YIELD RESPONSE OF DAIRY-COWS FED DIFFERENT PROPORTIONS OF ALFALFA SILAGE AND CORN-SILAGE

Forty-five multiparous and 29 primiparous cows were used in a complete lactation study to determine milk yield and the potential for improvi ng N utilization by cows fed diets containing different proportions of alfalfa and corn silages. Cows were fed diets with a 50:50 forage to grain ratio. The forage portion of the diet was either all alfalfa sil age, two-thirds alfalfa silage and one-third corn silage, or one-third alfalfa silage and two-thirds corn silage (dry matter basis). Treatme nt diets were fed to 6 ruminally cannulated cows to study dietary effe cts on ruminal fermentation. Diets were fed as a total mixed ration. D ry matter intake as a percentage of body weight was higher for cows fe d the diet containing one-third corn silage. Mean 3.5% fat-corrected m ilk yield from wk 1 to 36 of lactation was 31.0, 32.9, and 31.8 kg/d f or cows fed the alfalfa, one-third corn silage, and two-thirds corn si lage treatment diets, respectively. For 305 d of lactation, milk yield for multiparous cows was 9593, 10,170, and 10,024 kg and for primipar ous cows was 8124, 8412, and 8168 kg for cows consuming the alfalfa, o ne-third corn silage, and two-thirds corn silage treatment diets, resp ectively. Diets containing two-thirds corn silage decreased milk fat c ontent of multiparous cows during early lactation. Ruminal NH3 concent ration was lower and N excretion in the environment was reduced by 6 t o 15% with the diets containing corn silage. Results suggested that co rn silage should constitute one-third to two-thirds of dietary forage dry matter when fed with alfalfa silage to derive maximal benefit.