The objective of the study was to evaluate the effects of increase levels of whole-plant soybean silage (SS) replacing corn silage in diet on DMI, milk yield and composition, food efficiency and FCM of dairy cows. Twenty-four Holstein cows were used in a replicated 4 × 4 Latin square design experiment, with 21-d periods (last 7 d for sampling). Treatment sequences consisted of a control diet (SS-0; with no SS), and SS replacing corn silage at rates of 16.7% (SS-16), 33.3% (SS-33), or 50.0% (SS-50) on diet DM basis. Feed intake and milk yield were recorded daily. Cows were milked twice daily and milk samples were collected in 6 consecutive milking. Milk samples were analyzed for fat, true protein and lactose using a ultrasonic milk analyzer (Lactoscan, MCC, Milktronic Company, Nova Zagora, Bulgaria). Data were analyzed using the MIXED procedure of SAS 9.3. Whole-plant soybean silage linearly decreased DMI, milk yield, FCM, milk solids yield, as well as protein and lactose content (Table 1). The replacement of corn silage by whole-plant soybean silage decrease de milk yield and composition, despite did not alter the fat content and food efficiency of cows. Table 1.

Item	Treatments				SEM	P-value
SS-0	SS-16	SS-33	SS-50	Linear	Quadratic
DMI, kg/d	23.6	23.6	23.1	22.9	0.351	0.020	0.505
Milk yield, kg/d	33.0	32.3	31.2	31.6	0.533	<0.001	0.115
Feed efficiency (milk yield/DMI)	1.40	1.37	1.37	1.38	0.023	0.476	0.162
FCM, kg/d	32.3	31.1	30.5	30.3	0.506	0.002	0.236
Fat, kg/d	1.10	1.05	1.04	1.03	0.191	0.012	0.222
Protein, kg/d	1.08	1.05	1.02	1.02	0.017	<0.001	0.136
Lactose, kg/d	1.62	1.57	1.52	1.53	0.025	<0.001	0.140
Fat, %	3.38	3.29	3.37	3.30	0.048	0.382	0.737
Protein, %	3.29	3.27	3.26	3.25	0.010	0.003	0.893
Lactose, %	4.93	4.90	4.90	4.86	0.015	<0.001	0.728