium-sized and > 10 mm, large) also displayed a wave pattern similar to that of the dominant follicle, with a marked reduction in the number of subordinate follicles as the dominant follicle grew and reached its maximum size. In Expt 1, BST treatment increased the number of small follicles and caused a rise in peripheral insulin concentrations (P < 0.01) throughout the treatment period. However, there was no effect of BST on the timing for the pattern of follicular waves during the oestrous cycle, nor on the number of medium-sized or large follicles at each follicular wave. In the second experiment, the temporal change in the number of small follicles following BST treatment was positively correlated with the changes in the peripheral IGF-1 and insulin concentrations. IGF-1 and insulin concentrations increased 48 h after BST injection, and the number of small follicles had increased 24 h later and remained higher during the period when peripheral IGF-1 and insulin concentrations were high. These results demonstrate first, that the number of small follicles was reduced as the dominant follicle grew and reached its maximum size and second that BST treatment could enhance the recruitment of small follicles in heifers. This increase in the number of small follicles was positively correlated with peripheral IGF-1 and insulin concentrations. Third, BST did not affect the turnover of follicular waves, nor the inhibitory action of the dominant follicle on its subordinate follicles. We conclude that BST affects the recruitment of small follicles by increasing peripheral concentrations of IGF-1, or of insulin or both concentrations. Moreover, the effect of BST on the small follicle population was not mediated through the mechanism(s) by which the dominant follicle inhibits subordinate follicles.
Department of Biotechnology, Escuela Superior de Ciencias Agropecuarias, Departamento de Genética y Reproducción Animal, Division of Animal Sciences, Institute of Farm Animal Genetics, Friedrich-Loeffler-Institute (FLI), Höltystrasse 10, 31535 Neustadt-Mariensee, Germany
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IGF1 plays an important role in bovine follicular growth, acquisition of oocyte competence and embryo viability. Current data also indicate a critical role for IGF1 in both the ovarian response and the embryo yield following the superovulatory treatments. IGF1 can have either positive or negative effects on embryo viability which is related to the concentration of IGF1 induced by superovulation treatment. These effects impact either on oocyte competence or directly on the embryo. Concentrations in the physiological range appear to result in the production of higher quality embryos, mainly due to the mitogenic and the anti-apoptotic activities of IGF1. However, high superovulatory responses are associated with decreased embryo viability and a concomitant increase in apoptosis. Studies in mice suggest that this increase in apoptosis is related to the downregulation of the IGF1 receptor in the embryo associated with high IGF1 concentrations. Strategies capable of controlling the IGF1 concentrations could be one approach to improve superovulation responses. A range of possible approaches for research within the IGF system in gonadotrophin-stimulated cattle is discussed in this review, including the possible use of superovulated female cattle as an alternative animal experimental model for research on reproductive disorders in humans associated with abnormal IGF1 concentrations.
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The study reports the development of a serum-free culture system for sheep thecal cells that overcomes the problem of spontaneous luteinization and the use of this system to study the control of proliferation and differentiation. Theca cells were isolated by enzymatic dispersion from small follicles (< 3.5 mm) and the effect of plating densities (25–100 × 103 cells per well), LH (0.001–100 μg l−1), insulin (1–5000 μg l−1), insulin-like growth factor I (IGF-I) analogue (1–100 μg LR3-IGF-Il−1) and epidermal growth factor (EGF) (0.005–50 μg l−1) on the number of cells and androstenedione and progesterone production were determined. Plating density had a marked effect on the pattern of hormone secretion with densities between 50 and 75 × 103 cells per well resulting in a high androstenedione: progesterone ratio at optimum doses of LH (0.1 μg l−1: P < 0.001). In the first 48 h, the production of both androstenedione and progesterone was stimulated in a dose-dependent manner by LH (P < 0.001). However, the production of androstenedione was ten times higher than that of progesterone and was more sensitive to LH (ED50 value 0.08 μg l−1 for androstenedione and 1 μg l−1 for progesterone). From 48–144 h of culture higher doses of LH (> 1 ng ml−1) inhibited androstenedione (P < 0.001) and stimulated progesterone (P < 0.001) and resulted in a marked change in cell morphology, thus reflecting both functional and morphological luteinization. At optimum doses of LH, both insulin and IGF stimulated cell proliferation (P < 0.001) and androstenedione production (P < 0.001) in a dose responsive manner and there was a significant (P < 0.001) interaction between them. In contrast, both insulin and IGF-I inhibited (P < 0.001) progesterone production in a dose responsive manner. EGF stimulated cell proliferation (P < 0.001) and progesterone production (P < 0.001), but inhibited androstenedione production (P < 0.001), in a dose responsive manner. In conclusion, this culture system exhibits physiologically relevant responses to known in vivo modulators of follicle development. The biphasic nature of the theca cell response to LH emphasises the exquisite sensitivity of theca cells to LH stimulation and highlights the importance of dose–response relationships in the gonadotrophic control of ovarian function.
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Placental growth and development is crucial for successful pregnancy. The aim of this study was to characterize the activity and localization of the matrix metalloproteinase 2 (MMP-2) and MMP-9, which are capable of degrading basement membrane collagen (predominantly collagen type IV), and their endogenous tissue inhibitor of matrix metalloproteinases (TIMPs), in amniotic fluid and in the developing ovine placenta. Cell deletion by apoptosis during placental development was also examined. Zymography with gelatin as substrate indicated that MMP-2 (72 kDa gelatinase A; predominantly latent form) was present in increasing amounts in amniotic fluid from day 70 of gestation to labour (days 140-145), and MMP-9 (92 kDa gelatinase B; predominantly latent form) was detectable from day 125 to labour; there was no increase in MMP-2 or -9 in labour. A broad range of TIMPs was detected in amniotic fluid; the molecular masses corresponded to TIMP-1, -2 and -3. Immunohistochemical techniques localized MMP-2, MMP-9 and TIMP-3 in the sheep placenta, predominantly in the trophoblast layer in uninucleate, but not binucleate, cells. However, MMP-2 and -9 activated proteins in placental homogenates were low throughout pregnancy. Apoptosis was identified by morphological criteria and also by TdT-mediated dUTP nick end labelling. Apoptosis was present in discrete regions in the placenta, predominantly in trophoblast cells near the tips and the basal regions of the fetomaternal interdigitations. During pregnancy the sheep placenta becomes more complex and the area of the fetomaternal interface increases. MMP-2 and -9 are likely to be involved in breaking down basement membranes to allow cell migration during this process. It is suggested that digestion of supporting extracellular matrix may trigger apoptosis and in some way increase the branching pattern in the villi.
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Summary. A high and a low response line in sheep were selected on the basis of the mean concentration of LH in 10-week-old Finn–Dorset ram lambs after an i.v. injection of 5 μg GnRH. After 8 male generations the mean LH response of the high line was more than 5-fold that of the low line and the heritability of the selected trait was estimated at 0·44 ± 0·015. Highly significant line differences in mean LH response to GnRH were also found in males at 20 weeks of age and females at 10 and 20 weeks of age and the genetic correlations between the four LH response traits appear to be close to unity. Large line differences in the mean FSH response to GnRH were also found in both males and females at 10 and 20 weeks of age. Selection had little effect on the physical characteristics of lambs. High-response line ewes entering their first breeding season at about 7 months of age showed oestrus earlier in the season and had higher ovulation rates and numbers of lambs born per ewe lambing than did low-response line ewes. In the second breeding season, at about 19 months of age, the only line difference was a higher ovulation rate early in the breeding season in high-line ewes. It is suggested that these changes may be mediated by a more rapid response in high-line ewes to increased GnRH stimulation at puberty or at the beginning of the breeding season.
Keywords: genetic selection; LH release; GnRH; sheep
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Summary. The incidence of oestrus (6/46) and ovulation (14/46) in ewes given antisera to androstenedione, oestrone, oestradiol and testosterone either separately or as a mixture of these sera at the time of treatment with progestagen sponges alone or progestagen sponges followed by LH-RH was similar to that of control ewes (2/13 and 6/13 respectively). The number of corpora lutea (CL) recorded for those ewes that did ovulate was, however, greater in the antiserum-treated ewes (22 CL/14 ewes) than in the controls (6 CL/6 ewes) at the first ovulation after sponge withdrawal. This superiority persisted to the second ovulation (53 CL/42 treated ewes compared to 13 CL/13 controls). The results for groups treated with antisera did not differ amongst themselves.
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Summary. Plasma progesterone concentrations in jugular vein blood samples collected every other day after calving from 13 Friesian dairy cows indicated that ovarian cyclic activity was initiated by 16·6 ± 1·1 (s.e.m.) days post partum, except for 1 cow which did not resume cyclic activity until Day 98 post partum. Rectal palpation of the ovaries indicated that a developing follicle was recognizable at a mean time of 15·7 ± 2·0 days after calving. During the first oestrous cycle after parturition there was a significantly shorter period when plasma progesterone levels were elevated than during the next 2 cycles. Concentrations of progesterone, LH, FSH and prolactin were determined for 4 cows, in blood samples taken every 6 h from 2 to 36 days post partum. Tonic LH release was lower during the first 10 days than subsequently, but the lack of change in pattern for FSH suggests dissimilar control mechanisms for these hormones during this time. Three cows showed evidence of a resumption of ovarian cyclicity during the sampling period: in 2 there was an initial LH surge of a magnitude which would normally give rise to ovulation, followed 4 days later by an increase in plasma progesterone lasting only 5 and 9 days. This progesterone was considered to be of follicular origin. A second LH surge was followed by the presence of a corpus luteum.
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Summary. Divergent selection in 10-week-old Finn-Dorset ram lambs was based on the luteinizing hormone (LH) response to a pharmacological dose of GnRH (5μg). After eight generations of selection, the LH responses of the two lines (low and high) to GnRH differed by a factor of five. This study investigates the pituitary sensitivity of the two lines to exogenous GnRH. Initially, two pilot studies were performed: one to determine the range of doses of GnRH which would stimulate LH pulses of similar amplitude to those seen endogenously, and the other to confirm that sodium pentobarbitone prevents pulsatile LH secretion in prepubertal ram lambs. The results indicated that barbiturate anaesthesia suppressed pulsatile LH secretion in castrated and intact ram lambs. A model system was therefore constructed in 18 10-week-old intact ram lambs (high n = 7, low n = 11), whereby endogenous pulsatile LH secretion was prevented by sodium pentobarbitone anaesthesia and the amplitudes of LH pulses produced in response to different doses of exogenous GnRH could be measured. The GnRH dose–response curves demonstrated that there was a five-fold difference in the sensitivity of the pituitary glands of the two lines to stimulation with GnRH. The projected minimum concentration of GnRH required to produce a measurable pulse of LH was 4·75 ng for the high-line animals and 26·6 ng for the low-line animals. The results indicated that the low-line animals required five times more GnRH than the high-line lambs to stimulate LH pulses of similar amplitude (high line 43·67 ng; low line 206·55 ng).
These results demonstrate that selection has produced two lines of sheep which differ in the control of LH secretion at the level of the hypothalamus–pituitary gland.
Keywords: pituitary sensitivity; GnRH; sodium pentobarbitone; ram lambs