Each calf, like each human, begins as an embryo. But important questions remain about the complex factors that shape bovine fertility and development during the earliest stages of life. Bit by bit, Jennifer Wood and her Husker colleagues in the Department of Animal Science are unraveling those mysteries.
The findings of Wood, a Ph.D. in molecular physiology and the immediate past president of the Society for the Study of Reproduction, and her colleagues deepen understanding of bovine reproduction and help producers more effectively use assisted reproductive technologies (ART) to improve cow reproductive success and calf health. Collaborative efforts are also identifying ways to pick better replacement heifers.
Innovative research by Wood, a professor in the department, has resulted in a range of notable basic science findings about bovine fertility and embryo quality. Maintaining consistent nutrition and appropriate body condition is clearly beneficial for the animal overall, but Wood has found it provides an important added benefit — increased chances that cows will produce healthy eggs capable of establishing pregnancy.
“It’s harder for a cow to get pregnant if she’s metabolically unstable,” Wood said. Dairy cows can face nutritional deficits when they’re lactating, for example. “On the beef cattle side, if there are changes in forage, you can get fluctuations in nutrient availability that could really impact the metabolism of the animal.”
Wood’s research shows that environmental stresses reduce the quality of a cow’s immature egg cells, or oocytes.
Under ideal conditions, Wood said, the mother’s genes and proteins support conception and the early stages of development. These factors are eventually cleared out to allow for continued development as the embryo grows. Environmental stresses, however, often disrupt these processes.
Wood’s work aims to identify ways to prevent or fix these stress-related complications, improve pregnancy success, support healthier embryo development and ultimately enhance calf performance.
Her work offers promise, too, for helping the cattle sector improve its assisted reproductive technologies.
“In vitro production of embryos has really taken off in the cattle industry,” she said. “People want to collect embryos from genetically superior cows and fertilize them with sperm from a genetically superior bull. People may think that it works perfectly — but it does not. We haven’t figured out the best ways to fertilize eggs and culture embryos in vitro that are optimized to get good development.”
On average, only a tenth of artificially fertilized eggs come to maturity.
“You have the idea, ‘I’m going to get 50 eggs from this really great cow,’” Wood said. “But then only five of those eggs are actually going to produce a calf.”
When lab technicians prepare bovine oocytes for in vitro fertilization, a range of lab conditions may wind up affecting the eggs, including fluctuations in temperature, pH of the media they’re in and lighting conditions.
Wood and colleagues are working to understand why lab-fertilized embryos often fail and how culture conditions can be improved.
More recently, Wood has begun studying how nutrition, heat stress and assisted reproduction procedures influence the developing placenta, which has implications for calf growth during pregnancy and long-term health.
The takeaway for producers: From nutrition and heat stress to embryo culture techniques, Wood’s research is uncovering ways to boost a cow’s reproductive success, helping producers achieve higher conception rates and the birth of healthy calves.
Another reproductive challenge involves heifers that naturally produce excessive androgens (steroid hormones), preventing normal ovulation. Wood collaborates with lead researcher Andrea Cupp, another reproduction-focused professor in the department, to study the biological causes and identify genetic markers for the condition.
As the Husker scientists expand such understanding, producers may be better able to identify replacement heifers with poor reproductive prospects.
Because human and bovine reproductive systems share important similarities, Wood’s findings may also inform research on Polyendocrine Metabolic Ovarian Syndrome, a condition associated with excess androgens and infertility that affects up to 10% of women of reproductive age.
Wood is passionate about translating basic science into real-world impact, an interest rooted in her early research on androgen-related fertility complications in women. She was impressed by the close interaction between basic and clinical scientists at the University of Pennsylvania Center for Research on Reproduction and Women’s Health and appreciates that university animal science departments are set up in a similar way.
Wood also finds it rewarding to mentor undergraduate and graduate students, especially helping them discover their passion for basic and applied research and turn it into a career.
Looking ahead, she sees great promise in an interdisciplinary, multi-institutional effort to study the range of reproductive and environmental factors that shape development during the first 1,000 days of life, which span pregnancy through the first two years after birth.
She believes that researchers could identify early-life factors that shape health for years to come. The goal, Wood says, “is not simply to understand development but to identify opportunities to give both children and animals the healthiest possible start to life.”
“It is becoming clear,” she said, ” that these early life events have the potential to set that tiny human or animal for good lifelong health.”