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Freeze-dried diets for cats - yes or no?

Freeze-dried diets for cats have become increasingly popular over the last five years, so today I'm going to talk about some of the positive and negative aspects of these diets, and also which cats they may be most suitable for.

Freeze-drying as a technology has been around for a long time, however it was from the 1950s onwards that it was really developed as a method of producing shelf-stable foods for astronaut and military rations.

How is freeze-dried cat food made?

Freeze-drying or lyophilization is a dehydration technique based on the sublimation of water in a product. What this means is that the product’s water content transitions from a solid to a gaseous state — or from ice to vapour — without going through the liquid state.

Commercial freeze-dryers can be very large and costly to both purchase and run.

In the case of cat food, the raw ingredients are mixed with any fats and supplements, and then rapidly cooled in a blast freezer. The frozen food is then placed in the freeze-dryer, and further frozen to a very low temperature. Primary and secondary drying phases then occur, and the end result is a very light weight product with less than 5% water content.

Freeze-dried foods can last for up to 25 years, so it’s an excellent method of preserving food for commercial or at-home use. Freeze-dried products are extremely light-weight, so they are convenient for manufacturers to ship, however freeze-drying as a process is very energy-intensive.

Are freeze-dried diets raw? Are they safe to feed?

A really important point to understand is that unless the food is cooked prior to freeze-drying, the end-result is a raw product. And, if you have a look at the image below of freeze-dried chicken breast, you can see that it’s a bit misleading, because it actually looks like dried cooked chicken, not raw chicken. So feline diets that are freeze-dried truly are raw diets, unlike air-dried or dehydrated diets (which are cooked at a lower temperature of about 70 degrees for a long time period).

In terms of food safety, feeding a freeze-dried diet is similar to feeding a raw diet – both can contain pathogenic bacteria and parasites, unless the manufacturer has either cooked the meat in the diet, or used high pressure pasteurisation (HPP) to kill these pathogens.

Salmonella can survive the freezing process, and recently freezing meat at -20 degrees for 14 days was shown not to inactivate toxoplasma, which is a very common parasite in game meats like kangaroo.

What are the pros and cons for freeze-dried diets?

Let’s talk about the positive aspects of freeze-dried diets first. Perhaps the main pro is that for many cats, freeze-dried foods are highly palatable when fed dry. This is the main reason why freeze-dried treats are everywhere – cats love them! Because of the way the freeze-drying process works, there is also excellent preservation of colour and flavour, and little loss of nutrients.

In terms of the negatives, there are some significant ones. Perhaps one of the most important drawbacks is that the diets often don't absorb enough water, and/or they become significantly less palatable when rehydrated to ~75% moisture (similar to the water content of most canned diets).

Powdered freeze-dried diets can absorb water a bit better, however the end result is often a consistency which isn’t hugely appealing to many cats. What this means is that many cat owners choose not to add much water to the diets, or they choose to feed the diet without rehydrating it at all. If you currently feed a freeze-dried diet to your cat, do you do some maths to work out how much water you need to add? Do you rehydrate the diet to at least 70% moisture?

The consequences of feeding freeze-dried foods that have not been adequately rehydrated can include constipation, obstipation, or even gastrointestinal obstruction. Remember that kibble typically contains about 10% water, and freeze-dried foods contain about 2% water, so these foods are really dry! Senior cats often experience constipation, so for older cats, freeze-dried foods can be particularly risky. We also know that high moisture diets may provide health benefits for cats, so it’s not a good idea to feed freeze-dried diets that haven’t been properly rehydrated.

Another potential negative that I mentioned before is that the process of freeze-drying involves no kill step, so there is a risk that these diets can still contain pathogenic bacteria like salmonella. Given that the FDA now has a zero tolerance level for salmonella in pet food in the USA, this has become a big problem for some manufacturers. As I mentioned previously, high pressure pasteurisation is increasingly used to kill pathogens in the meat prior to freeze-drying.

In Australia and New Zealand though, this isn’t required, so essentially you are feeding raw, pet-grade meat, offal and bone. So obviously be very careful with how you handle these diets, especially once they have been rehydrated.

Can I feed freeze-dried treats to my cat?

As I mentioned previously, freeze-dried meat and fish are generally very palatable to most cats, so these foods can make useful treats. A lot of pet food manufacturers sell powdered freeze-dried meat and fish as toppers; adding a small sprinkle may be an effective way of increasing interest in the meal.

However, it’s important to remember that even small amounts can increase the risk of constipation in some cats, so make sure that your cat is still toileting normally. If you noticed decreased frequency of defecation, or drier stools, stop or reduce the amount of freeze-dried treats you are feeding.

It’s also important to keep track of how many calories you are actually feeding. For example, if you were to eat 100 grams of freeze-dried watermelon, it’s equivalent to eating 1.25 kg of fresh watermelon! So, most freeze-dried treats for cats are a concentrated source of calories, and also nutrients like phosphorus. For cats with kidney disease, these treats aren't generally a good option, because you can add a lot more phosphorus to your cat's diet, without realising. Finally, keep in mind the risks of feeding and handling raw meat, especially in households with young children or immunocompromised people.

So, should I feed a freeze-dried diet to my cat?

To summarise, we only generally recommend feeding a freeze-dried diet as part of your cat's main diet if you are able to adequate rehydrate the food to 70 to 80% moisture. If your cat doesn't find this palatable, then you are probably best to opt for another type of diet. Also, try to choose freeze-dried diets produced by manufacturers using HPP to destroy pathogens in the raw meat. If you aren't able to do this, remember that food safety is just as important for these diets, as it is for raw meat-based diets. Finally, be very careful to keep freeze-dried treats to a minimum if your cat has problems with constipation.

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