When subjected to a timed AI program utilizing GnRH, the majority of anovular cows experience a synchronized ovulation, but conception rates remain low (26).
Rutigliano and Santos (25) evaluated the risk for late embryonic loss in lactating dairy cows classified as cyclic or anovular at 65 d postpartum and subjected to synchronization of estrus or ovulation for first postpartum AI.
2) reviewed several studies with high-producing dairy cows and observed that 15,7 and 26,3% of the pregnancies were lost in cyclic and anovular cows, respectively.
Follicular size and response to Ovsynch versus detection of estrus in anovular and ovular lactating dairy cows.
Risk for pregnancy loss between 30 and 58 d of gestation in cows classified as cyclic or anovular by 65 d postpartum (25).
Part of the improvement in fertility of dairy cows as first AI is delayed past the traditional 60 to 70 d postpartum is the improved uterine health, as involution has completed is almost all cows, but also the reduced prevalence of anovular cows as the lactation progresses.
A method to induce cyclicity in anovular cows is to administer exogenous progesterone by using controlled internal drug releasing (CIDR) impregnated with progesterone (13).
The use of supplemental progesterone to reestablish ovulatory cycles in high-producing anovular cows does not seem to be warranted.
Two major impediments for the success of programs that are based solely on estrous synchronization are the poor expression of estrus in high-producing cows and the high prevalence of anovular cows in the first 60 d postpartum (4, 8).
However, frequency of anovular cows and lack of optimal estrous detection can have a major impact on the number of cows responding to [PGF.