| Abstract: | During early pregnancy, a "critical period" may be defined between Days 15 and 17. Embryonic mortality associated with this period causes significant economic losses to the cattle industry. During this period, the endometrium will follow a default program to release luteolytic pulses of PGF2alpha, unless the conceptus sends appropriate antiluteolytic signals to block PGF2alpha, production. Maintenance of pregnancy is dependent on a successful blockage of endometrial PGF2alpha production. Biology of the critical period is complex and multifactorial. Endocrine, cellular and molecular factors, both from maternal and conceptus origins act in concert to determine whether luteolysis or maintenance of pregnancy will prevail. Understanding the influences of such factors in the biology of the critical period allowed researchers to produce a series of strategies aiming to favor maintenance of pregnancy in lieu of luteolysis. Strategies include hormonal and nutritional manipulations to decrease plasma concentrations of estradiol 17beta (E2) while increasing those of progesterone (P4), and inhibiting the PGF2alpha-synthesizing enzymatic machinery in the endometrium during the critical period. Experimental results indicate that use of such strategies has improved pregnancy rates following artificial insemination and embryo transfer programs. |
