ABSTRACT The objective of this study was to evaluate the inclusion of cow cheese whey (CCW) in the diet for lambs on the ingestive behavior, ruminal and blood parameters. Twenty crossbred, male, non-castrated lambs with 25 kg body weight were assigned to four treatments: control diet (composed of corn, soybean meal and native pasture silage) and test diets (control diet + inclusion of CCW in increasing levels of 1.6, 2.7 and 4.0% in DM), in a completely randomized design with four treatments and five replications. Means were compared by Tukey’s test, and the strength of association between variables was tested by Pearson’s correlation. Regression analysis was also performed for data from the collection of ruminal fluid and blood. Behavioral assessments were made at a 24-hour interval in measurements taken every five minutes. The inclusion of CCW in the diet did not impair ruminal pH, but promoted a decrease in rumination and feeding times, also causing a lower number of cuds and a lower number of cud chews. The lowest concentration of ammonia nitrogen and total protein were found in lambs receiving the diet with 4% CCW. However, these values were within the range recommended for microbial growth. CCW is a potential protein alternative in lambs feed as it does not interfere with nutrient intake, ruminal and blood parameters, and favors a positive nitrogen balance.