By: Heather Smith Thomas
The Importance of Nutrition in Early Pregnancy
What a pregnant cow eats during early gestation—quantity and quality of various nutrients—can have long-lasting effect on the future of her calf. Most of the important organs and body systems of the fetus are formed during that time. Metabolism, muscle mass and consistency, and other important factors that become permanent traits for that calf are also influenced during those crucial early weeks.
Stephen P. Ford, PhD, Director, Center for the Study of Fetal Programming, University of Wyoming, did research on sheep for a number of years, and more recently with beef cattle. In 2001 he received a USDA grant to study impacts of decreased nutrition in cows, on growth and development of the fetus, and post-natal development.
Many producers calve early so they can take advantage of grass when it is most productive. “Females on a range/forage-based diet tend to be undernourished during the first half of gestation,” he says. Fall forage may be dry, and some of the winter feeding programs may be inadequate for both the cows’ and fetuses’ needs. Cows may lose weight until green grass appears.
“We used to think these tiny fetuses didn’t need much nutrition in early gestation. Producers supplement cows during the last 1/3 of gestation, to bring body condition up before calving. But unfortunately this may be too late. We saw this after the drought in Wyoming. Quality of calves were born during those years was significantly reduced, even though body condition of cows at calving was good. But they’d been undernourished earlier–with poor grass growth during the drought,” says Ford.
During the first half of gestation is when the placenta develops (carrying all the nutrients to the fetus) and many vital fetal organs are developing. “They are developing the composition of cells they need, to function at normal level. If cellular composition is altered, even if you increase the fetal size during late gestation with supplemental feeding, the composition will still be abnormal,” he explains.
He conducted an under-nutrition study in which a group of range beef cows from the University of Wyoming was underfed from day 30 to day 125 of gestation. “It is during this period that skeletal muscle fibers develop, and the pancreas, kidneys brain and other important organ systems are developing in the fetus. I wanted to under-nourish them 50% like we did with our sheep studies, but due to factors beyond my control, we didn’t drop to that level; they were fed about 60 to 70% of requirements,” says Ford.
“We had two groups. We underfed one group from day 30 to day 125 and fed the other group a normal maintenance ration. At day 125 we collected some fetuses, and fed the remaining undernourished cows—from day 126 to term—to bring body condition scores up so they equaled the normal group by day 220 of gestation.” This is similar to what happens on ranches when producers supplement their thinner cows during the latter part of gestation.
“We collected some fetuses at mid-gestation. We found there was an effect of cow age on how the cows and fetuses responded to under-nutrition. We had randomly assigned cows to these groups, but observed two distinct responses in our undernourished cows. Younger cows—either first or second calvers—gave different results than cows that had produced 3 or more calves prior to the study,” says Ford.
In younger cows, by mid-gestation their fetuses were significantly smaller than the fetuses of control-fed cows due to intra-uterine growth retardation. Up to about 4 years of age, cows are still growing, so some of the nutrition goes toward continued growth of the cow’s body rather than into her fetus. Fetuses from those individuals were significantly deprived of nutrition, which decreased their growth rate.
By contrast, the older cows tended to have fetuses near normal in size at mid-gestation. “In the growth-retarded fetuses from young cows, we found enlarged hearts, altered pancreatic and kidney development, and increase in brain size. The brain tends to grow at a normal rate even if the fetus is undernourished, because the brain is vital for fetal survival. There was a much heavier brain-weight-to-body-weight ratio in those growth-retarded fetuses,” explains Ford.
“We also saw decreases in skeletal muscle fiber development in undernourished fetuses. Since embryonic development of muscle tissue is complete by mid-gestation, this would theoretically result in decreased skeletal muscle mass in post-natal development. We let some fetuses go to term and discovered the insidious nature of this situation. All the calves were born at a similar weight, whether from the controls or the undernourished (and later “caught up”) animals. So the producer would never know, based on weight of the calf, whether the fetus had been deprived of nutrition at a critical point during gestation,” says Ford.
Post Natal Consequences
Calves born from nutrient-deprived cows had long-lasting effects. They seemed normal at birth, but were unable to remain healthy and perform optimally. Early deficiencies affect them the rest of their lives.
“We collected some fetuses right before term and found the one big difference—even though they had equalized in weight by the end of gestation—was that the early-deprived fetuses had about half the normal number of nephrons in their kidneys. The nephrons are very important in helping remove toxins and metabolites from the blood stream for excretion. If the number of nephrons is reduced and you put these animals in a feedlot, they won’t be able to process toxic compounds as efficiently. They are fed maximal amounts of nutrition and generating tremendous amounts of metabolites. If their kidneys are not functioning properly, they can’t filter these metabolites as efficiently, which will affect growth rate and health,” Ford explains.
“If the kidney doesn’t accomplish enough filtration, it produces a hormone that increases blood pressure, to force more blood through the kidney. This increase in blood pressure can have significant health effects, since these animals’ cardiovascular system is adversely affected and their hearts are already enlarged and sub-functional,” says Ford.
There were decreases in skeletal muscle mass in the nutrient-deprived off spring as they grew, and increases in adipose (fat) tissue. Early fetal malnutrition shifted carcass characteristics in a negative way.
“Young cows are growing until they are at least 4 years old. In Wyoming, and many other areas in the West, producers tend to baby first calf heifers—putting them in their own pastures and supplementing with extra nutrition. But once they’ve had a calf, these younger cows get thrown in with older cows.” They can’t compete effectively with older animals for feed, and tend to lose weight.
“Our data suggests that there are significant alterations in the quality of their calves if they are undernourished during this critical time in early gestation,” says Ford. Even is birth weight is normal and these calves have normal viability, the way they respond to later situations in life is abnormal.
“Most people have heard about genotype and DNA and that a particular set of genes make that animal what it is. In recent years, we’ve found that intrauterine environment can alter gene expression patterns of an animal after birth, a process referred to as epigenetics. These changes in gene expression will alter the phenotype of an animal and thus its quality,” he explains.
Even though you have two animals with identical genotype, if they are gestated in females on different nutritional regimens, they will turn out different. “They may look the same at birth, but if you put them both in a feedlot one of them may get sick and the other may not. One may grow well and the other may not. The animal undergoes many more changes before birth than it ever will after birth,” he says. If we don’t enable the fetus to develop optimally and express a normal pattern of organ and tissue development, we alter the composition and quality of those organs. No matter what is done to the animal after it is born, we can’t fully correct this early damage.
There are many implications for ranchers, to help them raise better quality calves. “Understanding nutritional needs of young cows versus older cows is important. We are learning more about fetal programming, and that we are actually able to change the phenotype of the fetus.”