... aborted will do so again unless carefully treated. So contagious is the disease that the germs introduced into a perfectly healthy cow will cause her to abort, and it is no uncommon thing for the infection to spread through an entire herd in a single season. The herd bull readily becomes a source of herd infection, and service from a bull, where there are aborting cows ... — Pratt's Practical Pointers on the Care of Livestock and Poultry • Pratt Food Co.
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