Fermented foods can be a beneficial addition to your pet's diet, as they promote a healthy gut and provide numerous health benefits. They are rich in probiotics, enzymes, and nutrients that can improve digestion and overall well-being.

One example of a DIY fermented food for pets is sauerkraut. Sauerkraut is made by fermenting cabbage with salt, which encourages the growth of beneficial bacteria. It is important to note that sauerkraut should be prepared without any added spices or seasoning, as these can be harmful to pets.

Another option is homemade yogurt. Yogurt contains live cultures of bacteria, such as lactobacillus acidophilus, which can help populate the gut with beneficial microorganisms. You can make yogurt by fermenting milk with a yogurt starter culture or by using a small amount of store-bought plain yogurt as a starter.

When introducing fermented foods to your pet, it is crucial to start with small amounts and monitor their reaction. Some pets may have a sensitive stomach and may need to gradually adjust to the new addition in their diet.

References:

1. Jurgens, M. H., R. P. A. Rikken, and M. C. J. W. H. Buijssen. "Fermented infant formula: a nutritional approach." Nutrition 16.7-8 (2000): 654-656.
2. Parvez, S., K. A. Malik, S. Kang, and H. Y. Kim. "Probiotics and their fermented food products are beneficial for health." Journal of applied microbiology 100.6 (2006): 1171-1185.

By incorporating homemade fermented foods like sauerkraut or yogurt into your pet's diet, you can help promote a healthy gut and improve their digestion. However, it is always recommended to consult with a veterinarian before making any significant changes to your pet's diet.