Which of the following helps prevent hardware disease in ruminants?

Rumen magnets are specifically designed to help prevent hardware disease in ruminants, which is a condition caused by the ingestion of foreign objects, particularly metal, that can lead to serious health issues such as puncturing the stomach or other internal organs. By using rumen magnets, these objects are attracted to the magnet and thus prevented from causing harm.

The other options, while they have their own benefits in animal health, do not directly address the prevention of hardware disease. Feed additives, for instance, can enhance nutrition or improve digestion but do not specifically target the issue of foreign objects in the digestive system. Probiotics may support gut health and improve the balance of microorganisms in the rumen, but they do not prevent the ingestion of metal objects. Vaccines are crucial in preventing infectious diseases but do not play a role in the mechanical issues caused by hardware disease. Therefore, the significance of using rumen magnets lies in their direct impact on preventing the ingestion of harmful materials, making them the correct choice for this question.