Alimentos para vacas de leite

Babcock Institute for International Dairy Research and Development University of Wisconsin-Madison

Dairy Essentials

6) FEEDS FOR DAIRY COWS
Michel A. Wattiaux
Babcock Institute

W. Terry Howard
Department of Dairy Science

INTRODUCTION In general, feeds are classified into one of the following categories: • Forages; • Concentrates (energy and protein feeds); • Minerals and vitamins. This classification is a convenient way to group feeds, but it is somewhat arbitrary. Classifying feeds is not as important as knowing which feeds are available, their nutritive value, and the factors that affect their utilization in a ration. FORAGES In general, forages are the vegetative parts of grasses or legume plants containing a high proportion of fiber (more than 30% neutral detergent fiber). They are required in the diet in a coarse physical form (particles with a length of more than 2.5 cm) to help rumen function. Usually, forages are grown on the farm. They may be grazed directly or harvested and preserved as hay or silage. Depending on the cow's stage of lactation, they should contribute from almost 100% (for nonlactating cows) to no less than 35% (for cows in early lactation) of the ration dry matter. The general characteristics of forages are as follows: • Bulky: Bulkiness puts limits on how much a cow can eat. The energy intake and the milk production of a cow may be limited by too much

forage in a ration. However, bulky feeds are essential to stimulate rumination and maintain the health of the cow. • High Fiber and Low Energy: Forages may contain from 30 to 90% fiber (neutral detergent fiber). In general, the higher the fiber in a forage, the lower the energy content of the forage. • Variable in Protein: Depending on the stage of maturity, legumes may contain 15 to 23% crude protein; grasses typically contain 8 to 18% crude protein (depending on the level of nitrogen fertilization), and crop residues may have only 3 to 4% crude protein (straw). From a