Maternal recognition of pregnancy in domestic animals Submitted by:-

Deepak Dhillon

(2006V17B)

The presence of a, viable, developing embryo(s), prevents the CL from regressing and thus, in polyestrous spp., inhibits the return to oestrous

It is particularly interesting because this maternal endocrine response is detectable before the blastocyst is attached to the endometrium by microvili.

Time of maternal recognition of pregnancy

Sheep

A type 1 interferon ovine tau interferon (oIFN-τ) is produced by trophectoderm from about day 10, at the time the blastocyst starts to elongate.

IFN-τ secreted by embryo prevents rise in endometrial oestrogen-α receptors that precedes the rise in endometrial oxytocin receptors. Oxytocin of luteal (and possibly a central) origin can thus no longer bind to the uterus, and this results in a reduction in the pulsatile secretion of PGF2α (Spencer & Bazer 2004)

Other view is that a reduced luteal sensitivity to PGF2α and enhanced production of luteotrophic PGE2 as the dominant mechanisms in the maternal recognition of pregnancy in sheep (Costine et al 2007)

Cattle

A tau interferon(bIFN-τ) with maximum secretion occurring between days 16 and 19 of gestation; it is first secreted at the time of elongation of blastocyst and, continues to be secreted until day 38 of gestation

It is likely that bIFN-τ exerts its antiluteolytic effect by modifying oxytocin receptors, thereby inhibiting the synthesis from arachidonic acid and subsequent release of PGF2α

Goat

The caprine conceptus secretes a protein, originally designated cTP-1 which suppresses pulsatile prostaglandin secretion from the endometrium.

This apparently also occurs spontaneously in pseudo pregnancy in this species, when in unmated does the CL persists and fluid accumulates in the uterine lumen.

Pig

After embryo enter in uterus on day 4, some 2 days after ovulation, embryos start migrating throughout both uterine horns so that by day 12 they have more or less become evenly distributed; a process called ‘spacing’.

The early porcine conceptus has been shown to convert progesterone to oestrone & oestradiole-17β, as well as 16α, 17-oestradiol. This oestrogen production by conceptus plays a vital role in maternal recognition of pregnancy and extension of the life span of CLs.

After the initial secretion of oestrogens at day 11, a second sustained release of oestrogens by the conceptus is necessary between days 14 and 18 for luteal persistence beyond day 25 (Geisert et al 1990)

Conceptus-secreted oestrogens prevent luteal regression by direct luteotrophic effect (maintenance of LH receptors in the CLs and secretion of PGE2 to protect the CLs against the luteolytic action of PGF2α.

Fetal membranes readily metabolize PGF2α to PGFM(15-keto-13, 14 dihydro-PGF2α),which is inactive.

Horse

The nature of embryonic signal that prevents luteolysis in the mare is still not clear.

A low molecular weight protein has been identified in the uterine flushings of mares in dioestrus; this persists during pregnancy(McDowell et al 1982)

The importance of the migration of the spherical conceptus within the uterine lumen until it becomes ‘fixed’ at 16-18 days of gestation at the base of the uterine horn has been demonstrated in some elegant experiments by McDowell et al (1988)

It is likely that the stimulus elicited by the migratory conceptus in its contact with the endometrium is comparable with the stimulus associated with the rapid elongation of the blastocyst in ruminants and the pig.

Dog

The bitch is atypical in that the length of the luteal phase (metoestrus/dioestrus) hardly differs from that of pregnancy. Surgical removal of the nonpregnant uterus in metoestrus/dioestrus does not prevent the demise of the CLs and there appears to be no need for maternal recognition of pregnancy to maintain the life span of CLs and the continuation of progesterone production.

Cat

The length of luteal phase in mated but non-pregnant (pseudopregnant) queen is about 40 days, while in pregnant females luteal progesterone production continues for another 20 days. Little is known about the mechanisms underlying the meternal recognition of pregnancy in the queen.