A premix for an animal feed that has a long shelf life comprising: a) 0.04 to 5% (w / w) of at least one avermectin compound； b) a pharmaceutically acceptable excipient comprising: i) 5 to 15% (w / w) of a surfactant in which said surfactant is selected from the group consisting of polyoxyl 40 hydrogenated castor oil, PEG-50 castor oil, PEG-60 corn glyceride, PEG-60 almond oil, PEG-40 palm almond oil and PEG-60 corn oil； ii) 5 to 25% (w / w) of a wax in which said wax is selected from the group consisting of distilled monoglycerides, glyceryl tribehenate, glyceryl trimiristate and hydrogenated coco glycerides； iii) 0.1 to 2% (w / w) of an antioxidant in which said antioxidants are selected from the group consisting of butylated hydroxyanisole, butylated hydroxytoluene, ascorbic acid, sodium metabisulfite, propyl gallate, sodium thiosulfate and a mixture thereof； iv) 60 to 80% (w / w) of a pharmaceutically acceptable vehicle in which said vehicle is selected from the group consisting of finely ground corn cobs, crushed limestone and dried grains； c) a pharmaceutically acceptable stabilizer in an amount effective to adjust the pH of the premix formulation in a range of 4 to 6 to decrease the acid or base catalyzed decomposition of at least one avermectin compound, wherein said stabilizer is acidic Anhydrous citrus present in an amount of 0.3 to 1.5% (w / w)； and d) optionally, an effective amount of at least one insect growth regulator compound selected from the group consisting of meprene, pyriproxyphene, hydroprene, ciromazine, lufenuron, 1- (2,6-difluorobenzoyl) -3- (2-fluoro- 4- (trifluoromethyl)) phenylurea, novaluron and a mixture thereof.Una premezcla para un pienso para animales que presenta una vida útil prolongada que comprende: a) del 0,04 al 5 % (p/p) de al menos un compuesto de avermectina； b) un excipiente farmacéuticamente aceptable que comprende: i) del 5 al 15 % (p/p) de un tensioactivo en el que dicho tensioactivo se selecciona del grupo que consiste
