Bran mash isn't even good for horses. The pigs and horses may like it but it's hard on their digestive tract. It can lead to health issues especially if given frequently. Occasionally some people will use oats or oatmeal in small amounts to add weight to sick or elderly pigs but a better choice for a treat is a pellet mash. Here is an example of a pellet mash I made for mine last christmas:
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It's pellets soaked in plain fruit juice with bits of chopped up carrots, apples, and cilantro. You can serve it warm or cold but if you heat things it's better to use hot water or place it on the stove than just microwaving it. The microwave breaks down nutrients and lessens the flavor. Plain fruit juice has no added sugars like fructose, corn syrup, or sucrose. I used blueberry Naked Juice. Odwalla is also a popular plain fruit juice mix that people have used to flavor things like pellet mash for sick pigs.