What are some common by-products of the animal industry?

In the context of the animal industry, by-products refer to the secondary products generated during the processing of animal products or the utilization of animals themselves for various purposes. The correct identification of blood and bone meal highlights their significance as valuable by-products.

Blood can be collected during the processing of meat, where it is often rendered into various products such as blood meal, which is high in protein and commonly used as a fertilizer or animal feed. Bone meal is produced from the processing of bones and is rich in phosphorus and calcium, essential for plant growth and also used in animal nutrition. Both blood and bone meal serve crucial roles in agriculture, enhancing soil fertility and providing nutrients for livestock.

The other options mention products that are usually considered primary products of animal husbandry. For example, milk and eggs are direct consumables produced by animals, while leather and feathers are derived from the skin and outer coverings of animals but are not categorized in the same way as blood and bone meal, which are specifically by-products of the animal processing stages. Fibers and hides also appear as products obtained from animals but again are typically viewed within the context of direct use rather than by-products in the sense of secondary processing.