Over the past ten years there has been a significant shift from autoclaving to irradiation to sterilize laboratory animal diets. Throughout the United States, irradiated diets account for a clear majority of all sterilizable diets used, with the percentage being over 80% in some geographic areas. The rate of use of irradiated diets is increasing steadily in labs of all kinds, pharmaceutical companies, universities, research institutes, and government agencies. In fact, virtually all major pharmaceutical companies and universities have replaced routine autoclaving with irradiation.

The common experience is that, when feeding lab animals irradiated diets, no instances of food-borne pathogen contamination occur even over periods of ten years or more.

	Irradiated Diets	Autoclaved Diets
Nutrition	There is virtually no loss of any nutritional component in irradiation	Autoclaving causes significant degradation of several vitamins; the prolonged high heat is commonly believed to cause other nutritional loss of unknown proportions. Furthermore, this degradation will vary unpredictably from batch to batch.
Sterility	Consistent virtual sterility from batch to batch. Viruses, bacteria, and other organisms are inactivated, parasite ova are neutralized. As long as seals are left unbroken, irradiated diets remain sterile for at least as long as their typical six-month shelf life.	Varies depending upon temperature, amount of food in the autoclave, length of time in heat, length of “cool-down” time.
Labor	Exterior of bags are sprayed with disinfectant and then contents transferred to clean room through barrier facility airlock.	Bags must be loaded onto carriers, wheeled into autoclaves, heated for 20-30 minutes depending on protocol, unloaded, and transferred to clean room through barrier facility airlocks. Typically extensive time must be spent breaking up clumped and hardened food.
Odor	No odor	Offensive, persistent odor. Potential personnel irritant.
Palatability	Consistent. Indistinguishable from non-irradiated food.	Inconsistent. Often much less palatable than non-autoclaved food. Results vary by diet and batch.
Hardness & Texture	Hardness and textured unchanged.	Hardness and texture are compromised significantly. Food typically hardens and clumps together, inconsistently from bag to bag and within each bag.
Moisture content	Moisture content unchanged. Retards mold growth in feeders.	Autoclaving can unpredictably and inconsistently increase moisture content, supporting mold growth in the feeder and increasing the amount of diet that must be discarded.
Value	Irradiated diets cost more to purchase than non-irradiated diets—but that cost is consistent and predictable. When adding costs of— autoclave fuel & water usage, depreciation and maintenance, operating & additional labor, and wasted food, irradiated diets actually cost less.	Non-irradiated diets cost less, but the process and complications of autoclaving make them more costly and of less value: · The autoclaving operation process requires considerable labor time. · Additional labor time must often be spent in breaking up clumped food, re-packaging, removing molded food from feeders. · Clumped, hardened, molded, and unpallatable food can result in large amounts being discarded.* · Electricity, water, autoclave maintenance, repair, and depreciation add considerable “hidden” costs.

* One study found that most facilities discard about 25% of autoclaved diets during the summer months due to excessive hardness or mold. Anecdotal evidence indicates common occurrences of even higher levels of wastage.

TMC 0404