Nutritional evaluation of ensilage made from intercropped corn and sunflowers

Abstract

The feeding value of sunflower–corn silage relative to that of corn silage as the only forage fed lactating cows was established using 12 lactating Holstein cows in an experiment with a 2 × 2 Latin square design. Treatment periods were 5 wk and there was no changeover period between 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 proportions of volatile fatty acids and plasma metabolites. The sunflower–corn silage was lower in DM content (25.4 vs. 29.2%), but higher in protein (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 for 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, both milk fat (3.19 vs. 3.87%) and milk protein (3.04 vs. 3.26%) were lower (P < 0.05) for cows fed sunflower–corn silage, resulting in a higher (P < 0.05) fat-corrected milk yield (30.5 vs. 28.4 kg d−1) for the cows fed corn silage. Type of silage fed did not alter rumen pH, but the 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 triglyceride (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. 191.0 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 composition. Key words: lactating cows, sunflower–corn silage, milk yield, milk composition