were assigned to an estrus synchronization protocol with the purpose of
attaining heifers with no luteal P4 synthesis but similar
and substantial plasma P4 concentrations originating
from an exogenous source.Heifers received a 100-μg
treatment of GnRH (Cystorelin; Merial Ltd., Duluth,
GA) and a controlled internal drug-releasing device containing
1.38 g of P4