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The whole idea behind pasturing dairy cows is to produce as much (if not more) milk than when you feed in the barn and save on feed costs. But if your nutritionist doesn't understand some critical differences about balancing rations for grazing cows, you won't realize the feed savings or increased production, says Tom Tylutki, a Cornell Cooperative Extension area dairy specialist based at the Cornell Teaching and Research Center, Dryden, N.Y.

Here are some key points he suggests discussing with your nutritionist:

Boost maintenance. Compared with cows loafing in the barn, grazing milkers use more energy foraging for their feed. Assuming a well-managed pasture system -- lush pastures located close to the barn, good lanes, easy access to water, at least a daily rotation, and no limitations on forage availability -- boost energy requirements for maintenance by 10 to 15 percent. With thin pastures, longer rotations, boggy lanes or more walking for water or feed, allow at least 15 to 20 percent more energy in the rations to cover maintenance requirements.

Adjust NEl values. Lab analyses of forage samples don't directly measure net energy for lactation (NEl). Instead, these figures are calculated from acid-detergent fiber (ADF) measurements. Consequently, labs consistently overestimate NEl of pasture by about 10 to 15 percent, and sometimes by as much as 20 percent for spring grass pasture. When determining energy requirements for supplemental rations, you need to reduce NEl figures from the lab for pasture forage by a similar amount.

"It's a double whammy," says Tylutki. "Your cows have higher maintenance energy needs and the lab figures overestimate the amount of energy available from pasture." If you don't take these factors into account when calculating supplemental rations, your cows will likely suffer lower production, reduced body condition scores (BCS), and/or poor reproductive performance, he adds.

Watch the heat. Cows' maintenance requirements also rise when average daily temperatures climb above 68 F. An increase of about ten degrees F above this optimum temperature will increase maintenance requirements by nearly half, Tylutki estimates, and 12 hours of direct sunlight will produce a similar increase. High humidity can make matters even worse. Fortunately, most years New York graziers only have to contend with a week or two when there's no night cooling to balance out hot days. During these times, Tylutki suggests bringing them into the barn and running the fans during the middle of the day.

Boost intake figures. The neutral-detergent fiber (NDF) of pasture is highly fermentable, so NDF intake will be 5 to 10 percent higher on pasture compared with cows fed in confinement, estimates Tylutki. Cows will consume NDF from silages and dry hay at a rate of 1.0 to 1.1 percent of body weight, he explains. But with the higher quality NDF of pasture, their capacity increases to 1.2 to 1.4 percent of body weight.

For example, a 1,400-pound cow fed 55-percent NDF silage in the barn would have a forage capacity of 28 pounds (1.1% x 1,400/55%). The same cow grazing 40-percent NDF pasture has a capacity of 49 pounds (1.4% x 1,400/40%).

"Since most farmers are feeding some forage in the barn, the intake for that cow would probably somewhere between 1.2 and 1.3 percent of body weight, or 31 to 40 pounds, depending on quantity and quality of what's fed in the barn," says Tylutki. "It's a tradeoff. The more forage you feed in the barn, the less pasture she's going to eat. But it's not a simple one-for-one substitution. For every pound of forage she eats in the barn, she's going to eat a pound plus 5 to 10 percent less on pasture."

Freeze samples quickly. Before you even consider protein, it's important to make sure that the information you get from forage samples is reliable. That means rushing them out of the field and freezing them as quickly as possible, even to the point of using a semen tank and liquid nitrogen if available, suggests Tylutki. "If you don't freeze the samples right away, the analyses are misleading and a waste of money," he warns. Poor handling drastically affects soluble protein readings in particular. Analyses over 45 percent soluble protein are highly suspect and those over 40 percent are questionable, Tylutki says.

Forget crude protein. To balance rations on pasture, it's important to go beyond crude protein and take into account the form of protein -- soluble, degradable and undegradable. "Your goal is to match the protein and carbohydrate degradation rates as closely as possible so the nutrients are used efficiently before the feed passes out of the rumen," says Tylutki. Pasture forage is primarily highly degradable protein, sugars and fermentable NDF, he adds. (See box, "What's In Your Pasture," below.) If you're pushing for maximum milk production, consider undegradable protein sources such as expeller or heat-treated soybeans or distillers grain. If pastures are low in soluble proteins, you may need to feed some urea.

"Soak-up" excess protein. "No matter what you do, the biggest problem you'll face supplementing rations on pasture is overfeeding protein," observes Tylutki. Cows will require even more energy to get rid of the excess nitrogen. A good strategy is to feed starch sources -- such as corn silage, flaked corn, corn meal or cracked corn -- that can feed the rumen microbes that thrive on non-structural carbohydrates, and help them "soak up" urea and ammonia. "You end up with volatile fatty acids and microbial proteins -- the cheapest source of protein you can feed a cow," explains Tylutki. "The underlying premise is that you don't really feed the cow -- you feed the rumen microbes and supplement the cow."

Doublecheck minerals. NIR (near-infrared spectrometry) tests can provide quick turn-around for NDF, crude protein, and soluble protein. But the figures returned for minerals are only "book" values -- not actual analyses. For a more accurate reading, request "wet-chemistry" tests at least once a year. This is especially crucial for dry cows grazing paddocks that have received lots of manure, where forage often tests 3 to 4 percent potassium. "You can't balance magnesium, calcium and potassium on these paddocks using book values," warns Tylutki. (See "More On Minerals," below.)

Be generous. One mistake Tylutki has seen even experienced graziers make is not providing enough pasture for the cows. "Don't make the milkers graze too close," he cautions. "They'll expend more energy grazing and you'll force them to consume the lower-quality growth close to the ground."

Get help. If you need help balancing rations on pasture, start with your local Extension office or area Extension dairy specialist, or call the Graze-NY toll-free hotline: (800) 472-0399.

What's In Your Pasture?

Below are average ranges typical for cool-season pastures in New York. Your actual field values will vary depending on predominant species (grass vs. legume), stage of growth, growing conditions (especially temperature and water availability), and soil fertility.

*Lignin values of well-managed, grass in vegetative stages will be in the 3- to 4-percent range. Mature grasses will reach 5 to 6 percent lignin. Well-managed legumes will be in the 5- to 6-percent range, while mature legumes can be as high as 10 percent lignin. Lignin is totally unavailable to the animal. Use lignin values from lab tests in conjunction with NDF figures to evaluate your pasture management. Well-managed systems should be towards the lower end of the ranges throughout the growing season.

More On Minerals

Mineral values from NIR (near- infrared spectrometry) forage analyses are more than just "book values," says Paul Sirois, forage lab manager for the Northeast Dairy Herd Improvement Association. "NIR mineral values are estimates based on changes in other nutrients that can be associated with minerals," explains Sirois. "While the estimates are not direct mineral measurements, they are much closer to actual mineral values than simple book or average values would be." For example, the estimates take into account protein and fiber levels, Sirois adds. As protein levels increase and fiber decreases, mineral levels are adjusted upward to reflect the greater percentage of legume in the sample. Sirois suggests using wet chemistry analsyses in the following cases: If forage quality is extremely good (crude protein greater than 30 percent) or poor (crude protein less than 5 percent). If you are balancing cations and anions in dry cow rations. "The precise nature of balancing for these components requires a wet chemistry analysis for best results," says Sirois. If you are growing atypical forages that were not included in the calibration work used to develop the estimates, such as warm-season grasses. "There are some forages that just don't analyze well. But the NIR instrument identifies them and we submit them to wet-chemistry tests to verify the results," says Sirois. NIR is a reliable technology, and can provide timely and accurate information, if you keep these exceptions in mind, he concludes. (Back to main text.)

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