A premix for an animal feed that exhibits an extended shelf-life which comprises: 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 wherein 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 kernel oil, and PEG-60 corn oil; ii) 5 to 25% (w/w) of a wax wherein said wax is selected from the group consisting of distilled monoglycerides, glyceryl tribehenate, glyceryl trimyristate, and hydrogenated coco-glycerides; iii) 0.1 to 2% (w/w) of an antioxidant wherein said antioxidants are selected from the group consisting of butylated hydroxyanisole, butylated hydroxytoluene, ascorbic acid, sodium metabisulphite, propyl gallate, sodium thiosulphate, and a mixture thereof; iv) 60 to 80% (w/w) of a pharmaceutically acceptable carrier vehicle wherein said carrier vehicle is selected from the group consisting of fine 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 to a range of 4 to 6 in order to decrease the acid or base catalyzed decomposition of the at least one avermectin compound, wherein said stabilizer is anhydrous citric acid present in an amount of 0.3 to 1.5% (w/w); and d) optionally, an effective amount of at least one insect growth regulating compound selected from the group consisting of methoprene, pyriproxyfen, hydroprene, cyromazine, lufenuron, 1-(2,6-difluorobenzoyl)-3-(2-fluoro-4-(trifluoromethyl) phenylurea, novaluron and a mixture thereof. 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 wherein 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 kernel oil, and PEG-60 corn oil; ii) 5 to 25% (w/w) of a wax wherein said wax is selected from the group consisting of distilled monoglycerides, glyceryl tribehenate, glyceryl trimyristate, and hydrogenated coco-glycerides; iii) 0.1 to 2% (w/w) of an antioxidant wherein said antioxidants are selected from the group consisting of butylated hydroxyanisole, butylated hydroxytoluene, ascorbic acid, sodium metabisulphite, propyl gallate, sodium thiosulphate, and a mixture thereof; iv) 60 to 80% (w/w) of a pharmaceutically acceptable carrier vehicle wherein said carrier vehicle is selected from the group consisting of fine ground corn cobs, crushed limestone, and dried grains; i) 5 to 15% (w/w) of a surfactant wherein 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 kernel oil, and PEG-60 corn oil; ii) 5 to 25% (w/w) of a wax wherein said wax is selected from the group consisting of distilled monoglycerides, glyceryl tribehenate, glyceryl trimyristate, and hydrogenated coco-glycerides; iii) 0.1 to 2% (w/w) of an antioxidant wherein said antioxidants are selected from the group consisting of butylated hydroxyanisole, butylated hydroxytoluene, ascorbic acid, sodium metabisulphite, propyl gallate, sodium thiosulphate, and a mixture thereof; iv) 60 to 80% (w/w) of a pharmaceutically acceptable carrier vehicle wherein said carrier vehicle is selected from the group consisting of fine 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 to a range of 4 to 6 in order to decrease the acid or base catalyzed decomposition of the at least one avermectin compound, wherein said stabilizer is anhydrous citric acid present in an amount of 0.3 to 1.5% (w/w); and d) optionally, an effective amount of at least one insect growth regulating compound selected from the group consisting of methoprene, pyriproxyfen, hydroprene, cyromazine, lufenuron, 1-(2,6-difluorobenzoyl)-3-(2-fluoro-4-(trifluoromethyl) phenylurea, novaluron and a mixture thereof.