An Outline of Nutritional Status

By Kristen Tribe

Short of spoon-feeding, there is no real way to know exactly what your cattle eat, but fecal sampling has proven to provide some insight. It’s the first step in knowing your herd’s nutritional status.

"The real problem with range animals is figuring out what they eat," says Dr. Robert Lyons, Extension range specialist, Uvalde, Texas. "You put them in a range situation and they may only eat one or two plants early in the season, but they’ve got a choice of 15 to 20 different grass species. The idea behind fecal sampling is that the feces is a byproduct of what animals eat."

Fecal samples are tested for crude protein and digestibility. These numbers are valuable because when protein and energy are in balance, nutrients can be better utilized, creating a more efficient and productive herd. The results of fecal sampling, used in conjunction with other tools, will also help you make more informed management and pasture decisions.

Lyons says fecal samples are easier to obtain than those used in other methods, and it’s a more practical procedure for the average producer.

Although collecting fecal samples is relatively simple, for obvious reasons, it’s not always pleasant. Locate about 10 fresh fecal piles and collect a heaping teaspoon from the center of each. Put them in a freezer bag and be sure it is well mixed. After the sample cools, label the bag with sample or pasture ID, date collected and any other important information before you mail it to the Grazingland Animal Nutrition Lab at Texas A&M University. The GAN Lab suggests mailing it in a Styrofoam box with a frozen ice substitute to keep it fresh. There is also some required paperwork.

Once the sample arrives at the lab, it’s dried and ground into smaller particles. After all the excess moisture has been removed, a representative portion of the sample is scanned using near infrared reflectance spectroscopy, which was first used in the mid-’70s testing the moisture content of grains.

Lyons says if you want to measure the diet quality of grazing animals, this is the best way to do it, but he stresses fecal sampling should be used in conjunction with body condition scores and computer programs to make the data truly valuable.

"The computer program gives you an estimate of intake, and body condition scoring is used to validate not only the estimates from fecal sampling and computer modeling for future reference, but also in telling you where you need to go," he says.

Lyons says there are other programs available, but the GAN Lab uses the Nutritional Balance Analyzer software package. You can purchase the program and run it yourself or request that the lab run the program for you after they test the fecal samples.

The values for crude protein and digestible organic matter that are obtained by NIRS are used in NUTBAL along with a list of other factors that all have an effect on intake. Breed, physiological stage, air temperature and current body weight are all included, just to name a few. Lyons says that after you describe these parameters in the computer program it will give you an estimate of performance.

"When I’m using these tools, the fecal sampling and computer program, I always question what I see," says Lyons. "When I get a report back, I ask myself if it makes sense for this time of year or whatever. It’s okay to be skeptical or critical. You don’t want to just let a computer program lead you by the nose. One of the things I’ve observed about using these tools is that they can answer some questions, but they also make you think.

"For example," he continues, "the program says your animals should have gained a condition score, or even half a condition score. Well, if they didn’t, is there a reason for that, other than the computer doesn’t know what it’s doing?"

First, you might want to double-check the data that you entered. Lyons says if you put garbage in, you get garbage out, but if all the data appears to be correct, there’s a strong possibility that the problem isn’t forage quality, but quantity.

Lyons says there was a study done in California that found when cows were eating dry, mature forage, they ate six hours a day, but when they were grazing short, green material, they grazed 13 hours a day because they were constantly looking for it.

"We have to be careful not to assume that cows think like we do," Lyons says.

Let’s say you had been eating meatloaf for a few days, but when you went to the refrigerator one day, there was no more meatloaf. Lyons says most people would just switch to something else – find something else to eat. But cattle keep looking for that meatloaf.

The "meatloaf" may be good quality, but if the cattle aren’t getting enough of it, it won’t make a difference. If you find yourself short on quantity, ask yourself a few questions. Is the pasture too small? Should I implement rotational grazing? Is the stocking rate too high?

To get the process started, Lyons recommends you take a fecal sample once a month to get an idea of where your cattle stand throughout the year.

An animal’s nutritional needs change with age, physiological stage and season, and forage quality changes seasonally, too. "We know these things are happening, but the advantage of fecal sampling is we can put some numbers on them. I think it just helps you visualize things more. I think these things can give you a clearer picture," says Lyons.

"To be honest with you, I wouldn’t bother taking just one [test] because you don’t know where you are," he continues. "You know that’s the diet quality right now, but you don’t have very much reference.

"We’ve been telling people for quite a while that the most economical time to get animals back in condition is during the dry period. The ideal situation would be to get that two-year trend, then monitor from weaning to calving – or at a minimum, weaning to calving."