Life's Work

Scientists in the University of Florida's Interdisciplinary Reproductive Biology Group have spent nearly 30 years studying how life begins

By Michael Podolsky

Birds do it, bees do it, and at the University of Florida researchers are trying to make cows, sheep, pigs and horses do it better, keep pesky bugs from doing it at all and figure out why alligators in a polluted lake can't do it.

For nearly three decades, researchers in the University of Florida's Interdisciplinary Reproductive Biology Group have probed the mysteries of fertility in good species and bad.

Today, more than 50 faculty members in fields as diverse as animal science, cell biology, medicine, pediatrics, zoology and entomology carry on the work begun in 1969 by several recently hired faculty members, including Professor Donald Henry Barron, known as "The Father of Fetal-Placental Biology."

Livestock Lifestyle

A primary focus of the IRB is increasing efficiency in breeding cows, sheep, pigs and horses.

A drive through Florida farm country would make it seem like foals, calves, piglets and lambs are plentiful. But for most livestock, a successful birth is far from certain, says animal science Professor Michael Fields, who coordinates the group.

"A quarter of all cow pregnancies fail, many in the first few days after conception," Fields says. "If we have a failed pregnancy, then we throw the timetable off. And then when we do have a successful pregnancy, when the calves go to market, they weigh less and there is less return."

In the horse, Professor Dan Sharp in the animal science department says, timing is even more critical.

"You want to get a foal to ground as close to Jan. 1 as possible, so it qualifies for that year," he says. "The older the horse, the better racing prospect it is."

And increasing the efficiency of pig reproduction could add billions to the market value of that livestock animal, Fields adds.

At the heart of most of the animal science research is the embryo and how it communicates with the mother's body.

"The central focus is on the relationship between the mother and the embryo," says Fields. "What are the signals that the embryo gives to the mother that tells her that she is pregnant, and how can we make sure that these signals are correctly interpreted?"

Fields describes pregnancy as a "conflict" within the female.

"The drive to reproduce is strong," he says. "When conception occurs, there has to be a way for the conceptus to communicate to the mother that it is time to start concentrating on growing the embryo rather than attracting the male."

In 75 percent of the cases, the pregnancy is strong enough to overcome that drive, Fields says. But in a quarter of the cases, the pregnancy fails. Increasing this percentage is the goal of Fields and his IRB colleagues.

Professors William Thatcher and Peter Hansen in the dairy and poultry sciences department are studying the hormones produced by the mother and the embryo that signal pregnancy.

The hormone progesterone is produced by a structure called the corpus luteum, located on the ovary. During the very early stages of pregnancy, progesterone prepares the uterus to nurture the embryo. The hormone prostaglandin F2 Alpha, on the other hand, degenerates, or breaks down, the corpus luteum, preventing a successful pregnancy and signaling to the mother to begin another ovulation cycle.

Somehow -- and this is the focus of Thatcher's and Sharp's research -- the embryo itself signals a reduction in prostaglandin production, allowing the progesterone to prepare the uterus. In unsuccessful pregnancies, the embryo's signals are too weak to prevent the degradation of the corpus luteum, which produces the progesterone.

"We are trying to figure out exactly how the embryo tells the mother's body what to do," Thatcher says. "If we can come up with some way to enhance that, then we can cut down on the number of unsuccessful pregnancies."

Thatcher and Hansen also are conducting research into creating a more efficient reproductive cycle in cows during the summer months, when heat stress takes a staggering toll on successful pregnancies.

"The success rate on pregnancies drops to less than 10 percent during the summer months," Hansen says. "That's an incredible decline that leads to a seasonal shortage in the milk supply."

This is so because cows begin producing milk after calving, so a drop in the number of cows becoming pregnant is followed by a drop in the number of cows that begin lactation.

"As a result," Hansen says, "during the summer, Florida dairies cannot meet the needs of the state for fluid milk."

Modern dairy cows have been bred for maximum milk production. But their higher metabolism also makes it difficult for them to rid themselves of excess heat. And high body temperatures make successful reproduction extremely difficult.

First, heat-stressed cows do not display signs of estrus, so farmers have no way of knowing when to artificially inseminate them. And even if the cow is successfully inseminated, heat stress more than likely will result in an unsuccessful pregnancy.

An economic analysis by Thatcher and dairy and poultry sciences Professor Mike De Lorenzo indicates that doubling the pregnancy rate for Florida cows during the summer would result in an additional $34 million in dairy revenues annually.

Scientists at UF are researching three ways to deal with heat stress: embryo transfer, antioxidant therapy and regulation of heat shock proteins.

Embryo transfer involves implanting an in vitro embryo into a cow. The in vitro embryos have been produced in the lab and protected from heat during the critical first week of growth. Thatcher and Dr. Maarten Drost, in the College of Veterinary Medicine's large animal clinical sciences department, have shown that transferring embryos during the summer increases pregnancy rates. However, frozen embryos have a low survival rate, so freshly fertilized embryos must be used. That drives the cost up.

Antioxidants may offer another approach to increasing pregnancy rates in the summer.

Antioxidants are chemicals that neutralize a damaging form of oxygen molecule, called a free radical, that can be produced through heat stress. Free radicals contain an unpaired electron that makes them reactive and dangerous, leading to cellular injury or death.

Antioxidants, including beta carotene, seem to scavenge free radicals. Beta carotene has also been shown to increase milk yield and in one study by Hansen to increase pregnancy rates.

Regulation of heat shock proteins is the most experimental of Hansen's research areas. With this technique, Hansen is exposing in vitro embryos to low levels of heat in an attempt to trigger heat shock protein 70 (HSP70), which can stabilize cells against heat stress.

"In lab experiments, if we expose the embryo to mild heat shock -- enough to produce HSP70 -- then we find it is more resistant to heat shock later," Hansen says. "We've been able to do it in the lab so now we have to figure out a way to make it happen in the field."

Controlling Bug Births

Not all IRB members are interested in increasing the rate of reproduction. Some, in fact, make it their job to disrupt the life cycle altogether.

Peter Teal, with the U.S. Department of Agriculture's Center for Medical, Agricultural and Veterinary Entomology and a courtesy professor in the Department of Entomology and Nematology, is exploring new ways to disrupt reproduction of insect pests.

"We're looking at the signals insects put out when they are ready to mate," Teal says.

Focusing on the corn ear worm moth, which attacks Florida's lucrative sweet corn crop, Teal has determined that neuropeptides produced by the brain are responsible for the mating signals. Introducing neuropeptides artificially activates an insect's sex pheromones even though the female insect is not physiologically ready to reproduce.

"We can induce females to produce pheromones on a daily basis," he says. "Eventually, they just run out of gas."

To penetrate an insect's waterproof skin, known as cuticle, Teal and colleague Ron Nachman have attached the active part of the water-soluble neuropeptide to a lipid, or fatty compound, which can be absorbed through the insect cuticle.

The next challenge is to find an environmentally friendly compound that will trigger pheromone production in the right amount at the right time.

Teal and his team hope to eventually apply their research to cockroaches, creating a compound that will control the pests without poison.

Teal also is working to develop more effective controls for the Mediterranean fruit fly, which plagues Florida's billion-dollar citrus crop.

Traditional treatment calls for the release of sterile male medflies to control an outbreak. However, it takes several days for the sterile flies to become ready to respond sexually to the female flies.

"During that time," Teal says "they are exposed to tremendous predation. A week is a long time for this insect."

Using a hormone, Teal can accelerate sexual maturity in the male flies by three or four days, a significant decrease in time.

"These animals can be ready to go when you release them," he says. "We can accelerate their maturation, and that is significant."

Alligator Estrogen

While much of the IRB research involves altering animals' reproductive environments, it is changes in our own environment that interest zoology Professor Louis Guillette Jr.

Since 1986, Guillette has been studying the effects of a serious pesticide spill in the early 1980s on the alligators of Lake Apopka, near Orlando. Alligators make ideal study animals because they are plentiful, at the top of the food chain, long lived and territorial.

"What we saw in Apopka was very low viability of eggs," Guillette says. "That was significant, but then we decided to study what happened to the animals that did hatch from these eggs."

His findings created a stir in scientific fields.

Guillette and colleagues blame estrogens in the pesticides for serious reproductive anomalies in both male and female alligators. Male alligators have low testosterone levels and decreased penis size, while female alligators are exhibiting some male traits.

"What we are seeing is a convergence," Guillette says. "There is no longer as significant a difference between males and females. The contamination seems to have blunted the sexual dimorphism of the animal."

His findings were significant enough that PBS' Frontline featured his work on a recent episode, titled "Fooling with Nature." The episode also has an accompanying website, available at http://www.pbs.org/wgbh/pages/frontline/shows/nature/

Guillette stresses that while the pesticide levels in Lake Apopka are particularly elevated due to the spill, the long-term effects of pesticide use are still unknown.

"This can happen to any lake," he says. "We have to seriously examine the benefits versus the costs of the chemicals that we use in today's society."

In all, the work of the IRB covers the reproductive spectrum. From Hansen's and Thatcher's work in improving livestock reproduction to Teal's efforts to eliminate insect pests and Guillette's work to determine what reproductive dangers our environment poses, the researchers are doing their part to piece together how the life cycle works.

Michael J. Fields
Professor, Department of Animal Science,
(352) 392-9566, fields@animal.ufl.edu

Louis Guillette Jr.
Professor, Department of Zoology,
(352) 392-1098, ljg@zoo.ufl.edu

Peter J. Hansen
Professor, Department of Dairy and Poultry Sciences,
(352) 392-5590, hansen@dps.ufl.edu

Peter E. A. Teal
Courtesy Professor, Department of Entomology and Nematology,
(352) 374-5707, peat@nervm.nerdc.ufl.edu

William Thatcher
Graduate Research Professor, Department of Dairy and Poultry Sciences,
(352) 392-5590, thatcher@dps.ufl.edu

Related Web Site:
gnv.ifas.ufl.edu/~irbweb/