Which parasite is most likely to be detected first in the fecal float of a young foal?

Strongyloides westeri is the parasite most likely to be detected first in the fecal float of a young foal primarily due to its life cycle and the age at which young horses are typically exposed to it. This parasite is known to be a common cause of diarrhea in foals and can be transmitted through the mare's milk.

Young foals may become infected quickly after birth, and since Strongyloides westeri excretes eggs relatively soon after infection, it allows for earlier detection in feces. This rapid egg production and shedding are what lead to their early identification during fecal examinations. In contrast, other parasites like Fasciola hepatica and Necator americanus are not typically relevant or are less common in equine hosts, especially in the context of young foals. They have different life cycles and routes of transmission that do not align with the circumstances of a young foal. Parascaris equorum, while also significant in equine parasitology, tends to shed eggs later than Strongyloides westeri, making it less likely to be detected in the very early stages of a foal's life.

Thus, the likelihood of encountering Strongyloides westeri first in