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Copyright © 2015
Angus Journal


Heat Stress Affects Fertility


Steps to managing the effects of heat stress on female fertility.

by Katy Kemp for Angus Journal®

STILLWATER, Okla. (Oct. 8, 2014) — Peter Hansen, University of Florida, gave attendees of the 2014 Applied Reproductive Strategies in Beef Cattle (ARSBC) symposium five “take home” messages when considering heat stress and its effects on reproduction.

No. 1: Heat stress affects most aspects of reproduction, but especially fertility. Only a limited number of reproductive management techniques increase fertility during heat stress, but there are steps to monitor and account for its effects.

The normal rectal temperature for beef cows is 101.3°-101.5° F. Hansen suggested conception rates can decline when rectal temperatures reach 102.2°.

A cow experiencing heat stress will first exhibit low estrous behavior, according to Hansen. This is often observed in lactating cows, in which anestrous occurs.

“Lactating cows burn as much energy as human athletes but must lose heat to prevent hyperthermia,” Hansen said. “Lactation really makes the cow susceptible to heat stress.”

No. 2: Heat stress can compromise fertility many weeks later. A follicle today started its cycle 120 days prior to ovulation. Hansen addressed the issue of heat stress “compromising an oocyte” both prior to ovulation and several weeks later, including disrupting fertilization, and fetal growth.

“Heat stress has a long carryover effect on oocyte production,” he said. “This also occurs in the cycle of sperm production.”

No. 3: An easy and effective way to determine whether cows are suffering from heat stress is to measure body temperature. Hansen emphasized proper temperature monitoring is measuring body temperature, not the outside temperature. To effectively monitor heat stress, he suggested use of an iButton device, approximately the size of a dime, which can fit inside a CIDR. The reusable iButton downloads and sends data for rectal temperature to a computer for monitoring.

No. 4: To date, Hansen’s research suggested the only reproductive technique known to increase fertility during heat stress is embryo transfer; the rest is management of cattle exhibiting heat stress.

No. 5: Hansen noted that the best long-term solution to heat stress is to use cattle that are genetically adapted to heat stress.

Hansen spoke during Wednesday's ARSBC session on the impact of environment and management on cow herd efficiency. For more information, visit the Newsroom at www.appliedreprostrategies.com to view his PowerPoint, read the proceedings or listen to the presentation.

Comprehensive coverage of the symposium is available online at www.appliedreprostrategies.com. Compiled by the Angus Journal editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force.

Editor's Note: This article was written under contract or by staff of the Angus Journal. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.