This study was conducted to test the hypothesis that the inclusion of crude glycerin of up to 21% of DM in the diets of lambs will not compromise variables related to animal production or health. Forty-four uncastrated Santa Inês crossbreed lambs with an average age of 5 mo and a BW average of 23.9 ± 0.34 kg (mean ± SD) were distributed into four treatment groups (11 replicates per group) including 0%, 7%, 14%, or 21% crude glycerin on a DM basis. The inclusion of crude glycerin in the diets promoted a quadratic increase in DM (P = 0.018), CP (P = 0.004), and TDN (P = 0.017). There was a linear decrease (P < 0.001) in NDF and nonfibrous carbohydrate (NFC) intake caused by glycerin in the diets. There was a linear increase (P < 0.001) in ether extract (EE) intake. There was a linear reduction in NDF (P = 0.011) and NFC (P < 0.001) for effective consumption of the diets. There was a linear increase (P < 0.001) in EE effectively consumed by the lambs, and there were no differences in the CP that was effectively consumed (P = 0.267) by glycerin. Digestibility coefficients of DM, CP, NDF, NFC, and TDN presented a linear decrease in crude glycerin inclusion. The EE digestibility presented a linear increase. The inclusion of crude glycerin in the diets promoted a quadratic increase in final BW (P = 0.015), ADG (P < 0.001), and G:F ratio (P < 0.001). There was no effect (P > 0.05) of crude glycerin inclusion in the diets on time spent (%); number of events per day; duration of events (minutes) for feeding, rumination, and idling; number of chews per bolus; or total chewing time for the lambs. The inclusion of crude glycerin in the diets improved feeding efficiency of DM (P = 0.005) and NDF (P = 0.004). The rumination efficiency of DM (P < 0.001) and NDF (P < 0.001) presented a linear decrease. The total protein, albumin, globulin, albumin:globulin ratio, triglycerides, alanine aminotransferase levels, aspartate aminotransferase, and gamma glutamyl transferase serum concentrations did not differ (P > 0.05) through the addition of crude glycerin to the diets of the lambs. However, the crude glycerin in the diets led to a linear decrease in urea-N (P = 0.004) and glucose (P <0.001), as well as a linear increase in the cholesterol (P = 0.043) serum concentrations of the lambs. The recommended inclusion of crude glycerin is up to a 4.7% DM level because of improved performance growth without compromising feeding behavior and blood metabolites.