Nutritive value and forage quality are often used interchangeably, but they are not synonymous. If the terms were Russian nesting dolls, the former would fit inside the latter, representing one piece of a larger puzzle.
In an article from the Midwest Forage Association’s Forage Focus newsletter, Yoana Newman with the University of Wisconsin-River Falls clarifies that nutritive value refers to the chemical composition of forage based on components like energy, fiber, protein, fat, and minerals. Forage quality, on the other hand, is a broader term that encompasses nutritive value in addition to forage intake and antiquality components.
According to Newman, nutritive value is responsible for about 30% of animal performance factors like average daily gain and milk production. The extension forage specialist adds that the remaining 70% is attributed to forage intake.
Estimating nutritive value and forage intake in a grazing system can be more difficult than measuring those aspects of fed hay. In general, managing pastures to maximize plant leaf material in the canopy and implementing strategic grazing to target those leaves will enhance the overall quality of the forage cattle consume.
Take half, leave half
Grazing intensity affects stubble height, with heavy and prolonged stocking rates resulting in overgrazed pastures. Newman suggests moving livestock to a new paddock once the herd has defoliated one-third to one-half of the pasture canopy. A quick, effective rotation will ensure cattle eat leafier diets that include fewer stems, which inherently improves forage nutritive value and intake. Rotational grazing also promotes stand health.
“Heavy grazing will force animals to eat lower into the canopy, consuming more stems with less nutrient concentration,” Newman states. “If forced to stock heavy, a longer rest period is needed to avoid slower forage regrowth or persistence issues.”
With that said, different forage species offer different nutrient profiles, and thus, different forage quality potential. For example, cool-season grasses — including annual and perennial grasses — are typically higher quality than warm-season grasses. Legume species tend to be even greater quality than all types of grass.
Brassicas and mustards, like turnips and radishes, are especially high in energy and protein. Newman suggests these forages can be excellent additions to fall pastures. These frost-resistant species are not winterhardy, though, and they will winterkill. Brassicas and mustards can also cause forage disorders.
“Care must be taken since they are high in potassium. Excessive potassium can lead to hypomagnesemia or grass tetany,” Newman writes. “Brassicas are also high in sulfur-containing, antiquality compounds which can produce anemia.”
Of course, forage nutritive value and overall quality decline with plant maturity for all species to some extent. Creating a grazing plan and mapping out pasture moves will help manage forage utilization throughout the season. Newman also suggests analyzing forage tests and supplementing livestock during the times of year when forage may not supply sufficient nutrients on its own.
