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.
Risk for pregnancy loss between 30 and 58 d of gestation in cows classified as cyclic or anovular by 65 d postpartum (25).
The
anovular conditions in this study may be due to non-existence of an LH surge which is needed for ovulation and resultantly the animal remains anovulated.
The three patterns characteristic of catamenial epilepsy were perimenstrual or periovulatory exacerbations during normal cycles, and exacerbations during the second half of
anovular cycles (Ann.
Insulin resistance in PCOS is more prominent in
anovular woman than equally hyperandrogenic women with regular menses.18 This finding correlates well with our study as majority of our patients with insulin resistance had menstrual irregularities like oligomenorrhea or secondary amenorrhea in addition to obesity.
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).