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Minimize Three Main Types of Stress

Physiologic, physical and psychological stress can reduce reproductive success.

Reinaldo Cooke“There is a direct connection between cortisol levels and pregnancy conception rates,” said Reinaldo Cooke, associate professor at Oregon State University. “We must understand and recognize the three stressors and find an alternative to alleviate the stressors.”

The definition of stress is the sum of reactions that influence an animal’s homeostasis, explained Reinaldo Cooke, associate professor at Oregon State University. Cooke detailed the implications stress may have on female reproductive systems on Aug. 29 at the 2017 Applied Reproductive Strategies in Beef Cattle (ARSBC) Workshop in Manhattan, Kan.

Cooke began by defining homeostasis as any action within your comfort zone. Anything that takes you away from a comfort zone is a type of stressor. He described three main types of stress:

When the body encounters stress, two systems are engaged, he said. Sympathetic nervous system and hypothalamic-pituitary-adrenal (HPA) response are engaged to bring the body back into homeostasis.

As soon as an animal is faced with stress, the body begins to produce cortisol at a higher rate than it produces epinephrine.

“Cortisol goes up and stays up much longer than levels of epinephrine,” said Cooke. “It is the main link between stress and productivity in livestock.”

While the body is producing high levels of cortisol during stress, it is also releasing key elements like creatine and sugars, which can be detrimental to the animal’s productivity, specifically the reproductive systems productivity. With increased levels of cortisol, there is decreased follicle growth and estrogen levels, which can lead to a change in ovulation success, he said.

“There is a direct connection between cortisol levels and pregnancy conception rates,” said Cooke. “We must understand and recognize the three stressors and find an alternative to alleviate the stressors.”

Cooke said that nutrition could be considered a physiological stressor. If heifers are born on pasture and are moved to drylot systems after weaning, they experience a stressful change of environment. The pasture was considered their comfort zone, and they left homeostasis when they were moved to a crowded drylot pen.

“You must give their bodies a chance to adapt to the changes before breeding,” said Cooke.

Pregnancy rates fell after the heifers were bred in a drylot facility and turned out to pasture two weeks later.

“The animals didn’t know how to graze and their average daily gain dropped significantly,” said Cooke.

Relocating cattle between Day 7 and Day 21 can be detrimental to their pregnancy, he continued. Producers should consider avoiding major changes in diet and environment directly after breeding.

Cooke suggested utilizing trace minerals, sugars, amino acids and progesterone to alleviate nutritional stressors. Aim to keep body conditions healthy, not overly conditioned or too thin to avoid unnecessary stressors.

Temperament can be another factor in determining successful reproductive systems, he continued.

“Cows act excited or aggressive around humans because they’re not comfortable around us,” Cooke said. “They are trying to run away or run over us as a fight or flight response. Fear is a psychological stress.”

By studying and classifying females by temperament, Cooke’s research found that stressed or nervous cows weaned lighter calves. Weaning lighter calves led to a $52 decrease per cow, he said.

“Stress has direct implications on reproduction success,” Cooke said.

Cooke spoke during Tuesday’s ARSBC session focused on foundation principals. Visit the Newsroom at, which features comprehensive coverage of the symposium, to view his PowerPoint, to read the proceedings or to listen to the presentation. Compiled by the Angus Journal editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force. To access video of the presentations, visit the Beef Reproduction Task Force page on Facebook.

The 2017 ARSBC Symposium was hosted by the Task Force and Kansas State University Research & Extension. Next year’s symposium will be Aug. 29-30 in Ruidoso, N.M.

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