June 05, 2019

Interpretive Summary: Postnatal consequences of in utero heat stress in pigs

Interpretive Summary: Postnatal consequences of in utero heat stress in pigs

By: Jackie Walling

An article published in the February 2019 Issue of the Journal of Animal Science studies the postnatal consequences of in utero heat stress (IUHS) in pigs.  As global temperatures rise, heat waves are expected to challenge pig health and performance.  Prenatal heat stress effects may be reducing profitability of production.  This article acknowledges previous studies to describe phenotypic effects of IUHS on postnatal thermoregulation, growth, nutrient partitioning, reproduction, and stress responses in pigs.

Prenatal heat stress indirectly effects pigs because the fetus is adapting in utero to the mother’s heat response.  Adaptations in utero may not be compatible with postnatal conditions for survival.  Regarding thermotolerance, IUHS pigs have increased core body temperature set-points regardless of environmental temperature.  Observations of IUHS pigs indicate increased sensitivity, greater body temperature increases, and an inability to cool themselves effectively in postnatal heat stress conditions.

Heat stress can elicit survival mode in sows compromising production performance.  Fetal growth and development is likely restricted leading to negative impacts on muscle, fetal weight, intestinal development, and growth performance in offspring.  Prenatal heat stress is thought to reduce feed efficiency and birthweight.  IUHS pigs require increased feed intake and feed allowance, but lack an adequate growth rate response diminishing profitability.  Prolonged heat exposure could also lead to fetal malformations including reduced head size.  This could impede neurological developments effecting physiological functions such as metabolism.

Nutrient partitioning in IUHS pigs allocates more energy to adipose tissue deposition over protein deposition likely caused by changes in postabsorptive metabolism.  This results in less lean tissue and decreased meat quality for consumers.  Heat stress increases production of cortisol (stress hormone) possibly altering metabolic processes.  This could be associated with increased levels of insulin predisposing IUHS to accumulate adipose tissue.

IUHS pigs are likely to suffer negative reproductive performance later in life.  IUHS seems to target male reproduction by reducing sperm production, increasing tail abnormalities, and reducing testicular size.  Sows see a reduction in piglets weaned and protein content in milk.  There is concern for oocyte damage because the development of ova takes place in utero.

General stress responses in postnatal experiences of IUHS pigs are heightened. Fetal tissue is receptive to glucocorticoids in the mother which effect the hypothalamic-pituitary-adrenal axis causing cortisol concentrations to increase.  Stress in the mother increases glucocorticoids which ultimately effects neural development of their offspring.  If IUHS pigs experience increased cortisol concentrations in utero, the concentrations increase after farrowing. 

Overall, addressing prenatal heat stress could be key to saving economic losses in production.  Prenatal heat stress is thought to increase body temperature, lower feed efficiency, alter body composition, and reduce fertility.  Not all studies used in this article showed consistent results indicating the need for more research.

 For the full article, visit the Journal of Animal Science.