Despite what the cynics say, you don’t need animals or animal products to grow a successful garden.
None of the nutrients required for soil fertility originate in animals. The nutrients that are found in animal manure come from plants, or plant based feeds that animals have ingested. In other words, the key to soil fertility is plants.
Although the notion of growing food crops without the use of animal manure is unfamiliar, history shows that well before we had domestic animals on the scale there is today, farmers relied largely on green manures and other plant based techniques to create thriving gardens.