Abstract The objective of this study was to evaluate the effect of diet (grazing vs. pasture silage with concentrate) and changes in diet on n-alkane concentrations in cattle feces. The experiment lasted 35 d (15 d of adaptation and 20 d of sampling). Thirty Holstein-Friesian steers were divided into three groups of ten, and each group was randomly allocated to one of the following three treatments: GZ, diet consisting of 100% pasture; SC, diet consisting of pasture silage: concentrate in a 60:40 ratio; and MX, diet consisting of a gradual decrease in pasture and a gradual increase in SC. Fecal samples were taken daily from every animal, and their n-alkane content was analyzed using gas chromatography. The data obtained in this study showed detectable changes in n-alkane concentrations in steer feces. The changes were noticeable within two to three d after a change in diet, whereas concentrations of n-alkanes remained stable in the feces of animals that did not experience any change in diet. These results can be used as the basis for developing a tool that can determine the type of feed bovines received prior to slaughter.