Preferential selection of fecal pats for oviposition byMusca sorbensWiedemann from cows fed different rations was studied. Caged ovipositingM. sorbenswere overwhelmingly attracted to feces from cows fed concentrated feed supplements over feces from cows fed only grass. Gravid flies showed restraint in ovipositing on feces from cows fed on grass when confined in insect cages for protracted periods with no other breeding media available. Weight of fly puparia reared from preferred feces was 46.7% greater than that of puparia from feces ignored by ovipositing flies at the same dairy. Fresh samples of cow fecal pats were classified as either attractive or unattractive to ovipositingM. sorbensbased on the presence or absence of egg clusters and were analyzed for differences in crude protein content. Results showing similar crude protein content in both samples indicated that protein residues were not responsible for ovipositional preference. These studies suggested that (1)M. sorbensrefrains from ovipositing unless specific odors from digestive residues of concentrated feed supplements in cow feces are present; (2) fecal odors attracting ovipositingM. sorbensare related to nutritional needs of fly larvae; and (3) odors from digestive residues other than protein may be responsible for this attraction.