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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #414762
Research Project: Applying Nutritional Strategies to Improve Early Embryonic Development and Progeny Performance in Beef Cows

Location: Livestock Bio-Systems

Title: Heat stress during gestation induces follicular and ovarian changes in 30 day old IUGR-born lambs

Author
item Snider, Alexandria - Alex
item GIBBS, RACHEL - University Of Nebraska
item YATES, DUSTIN - University Of Nebraska
item CABARET, CAITLIN - Colorado State University

Submitted to: Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2024
Publication Date: 5/3/2024
Citation: Snider, A.P., Gibbs Wilson, R., Yates, D., Cabaret, C. 2024. Heat stress during gestation induces follicular and ovarian changes in 30 day old IUGR-born lambs. Symposium Proceedings. Rocky Mountain Reproductive Science Symopoium.

Interpretive Summary:

Technical Abstract: Previous studies have demonstrated that sustained heat stress during gestation causes placental insufficiency inducing in-utero adaptations that result in intrauterine growth restriction and program animal performance lifelong. However, there is a gap in knowledge regarding how these adaptations manifest in reproductive tissues, thus, our objective was to investigate potential tissue specific differences in the ovary of ewe lambs born from heat stressed dams. Time pregnant ewes were exposed to elevated ambient temperature (40°C,35% RH) from 49-95 days of gestation (dGA) to cause placental insufficiency (IUGR; n = 6). Control ewes were housed in thermoneutral conditions for the entirety of gestation (CON; n =7). Lambs were weaned at birth, hand-reared on commercial milk replacer, and euthanized at 30 days old where ovaries were excised, weighed, and collected for further analysis. One ovary was fixed in 4% paraformaldehyde, cryosectioned at 10 µm, and utilized for immunohistochemistry. Sections of ovary underwent hematoxylin and eosin staining to determine follicular populations of primordial, primary, secondary, and antral follicles. Additional sections were utilized for immunofluorescence staining for AMHR, ERa, ERß and PCNA. The other ovary was snap frozen and qPCR was performed to measure transcript abundance of AMHR, ERa, ERß and PCNA. Ovarian weights did not differ between CON and IUGR lambs. Primordial follicle populations were reduced (P < 0.05) in IUGR lamb ovaries compared to CON, with no differences in primary, secondary, or antral follicle counts between groups. Fluorescent intensities of AMHR, ERa, and PCNA were reduced (P < 0.05), and ERß fluorescent intensities tended (P < 0.10) to be reduced in IUGR lambs ovaries compared to CON. Transcript abundance of PCNA and ERß was reduced (P < 0.05) in IUGR lamb ovaries compared to CON, while transcript abundance of AMHR and ERa did not differ. Taken together, this data indicates that gestational heat stress negatively impacts key markers of follicular development and ovarian function at 30 days of age. The reduction in the primordial pool and AMHR fluorescent intensity is consistent with a reduced ovarian reserve. Reduced ERß and PCNA can affect estrogen binding and theca and granulosa cell proliferation, respectively, which impedes normal follicular development. Long-term these adaptations may impact fertility and reduce reproductive efficiency in ewe lambs born from heat stressed dams. This research was supported in part by the USDA National Sheep Industry Improvement Center Grant FE153759, and the USDA National Institute of Food and Agriculture Foundation Grants 2019-67015-29448 and 2020-67015-30825. USDA is an equal opportunity employer and provider.