Water Activities and Animal Feed

How Water Activity Is Measured

• A sensitive tool called a hygrometer measures water activity. For the simplest hygrometers, a small sample of the animal food is ground to a powder and placed in a dish. Then, the water activity is taken for standards made of different concentrations of salt to calibrate the hygrometer. The ground pet food's water activity is then measured. It is important during the test to keep the ground food covered so it does not absorb moisture from the air.

Importance of Water Activity

• Most bacteria that will make an animal sick grow in a water activity range of 0.90 and higher. For example, the bacteria that causes botulism needs a minimum water activity of 0.97. Molds that cause animal feed to spoil need a water activity of at least 0.70. Feeds with water activities lower than 0.60 have a lengthy shelf life because microorganisms cannot grow in an environment with such low water availability.

Water Activities of Animal Food

• The water activities of wet pet food range from 0.83 to 0.99. Spoilage is prevented in these foods through the canning process. Moist foods such as soft cat treats or moist dog kibble have water activities anywhere from 0.53 to 0.82. These foods have a limited shelf life without the addition of preservatives. Dry animal feeds include anything from dry cat food to rabbit pellets. These foods have water activities below 0.50 and have very long shelf lives if kept away from moisture.

Working with Water Activity

• Pet food developers working on new products strive for a balance between palatability, nutrition and shelf life. Using humectants such as propylene glycol, salts and sugars, manufacturers can lower the water activities of moist foods. Moist foods are more palatable to pets than dry foods, but dry foods scrape and clean the teeth as the animal chews. Using water activity knowledge and humectants, moist kibble and dry kibble can be combined into one package without spoilage and without the dry food becoming soft.