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.
Highlights
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
The objective of this study was to investigate the impact of controlled elevated temperatures (ET) during early-mid gestation (d40 to d60 of gestation) on placental and fetal development in pregnant pigs
There was an interaction between gestational temperature and exposure day (P = 0.017), such that ET pigs had the highest respiration rate on d1, followed by a gradual decrease to the lowest point on d21, while the respiration rate of TN pigs remained constant throughout the experimental period (Fig. 1a)
Summary
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. It is known that pigs reared under elevated environmental temperatures are more prone to deposit adipose tissue than pigs reared under optimal ambient conditions[18,19] This has been observed in progeny born from pregnant pigs that experienced heat stress during gestation, even when they were reared under normal postnatal environmental conditions[16,20]. These findings indicate that elevated temperatures in utero may cause a long-term postnatal change in phenotypes of the progeny. The objective of this study was to investigate the impact of controlled elevated temperatures (ET) during early-mid gestation (d40 to d60 of gestation) on placental and fetal development in pregnant pigs
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