The old days of treating everything in the fall with an ivermectin-type (macrocyclic lactone) product year after year and always expecting excellent results are perhaps going away.

Animal Health: Parasite control is complicated, and herd management needs to be reviewed from time to time
Cooler, wetter spring could favour the pests this year
Pests, toxic plants and disease can all thrive under dry conditions
Don’t mix treated and untreated cattle, and apply products at the proper dosage and at the proper timing