You should monitor iodine values (IV) of the fat as an estimate of the degree of unsaturation and remain with a reputable supplier. The higher the IV number, the greater the degree of unsaturation and risk of rancidity if antioxidants are not used. The average IV number for tallow is 48; for pork fat (white grease), 62; for restaurant grease, 72; for corn oil, 126; and for soybean oil, 131 (NRC, 2001). The cows should not be backing off on intake when feeding the choice white grease. One suggestion is to introduce the new odor of grease in the barn or feeding area before adding the ingredient to the ration so the cows get used to the odor and then add small amounts initially to the ration.
Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET
