Relationships between ovulation rate and embryonic and placental characteristics in multiparous sows at 35 days of pregnancy

Abstract

The objective of this study was to investigate relationships between ovulation rate (OR) and embryonic and placental development in sows. Topigs Norsvin ® sows (n = 91, parity 2 to 17) from three different genetic backgrounds were slaughtered at 35 days of pregnancy and the reproductive tract was collected. The corpora lutea (CL) were counted and the number of vital and non-vital embryos, embryonic spacing (distance between two embryos), implantation length, placental length, placental weight and embryonic weight were assessed. The difference between number of CL and total number of embryos was considered as early embryonic mortality. The number of non-vital embryos was considered as late mortality. Relationships between OR and all other variables were investigated using two models: the first considered parity as class effect (n = 91) and the second used a subset of sows with parities 4 to 10 (n = 47) to analyse the genetic background as class effect. OR was significantly affected by parity ( P < 0.0001), but was not affected by the genetic background of the sows. Parity and genetic background did not affect embryonic and placental characteristics at 35 days of pregnancy. OR (varying from 17 to 38 CL) was positively related with early embryonic mortality (β = 0.49 ± 0.1 n/ovulations, P < 0.0001), with late embryonic mortality or number of non-vital embryos (β = 0.24 ± 0.1 n/ovulations, P = 0.001) and with the number of vital embryos (β = 0.26 ± 0.1 n/ovulations, P = 0.01). However, dividing OR in four classes, showed that the number of vital embryos was lowest in OR class 1 (17 to 21 CL), but not different for the other OR classes, suggesting a plateau for number of vital embryos for OR above 22. There was a negative linear relationship between OR and vital embryonic spacing (β = −0.45 ± 0.1 cm/ovulation, P = 0.001), implantation length (β = −0.35 ± 0.1 cm/ovulation, P = 0.003), placental length (β = −0.38 ± 0.2 cm/ovulation, P = 0.05) and empty space around embryonic-placental unit (β = −0.4 ± 0.2 cm/ovulation, P = 0.02), indicating uterine crowding. Further analyses showed that effects of OR on embryonic and uterine parameters were related with the increase in late mortality and not early embryonic mortality. Therefore, we conclude that a high OR results in an moderate increase in the number of vital embryos at day 35 of pregnancy, but compromises development in the surviving embryonic/placental units, suggesting that the future growth and survival of the embryos might be further compromised.

Gene Expression Profiling of Corpus luteum Reveals Important Insights about Early Pregnancy in Domestic Sheep

“…On the other hand, Finnsheep (63%) and F1 cross (48%) had a remarkably low embryo survival rate. While these findings are based on fewer animals, the results are in agreement with earlier studies [39,40] where typically higher litter size is associated with higher embryo mortality and vice versa. It would be of great interest to determine if productivity follows the same pattern in F2 (i.e., F1 × F1) crosses, backcrosses and presumably also in a reciprocal cross.…”

Recent advances in pig reproduction: Focus on impact of genetic selection for female fertility

“…That current high ovulation rates indeed affect embryo survival and embryo quality has recently been corroborated by Da Silva et al. (), Da Silva, Broekhuijse, et al. (), for sows and gilts, respectively.…”

“…In both their study and the study of Da Silva et al. () with sows, these effects on the embryo‐placental units were related to the level of late embryonic mortality, indicating that high ovulation rates combined with uterine crowding compromises the development of the remaining embryo‐placental units.…”

“…Moreover, in gilts (Da Silva, Broekhuijse, et al., ; Da Silva, Laurenssen, et al., ) high ovulation rates were related to higher within litter variation in weight ( ß = 0.01). In sows, high ovulation rates were related with lower placental lengths, where each additional CL represented a decrease in placental length of 0.38 cm at day 35 of pregnancy (Da Silva et al., ).…”

Genetic selection against intrauterine growth retardation in piglets: a problem at the piglet level with a solution at the sow level

“…An alternative effect of selection for lower rates of IUGR may be more evenly spaced embryos. Lents et al [ 69 ] reported negative relationships of ovulation rate with embryonic spacing and with empty space around the embryonic-placental unit, which both indicate crowded uterine conditions. Other studies have shown that mouse lines that lack lysophosphatidic acid, a phospholipid involved in uterine peristaltic movements that facilitate embryo separation [ 69 ], have blastocysts that remain clustered in the vicinity of the cervix, whereas non-deficient lines have blastocysts that are evenly distributed along the uterine horns [ 70 ].…”