Programs for synchronization of the estrous cycle and
timed artificial insemination (AI) increase pregnancy rate by
maximizing submission to AI [1], which has stimulated their
use for management of reproduction in dairy herds worldwide.
Despite the improvement in reproductive performance
associated with the use of timed AI over the past decade,
individual fertility measured as pregnancy per AI (P/AI) has
not changed [2]. This scenario highlights the importance of
developing strategies applicable to large groups of cows that
benefit the establishment and maintenance of pregnancy.
Exposure to insufficient concentrations of progesterone
during the growth of the ovulatory follicle is one of the
important factors that affect fertility in high-producing dairy
cows [3,4]. The decrease in P/AI observed in cows that lack a
functional CL at the initiation of the synchronization protocol
and the benefits from supplementing progesterone to this
cohort of cows have been reported [4–6]. Nevertheless, previous
results suggest that cows with CL might also have
insufficient circulating progesterone associated with
increased catabolism by splanchnic tissues [7] and are expected
to benefit fromprogesterone supplementation during
the timed AI program [8–10].