Swine Heat Stress: You can’t influence the forecast. But you can influence the outcome.

The hidden impact of heat stress

When fetuses are exposed to elevated temperatures during gestation — a condition known as in utero heat stress — piglets may be born lighter, with a compromised gut microbiome, weakened immune function, and a heightened vulnerability to stress later in life. These effects are not always immediately obvious, yet they are essential to recognize and prevent.

Every degree above 25°C impacts performance:

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Daily feed intake per sow ^*

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Mile production per day ^*

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Three critical moments

The severity of heat stress depends on the stage of pregnancy. Sows bred during hot periods tend to have a higher proportion of low-birth-weight piglets (<1.1 kg) and lower total litter birth weight compared with sows bred under cooler conditions.

Early gestation

(Mating to ~Day 14)

During the first two weeks of pregnancy, embryos are developing and implanting in the uterus. Heat stress increases the sow’s core body temperature and alters the uterine environment (blood flow, hormones, and oxidative balance). These changes can reduce embryo survival and increase early embryonic loss, leading to fewer total pigs born.

Early gestation

Mid-gestation

(~Day 30 to 60)

Between days 30 and 60, major fetal organs and the placenta are developing. Heat stress during this period can reduce placental efficiency and nutrient supply to the fetus. In female fetuses, this stage also overlaps with important phases of ovarian development. Excessive heat exposure may affect the formation and survival of early germ cells (future oocytes), potentially influencing the reproductive capacity of the offspring gilt.

Mid-gestation

Late gestation

(Final weeks before farrowing)

In late pregnancy, heat stress increases oxidative stress and causes the sow to redirect blood flow toward the skin to dissipate heat. This can reduce blood flow to the uterus and placenta. As a result, oxygen and nutrient delivery to the fetuses may be compromised, increasing the risk of stillbirths, lower birth weight, and weaker piglets at birth.

Late gestation

Preparation starts long before each stage

Heat stress during these phases can reduce embryo survival, fetal development, and birth weights.

How heat stress affects the sow

In response to high temperatures, the animal diverts blood flow away from internal organs and toward peripheral tissues such as the skin and ears to improve heat dissipation. As a consequence, blood flow to internal organs is reduced, particularly to the gastrointestinal tract.

Metabolic impact

Gut integrity

Reproductive function

Heat stress before birth affects lifetime performance

Heat stress not only affects sow performance but also programs the unborn piglet. In utero heat stress is associated with lower birth weight, altered body composition, and increased stress sensitivity after birth.

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Body weight at 10 days of age^*

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Lipid deposition (increased fat)^*

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Higher preening mortality gilts’ litters^*

Ready for key pressure moments

Cinergy brings together a portfolio of targeted micronutrition solutions to help build health early across all life stages, supporting steady, reliable performance.

Lactation under heat stress

Lactation is the most energy-demanding stage in a sow’s life, and heat stress greatly amplifies this burden. Beyond these productive losses, heat stress disrupts gut integrity by increasing intestinal permeability (“leaky gut”) and elevating systemic inflammation. Combined, these physiological strains heighten vulnerability to disease and substantially increase the risk of sow mortality during the summer months.

Under elevated temperatures, sows reduce feed intake to limit metabolic heat production, which in turn reduces milk yield, slows piglet growth, and prolongs the weaning‑to‑estrus interval.

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