Feeding for Heifers Who Are Pregnant

Cows have different nutritional needs at different stages of gestation. A cow's nutrient requirements in early gestation aren't much different from her maintenance requirements, but her needs increase as the fetus inside her grows. And if a cow is lactating, she needs a much higher level of protein and energy than during pregnancy.

While protein requirements for all pregnant cows increase in the later stages of gestation, they're highest for young cows. This can be managed by separating the first- and second-calf heifers from the main herd, and supplementing the younger females with protein, or a higher level of protein. Mature cows, which aren't growing, can be roughed through winter and early spring (as they approach calving) much more easily than younger cows.

Whether to supplement pregnant cows with protein depends on the protein levels of winter forage, as well as the performance expected from those cows. David Bohnert, Oregon State University Extension beef specialist and a ruminant nutritionist, advises using National Research Council guidelines to calculate protein requirements at various ages and stages of pregnancy, as well as lactation.

"More important is figuring out how we're going to meet those requirements, and how close we can come to meeting our expected performance for those cattle. It may not be necessary to meet the cow's exact protein needs, but we need to determine what we should provide in order to get an acceptable level of performance," he says.

Ken Olson, South Dakota State University Extension beef specialist, stresses the need for protein supplementation, particularly for spring-calving herds using low-quality forage such as winter range, crop residues or baled straw.

"The first limiting nutrient is protein, simply because the ruminant needs protein to digest forage. If the cow doesn't have enough protein to create a proper environment for rumen microbes, she can't digest the fiber in low-quality forage to extract the energy value in it," Olson says.

He says the goal is to meet the requirements of the gut bugs, so they can digest the feed and meet the requirements of the cow. "We feed the rumen bugs to grow more rumen bugs. After they digest the fiber and pass on into the small intestine, these microbes also become supplemental protein for the cow. It's a very efficient system," Olson says.

This not only meets the cow's needs, but also helps her maintain body condition during pregnancy and post-calving. "We need her to be in good body condition in the spring so she can lactate, start cycling again and get pregnant at the beginning of the next breeding season," Olson says.

Supplemental protein also sets up that cow to provide better colostrum, and more and better-quality milk, to help the newborn calf get off to a good start, he says. "We know if we feed the cow well, we reduce calving difficulty. The cow is healthier and stronger, and we have fewer weak calves at birth," he says.

Fetal programming benefit

There are also positive effects on the growing fetus. "We're finding that how we feed the pregnant cow affects development and the genetic potential of her fetus, changing how it performs after it is born — and apparently for the rest of that calf's life," Olson says.

Research data indicate proper nutrition of the fetus enhances the feedlot performance of the eventual calf, with boosts shown in improved immunity and even improved carcass composition, Olson points out. What's needed is more data on how best to manage fetal programming for the best possible outcomes, he adds.

While there's much to learn regarding the effects of various levels of nutrient restriction, Olson says it does appear to matter. "At some levels, we get one outcome; at other levels, we see something different. The stage of gestation at which the restriction occurs appears to have tremendous importance."

Various organs, such as the heart and lungs, immune system and various body tissues, are formed at different points in fetal development. Olson says mid-gestation seems to be important for muscle-fiber development, while proper nutrition during other stages of gestation is important for development of fat cells. How the cow is fed may even affect yield and marbling in the ultimate carcass of her calf.

"People now realize a cow needs a reasonable plane of nutrition all the way through pregnancy, but recent data from my SDSU colleague, Amanda Blair, suggests a mild, mid-gestation energy restriction can actually increase the marbling score of that future calf. Perhaps we're increasing marbling while decreasing muscle-fiber generation and changing the proportion of fat cells to muscle cells," he says.

"So having the cow a little short on energy in mid-gestation may not be a bad thing, but this is based on just one experiment. Much more work remains to ensure this was not just a one-time outcome. We need to better understand how to manage cow nutrition to make this happen in a predictable fashion," Olson explains.

Cattle are versatile

Ruminants have a remarkable ability to manage under less-than-perfect feed conditions, Olson points out. Cows can lose weight in winter (early to mid-gestation), regain weight with green grass in the spring and give birth to healthy calves.

"Beef cattle can utilize low-quality forages and deal with nutrient shortages. But just because they can do it doesn't mean it's the most productive way to raise beef animals," Olson says. What's needed is the optimum type of management to tweak cows' abilities to the best benefit.

He says research is underway across the country to address this topic. Some studies are investigating the effect of fetal programming on the resulting feeder calf and replacement heifer. For instance, University of Nebraska research by Rick Funston, a beef reproductive specialist, shows that nutrient restriction of the dam in winter can have negative effects on the fetus if it's a heifer calf. Age of puberty and fertility seem to be most compromised.

The bottom line, Olson says, is there's much to be learned, and those results could change the way beef cows are fed in winter. "We need to find the best ways to supplement cows so they can continue to graze low-quality forages and not compromise their unborn calves," Olson says.

That may entail being more strategic in the timing of supplementation, and how much supplement is fed.

"In the past, if cows were in good body condition in the fall, we felt we could under-supplement them in the winter, knowing they can utilize their excess body reserves. This may get her through the winter and she may still be fertile the next breeding season, but we don't know what it means for the fetus. We must reconsider and figure out strategic supplementation that still minimizes the cost of doing it, but overcomes any negative issues in fetal programming," Olson explains.

Assess your cows' goals

Some cattle are more efficient than others because of selection over the years. Such cattle are well-adapted to a harsh range environment. Meanwhile, other cows placed in that same environment might fall apart and lose weight; they might raise a poor calf and fail to breed back.

"The question of 'How much protein do I need for my cows?' is not easily answered. The answer for one herd might not be the same for another," Bohnert says.

He suggests each producer set performance goals for his cows and then determine whether they're receiving what they need to achieve those goals. The goals may differ, depending on whether cattle are in small pastures on an eastern farm, or running on thousands of acres of public rangeland in Nevada during winter.

"If cattle are on desert range, you may have limited ability to do much about some of these things. But if you are five miles down the road from an ethanol plant and have easy access to distillers grains, your goals and options may be quite different," Olson says.

Sometimes you can innovate, realizing there's an option you haven't considered. "Folks thinking outside the box, looking for ways to tweak their own system to make it better, are those who can make it work," he says. A person might be able to use part of an idea that might work, even if it's not a typical way to do it.

Learning more about the cow's protein needs, and how supplementation fits into the whole picture of the way her calf will develop and perform, can help in formulating future management plans, Olson says.

Bohnert says flexibility is also important in a supplementation strategy that works with the available resources. "This goes beyond traditional thinking that a cow needs X amount of protein or 5 pounds of alfalfa per day. We try to find supplemental strategies for protein and energy that save money while maintaining acceptable performance," he explains.

Heather Thomas is a rancher and freelance writer based in Salmon, Idaho.

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Source: https://www.beefmagazine.com/nutrition/when-you-re-feeding-pregnant-cow-you-re-feeding-two

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