ABSTRACT The objective was to evaluate the feeding behavior, physiological responses, and rumen heat emission of lambs fed with safflower grains. Eighteen lambs were randomly distributed in a completely randomized design. Safflower grain was added to the diets in the proportions of 0.0; 7.5 and 15%. The safflower grain did not change the patterns of eating, leisure, or rumination; however, it improved the efficiency of NDF ingestion, by 26%. The head temperature decreased by 1.5 ° C to include 7.5% safflower; and the rectal temperature decreased quadratically with the addition of safflower (39.5 and. 39.08 ° C). There was a linear trend of decreasing head temperature as the inclusion of safflower increased. The temperature of the eyeball decreased by 1.1 ° C when 7.5% of safflower DM was added to the diet and increased by 0.6 ° C when a 15% safflower was added. The ruminal temperature increased linearly for the addition of safflower (1.8 ° C). Safflower improves the efficiency of the use of NDF and the inclusion of 15% safflower can be used without effects on ingestive behavior. The head, eye, and left flank areas can be used; however, the left flank appears to be the best region for this type of study. Infrared thermography can be useful as a non-invasive assessment of lambs' diets.