Two studies were conducted with the objective of evaluating the effects of feeding different levels of whey ensiled with wheat straw and wheat middlings (whey silage) compared to control diets on production parameters in growing cattle. Whey silage was included in diets at 55 and 65.5% on a dry matter basis with net energy for maintenance and crude protein calculated to be similar to control diets containing a combination of alfalfa hay, corn silage and wheat middlings at 1.74 Mcal kg-1 and 13.4%, respectively. Dry matter intake averaged 8.41 versus 8.91 kg d-1 (P < 0.05) and 8.68 versus 7.09 kg d-1 (P < 0.05) when whey silage was included at either 55 or 65.5% of the diets compared to the control diets. Average daily gains of cattle fed whey silage incorporated at 55% was 1.00 versus 1.14 kg d-1 (P < 0.05), and reflected the difference in dry matter intake; no differences (P > 0.05) in feed efficiency (8.73:1 versus 8.71:1) were observed. However, the higher dry matter intake (DMI) of cattle fed diets with whey silage incorporated at 65.5% did not (P > 0.05) translate into higher average daily gain (1.23 versus 1.18 kg d-1), resulting in a higher (P < 0.05) feed to gain (7.00:1 versus 6.01:1) for the whey-based silage diets. Incorporation of whey silage in diets at 55% increased (P > 0.05) the dry matter digestibility by 12%, whereas incorporation at 65.5% decreased (P < 0.05) dry matter digestibility by 12% compared to control diets, with no differences (P > 0.05) in percent neutral detergent fiber digestibility (NDFD) at either level. We conclude that whey silage can be included at between 55 and 65.5% of the total dry matter in diets with no adverse effects on production compared to cattle fed diets containing a combination of alfalfa hay, corn silage and wheat middlings.