PMID: 2103571Oct 1, 1990Paper

Hypothyroidism affects reproductive refractoriness and the seasonal oestrous period in Welsh Mountain ewes

The Journal of Endocrinology
B K Follett, C Potts

Abstract

Welsh Mountain ewes (n = 6) were rendered hypothyroid by daily treatment with methylthiouracil (35 mg/kg), beginning in early August and ending in late February. Plasma thyroxine levels were reduced by mid-September to about 33% of those in untreated ewes (n = 6). The two groups of ewes were held under natural daylengths until 5 October, then on 12 h light: 12 h darkness (12L:12D) until 28 February when the photoperiod was reduced to 8L:16D. The onset of reproductive cyclicity in October was similar in both groups of ewes but the end of the reproductive period occurred later (P less than 0.05) in the hypothyroid ewes (29 January +/- 7 days (S.E.M.] than in the untreated controls (6 January +/- 7 days). As a result, the duration of the seasonal reproductive period was significantly (P less than 0.05) longer in the hypothyroid (122 +/- 9 days) than in the untreated ewes (91 +/- 10 days). The number of oestrous cycles (duration 15.4 and 15.7 days in the hypothyroid and untreated ewes respectively) was 7.0 +/- 0.6 in the hypothyroid ewes and 5.0 +/- 0.5 (P less than 0.05) in the normal ewes. Reducing the photo-period overcame the reproductive refractoriness and anoestrus in both groups, the hypothyroid ewes beginning to cycle on 13...Continue Reading

Citations

Mar 1, 1993·Journal of Applied Toxicology : JAT·W G FosterP R Lecavalier
Aug 1, 2007·Animal : an International Journal of Animal Bioscience·L Todini
May 1, 1994·Research in Virology·J PalacioG E Griffin
Mar 4, 2006·Trends in Endocrinology and Metabolism : TEM·David G Hazlerigg, Gabriela C Wagner
Dec 3, 2014·Frontiers in Neuroendocrinology·Tyler J Stevenson, Brian J Prendergast
Jan 23, 1995·Proceedings. Biological Sciences·T J Parkinson, B K Follett
Jan 5, 2012·Journal of Biological Rhythms·David G Hazlerigg, Gerald A Lincoln
Mar 7, 2021·Animals : an Open Access Journal From MDPI·Javier AsínFrancisco A Uzal

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