Which preventive measure is least effective against external parasites?

Providing regular exercise is indeed the least effective measure against external parasites. While regular exercise is important for a pet's overall health and well-being, it does not directly impact the prevention of external parasites such as fleas and ticks. Exercise alone does not create an environment that repels these parasites, nor does it provide any type of physical barrier or treatment to reduce the likelihood of infestation.

In contrast, using flea and tick preventive products is specifically designed to target and eliminate parasites on pets, making it a direct and effective approach. Maintaining a clean home environment helps reduce the chances of parasites residing indoors and limits their access to hosts. Ensuring timely veterinary visits allows for professional advice and the necessary treatments to be administered, which can include vaccinations, parasite testing, and preventative medications tailored to the pet's needs. Thus, while all preventive measures can contribute to a pet's health, regular exercise does not specifically address or prevent external parasite infestations.