Raising strong sheep, goat offspring begins during pregnancy

Drought affects the growth and birth weight of lambs and kids — the hardships it causes for pregnant animals reduce placental function and the nutrients available to a developing fetus, according to a Texas A&M AgriLife Research scientist.

With growing concerns about climate change, Carey Satterfield, Ph.D., an associate professor in the Department of Animal Science, College of Agriculture and Life Sciences, said researchers must be forward-thinking to help protect the small ruminant livestock industry.

“Extreme weather conditions, whether hotter or drier, will impact our animal agriculture, so we need to have strategies available to allow producers to deal with these changes,” Satterfield said. “Drought during pregnancy is the biggest cause of nutritional hardship, but heat stress can also cause poor placental function, so that would be a secondary factor we deal with here in Texas. We need to have cost-effective strategies that we can apply to these situations to reduce perinatal mortality as well as enhance postnatal growth and performance.”

Satterfield will lead a team in identifying novel ways to improve placental growth and improve birth weight of offspring during these periods of nutritional hardship that are common in ruminant livestock species. The research, supported by a $500,000 U.S. Department of Agriculture National Institute of Food and Agriculture grant, will test two novel nutraceutical products — citrulline and putrescine — to determine if they improve placental growth and function when supplemented during pregnancy. 

Joining Satterfield on the research are fellow Department of Animal Science researchers Guoyao Wu, Ph.D., distinguished professor and AgriLife Research Senior Faculty Fellow; and Fuller Bazer, Ph.D., Regents Fellow, Distinguished University Professor, Presidential Impact Fellow and holder of the O.D. Butler Chair in Animal Science. Additionally, the team includes Greg Johnson, Ph.D., professor and EDGES Fellow in the Department of Veterinary Integrated Biosciences in the School of Veterinary Medicine and Biomedical Sciences, and Kayla Bayless, Ph.D., associate professor in the Texas A&M Health Science Center Department of Molecular and Cellular Medicine.

Tackling low birth weight

The team is prioritizing the development of cost-effective strategies for producers seeking to improve the birth weight of a fetus, Satterfield said, because low birth weight is the biggest cause of death for small ruminants.

“At least for our sheep and goats, we’re a lot more worried about small babies that aren’t thrifty; they don’t get up, they don’t nurse, and then they succumb to the environment or predators,” he said. “If these nutritional treatments work, we will have slightly bigger babies that are more vigorous and that should help reduce our death loss.”

Satterfield said based on the known functions of citrulline and putrescine in other systems, their hypothesis is they will promote vascular development, but that hypothesis has to be tested. Citrulline is an amino acid and putrescine is a metabolite of amino acids. Citrulline is a precursor for arginine and is considered conditionally essential.

“In regard to growing a good baby, you have to first have a good placenta,” he said. “These nutrients we are providing should stimulate the development of the blood vessels. By doing that, we’re basically creating a highway system that’s needed to transport the nutrients that the baby’s going to need.”

Bayless has a very sophisticated cell culture system that can test how nutrients influence angiogenesis, which is the growth of new blood vessels. Johnson, as a histology expert, will be able to quantify the vascular development in the placenta and sheep.

Promoting placenta growth

Satterfield’s team will use sheep as their model animal. Some of the pregnant ewes will receive nutrient treatments to see if the fetal development can be rescued or enhanced.

The pregnant sheep will receive supplements throughout placental development, or days 28-84 in their 147-day gestation cycle, he said. The timing during pregnancy will be refined once the proof of concept is complete.

“There are certain times when the animal cannot make enough of these nutrients on its own, and so we know they need supplementation,” Satterfield said. “We will supplement twice a day, based on our previous research of how long it takes for those nutrients to be metabolized in the animal and how long they stay in the system.”

Citrulline, the team discovered, isn’t degraded in the rumen like other amino acids, which is part of the reason for choosing to use it. Because the supplement doesn’t have to be protected or encapsulated or require advanced treatments, it would be very cost effective, he said.

Once the proof-of-concept work is done, there will be a need for product development, Satterfield said. The product is not widely available, because there hasn’t been a reason to use it, but eventually these nutrients could be put into a lick tub or feed supplement and placed in front of pregnant livestock.