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your nutritionist needs to know to design the best rations for your cows on
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
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.
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.
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.
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."
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,
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.
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.)
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."
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.
||Percent of Crude Protein|
||30% to 40%|
||75% to 80%|
||20% to 25%|
||Percent of Dry Matter|
|Non-structural carbohydrates (NSC)
||10% to 20%|
|Neutral-detergent fiber (NDF)
*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. |
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:
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.
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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