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Know What You've Got
Sampling pastures helps you cut feed costs.

You wouldn't dream of trying to balance your rations in the barn this winter without knowing the quality of the ingredients in your mix. Yet during the growing season, some graziers try to determine how much grain and supplement to feed without analyzing their most important feed source -- their pasture.

"I've heard some say, `I've been grazing for years. I know what's out there,'" says Karen Hoffman, a dairy grazing nutrition specialist with Cornell Cooperative Extension based in Norwich, N.Y. "But pasture quality not only changes during the growing season, but also varies from year to year. If you don't sample your pasture forage from time to time, you won't know for sure what you've got. You're just guessing."

Guessing wrong can hurt you several ways. Underestimating pasture can cost you in wasted feed. Overestimating can hurt you in lost milk production. (The "Ouch Factor" Hoffman calls it, when you check the milk tank and say, "Ouch! I guess I didn't get the ration right.") Mistakes can cause cows to lose condition and reduce reproductive performance, she adds. "I've seen cases where samples from the pasture showed protein levels were 4 to 5 percentage points higher than expected," says Hoffman. "There was too much protein and not enough energy in the supplemental ration, and the cows were losing a lot of condition getting rid of the excess protein."

You don't have to sample every paddock each rotation to avoid these problems. But knowing when to test and what to look for can help you get more from your cows and grass. Hoffman suggests sampling pastures at least three times during the season, focusing on times when pasture quality is likely to change:

Spring lush. Sample regrowth after your first rotation. This will give you a good idea of what to expect from pastures at their highest quality during the most productive part of the growing season.

Summer slump. Most years, fiber levels increase and quality decreases as temperatures rise and pasture growth slows, observes Hoffman. But that's not always the case, and you shouldn't just rely on previous years' forage analyses to calculate your supplemental rations.

"This past summer ('96) was a great example," says Hoffman. "It was wet and never got really warm. In many cases, protein levels in pasture forage stayed pretty high." That was especially true for graziers who were able to keep up with the relatively steady pasture growth and consistently offered their stock forage around the ideal height of about 6 inches. Those who were unable to keep up with the grass and grazed stock on taller, more mature forage were more likely to experience the drop in quality typical of the summer slump. "Only by testing can you tell how much, if any, quality you lost," says Hoffman.

Fall rebound. "Many graziers don't think of fall as a particularly difficult time to manage pasture. But it can be challenging," says Hoffman. If August is hot and dry, pasture growth rates can take off when temperatures cool down and fall rains arrive. But as nighttime temperatures drop into the 40s F and days grow increasingly short, pasture growth can slow dramatically. Depending on weather and management, protein levels tend to rebound from summertime lows, and the protein fractions often shift. Again, one of the most common problems Hoffman sees at this time of the year is loss of condition when supplemental rations underestimate the high levels of protein in the pasture. "And you don't want your cows too skinny going into winter," she says.

Other times. Because weather can cause major changes in pasture quality, Hoffman suggests sampling pastures whenever there is a significant change in weather patterns. Also be sure to sample paddocks where you've introduced legumes by frost seeding, or where the legume component of the stand has changed significantly because of shifts in weather or management. "If you reseed and change species, be sure to take samples," she suggests. "Grass isn't just grass. Each species has its quirks and different species can respond to changing conditions in different ways."

Take representative samples and only harvest those parts of the plant that your stock are actually consuming. And don't forget to rush samples out of the field and freeze them quickly, as heat can drastically alter the analysis, especially of soluble protein. Discuss results with your nutritionist to determine the best ration to make the most of your pasture. (See "Better Balancing.")

Also make sure you have good analyses of your silage and stored forages, cautions Hoffman. "I can't do a good job balancing pasture rations unless I have analyses from the other feeds. Silage and forages can vary as much as pasture depending on weather, what field they were grown in and when they were harvested."

Time is the biggest barrier to better pasture forage analysis, she adds. But the potential payoff in more milk and healthier cows far outweighs the extra effort.

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