EFFECT OF INCLUDING EXTRUDED, ROLLED OR GROUND CORN IN DAIRY COW DIETS BASED ON DIRECT CUT GRASS SILAGE

A study was conducted to determine the effect of corn (Zea mays L.) grain processing on intake, digestibility of nutrients and milk production and composition. The effect of extrusion on nutrient digestibility was evaluated in trial 1, using ground corn as a control. In trial 2, the effect of extrusion on intake was evaluated, comparing extruded corn of two densities (357 and 308 g L-1) with rolled corn (507 g L-1) as a control. In trial 3, the effects of extrusion on milk production, digestibility and intake were evaluated; using steam rolled corn and ground corn as controls. No effects on dry matter and metabolizable energy intakes due to differences in the extruded corn grains were observed. Digestibility of dry matter, organic matter, crude protein, gross energy and neutral detergent fiber did not differ among treatments, although a greater digestibility of non-fibrous carbohydrates was observed. Higher milk production was obtained in treatments including extruded and steam rolled corn (21.4 and 21.6 L d(-1)), compared to ground corn (20.5 L d(-1)) but differences disappeared when standardizing for fat content. Milk composition was not affected by treatments. Daily protein production was greater (P < 0.01) in treatments including extruded and rolled corn. Blood parameters (beta-hydroxybutyrate, urea) and milk urea remained within normal reference values. It was concluded that using extruded corn had no adverse effects on digestibility or forage and total intake with a small advantage in milk protein yield comparing with ground corn, but without clear differences compared to steam rolled corn.