A bad day is when a cow loses weight due to stressors like poor nutrition, disease challenges and harsh environment. Bad days lead to bad weeks, and bad weeks can result in bad months. Before you know it, a cow has had a long, stressful pregnancy. Those stressors occur externally, but they impact the cow’s entire metabolism and how nutrients flow to the growing fetus.

Scott ron
Director of Beef Technical Innovation / Purina Animal Nutrition

Reducing the number of bad days or stressful events for a cow means we have a better chance of positively influencing fetal growth.

But what exactly does a bad day mean for the growing fetus? Why is it so important to keep stress low?

For those answers, we’ll break down fetal growth by trimester:

First trimester: The foundation

You might be wondering, why is a little bitty fetus only an inch or two long such a big deal?


The first trimester is where you’re building the foundation of life for a calf.

The placenta is formed and serves as both the hotel and room service for the fetus for the remainder of the pregnancy. The placenta is a direct connection between the dam and her developing calf and provides oxygen and nutrients to the fetus through blood flow.

If the placenta is not well developed because a cow is stressed, there can be reduced blood flow to the fetus. Reduced blood flow negatively impacts the nutrition the fetus receives throughout the entire gestation.

The first trimester is also when the fetus’ brain, heart, liver and reproductive organs start to form.

We typically don’t think about replacement heifer development until there’s a living, breathing calf on the ground. But developing a successful replacement heifer begins in the first trimester when germ cells start forming the reproductive system.

It’s hard enough to get a first-calf heifer re-bred. Now back up a few years and imagine her situation in utero. Was that heifer’s dam going through unnecessary stress? Was her dam getting the nutrition she needed to feed her fetus and build reproductive organs?

Second trimester: Making muscles

The second trimester continues to build and grow organs, establishing internal systems that will impact how those organs function throughout life.

But cattle produce muscle that we sell in the form of weight, and muscle development begins during the second trimester. A stressed cow during this trimester can lead to reduced muscle fiber development, total muscling and ultimately, carcass weights for the developing calf. When you think about what we sell as an industry, the second trimester is vital.

Third trimester: Ready for departure

Rapid growth happens during the last trimester, but just as important are the things happening to get the growing calf ready for departure. The calf has (hopefully) been in an excellent environment in the placenta getting all of its nutrition and oxygen from the dam. Then the calf is born and has to learn how to breathe, making lung development during the third trimester critical.

Once that calf is born, it’s also going to need a nutritious diet. Stress and nutrition for the cow during the third trimester also impacts colostrum quality and quantity. If compromised, calves may be at risk for health challenges or even death.

Which is most important?

Is there a most important trimester? That’s like asking a parent to pick their favorite child. Each trimester is important in its own way.

Historically, the last trimester has been considered the most important because that’s when over 75 percent of fetal growth occurs. Recently, more attention is being paid to the first trimester when the foundation of life is occurring.

Compromises during the first trimester are ones that last a lifetime for the calf. But the story of the first trimester is still developing. More research and evidence is being done to determine just how important this stage really is.

One thing is clear – every trimester plays a significant role in the future of that animal’s performance down the road. To help make sure that calf is on the path to success it’s important to provide consistent, daily nutrition to the dam during gestation. A consistent diet can help avoid the bad days where cows lose weight and shortchange their developing fetus.

Take out the guesswork

So what does that mean for your nutrition program? You don’t want to overfeed because it means you’re overspending and giving up some profitability. At the same time, feed is an investment, and having good, quality forage available is essential. It’s especially important to have quality feed available during the times of the year during extreme heat or cold when energy intake is compromised.

Cattle nutrition needs change as the seasons change, and it can be a challenge to know what you should be providing your cows on any day of the week. One solution that can help take the guesswork out of cow nutrition requirements are supplements with intake control properties. Those supplements are designed so that cows only consume them when they need them, which allows your cows to get the nutrition they need without unnecessary guesswork.

Three trimesters and zero bad days. Take a look at your herd. See if there are ways you can reduce stress, provide more consistent cow nutrition and set your calves up for a bright future.  end mark

For more tips to achieve consistent nutrition, visit Purnia all Season Cattle Nutrition Program.

PHOTO: Which trimester of a cow’s pregnancy is most important? What can a “bad day” mean for her and her developing calf? Taking a look at fetal growth by trimester can help provide answers. Photo by Purina Animal Nutrition.

Ron Scott
  • Ron Scott

  • Director of Beef Research
  • Purina Animal Nutrition