Controlled elevated temperatures during early-mid gestation cause placental insufficiency and implications for fetal growth in pregnant pigs

Abstract

It is known that pig offspring born from pregnant pigs exposed to elevated ambient temperatures during gestation have altered phenotypes, possibly due to placental insufficiency and impaired fetal growth. Therefore, the objective of this study was to quantify the effect of maternal heat exposure during early-mid gestation, when pig placentae grow heavily, on placental and fetal development. Fifteen pregnant pigs were allocated to thermoneutral (TN; 20 °C; n = 7) or cyclic elevated temperature conditions (ET; 28 to 33 °C; n = 8) from d40 to d60 of gestation. Following euthanasia of the pigs on d60, placental and fetal morphometry and biochemistry were measured. Compared to TN fetuses, ET fetuses had increased (P = 0.041) placental weights and a lower (P = 0.013) placental efficiency (fetal/placental weight), although fetal weights were not significantly different. Fetuses from ET pigs had reduced (P = 0.032) M. longissimus fibre number density and a thicker (P = 0.017) placental epithelial layer compared to their TN counterparts. Elevated temperatures decreased (P = 0.026) placental mRNA expression of a glucose transporter (GLUT-3) and increased (P = 0.037) placental IGF-2 mRNA expression. In conclusion, controlled elevated temperatures between d40 to d60 of gestation reduced pig placental efficiency, resulting in compensatory growth of the placentae to maintain fetal development. Placental insufficiency during early-mid gestation may have implications for fetal development, possibly causing a long-term phenotypic change of the progeny.

Effects of cooling systems on physiological responses and intestinal microflora in early gestating sows exposed to high-temperature stress

“…Similarly, Zhao et al. [ 22 ] reported lower respiration rates (23 vs. 101 breaths/min) and skin temperatures (30.3°C vs. 36.6°C) in early-to-mid gestating sows kept at TN conditions of 20℃ compared with sows subjected to cyclic HS at 28°C–33℃. Another study reports lower respiration rate and temperature of ear and shoulder in pregnant sows under TN compared with HS [ 4 ].…”

“…Similarly, Liao and Veum [ 25 ] reported that subjecting pigs to cyclic or constant HS in early pregnancy does not influence the parameters tested in our study. In addition, sows housed under TN conditions (20°C) rather than cyclic HS conditions (28°C–33°C) during 40–60 days of gestation were not affected in terms of corpus luteum number and embryo survival rate, but instead a numerical increase was observed in the TN group [ 22 ]. Omtvedt et al [ 8 ] reported no effects on the performance of piglets produced from sows treated with HS during the mid gestating stage.…”

“…However, HS is closely related to swine reproduction as it can (i) postpone the onset of puberty, (ii) compromise fertility, embryo development, and parturition rate, and (iii) reduce piglet performance [ 5 , 6 , 30 ]. This may be due to the insufficiency of the placenta according to results that show decreased placental nutrient transporter gene expression and epithelial layers [ 22 ]. Omtvedt et al [ 8 ] also reported that HS at 32°C–38°C during days 0–8 or 8–16 of gestation can, in fact, reduce the number of corpus lutea and viable embryos in sows.…”

“…(iii) reduce piglet performance [5,6,30]. This may be due to the insufficiency of the placenta according to results that show decreased placental nutrient transporter gene expression and epithelial layers [22].…”

“…Lactating sows reared with HS at 32°C showed increased respiration rates and rectal temperatures compared with pigs reared under thermoneutral (TN) conditions (21°C)[21]. Similarly, Zhao et al[22] reported lower respiration rates (23 vs. 101 breaths/min) and skin temperatures (30.3 vs. 36.6°C) in early-to-mid gestating sows kept at TN conditions of 20°C compared with sows subjected to cyclic HS at 28-33°C. Another study reports lower respiration rate and temperature of ear and shoulder in pregnant sows under TN compared with HS[4].…”