For the first few months after breeding, you can’t tell by looking whether a cow is pregnant. After 60 days, the fetus is only about 2.5 inches long. Skilled palpators can detect a cow’s pregnancy 30 days after breeding, but most check after 90 days, when pregnancy becomes more apparent.
The cow’s body, however, recognizes its pregnancy soon after breeding and undergoes dramatic changes. Within just a few weeks, the placenta that will supply the growing fetus its nutrients and oxygen through gestation is forming rapidly. The tiny fetus doesn’t eat much at this stage, but it is beginning to develop its organs, and its support system is critical.
And as the cow develops that support system, research increasingly shows that her nutrition can affect, positively or negatively, the health and performance of the calf long after its birth.
Reproductive physiologist Kim Vonnahme, PhD, at North Dakota State University’s Animal Science Department, says scientists define fetal programming as the concept that a maternal stimulus or insult at a critical period in fetal development has long-term impacts on the offspring.
The concept’s application to livestock evolved from work in human nutrition and medicine, in which research has shown that nutritional deficiencies early in a woman’s pregnancy can correspond with health problems, including obesity, diabetes and cardiovascular disease, later in life.
Researchers have studied the effects more extensively in sheep but now are exploring how it applies to cattle, particularly during early pregnancy. Vonnahme says there is considerable opportunity for progress in improving calf health and performance.
Low birth-weight calves are a well-documented result of poor cow nutrition, but Vonnahme notes that variations in maternal under-nutrition, particularly during early stages of pregnancy, do not always result in a reduced birth weight. Other consequences suggest that birth weight alone might not be the best predictor for calf survival and productivity.
Research has shown, for example, that early in the life of a calf, starch consumption, which converts to glucose, allows development of fat cells that later create marbling. There is a possibility that maternal diet during pregnancy may influence the developing muscle and/or fat cells that ultimately could impact carcass quality. Currently, physiologists, nutritionists and meat scientists at NDSU are planning collaborative trials to explore how the cow’s nutrition during gestation affects the eventual carcass merit of her offspring. “Cattle first need genetic potential for carcass traits such as marbling, but understanding how maternal nutrition during pregnancy could influence that genetic potential would be of great benefit to the beef industry.”
Research investigating maternal nutrition during pregnancy in other species has demonstrated that lung development is impaired. There is a possibility that the cow’s nutrition early in gestation might affect the development of her calf’s lungs and, thus, lung function later in life. So, better cow nutrition potentially could help reduce respiratory disease. Vonnahme notes that respiratory disease currently accounts for the majority of sickness and death loss in feedlot cattle.
Fetal programming also appears to affect feedyard performance. Research out of Australia and at the University of Nebraska has shown that steers from cows which were nutritionally restricted during gestation had lower live and carcass weights at slaughter compared to steers from adequately fed cows.
While the cow’s nutrition during early gestation affects development of her placenta and early development of the fetus, nutrition later is critical for supporting rapid growth. About 75 percent of the growth of the fetus occurs during the final two months of gestation, putting considerable demand on the cow.
Inadequate nutrition at this stage can have significant consequences for the calf. Animal Scientist Rick Funston, PhD, and fellow researchers at the University of Nebraska have conducted research demonstrating that protein supplements during the final trimester can positively influence the reproductive performance of the offspring.
Funston notes that nutritional requirements of spring-calving cows grazing dormant forage, such as in the Nebraska Sandhills, during late gestation exceed the nutritional value of the forage. Providing protein supplement during this stage to maintain cow body condition adds to production costs, but earlier Nebraska research showed that improved calf performance at weaning and in the feedyard can account for the cost of the supplement.
The researchers subsequently conducted trials examining the effects of supplements during late gestation on the performance of heifer calves. In the three-year study, dam nutrition did not affect heifer birth date or birth weight, but supplementing cows with protein during late gestation increases subsequent heifer weaning weights and adjusted 205-day weights. Pre-breeding weight was greater for heifers from protein-supplemented dams than heifers from non-supplemented dams.
Some of the biggest differences were in reproductive performance. First-service pregnancy rate was 77 percent for heifers from protein-supplemented dams and 49 percent for heifers born to non-supplemented cows. Overall pregnancy rate was 93 percent for heifers from protein-supplemented versus 80 percent for those from non-supplemented dams.
Heifers born to the supplemented cows also calved earlier and had 78 percent unassisted births compared with 64 percent for those from unsupplemented cows.
The researchers conclude that supplementing cows with protein during late gestation not only affects the nutritional plane of the cow, but has lasting effects on calf weights and reproductive performance in their heifer offspring.
Programming in practice
Much remains to learn about the effects of a cow’s nutrition on her calf, and Vonnahme says researchers will be looking closely at fetal programming and its implications for beef production. One of the next steps, she says, is to attempt to identify critical times during a cow’s pregnancy when inadequate nutrition can affect the calf. Another research focus is to identify specific nutrients that can make a difference in fetal programming and to develop management guidelines accordingly.
Even as researchers continue to explore the issue, producers can take some practical steps toward improving their calf crops.
Generally, Vonnahme says, it is just a good idea to provide adequate nutrition and prevent weight loss from breeding through gestation. In many parts of the country, forage quality is fairly high at breeding and shortly after for spring-calving herds, but by July and August, heat and dry weather can begin to take a toll on pastures and cow nutrition.
Vonnahme says dietary protein in particular appears to be critical during this early gestation as well as later in a cow’s pregnancy. Generally, she adds, a good, balanced diet including energy, protein, minerals and vitamins likely will prevent deficiencies that could affect the developing fetus. If the diet is balanced, she says, a moderate restriction in the cow’s intake might not be as significant as a deficiency in a particular nutrient.
Ron Scott, PhD, director of beef cattle research for Land O’Lakes Purina Feed, says that the time involved makes research into fetal programming difficult and expensive. But he believes that proper nutrition during gestation has potential for improving overall herd health and productivity. “In spite of all our advances in veterinary medicine,” he says, “with increasingly effective vaccines and treatments, the incidence of disease among cattle has not really declined.” Better nutrition during the cow’s gestation could be a way to make progress.
Acknowledging they have not conducted a controlled scientific trial, Scott says some of his company’s customers have seen benefits from supplementing cows year-round, with higher pregnancy rates and higher weaning weights.
The idea, he says, is to provide a consistent, steady level of nutrition with no major deficiencies at any time of year. What often happens otherwise, he says, is that as forage quality declines late in the season, producers don’t notice nutritional shortages until the cows’ body condition declines. Once the cows lose condition, it is more difficult to get it back and damage could already be done.
Surprisingly, he says, with the supplement available all year, the cows actually consume less than if managers feed the product for just a couple of months. He theorizes that cows with nutritional deficits are playing catch-up after losing condition and consume more supplement than those that maintained condition all along. Even with more supplement intake, their reproductive performance suffers.
“We know that good nutrition during gestation is important to the outcome,” Vonnahme concludes, “but we’re now learning that the impacts go beyond birth weight and calf survival to include long-term effects such as fertility in heifers, feedlot health and carcass quality.”