Abstract: A supplementary strategy and feedlotting method for yak calves was sought as a new approach to alleviate the pressure on natural grasslands and allow recovery of natural vegetation. A 3×3 Latin square test of digestive and metabolic trials was designed in Dawu township of Guoluo Prefecture. Three yak calves per treatment were fed with 3 different diets: (A) 100% Elymus nantus silage, (B) 40% concentrate+60% E. nantus silage, and (C) 60% concentrate +40% E. nantus silage.1) There were significant differences in digestibility of dry matter, organic matter, crude protein and energy with the different diets, but there was no significant difference for crude ash. With an increase in percentage of concentrate in the diet, the digestibility of every nutrient ingredient in the different diets gradually decreased; 2) The metabolizability of energy for diet C was significantly lower than that for diets A and B, but the efficiencies of digestive energy conversion into metabolic energy (ME/DE) were not significantly different between the 3 diets. The average conversion efficiency was 0.78; 3) Calcium (Ca) extracted from faeces and urine was significantly different between the diets, while phosphorus (P) differed significantly from urine from the three diets but not from faeces. Ca sediment decreased with the increase in percentage of concentrate, but P sediment was maximum in diet A and minimum in diet B. These results showed that the digestive and energy metabolisms of diets for yak calves were closely bound up with dietary composition. Apparent digestibility decreased with an increase of dietary level. These result provide a scientific basis for supplementary feeding and celerity fattening, which would be an effective approach to speed up turnover of drove and to increase the merchandise ratio of yaks.