These are the larvae of Hypoderma bovis or H. lineatum (the common and northern cattle grub, respectively) and pour-on moxidectin or eprinomectin are approved for use in both lactating dairy and beef cattle.
Other products are approved for non-lactating and beef cattle.
Withdrawal times must be followed.
Organophosphates are not approved for this use in cattle in the United States.
While the grubs can be manually expulsed/squeezed out, care must be taken to prevent rupture of the grubs.
Crushed larvae release antigens leading to a systemic anaphylactic reaction in cattle.
These pests are less common now since macrocyclic lactones gained widespread use in the last few decades.
The adult flies (gad flies or heel flies) lay eggs on the lower limbs of cattle over the summer.
The larvae penetrate the skin and migrate to their respective preferred locations.
By early winter, the larvae arrive in the subcutaneous tissues of the back and make breathing pores.
This cyst/warble stages lasts four to eight weeks, culminating in 3rd-stage larvae dropping to the ground and completing the life cycle.
Clinical presentation of the larval infections range from localized tissue trauma around the warbles/cysts to periostitis, osteomyelitis, and neurological dysfunction.
Death of 1st-stage larvae in the esophagus or spinal canal can lead to location-specific clinical signs.
Cattle bothered by adult flies in summer show âgadding behaviorâ â stamping and running with tails in the air.
Dx: Identify 3rd stage larvae.
Image courtesy of Lucyin.
