Date Full Report Received


Date Abstract Report Received



Primary Investigator:

High temperatures and humidity have been shown to have direct, detrimental effects on pregnant gilts and their developing litters. In 1968, Teague et al. determined that heat stressed females had lower ovulation rather than those housed in cooler temperatures. Similarly, Warnick et al. (1965) determined that females housed at high ambient temperatures from conception through d 25 of gestation had fewer embryos than those housed in thermoneutral environments. Late gestational heat stress has been shown to decrease the number of live pigs per litter and increase the number of still born piglets (Omtvedt et al., 1971) Heat stress during late gestation may also cause lower piglet birth weights (Omtvedt et. al, 1971). Heat stress has also been shown to affect feed intake during lactation (Quiniou and Noblet, 1999: Williams et al., 2013).
These negative effects, coupled with effects on growth and carcass composition, have been estimated to cost the swine industry one billion dollars annually (Pollman, 2010). In order to determine the full magnitude of the effect of gestational heat stress, it is important to understand if gestational heat stress can affect future generations. Black and Erickson (1968) determined that the ovary undergoes rapid development from days 30 to 60 of gestation. Therefore, by collecting reproductive tracts of pregnant gilts that have been housed in heat stress environments during gestation, we can determine whether the fetal ovary has been damaged and if gestational heat stress affects future generations.

Gestational heat stress may lead to effects on the fetuses (i.e. transgenerational changes) in the reproductive capacity of boars and gilts. The objective of this study was to assess fetal and placental development and the development of gonads in conceptuses whose mother was subjected to gestational heat stress (GHS; 28 to 38o C; 65 to 88% relative humidity; n=16) or thermoneutral (GTN; 17 to 22oC; 56 to 65% relative humidity; n=14) conditions during weeks 4-8 of pregnancy. High temperatures increased rectal temperature (38.5±.04 vs. 38.0±.04 oC; P<.001), skin temperature (35.5±.2 vs. 28.7±.2 oC; P<.001), and respiration rate (44.3±2.6 vs. 19.5±2.7 breaths per min; P<.001) in pregnant gilts. Surprisingly, weight of the pregnant tract (12.0±1.2 vs. 12.5±1.3 kg), number of viable conceptuses (13.8±.8 vs. 15.3±.9), number of non-viable conceptuses (.3±.2 vs. .1±.2), the number of mummies (.2±.1 vs. .3±.1), and the %survival (number of viable conceptuses/number corpora lutea; 89±4 vs. 90±5%) did not differ (P>.10) for GHS vs. GTN, respectively. Upon dissection, neither did weight of the fetus (82.3±3.6 vs. 84.9±3.8 g), placenta (155.5±14.7 vs. 170.1±15.6 g), or fetal fluid (80.4±10.0 vs. 90.4±10.6 g), (P>.10) for GHS vs. GTN, respectively. The ratio of male to female fetuses was similar (P>.10). The weight of male fetuses (86.2±3.8 vs. 86.4±4.0 g), combined testis weight (34.2±1.4 vs. 32.8±1.5 mg), and combined testis weight as a % of fetal weight (.040±.001 vs. .038 ±.001) did not differ (P>.10) for GHS vs. GTN, respectively. The weight of female fetuses (81.2±3.6 vs. 83.5±3.8 g), combined ovarian weight (25.2±1.0 vs. 26.1±1.1 mg), and combined ovarian weight as a % of fetal weight (.031±.001 vs. .031 ±.001) did not differ (P>.10) for GHS vs. GTN (respectively). While the numerical differences between treatment groups generally were in favor of the GTN environment, lack of statistically significant difference leads to the conclusion that heat stress from wk 4 to 8 of gestation in gilts did not change the growth of the fetus, placenta, ovary or testis at mid-gestation.
This project was specifically designed to go beyond direct effects of heat stress on pregnant sows and to evaluate the effect of being heat stressed as a fetus; i.e. transgenerational effects of in utero heat stress. Gestational heat stress has previously been shown to impact subsequent growth and carcass composition at slaughter. Boddicker et al. (2014) found that pigs exposed to heat stress in utero exhibited an increase in subcutaneous fat thickness compared to pigs who were exposed to thermoneutral conditions in utero. Pigs heat stressed in utero may also have heavier hot carcass weights at slaughter compared to pigs that developed under thermoneutral conditions in utero (Cruzen et al. 2015). Johnson et al. (2015) also determined that gestationally heat stressed pigs experience a reduction in protein accretion rate and feed efficiency. Although research has been done to determine the transgenerational effects of in utero heat stress on carcass composition and growth, little work has been done on the transgenerational effects of in utero heat stress on the reproductive capacity of gestationally heat stressed gilts. The studies conducted by Boddicker et al. (2014), Cruzen et al. (2015), and Johnson et al. (2015) suggest that because growth traits are affected by gestational heat stress, it is possible that reproductive characteristics may also be affected in gilts heat stressed in utero. By further understanding how gestational heat stress affects the developing fetus, producers will have more accurate estimates on the total costs of heat stress.

Gestational heat stress may lead to transgenerational changes in the reproductive capacity of boars and gilts. The objective was to assess pregnancy development in gilts whose mothers were subjected to heat stress (GHS; n=23; 28 to 38 oC; 65 to 88% relative humidity) or thermoneutral (GTN; n=25; 17 to 22 oC; 56 to 65% relative humidity) conditions as a developing fetus (in utero) from wk 4 to 8 of pregnancy. Female progeny (generation 1; G1) from both GTN and GHS mothers remained on farm under commercial conditions and were artificially inseminated at second estrus. During the 8th wk of gestation, gilts (GTN-G1; n=55 and GHS-G1; n=50) were sacrificed for the collection of the reproductive tracts and fetal tissues. Data were obtained from four replicates, and replicates differed for weight of the pregnant tract (9.9±1.0 vs. 11.7±0.7 vs. 15.0±1.0 vs. 13.6±0.7 kg; P<0.003). Two possible explanations are offered for these replicate effects: different Duroc boars were used for two replicates due to a PRRS outbreak; and environmental conditions at the farm for the portion of gestation of the grand-dams could have differed as the replicates were all within one year’s time. Thus effect of temperature at other points in gestation or adaptation to temperature extremes due to previous environments are possible. The weight of the pregnant tract (12.7±0.6 vs. 12.4±0.6 kg), number of viable conceptuses (12.3±0.6 vs. 12.7±0.5), and the %survival (number of viable conceptuses/number corpora lutea; 77±4 vs. 75±3%) did not differ (P>.10) for GHS-G1 and GTN-G1 (respectively). A sex-specific transgenerational effect on fetal weight was observed, because male fetuses from GHS-G1 had increased weight (129.0±4.8 vs. 119.5±4.5 g) but female fetuses were similar (117.4±4.7 vs. 115.8±4.5 g) (GHS-G1 vs. GTN-G1; Treatment by sex, P<0.012). The conclusion was that in utero heat stress from wk 4 to 8 of gestation had gender-specific transgenerational (first generation) effects. The fact that these effects were observed despite essentially no measurable direct effects points to the likelihood that the impact of heat stress on swine production has been underestimated.

Key Findings:
• physiological coping mechanisms to heat stress were observed (higher respiration rate and skin temperature), but were incapable of preventing the rise in rectal temperature.
• physical reproductive parameters were the same for gilts heat stressed as those housed under thermoneutral conditions.
• -GHS and GTN piglets did not differ for anogenital distance or size of fetal ovaries or testes at 60d of gestation.
• -GHS and GTN piglets taken to term also did not differ.
• -GHS and GTN gilts mated and slaughtered at d60 of pregnancy were strikingly similar.
• While many numerical differences favored the GTN gilts, very few were statistically different.
• -male fetuses of GHS gilts were heavier than GTN male fetuses, though female fetuses did not differ between treatments.

Dr. Tim Safranski
University of Missouri
(573) 884-7994