This is a very simple question with a simple answer that isn’t simple to implement.
The answer is only as much as it needs. But how much that is is dependent on the size, age, activity and DNA of the pet and also the type of food. This simple answer should be less if they are too fat and more if they are too skinny. Many people unfortunately do not know (or like to admit) their pet is overweight. If you know your pet is overweight and the food type and amount hasn’t changed recently, weigh the pet accurately first. You are always welcome to pop down to the clinic with your pet to weigh them any time we are open (no appointment necessary and no charge). We can help decide on a target weight for good health for your pet. An end point to aim for.
Now measure with a cup or scale the amount of food your pet has been receiving. Reduce this by 20%, measure, be consistent and weigh the pet again in 6-8 weeks. If the pet has lost at least 5% of their body weight you know you are on the right track. If they haven’t lost any weight, then reduce by a further 20% and repeat. Either that or talk to us about lower energy foods designed to make weight loss easier.
Make sure all the people in the house are on the same page when it comes to the diet. If a family member is overfeeding the pet and “feels sorry” for the pet I am happy to be the bad guy and take responsibility as the “bloomin’ vet” who said to feed them less. Unfortunately I see overweight pets on a daily basis who are dying or have more uncomfortable lives from diabetes, lameness and arthritis and heart problems directly caused by being overweight.