Does inadequate luteal function limit the establishment of pregnancy in the early post-partum ewe?

Abstract

observed in 2 of 7 (0\m=.\28)lactating and 4 of 9 (0\m=.\44)early weaned ewes compared with corresponding values of 1 of 13 (0\m=.\08) and 2 of 11 (0\m=.\18) in the 35-day post-partum group. Luteal function was normal in all standard ewes. The proportion of successful pregnancies in the standard ewes was 0\m=.\80 (12 of 15) compared with 0 in lactating and early weaned ewes in the 21-day group and 0\m=.\08 (1 of 13) and 0\m=.\36 (4 of 11) respectively in the 35-day group.The incidence of inadequate luteal function is therefore independent of the suckling stimulus and is higher in ewes induced to ovulate on Day 21 than Day 35 post partum during breeding and non-breeding seasons. For early post-partum recipient ewes with normal luteal function it is suggested that the high incidence of pregnancy failure after transfer of embryos may be due to embryo mortality caused by an inappropriate uterine environment or the inability of the embryo to sustain its luteotrophic signal.

Successful pregnancies after transfer of embryos recovered from ewes induced to ovulate 24-29 days post partum

“…The results of our present study show that the incidence of luteal inadequacy, as assessed by peripheral progesterone concentrations, was greater in early weaned than in lactating ewes and confirms our earlier observation that the suckling stimulus per se does not contribute to abnormal luteal function in early post-partum ewes induced to ovulate during the non-breeding and breeding seasons (Wallace et al, 1989a). In earlier studies using lactating ewes, inadequate luteal function following induction of ovulation 28 days post partum was associated with complete failure of fertili¬ zation and low embryo recovery rates on Day 6 after oestrus (Wallace et al, 1989b).…”

“…Indeed, none of these post-partum ewes maintained their pregnancies after autotransfer. In a subsequent study (Wallace et al, 1989a) we demonstrated that good quality Day-5 embryos donated from ewes in which the interval from parturition was in excess of 150 days had a very low survival rate when transferred into the uterine environment of the early post-partum ewe (0 pregnancies in 16 ewes induced to ovulate 21 days post partum and 5 pregnancies in 24 ewes induced to ovulate 35 days post partum). In contrast, the results of the present study show that embryos recovered on Day 3 after oestrus from ewes inseminated between 24 and 29 days post partum are viable when transferred to a normal uterine environment.…”

“…This suggests that inadequate luteal function is not the only factor limiting the establishment of pregnancy in the post-partum ewe. Indeed, the transfer of good quality embryos into post-partum recipient ewes induced to ovulate 21 days after parturition and exhibiting normal luteal function failed to result in the establishment of pregnancy, suggesting that at this time the involuting uterus of the early post-partum ewe is an inappropriate environment for embryo development (Wallace et al, 1989a).…”

Characterization and autoradiographical localization of oxytocin receptors within the ovine endometrium in relation to post-partum corpus luteum function

“…Indeed, we have previously shown that the induction of ovulation during the post-partum period is associated with a high incidence of prematurely regressing corpora lutea which is independent of the suckling stimulus but dependent on the stage post par¬ tum (Wallace, Robinson & Aitken, 1989a;Wallace, Robinson, McKelvey & Aitken, 1989c). A large body of circumstantial evidence suggests that these prema¬ turely regressing corpora lutea result from enhanced or premature release of prostaglandin F2a (PGF2a) from the uterus (Troxel & Kesler, 1984; Copelin, Smith, Garverick & Youngquist, 1987;Lewis & Bolt, 1987;Copelin, Smith, Keisler & Garverick, 1989;Schirar, Meusnier, Paly et al 1989).…”

Development and Control of Luteal Function in Farm Animals

“…Recent evi dence indicates that the suckling-induced release of β-endorphins, which inhibit the release of GnRH, is responsible for the inhibition of ovarian func tion. [153][154][155] Ewes, [156][157][158] cows, [159][160][161][162] sows, 163,164 and does 165 can be induced to return to cyclic ovarian function (provided they have not become seasonally anestrous) by weaning of the young. In cattle, wean ing for a period as short as 2 days will induce estrus in a large percentage of the cows.…”