Happy, healthy cows are fertile cows

EDGAR, Wis. — Stress affects dairy cattle in many ways. Minimizing the stressors that cause impact is important.

University of Wisconsin-Extension Marathon County educator Heather Schlesser discussed how stressors affect reproductive health and efficiency during the UW-Extension’s Repro Roadshow Feb. 21 in Edgar.

“Stress is a biological response, and strain is the animal’s individual response to that stress,” Schlesser said. “Even though the stress is equally applied to the animals, the strain they exhibit is individual to that animal.”

Schlesser said that while stress cannot be eliminated from the lives of dairy cows, reduction of the stress cows are exposed to should be a priority, along with managing the strain each animal portrays.

“Selecting animals that are more resistant to certain stressors that are in our environments is one way to help manage that,” Schlesser said. “Some animals are more resistant to or tolerant of heat stress. Selecting those animals into our herds will help minimize the effects heat stress plays on our herd.”

Because cattle are a prey species, Schlesser said they experience both metabolic and behavioral changes in response to stressors. In turn, that affects overall health and efficiency, including reproductive efficiencies.

“Our goal is to minimize that stress, creating an environment that optimizes the ovarian and uterine function of our cows,” Schlesser said. “We can measure our success by ensuring each cow resumes cyclicity postpartum, has production and ovulation of a fertile ovum, and that her uterus is able to accept an embryo and sustain that pregnancy. If she can do those three things, we know we are successful in our goal.”

Schlesser said stressors affecting dairy cattle could be categorized as environmental, disease, production, nutrition and psychological.

Heat stress falls in the category of an environmental stressor that is applied equally to all animals, Schlesser said. Each animal’s response — elevated body temperature — is dependent on the animal and its genetic makeup.

“Heat stress impacts overall fertility, ovarian function, and ovum and embryonic development,” Schlesser said. “We need to keep in mind that heat stress doesn’t just affect the animal but future offspring as well. There is an epigenetic effect of heat stress.”

According to Schlesser, the greatest effects of heat stress can be seen in cows at the onset of estrus through the early post-breeding period. This impacts the developing ovum, which is what affects fertility.

Incidents of uterine disease, mastitis or other infections can negatively impact reproduction for several reasons, Schlesser said.

“Disease can result in damage to developing embryos and cause early CL regression, which creates a prolonged follicular phase,” Schlesser said. “That means the cow will be open longer than we want her to be.”

Increased body temperature due to a fever negatively affects the ovaries and also impacts the follicular development and oocytes produced.

Cows suffering from disease typically have decreased feed intakes, which creates a negative energy balance and leads to issues with reproduction. Immune system responses can initiate the release of endotoxins and cytokines, affecting the production of hormones required for cyclicity.

“Uterine diseases like metritis, endometritis and purulent discharge all affect reproduction,” Schlesser said. “We need to make sure we are paying attention to calving pen management and hygiene as these can play into the incidence of uterine disease.”

Herds that experience issues with uterine health can expect to have decreased conception with increased incidence of early embryonic loss and cows that are less likely to maintain a pregnancy, Schlesser said.

“Uterine disease affects follicular development,” Schlesser said. “Fertility may be compromised even after the uterine disease has been resolved.”

While uterine disease comes to mind when thinking of reproductive struggles, Schlesser said mastitis may not.

“Studies have shown that incidence of clinical mastitis in the days immediately before A.I., and up to 32 days after, negatively impact reproduction through embryonic loss,” Schlesser said. “It’s not just clinical cases either. Cows with high (somatic cell counts) may have poorer conception rates and greater early embryonic loss too.”

Similarly, Schlesser said lameness affects reproductive efficiency as well.

“If a cow is lame, she will have altered feeding behavior and estrus expression,” Schlesser said. “We will not see that increased locomotion or mounting behavior. Not eating well can result in delayed cyclicity, greater incidence of ovarian cysts and overall poorer fertility.”

The correlation between nutrition and efficient reproduction are closely tied, Schlesser said. Dairy farmers should be cognizant that their cows are getting enough feed to refrain from entering a negative energy balance. Cows with a negative energy balance experience errors in heat detection, delayed ovulation, retained placenta and endometritis.

“Acidosis can cause a chain of metabolic and hormonal reactions that will lead to suppression of the hormones GnRH and (luteinizing hormone), which are both needed for proper follicular function,” Schlesser said. “Acidosis decreases the synthesis of Prostaglandin-F2alpha, needed to progress the estrus cycle.”

Body condition scores are useful for monitoring cows to maintain reproductive efficiency, Schlesser said.

“Minimizing the loss of body condition in the transition period helps decrease the amount of time before a cow’s first estrus and ovulation post-calving,” Schlesser said.

Cows that lose less than a half-point of body condition score show their first heat in an average of 30 days, while a half to full point is an average of 36 days. Cows losing more than a full point may take up to 50 days.

Allowing cows to be cows minimizes the psychological stressors cows experience, Schlesser said.

“Give them enough time for eating, resting and socializing,” Schlesser said. “Minimize the time spent doing things she doesn’t like: moving pens and waiting to be milked.”

Optimizing first-service conception rates reduces the amount of handling cows experience.

“If she settles on the first service, we can leave her alone,” Schlesser said.

Overall, Schlesser said there are a number of things that can be done to boost reproduction numbers.

“Properly following breeding protocols, promoting low-stress animal handling, being vigilant of disease and proper nutrition increase conception and pregnancy rates,” Schlesser said. “We can’t eliminate all of the stressors affecting cows, but we can reduce the incidence and minimize the effects.”