What is true about worms in relation to livestock?

Worms, particularly intestinal parasites affecting livestock, have a reproductive cycle that includes the laying of eggs, which are commonly excreted in the feces of infected animals. This is why option A is true; manure serves as a critical environment for the eggs to be deposited and eventually develop into larvae, which can reinfect livestock or affect other animals in the area. It is essential for livestock management to monitor and control worm populations since their eggs can lead to further infestations.

In contrast, the other options do not accurately represent the role or impact of worms in livestock. Worms typically do not affect joints; their influence is more related to the gastrointestinal tract and overall health. While some worms do aid in nutrient cycling in soil ecosystems, they are not directly involved in the digestion of host livestock. Finally, while deworming treatments are vital for managing worm infections, worms themselves are not utilized in such treatments; rather, the treatments are designed to eliminate these parasites from the animal's system.