BACKGROUND: Mycotoxins are secondary metabolites produced by fungi, especially Aspergillus spp, on grains and animal feeds. The most important mycotoxins are aflatoxins, including aflatoxin B1, B2, G1, and G2. OBJECTIVES: The present study was conducted to determine the occurrence of aflatoxins (B1, B2, G1, and G2) in the feed ingredients of livestock and poultry and to evaluate the effect of the season and spatial variation on aflatoxin contamination. METHODS: Ninety-three feedstock samples were collected from three major factories in Kermanshah province, Iran, during four seasons. The samples were analyzed by HPLC, and values for aflatoxins were determined. The sum of the aflatoxins was determined as the total for each sample. Data were analyzed using the SPSS software version 23 using general linear model (GLM) based on complete block design (samples and seasons). RESULTS: Six out of 93 samples were positive for aflatoxin B1. Positive samples were mainly related to cold seasons. Moreover, no significant difference was found between the positive samples in terms of aflatoxins (B1, B2, G1, G2, and total). CONCLUSIONS: The aflatoxin B1 levels in animal feed were found higher during rainy seasons compared to the summer season. The aflatoxin B1, carried over from feed to livestock and poultry products in different seasons, may cause high contamination in livestock and poultry products at levels over the tolerance limit. Therefore, continuous surveillance of aflatoxins is required in animal feeds to reduce animal and consequently human exposure