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Light-induced sexually active rams prevent the seasonal inhibition of luteinizing-hormone in ovariectomized estradiol-implanted ewes

Abstract : The effect of the continuous presence of sexually active Rasa Aragonesa rams on the plasma luteinizing-hormone (LH) concentrations of ewes was studied from November to May. Light-treated rams wererendered sexually active (SA rams) by exposure to 2 months of artificially long days (16 h light/8 h dark)in one of two groups from either 1 November (SAR1, n¼3) or 1 December (SAR2, n¼3). Rams (n¼6) ina Control group were kept under the natural photoperiod. Thirty ewes were ovariectomized inSeptember and implanted with a subcutaneous implant (l¼15 mm) that contained estradiol-17b. Onegroup of ewes (SAR; n¼10) was housed with control rams from 1 October to 15 February before beinghoused with SAR1 rams from 16 February to 31 March, and with SAR2 rams from 1 April to 31 May. Asecond group of ewes (C; n¼10) remained with control rams throughout the experiment, and a thirdgroup was kept isolated from rams throughout the experiment (ISO; n¼10). Blood samples werecollected weekly from November to May, and plasma LH concentrations were measured. In the breedingseason (NovembereFebruary), plasma LH concentrations of ewes did not differ significantly betweengroups (SAR: 2.00±0.34; C: 1.88±0.16; ISO: 1.67±0.51 ng/ml). From March to May (seasonal anestrus),however, LH plasma concentrations decreased in the C and ISO groups (1.30±0.20 and 0.48±0.04 ng/ml,respectively), but remained at the same level as in the breeding season in the SAR group (2.30±0.17 ng/ml; P<0.001). Significant differences (P<0.01) between groups were observed from March onwards: LHconcentrations were highest in SAR ewes (P<0.001) and lowest in the ISO ewes. In conclusion, thecontinuous presence of sexually active rams prevented the seasonal decrease in plasma LH concentra-tions, probably by preventing the seasonal negative feedback of estradiol on LH secretion.
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https://hal.inrae.fr/hal-03116122
Contributor : Pascal Lallemant <>
Submitted on : Wednesday, January 20, 2021 - 9:57:28 AM
Last modification on : Wednesday, May 19, 2021 - 10:36:27 AM

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J.A. Abecia, M. Keller, C. Palacios, Philippe Chemineau, J.A. Delgadillo. Light-induced sexually active rams prevent the seasonal inhibition of luteinizing-hormone in ovariectomized estradiol-implanted ewes. Theriogenology, 2019, 136, pp.43-46. ⟨10.1016/j.theriogenology.2019.06.032⟩. ⟨hal-03116122⟩

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