We know the importance of colostrum at birth, good calf nutrition and sound weaning protocols in assuring calf health. We’re now learning more, however, about how the cow’s nutritional status during gestation can affect the expression of genes in the developing calf, influencing immunity, growth and reproduction over the calf’s entire lifetime. This phenomenon, known as “fetal programming,” has been documented in humans and other animals, but is not well understood and scientists currently are exploring implications for cow nutrition and cattle production.
During a recent veterinary nutrition conference hosted by Purina Animal Nutrition at the company’s research farm outside St. Louis, Ron Scott, PhD, director of beef research, outlined the current understanding of fetal programming and the importance of year-around cow nutrition for production of healthy, productive calves.
The concept of fetal programming involves the process of “epigenetics,” in which environmental factors cause genes to express themselves differently even though the genes themselves do not change.
Scott described several studies in human medicine that helped define fetal programming and demonstrate its effects. In England, for example, poverty and malnutrition in certain regions of the country during the early 20th Century led to high incidence of light birth weights for babies. Later, in the 1960’s and 1970’s, scientists found a high rate of coronary heart disease in the adults born in those areas during that period.
During World War II in the winter of 1944, the besieged people of the Netherlands experienced the “Hunger Winter,” suffering severe famine for three months. Scientists later studied the health of Dutch adults who had been gestating during that period. They found those who had been in their first trimester of gestation during the famine were more likely than average to be obese as adults, suffer cardiovascular disease and have high LDL cholesterol. Those who were in their second trimester were more likely to be glucose intolerant and suffer kidney disease, while those who were in their third trimester were more likely to have asthma.
As for cattle, conventional wisdom suggests the third trimester is the most critical, since 75 percent of fetal growth takes place during that period. However, placental and vascular development regulating blood flow to the fetus occur during the first and second trimester, as do organ differentiation and determination of the number of muscle fibers.
Scott notes that much of the fetal programming research done on animals has been designed to translate to human health, particularly with regard to obesity and excess nutrition, rather than exploring the effects of poor nutrition during gestation. However, a study in Ireland showed a restricted diet during the first trimester of gestation negatively affected the calf’s reproductive organs and heart.
In a University of Nebraska study, researchers grazed one group of cows on native range during their second trimester of pregnancy, and another group on improved pasture during the same period. Through the rest of gestation, both groups grazed native range. They then followed the calves from each group through finishing and found the calves from the improved-pasture group averaged 50 pounds heavier at finishing, had higher marbling scores and produced more tender beef. Much of the difference was likely due to production of more muscle fibers and fat cells, which occurs during the second trimester, in the calves from the improved-pasture group.
In another Nebraska study, researchers compared the effects of protein and energy supplements versus no supplements during the third trimester of pregnancy. Offspring of the supplemented group averaged 31 pounds heavier at finishing than offspring of the non-supplemented cows. A significantly higher percentage of the calves from the supplemented cows also graded choice or higher.
Another third-trimester study looked at the health of the offspring from cows supplemented while grazing either native range or crop residue. In both cases, the percentage of calves treated between birth and weaning were statistically equal, but from weaning to finishing a significantly higher percentage of calves from the non-supplemented groups required treatment at least once.
A study of heifers from cows either supplemented or not supplemented during the third trimester of pregnancy found that heifers from supplemented cows had a higher overall pregnancy rate and more of them calved during the first 21 days of the season and delivered their calves unassisted.
In a Florida trial looking at heat stress in dairy cows, researchers provided fans and sprinklers for one group of cows through gestation, and no cooling for another group. They found that heat stress during gestation decreased serum Immunoglobulin G in calves, impaired lymphocyte proliferation in calves and decreased milk production in offspring.
Scott pointed out that cattle diets, particularly in beef herds, can vary considerably in nutritional quality over the course of a year, and forage energy typically is lowest during the third trimester when cow requirements are greatest. He also noted that cows are eating for two, or three, every day of the year, since they are either lactating, gestating or both. Doctors, he notes, do not advise women to lose weight during pregnancy. And yet, in our production systems we typically expect gestating cow to lose weight and gain weight over the course of the year.
Scott concluded that year-around nutritional management in the cow herd can imprint the lifetime genetic potential and performance of subsequent generations, and that knowing the history of a calf crop, including the nutritional status of the cow herd during gestation, could help in culling and purchasing decisions.
Researchers at Purina and elsewhere continue to study fetal programming in cattle, and hope to better identify key nutrient requirements at various stages of gestation, and develop targeted nutritional recommendations based on those requirements.