There's a common idea, reinforced by some vets, that it's normal for cats to vomit. It isn't. Regular vomiting isn't always a sign of illness, but it's also not something to shrug off, it's something to investigate and resolve.
There are many reasons a cat may vomit, and we'll list some below, but first let's make the distinction between vomiting and regurgitation.
Vomiting:
Vomiting will occur some time before or after eating, and may contain food, or bile, or a foreign substance. Vomiting is usually a cause for concern, and you should seek to find the trigger so you can resolve the issue. Some reasons for vomiting are:
Hairballs .. As cats lick themselves, their rough tongues pull loose fur out of their coats, which is then swallowed. Large volumes of hair can accumulate in the stomach and aren't easily digested, leading the cat to vomit a hairball.
Gastroenteritis .. This can occur from eating inappropriate food items, ingesting toxins, or medication side effects. Some causes are mild and resolve on their own. Others are more serious and need a vet's attention.
Obstructions .. If your cat eats foreign objects, toys, string, etc, this will cause blockage and damage to the GI tract that can lead to vomiting. This is very serious and requires immediate veterinary attention.
Food allergies and inflammatory bowel disease .. Allergies or food intolerances can cause chronic vomiting. When cats eat a trigger food, the inflammation in their digestive tract may lead to vomiting, and some cats will also experience chronic diarrhoea as a result. We often see this when cats are being fed highly inappropriate commercial diets, especially dry food. In most cases, transitioning to a balanced raw diet will put an end to this vomiting. If vomiting persists on raw, it may be worth exploring an elimination diet to find a possible protein intolerance.
Systemic illnesses and nausea .. Chronic illnesses such as kidney disease, pancreatitis, and hyperthyroidism can all cause nausea and chronic vomiting. Addressing these requires identifying the underlying condition, and many require lifelong management.
Parasites .. More common in kittens, but can occur at any age. Occasionally you'll even see live worms in the vomit. The good news is that treating the parasites often resolves the vomiting.
Hunger pukes .. When your cat is raw fed, you may notice they vomit up some frothy yellow fluid on occasion. Raw fed cats need a much more acidic stomach environment to process raw meat, and when you're feeding set meals during the day, an interrupted schedule can result in a bile vomit. In anticipation of a meal, the stomach fills with the acid it needs to digest, and when that meal doesn't turn up, the body expels that acid so the stomach can return to a calmer state. This is not a vomit to be concerned about.
Regurgitation:
Regurgitation, by contrast, is bringing up food immediately after eating, and is caused by very few factors, all easily resolved.
Regurgitation soon after a meal is usually due to the food being too cold or eaten too quickly. Serving the meal at room, or "mouse", temperature will help, as will feeding on a slow feeding mat or bowl, or feeding smaller meals more often.
Feeding raw with a "dry" topper can also cause regurgitation, as the dryness tickles the throat and triggers the reflex. The same goes for a dry treat given soon after eating. Giving freeze dried treats away from feeding times is how we solve this one.
Throwing up during the transition to raw
Throwing up during a raw transition is common enough that it's worth knowing exactly what you're looking at, because the fix is different depending on which one it is.
First, work out if it's regurgitation or true vomiting, using the descriptions above.
Regurgitation during a transition has the same causes as regurgitation at any other time.. temperature and eating speed are the usual culprits, and the fixes above apply just as well here.
If it's true vomiting.. happening some time after eating rather than immediately, possibly containing bile, and the cat may seem uncomfortable or nauseous beforehand.. then something isn't agreeing with the cat, and during a transition specifically it usually comes down to one of the following.
Going too fast is probably the most common cause. A sudden full swap from commercial food to raw can overwhelm a gut that's used to something very different. The fix here is slowing the transition down.. smaller raw portions mixed gradually with the old food over a longer period, rather than a cold swap.
Portion size on its own can also cause true vomiting, even in a cat with a healthy gut. Raw is calorie dense and rich compared to most commercial diets, and a meal too large for where the cat is at in the transition can come back up some time after eating. Reducing the amount per sitting and feeding more frequently often solves this without changing anything else.
Protein choice matters too. Some cats will vomit on one protein and be completely fine on another. If the vomiting is tied to a specific protein rather than happening across the board, that's worth noting, and testing by removing it and trialling a different one, rather than assuming raw itself is the problem.
If none of the above fits, and especially if the cat has a history of poor quality commercial food or preservative-laden supermarket raw, the underlying gut damage described above may be at play, and it's worth stopping all raw, replacing it with a good quality canned food, and starting a probiotic containing prebiotics, before trying raw again.
Next time your cat throws up, ask yourself: is this a regurgitation or a vomit? What does it contain? How is my cat's behaviour and demeanour, is he acting normal or showing signs of discomfort or pain, is he nauseated?
Try offering more food and see if it stays down. Remember, if in doubt, or if your cat seems unwell, or the vomit contains a foreign object, please see a vet.