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The importance of a dam’s early-gestation nutrition, both for the short and long term, is drawing a lot more attention.
Early gestation is when the placenta, which carries nutrients to the fetus, develops; it’s also when the vital organs develop.
What a pregnant cow eats during early gestation – both quantity and quality – can have long-lasting effects on her calf. That’s a concept, however, that appears to be little understood or practiced by many producers.
“Many producers don’t think a tiny fetus needs much nutrition, and ranchers tend to supplement cows late, during the last trimester of gestation, in order to raise body condition scores before calving,” says Stephen P. Ford, director of the University of Wyoming (UW) Center for the Study of Fetal Programming. However, he explains, that might be too late.
“We saw this very clearly after an extended drought here in Wyoming. The quality of calves born during those years was significantly reduced, even though the cows’ body condition at calving was close to what it should have been,” Ford says.
Early gestation is when the placenta, which carries nutrients to the fetus, develops; it’s also when the vital organs develop. “If cellular composition is altered, even if you increase fetal size during late gestation with supplemental feeding, the composition will still be abnormal,” he says.
Work with cows and sheep
Ford has studied the impacts of nutrition in cows and sheep as it affects growth and development of the fetus and post-natal development. His purpose is to quantify the effects of what often happens in the West with lack of precipitation in summer and fall.
Females on a range/forage-based diet tend to be undernourished during the first half of gestation, he explains. Forage is dry and winter-feeding programs haven’t always started or are inadequate.
Ford’s work includes a study in which a group of UW range beef cows was underfed from day 30 to day 125 of gestation (see red section in Figure 1); that’s the period when fetal skeletal muscle fibers, pancreas, kidneys and brain are developing. One group of cows was fed 60-70% of requirements from day 30 to day 125, while the other group was fed a normal maintenance ration.
At day 125, fetuses were collected from some of the undernourished cows, while the remainder of the undernourished group was fed to bring them up to a condition level equal to that of the normal group by day 220 of gestation. Ford says this is analogous to what happens on ranches when producers supplement thinner cows during late gestation.
Ford says his team learned that cow age affects how cows and fetuses respond to under-nutrition. While cows were randomly assigned to the two groups, his team observed two distinct responses in undernourished cows. The response of first- or second-calf heifers was different than that of cows that had produced three calves or more.
For instance, the fetuses in undernourished young cows at mid-gestation were significantly smaller than fetuses of control-fed cows, due to intrauterine growth retardation. That’s because cows are still growing up to four years of age, and some nutrition is directed toward continued growth of the cow’s body rather than into her fetus, he says.
In contrast, older, undernourished cows had 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 increased brain size. The brain tends to grow at normal rate even if the fetus is undernourished, because the brain is vital for fetal survival. We found a much heavier brain-weight to body-weight ratio in growth-retarded fetuses,” Ford explains.
He also found decreases in skeletal muscle fiber development in undernourished fetuses. Since embryonic development of muscle tissue is complete by mid-gestation, this could result in decreased skeletal muscle mass in post-natal development, which is important for beef producers, he says.
“We let some fetuses go to term and discovered the insidious nature of this situation. All calves were born at similar weight, whether they came from controls or undernourished (and “caught up”) animals. So the producer would never know, based on the calf’s weight, whether the fetus had been deprived of nutrition at a critical point during gestation,” Ford says.