Plainview, Texas
August 10, 2006
Forage producers who want the best
silage, hay or grazing should remember that quality and
nutritive value are related, but not necessarily the same thing,
said a Texas
Cooperative Extension specialist.
"Nutritive value is what we read in the lab analysis," said Dr.
Larry Redmon, Extension forage program leader, at recent
workshop in Plainview.
"Forage quality encompasses nutritive value, but goes a step
further to include the livestock component.
"Do they prefer it over other feed? Is their intake good? Do
they gain well on this feed? These three things are the
livestock component of forage quality."
The "official" nutritive value from a lab analysis can affect
market value and livestock performance, he said. As managers,
forage producers have more control over nutritive value than
overall quality.
"There are three ways we can affect nutritive value," Redmon
said. "We can choose a different forage. We can change our soil
nutrient status. Or we can harvest our chosen forage at a
different growth stage.
Annual forages are more nutritious than perennial forages.
Cool-season forages rate higher than warm-season forages, and
legumes rate higher than grasses.
"If we rate them for digestibility, from top to bottom, legumes
are No. 1, cool-season annuals are second, cool-season
perennials are third, warm-season annuals are fourth, and
warm-season perennials come in fifth,"
Redmon said.
Nitrogen is the No. 1 soil nutrient in the forage nutrition
equation, he said. It enables plant growth and production of
amino acids that help determine crude protein.
When deciding when to harvest, producers should remember that
"maturity is the eternal enemy of forage nutritive value,"
Redmon said.
"Harvesting when the forage is young yields the highest
nutritive value. Wait until a later growth stage and it has less
nutritive value. As a forage matures, the good 'tasty'
components in the plant cells shrink because the cell walls
thicken to support the plant as it grows."
If the weather looks "iffy" at harvest time, it's best to
postpone cutting until better curing weather is forecast, Redmon
advised. Rain will leach carbohydrates out of cut forage lying
on the ground, reducing its total energy content.
"The most important thing we can do to preserve quality and
nutritive value after cutting and curing is put it in the barn,"
he said. "A good hay barn will pay for itself in three to five
years by protecting your forage from the elements."
A laboratory analysis that confirms nutritive value is also a
good marketing tool, he said. Labs typically analyze forages for
crude protein, net energy, fiber digestibility and
vitamin/mineral content.
Net energy is often expressed as total digestible nutrients or
in vitro true digestibility. Fiber digestibility, which affects
total digestibility and energy, is expressed as acid detergent
fiber and neutral detergent fiber.
"Neutral detergent fiber is associated with dry matter
intake...how much they eat," Redmon said. "Acid detergent fiber
is associated with dry matter digestibility. Both are valuable
ratings, but in-vitro true digestibility is probably the best
value/rating for comparing total nutritive value.
"It is a better measure of both digestibility and energy," he
said.
More information on forage selection, production, harvesting and
quality is available online at
http://forages.tamu.edu.
Writer:
Tim W. McAlavy |