Ruminants can tolerate moderate concentrations of dietary tannin, making it feasible to replace corn with sorghum in ruminant diets; however, conditioning temperature of pelleted total mixed ration (PTMR) greatly affects nutrient digestibility. The objective was to determine effects of grain type and conditioning temperature during pelleting on growth performance, ruminal fermentation, meat quality and bloodmetabolites of fattening lambs. This was a 2 x 3 factorial study, with corn and sorghum and three conditioning temperatures (65, 75 and 85 degrees C) in a randomized complete design, with 36 lambs (120 +/- 10.2 d and 24.9 +/- 3.3 kg) grouped by weight and randomly allocated. The resulting six PTMRswere referred to as 65-S, 75-S and 85-S for sorghum-based diets, and 65-C, 75-C and 85-C for corn-based diets, for low, medium and high pelleting temperatures, respectively. Therewas no grain type x conditioning temperature (Grainx Temp) interaction on growth performance and apparent nutrient digestibility. Furthermore, grain type did not affect DMintake (DMI), average daily gain (ADG) or feed conversion ratio (FCR) of fattening lambs. Pelleting at 75 degrees C improved ADG (P < 0.03) and FCR (P< 0.02) of fattening lambs compared to other temperatures. There was a Grain x Tempinteraction (P< 0.01) onruminalpH (lowest in lambs fed 75-S). There tended (P= 0.07) to be a Grain x Temp interaction for total volatile fatty acid (VFA), and therewere Grain x Temp interactions formolar proportions of acetate (P< 0.04), butyrate (P< 0.03) and branch-chained VFA (P< 0.01). Lambs fed sorghum-based PTMRhad greater molar proportion of propionate (P < 0.03) and lower acetate to propionate ratio (A:P, P < 0.04). Lambs fed sorghum-based PTMR had higher plasma concentrations of urea nitrogen (N) (P < 0.03), glucose (P < 0.01) and alkaline phosphatase (P < 0.05), whereas other blood metabolites were not affected by treatments. There were Grain x Temp (P < 0.03) interactions for color coordinates of longissimus and mid-glutealmuscle. Lambs fed sorghum-based PTMR had lower (P < 0.01) dressing percentage andmeat quality than those fed corn-based PTMR. We concluded that sorghumcan replace corn in lamb diets without compromising growth performance and feed efficiency; furthermore, feeding sorghum vs corn improved rumen fermentation, with reduced A:P ratio and enhanced N and glucose utilization. Finally, pelleting at 75 degrees C increased feeding value of either sorghum- or corn-based PTMR for fattening lambs. Crown Copyright (C) 2020 Published by Elsevier Inc. on behalf of The Animal Consortium.