Ideally, how often should horses be dewormed?

Deworming horses every 60-90 days is considered ideal for maintaining their health and preventing parasitic infestations. This frequency allows for effective control of common internal parasites, as many of these can reproduce quickly and create significant health issues if left unmanaged. Regular deworming helps to manage the parasite life cycle and reduces the likelihood of resistance developing against deworming medications.

It's essential to consider factors such as the horse's living environment, age, and overall health when determining deworming schedules. For instance, horses that are kept in high-density living situations or those that are young and have developing immune systems might require more frequent treatments.

The other options suggest either too frequent or insufficient deworming schedules. Monthly worming may lead to resistance, and less frequent treatments, such as annually or twice a year, may not adequately control the parasite population, which can put the horse's health at risk.