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J R McNeilly

Publications and source records attributed to J R McNeilly.

30 records · Page 2Linked to original sources
PubMed1988

Changes in the feedback control of gonadotrophin secretion in ewes from lines selected for testis size in the ram lamb.

The dynamics of FSH and LH secretion were studied in sheep genetically selected for High (H) and Low (L) rates of testis growth. Gonadotrophin secretion had previously been shown to be affected in the ram lamb with H-line lambs more sensitive to steroid feedback than L. While there were significant differences in mean LH concentrations during the luteal and follicular phases of the oestrous cycle, mean LH values were essentially similar in the two lines in response to ovariectomy, the effect of oestradiol implants on the response to ovariectomy and the response to LHRH. However, the frequency of LH pulses in the H line was similar during both phases of the oestrous cycle, showing a surprising insensitivity to steroid feedback. By contrast, LH pulse frequency was markedly lower in the L-line ewes in the luteal than the follicular phase (0.6 vs 1.1 pulses/h) as expected from the literature. Mean FSH concentrations were significantly higher in the L-line ewes during the follicular phase of the oestrous cycle and after ovariectomy but no significant differences were detected at the other sampling periods. There were no differences in ovulation rate between the lines. It was concluded that selection for testis size had affected the feedback control of gonadotrophin release in the ewe, as in the ram, and hence the expression of the genes controlling this is not sex limited.

Animals↗
PubMed1986

Endocrine differences in rams after genetic selection for testis size.

Testis diameter and body weight were recorded from 6 to 76 weeks of age in ram lambs from two established lines selected for high (H) and low (L) testis size. While testis growth was greater in the H line up to 14 weeks of age (P less than 0.001), body weight was significantly lower, with the L line rams being 10 kg heavier by 76 weeks. There were no differences in plasma LH up to 20 weeks of age, but FSH concentrations were significantly lower at 14 and 20 weeks in the H line. Testosterone concentrations were not significantly higher in the H line from 6 to 20 weeks. In lambs castrated at birth, significantly higher FSH values were recorded from 6 to 20 weeks of age in the H line (P less than 0.001) whereas there was no difference in LH concentration at 6 and 10 weeks of age between the lines. At 14 and 20 weeks, however, the concentrations of LH were greater in the H than L line lambs (P less than 0.05). After hemicastration at 6 weeks of age, the rate of growth of the remaining testis in the L line lambs was significantly faster than in entire lambs of that line from 10 to 20 weeks (P less than 0.05 at 10 weeks to P less than 0.001 at 20 weeks). There was no difference in the rate of testis growth between the the entire and hemicastrated lambs from the H line from 6 to 12 weeks of age. It can be concluded that there is an underlying genetic difference in pituitary gland and/or hypothalamic activity in ram lambs from the two selected lines.

Animals↗
PubMed1978

Spontaneous milk ejection during lactation and its possible relevance to success of breast-feeding.

In a woman suckling twins it became apparent that both suckling-induced and precisely timed, spontaneous bursts of milk ejection were occurring. Observations on days 14, 28, 56, and 112 of lactation disclosed highly significnat increases in intervals between episodes of spontaneous milk ejection. Furthermore, at all stages of lactation the interval between a feed and the next episode of spontaneous ejection was significantly longer than the interval between spontaneous ejections. The decrease in frequency of episodes of spontaneous milk ejection during lactation may be related to the decreasing release of prolactin in response to suckling. Spontaneous milk-ejection episodes are felt only when the breast is full and may signal its readiness for a further suckling episode. Such bursts of milk ejection may stimulate the suckling response in babies, suggesting that rigid three- or four-hour feeding regimens may be unphysiological and pose a threat to the success of breast-feeding in the early postnatal period.

Breast Feeding↗
PubMed1976

Development and application of a heterologous radioimmunoassay for ovine follicle-stimulating hormone.

A highly specific and sensitive heterologous double antibody radioimmunoassay for ovine follicle-stimulating hormone (oFSH) is described in detail. The assay using a rabbit antiserum to human FSH and either 125I-labelled rat FSH or 125I-labelled oFSH as tracer is specific for FSH. A maximum cross-reaction (B/Bo = 50%) of 0-1% was observed with other ovine, rat or human pituitary hormones or human chorionic gonadotrophin. Serum levels of oFSH in samples collected daily throughout the oestrous cycle showed large individual variations. In five out of nine animals a peak of FSH was observed on the day of oestrus.

Animals↗