Ten Sussex cattle are at Wildmoor Heath nature reserve for the summer and early autumn.
The ban came as a second infected calf was identified in Texas, and the US state declaring a state of disaster over the outbreak.
A calf near the US-Mexico border marked the first US case of a growing outbreak that is worrying cattle farmers.
The insect, which has been found in America for the first time since 1966, is a growing concern in the southern US.
A flesh-eating parasite that feeds on warm-blooded animals has been detected in the US for the first time since 1966.
They managed to get the 500kg (1,100lb) heifer safely back to her farm largely unscathed.
The chance of triplets being born is about one in 100,000, the National Farmers' Union estimates.
Defra confirms a decision to give permission to use an active culling licence is yet to be decided.
Hundreds of people have opposed the proposals, which they say are "cruel and inhumane".
