NUTRITIONAL-EVALUATION OF ENSILAGE MADE FROM INTERCROPPED CORN AND SUNFLOWERS

The feeding value of sunflower-corn silage relative to that of corn si lage as the only forage fed lactating cows was established using 12 la ctating Holstein cows in an experiment with a 2 x 2 Latin square desig n. Treatment periods were 5 wk and there was no changeover period betw een treatments. A constant grain intake to milk yield ratio of 1:4 was maintained. The comparison was based on dry matter (DM) intake. milk yield and composition, body-weight change, rumen pH and molar proporti ons of volatile fatty acids and plasma metabolites. The sunflower-corn silage was lower in DM content (25.4 vs. 29.2%). but higher in protei n (11.5 vs. 8.0%), acid detergent fiber (33.2 vs. 29.2 %). fat (8.1 vs . 2.1%) and total ash (10.6 vs. 4.9%). Silage DM intake was the same f or both silages, but milk yield was significantly greater (P < 0.05) ( 32.7 vs. 31.2 kg d-1) for cows fed sunflower-corn silage. However, bot h milk fat (3.19 vs. 3.87%) and milk protein (3.04 vs. 3.26%) were low er (P < 0.05) for cows fed sunflower-corn silage, resulting in a highe r (P < 0.05) fat-corrected milk yield (30.5 vs. 28.4 kg d-1) for the c ows fed corn silage. Type of silage fed did not alter rumen pH, but th e molar percentage of acetic acid was higher (P < 0.05) and the molar percentages of isovaleric and valeric acids were lower when sunflower- corn silage was fed. The feeding of sunflower-corn silage resulted in a significant increase (P < 0.05) in plasma urea nitrogen (10. 60 vs. 7.53 mg 100(-1)), cholesterol (7.36 vs. 5.63 mmol L-1) and triglycerid e (0.20 vs. 0. 18 mmol L-1). Plasma levels of methionine (29.9 vs. 18. 5 mmol mL-1) and valine (208.0 vs. 19 1.0 N mol mL-1) were greater for cows fed the sunflower-Corn silage. It was concluded from this study that intercropped sunflower-corn harvested and preserved as silage is an acceptable source of forage for lactating cows, but when fed as the only source of forage it may have a negative impact on milk compositi on.