What’s that awful smell?
Many times that’s the first thing someone asks after autoclaving an animal diet the first time. If it smells that bad the first time why do it a second time? In spite of a long list of negative effects of autoclaving, it is an effective method of sterilizing diets for use in barrier facilities.
The primary negative effect, namely vitamin degradation, is addressed by fortifying the diet with sufficient additional heat labile vitamins to allow for ample levels after proper processing. But what is proper processing? Unlike stainless steel surgical equipment, food is very sensitive to over processing with either excessive temperature or time. Or both. As little as an extra 20o F in temperature or an extra 10 minutes will produce a deficient diet.
Added to other negative effects of autoclaving, specifically, increased pellet hardness, reduced palatability (remember the smell?), damaged proteins, why is autoclaving still used to process diets?
In most cases it is because the autoclave equipment is available (already installed) and that’s the way it’s always been done. Autoclaved diets are sterile and if properly managed, acceptable results in animal performance can be achieved. But, can we do a better job?
Over the last 20 years irradiated diets have offered an option to process diets for barrier use.
There is little if any vitamin loss. Vitamin C levels are impacted but guinea pigs, non-human primates and fish are rarely fed autoclaved diets.
There is no increase in hardness, no loss of palatability and no protein damage. Pellet hardness is a factor that can reduce consumption with mice being the most sensitive to hardened pellets. In lactating mice this reduced consumption can decrease milk production, in growing animals it can retard growth rates.
Palatability is not impacted. The sense of smell is a large component in determination of what is delectable. It’s no wonder that such an offensive aroma as produced by autoclaving would reduce animal acceptance of a foodstuff. Rabbits are particularly hesitant to consume autoclaved foods. Fortunately rabbits do not require sterilized diets in most common environments.
Protein damage in the form of denatured proteins can reduce the digestibility of proteins and negatively affect the amino acid profile.
Are there any downsides to the use of irradiated diets? Irradiation sanitizes, it does not sterilize. Although there is a tremendous reduction in bioburden including the absence of nearly all single celled microbes, irradiation is less effective against viruses and prions due to their having less than a full complement of DNA. However, a long history of use of irradiated diets has yet to present evidence of a disease outbreak attributed to a contaminated diet.
As irradiated diets are used at greater volumes the additional cost of irradiation has declined to the point that the cost of in house processing and the reduced animal performance with autoclaved diets exceeds the increased cost per pound when comparing irradiated and autoclavable diets.
Click here for more information on processing Laboratory Animal Diets.