Breed anxiety (6)
I believe the answer is:
strain
I believe this is a double definition.
'breed' is the first definition.
(I know that breed can be written as strain)
'anxiety' is the second definition.
(thesaurus)
(Other definitions for strain that I've seen before include "Pass through a filter" , "Weaken -- sieve" , "Pull (a muscle?)" , "Pour through a sieve" , "Injure (a muscle); distinct breed" .)