The espohageally fistulated animal is a well recognized and accepeted range nutrition research tool. Esophageally fistulated animal studies have been conducted to evaluate diet differences between kinds and breed of animals, various grazing management strategies, different seasons of use, geographic locations, and diurnal diet patters. This study was conducted to determine how diet samples taken from one class of animals compare to diet samples taken from another class of animal within the same species. Cattle of mixed Bos taurus breeding prepresented by four esophageally fistulated mature steers and five esophageally fistulated growing heifers were used. the two groups were allowed to simultaneously graze tobosa (Hilaria mutica rangleland daily for a period of approximately 30 minutes between June 19 and June 29, 1979. The diet chemical components, crude protein and in vitro organic matter were analyzed. Analysis of the botanical components of the deit indicated five grasses thriteen forbs and three shrubs. This diversity in botanical composition contributed to a diet which had a mean grass, forb, and shrub content of 35, 51 and 14%, respectively. Analysis of the dependent variables indicated that deits between the animal higher (p<.10) in crute protein and three forb components. Heifer deits were 2.4% higher (P<.05) in crude protein compared to the steer diets. These results indicated caution should be used when extrapolating diet data collected from one class of animal to anohter class of animal within the same species. In addition to sex sex differences tarbush (Flourensia cernua), considered an invader shrub species, contrubuted to 92% fo g of the diets in which botanical components were analyzed.