Hostname: page-component-586b7cd67f-dlnhk Total loading time: 0 Render date: 2024-12-01T00:29:41.598Z Has data issue: false hasContentIssue false
  • English
  • Français

Effects of levels of food intake and body condition on the sensitivity of the hypothalamus and pituitary to ovarian steroid feedback in ovariectomized ewes

Published online by Cambridge University Press:  02 September 2010

S. M. Rhind ,
S. McMillen  and
W. A. C. McKelvey
S. M. Rhind
Affiliation:
Macaulay Land Use Research Institute, Pentlandfield, Roslin, Midlothian EH25 9RF
S. McMillen
Affiliation:
Macaulay Land Use Research Institute, Pentlandfield, Roslin, Midlothian EH25 9RF
W. A. C. McKelvey
Affiliation:
Macaulay Land Use Research Institute, Pentlandfield, Roslin, Midlothian EH25 9RF
Get access

Abstract

In two experiments involving ovariectomized Scottish Blackface ewes and steroid replacement therapy, the effects of level of food intake and of body condition on hypothalamic and pituitary sensitivity to progesterone and oestradiol feedback were investigated. In experiment 1, groups of 16 ewes in similar levels of body condition were given dried grass pellets ad libitum (mean dry-matter (DM) intake of 2481 (s.e. 71) g per head per day; group H) or 1105 g DM per head per day (group M). In experiment 2, groups of 16 ewes were fed so that they achieved body condition scores of 2·70 (s.e. 0040; group HBC) or 1·67 (s.e. 0·036; group LBC) prior to the start of the experiment. All ewes were then fed to maintain their respective levels of body condition. In both experiments, all ewes were ovariectomized and intravaginal progesterone pessaries and subcutaneous oestradiol implants were inserted; these were designed to induce circulating concentrations of these steroids within the normal range for intact ewes. Approximately 1 week later, blood samples were collected at 15-min intervals for 10 h, and at 10-min intervals for 8 h before and after pessary withdrawal respectively. All samples were assayed for LH and selected samples were assayed for FSH and progesterone. Gonadotropin profiles were also recorded during 2-h periods following injection (i.v.) of 0·25 μg and 5 μg GnRH. When circulating progesterone concentrations were elevated, due to the presence of a progesterone pessary, there was no effect of level of food intake on mean LH or FSH concentrations or mean LH pulse frequency but H ewes had a higher mean LH pulse amplitude than M ewes (P < 005). When the progesterone pessaries were absent, H ewes had a higher mean LH concentration (P < 001), mean LH pulse frequency (P < 001) and LH pulse amplitude (P < 0·01) than M ewes but mean FSH concentrations were similar in the two groups. Irrespective of the presence or absence of elevated progesterone concentrations, the pituitary responses to GnRH injection were either not significantly different or were lower in H compared with M ewes. In experiment 2, HBC ewes had a higher mean LH concentration (P < 001), LH pulse frequency (P < 0·001), pulse amplitude (P < 0·001) and FSH concentration (P < 001) than LBC ewes, irrespective of circulating progesterone concentrations. The mean heights and ‘areas’ of the LH peak induced by injection of 0·25 μg GnRH were larger in HBC than LBC ewes (P < 005) irrespective of circulating progesterone concentrations. When mean concentrations before injection were taken into account, the corresponding increases in FSH concentration were similar for the two groups. Following injection of 5 u.g GnRH, the differences in peak size were generally not significant. It is concluded that during the follicular phase of the cycle, a low level of intake is associated with increased hypothalamic sensitivity, but not pituitary sensitivity to oestradiol feedback. Body condition affects both hypothalamic and pituitary activity but the relative importance of direct and indirect effects of body condition on the sensitivity of these organs to steroid feedback, remains to be elucidated.

Keywords

body conditionewesfood intakeovariectomysex hormones
Type
Research Article
Information
Animal Production , Volume 52 , Issue 1 , February 1991 , pp. 115 - 125
Copyright
Copyright © British Society of Animal Science 1991

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Baird, D. T., Swanston, I. A. and Mcneilly, A. S. 1981. Relationship between LH, FSH and prolactin concentration and the secretion of androgens and estrogens by the preovulatory follicle in the ewe. Biology of Reproduction 24: 1013–1025.CrossRefGoogle ScholarPubMed
Clarke, I. J. and Cummins, J. T. 1982. The temporal relationship between gonadotrophin releasing hormone (GnRH) and luteinizing hormone (LH) secretion in ovariectomized ewes. Endocrinology 111: 1737–1739.CrossRefGoogle ScholarPubMed
Davis, K. E., Wright, P. J., and Clarke, I. J. 1987. Undernutrition increases the inhibitory effect of oestradiol on the plasma concentrations of FSH and LH in ewes. Proceedings of the Australian Society for Reproductive Biology, pp. 140.Google Scholar
Djahanbahkch, O., Swanston, I. A., Corrie, J. E. T. and Mcneilly, A. S. 1981. Prediction of ovulation by progesterone. Lancet 8256: 1164–1165.CrossRefGoogle Scholar
Foster, D. L., Ebling, F. J. P., Micka, A. F., Vannerson, L. A., Bucholtz, D. C., Wood, R. I., Suttie, J. M. and Fenner, D. 1989. Metabolic interfaces between growth and reproduction. 1. Nutritional modulation of gonadotropin, prolactin and growth hormone secretion in the growth-limited female lamb. Endocrinology 125: 342–350.CrossRefGoogle ScholarPubMed
Gordon, I. 1971. SC-9880-progesterone applications in the induction of early breeding in sheep. Journal of Agricultural Science, Cambridge 76: 343–346.CrossRefGoogle Scholar
Gunn, R. G. 1983. The influence of nutrition on the reproductive performance of ewes. In Sheep Production (ed. Haresign, W.), pp. 99–110. Butterworths, London.Google Scholar
Karsch, F. J., Dierschke, D. J., Weick, R. F., Yamaji, T., Hotchkiss, T. and Knobil, E. 1973. Positive and negative feedback control by oestrogen of luteinizing hormone secretion in the rhesus monkey. Endocrinology 92: 799–804.CrossRefGoogle ScholarPubMed
Mcneilly, A. S., Jonassen, J. A. and Fraser, H. M. 1986. Suppression of follicular development after chronic LHRH immunoneutralization in the ewe. Journal of Reproduction and Fertility 76: 481–490.CrossRefGoogle ScholarPubMed
Mcneilly, A. S., Jonassen, J. A. and Rhind, S. M. 1987. Reduced ovarian follicular development as a consequence of low body condition in ewes. Ada Endocrinologica 115: 75–83.Google ScholarPubMed
Mcneilly, J. R., Mcneilly, A. S., Walton, J. S. and Cunningham, F. J. 1976. Development and application of a heterologous radioimmunoassay ior ovine follicle stimulating hormone. Journal of Endocrinology 70: 69–79.CrossRefGoogle Scholar
Martin, G. B., Price, C. A., Thiery, J.-C. and Webb, R. 1988. Interactions between inhibin, oestradiol and progesterone in the control of gonadotrophin secretion i n the ewe. Journal of Reproduction and Fertility 82: 319–328.CrossRefGoogle Scholar
Rhind, S. M., Leslie, I. D., Gunn, R. G. and Doney, J. M. 1985. Plasma FSH, LH, prolactin and progesterone profiles of Cheviot ewes with different levels of intake before and after mating, and associated effects on reproductive performance. Animal Reproduction Science 8: 301–313.CrossRefGoogle Scholar
Rhind, S. M., Leslie, I. D., Gunn, R. G. and Doney, J. M. 1986. Effects of high levels of body condition and food intake on plasma follicle stimulating hormone, luteinizing hormone, prolactin and progesterone profiles around mating in Greyface ewes. Animal Production 43: 101–107.Google Scholar
Rhind, S. M., Mcmillen, S., Mckelvey, W. A. C., Rodriguez-Herrejon, F. F. and Mcneilly, A. S. 1989b. Effect of the body condition of ewes on the secretion of LH and FSH and the pituitary response to gonadotrophin-releasing hormone. Journal of Endocrinology 120: 497–502.Google ScholarPubMed
Rhind, S. M. and Mcneilly, A. S. 1986. Follicle populations, ovulation rates and plasma profiles of LH, FSH and prolactin in Scottish Blackface ewes in high and low levels of body condition. Animal Reproduction Science 10: 105–115.CrossRefGoogle Scholar
Rhind, S. M., Martin, G. B., Mcmillen, S., Tsonis, C. J. and Mcneilly, A. S. 1989a. Effect of level of food intake of ewes on the secretion of LH and FSH and on the pituitary response to gonadotrophin- releasing hormone in ovariectomized ewes. Journal of Endocrinology 121: 325–330.CrossRefGoogle ScholarPubMed
Russel, A. J. F., Doney, J. M. and Gunn, R. G. 1969. Subjective assessment of body fat in live sheep, Journal of Agricultural Science, Cambridge 72: 451–454.CrossRefGoogle Scholar