Masters Theses

Date of Award

12-2020

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

J. Lannett Edwards

Committee Members

F. Neal Schrick, Kyle McLean

Abstract

An acute heat stress event after LH surge increased intrafollicular interleukin 6 (IL6) levels in cows that became hyperthermic. To examine direct consequences of the physiologically-relevant elevated temperature of 41.0ºC on the cumulus-oocyte complex (COC), IL6 transcript abundance and related receptor components were evaluated throughout in vitro maturation. Because IL6 and LIF share a signal transducer, LIF was also examined. Abundance of IL6 was interactively influenced by temperature and time (P < 0.0001). Heat-induced increases in IL6 were first noted at 4 hIVM; peak levels occurred at 4.67 versus 6.44 hIVM for 41.0 and 38.5ºC COCs, respectively (SEM = 0.23; P < 0.001). Abundance of IL6R (P = 0.05) and IL6ST (P = 0.002) were also interactively influenced by temperature and hIVM. Peak IL6ST levels occurred at 6.95 versus 8.29hIVM for 41.0 and 38.5ºC, respectively (SEM = 0.23; P < 0.01). Transcript for LIF differed over time (P < 0.0001) but was not affected by 41.0ºC exposure. Blastocyst development after performing IVF was not affected by 41.0ºC exposure for 4 or 6 h. Progesterone released into maturation medium by COCs was interactively influenced by temperature and hIVM (P = 0.0116). When limiting analysis to when IL6 was temporally produced, progesterone levels were only impacted by time and temperature. Heat-induced shift in the temporal production of IL6 along with its impact on progesterone likely cooperate in heat-induced hastening of meiotic progression described by others.

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