Proceedings: Genetic effects on LH release by oestradiol and gonadotrophin-releasing hormone in prepubertal lambs

Bm, Bindon; Ts, Chang; Evans, Ryan T.

doi:10.1530/jrf.0.0360477

Cited by 12 publications

(5 citation statements)

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“…Previous attempts to establish breed differences with respect to pituitary activity have, for the most part, been unsuccessful (Bindon et al, 1974;Hanrahan et al, 1981). However, D'Occhio et al (1984) have studied several characteristics similar to those reported here, under a similar photo¬ periodic environment: their results were similar to ours in some, but not all, respects.…”

Section: Discussionsupporting

confidence: 78%

The response of rams and ewes of three breeds to artificial photoperiod

Poulton¹,

Robinson²

1987

Reproduction

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Rams and ewes of the Romney Marsh (N = 6), Dorset Horn (N = 8) and Australian Merino (N = 8) breeds were subjected to 4 successive periods of alternating 6 h light/18 h dark ('short' days) and 18 h light/6 h dark ('long' days) preceded by 16 weeks of 12 h light/12 h dark. The initial period was of 32 weeks (16 weeks 'short' days; 16 weeks 'long' days) and the next 3 were of 24 weeks (12 weeks 'short' days; 12 weeks 'long' days). Rams of all breeds showed a cyclic pattern of growth and regression of testes associated with plasma testosterone concentration, influenced by the change in light regimen 15-19 weeks previously. Sexual behaviour was also cyclic but lagged by some 6-7 weeks. The changes were greatest in the Romneys and least in the Merinos in which a higher degree of sexual activity was evident even when the testes were regressed (P less than 0.001). This was the major breed difference. All ewes of the Romney and Dorset breeds showed marked seasonality related to the imposed light regimen, whereas only 1 of the 4 Merinos did so. The mean peak of ovarian activity in the former 2 breeds coincided with that of maximum sexual activity of rams housed with them; that is, some 6 weeks after maximum scrotal volume. The rams and ewes were subjected to serial blood sampling episodes for plasma LH and testosterone and tested for plasma LH release following GnRH administration. There was little variation between breeds in LH concentration. Testosterone concentration varied greatly in the ram, highest levels associated with the developed phase of the testes and with maximum LH pulse frequency. The LH response to GnRH changed with respect to the state of the gonads. Maximal responses were observed in the developing phase of testicular growth although this variation was greater in the Romney and Dorsets than in the Merinos (P less than 0.001). In the ewes, maximal responses were seen in the follicular phase (P less than 0.001), with no difference between the luteal and acyclic phases. There were no breed differences. Plasma pooled from the serial blood sampling episodes was assayed for prolactin.(ABSTRACT TRUNCATED AT 400 WORDS)

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Section: Discussionsupporting

confidence: 78%

The response of rams and ewes of three breeds to artificial photoperiod

Poulton¹,

Robinson²

1987

Reproduction

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“…Selection for and against the incidence of multiple births has resulted in changes in the number of primordial follicles (Trounson, Chamley, Kennedy & Tassell, 1974), and has led to differences in plasma LH (Bindon & Turner, 1974) and FSH (Findlay & Bindon, 1976) concentrations at 4-5 weeks of age. Breed differences in plasma LH levels, both before and in response to oestradiol, have also been recorded at an early age (Thimonier, Pelletier & Land, 1972;Bindon, Ch'ang & Evans, 1974).…”

Section: Introductionmentioning

confidence: 92%

Oestrous and ovarian responses to exogenous progesterone and oestrogen in prepubertal ewe lambs in relation to the fecundity of their dams

Whyman¹

1978

Reproduction

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Oestrus was consistently induced by 20, 40 or 80 microgram oestradiol benzoate in progesterone-primed lambs aged 23 weeks and 17 weeks respectively in two experiments. The duration of oestrus increased linearly with increasing log dose of oestrogen, and was negatively correlated with the time of its onset. In the absence of progesterone there was a reduced incidence, later onset and shorter duration of oestrus. Progesterone alone did not induce oestrus. In lambs treated during January (Exp. 2), a later date of injection of oestrogen was associated with earlier onset and longer duration of oestrus. The induced oestrus was anovulatory. Oestrogen reduced the proportion of lambs with follicles greater than or equal to 3 mm in diameter whilst progesterone had no effect. Lambs which were the progeny of low- and high-fecundity dams did not differ in their oestrous or ovarian responses. Correlations between the dam's lamb production index and the time to onset and duration of the induced oestrus were also not significant.

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“…This could give further insight on the hormonal control of spermatogenesis and on its practical use as an indicator of the sperm output ability, or even of fertility, as suggested by Bindon & Turner (1974), Bindon, Chang & Evans (1974), Thibier (1977a) and Land (1978). Because hormone concentrations fluctuate randomly during the day (Thibier, 1975a(Thibier, , 1976a, the magnitude of the LH and testosterone responses in each individual to a uniform challenge was used for assessment (Thibier, 1977a Individual bulls respond to a single GnRH challenge in a repeatable manner when compared to their contemporaries after puberty (Thibier, 1976b(Thibier, , 1977a or even before and after the onset of puberty (Chantaraprateep & Thibier, 1979a These data on semen characteristics were used to classify bulls into so-called good, medium and poor semen producers (see Thibier & Colchen-Bourlaud, 1972b;Colchen-Bourlaud & Thibier, 1973 The other 29 bulls were treated i.m.…”

Section: Introductionmentioning

confidence: 95%