Prenatal Heat Stress and the Impact on Swine Performance during Postnatal Life

Prenatal insults have well-documented effects on the postnatal performance of multiple species. Negative effects range from reduced growth rates and altered post-absorptive metabolism to increased frequency of metabolic disease and teratogenicity. While the effects of heat stress (HS) on postnatal pig performance are well-defined, the postnatal consequences of in utero HS on swine physiology and performance have only recently been described. In utero HS (IUHS) has an immediate impact on litter characteristics and decreases offspring birth weight, which is likely an effect of reduced gestation length and in utero growth retardation. In addition to the immediate impact on offspring characteristics, a variety of postnatal bioenergetic and metabolic consequences resulting from IUHS have been described. Prenatal HS imprints a lasting increase on core body temperature set-point in pigs. Since heat loss depends on thermal gradients, a permanent core body temperature increase would reduce an animal’s ability to dissipate excess body heat, which has implications towards HS tolerance and survivability. Additionally, maintaining a greater core body temperature set-point would likely decrease energy efficiency due to increased thermogenesis and recent reports indicate that maintenance costs of IUHS pigs are increased during the growing phase. Feed efficiency is also reduced during postnatal life in IUHS pigs compared to in utero thermoneutral (IUTN) pigs despite similarities in feed consumption and this may be due to either the aforementioned increase in maintenance costs or altered postnatal body composition in which adipose tissue is deposited at the expense of lean tissue during the finishing phase. Because lean tissue accretion is more efficient than adipose tissue accretion, depositing adipose at the expense of lean tissue may lead to inefficiencies in the conversion of feed energy to body mass. Furthermore, the predisposition towards gaining adipose tissue may be a result of increased insulin production by IUHS pigs during postnatal life, since insulin is a lipogenic and antilipolytic hormone. Taken together, these data have implications towards the efficiency of converting feed energy to high quality animal protein in prenatally heat-stressed pigs.