Development of the fetus and fetal reproductive tract in gilts subjected to heat stress from week 4 to 8 of gestation

Abstract Text:

Gestational heat stress may lead to transgenerational changes in the reproductive capacity of boars and gilts. The objective 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 38^o C; 65 to 88% relative humidity; n=12) or gestational thermoneutral (GTN; 17 to 22 ^oC; 56 to 65% relative humidity; n=11) conditions during pregnancy. Gilts were housed in the Brody Environmental Chambers from week (wk) 4 to 8 of pregnancy before sacrifice during the 8^th wk of gestation for the collection of the reproductive tracts and fetal tissues. During pregnancy, GHS gilts had greater 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) compared with GTN. Sow was the experimental unit for analyses of fetal development. The 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), the 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, the 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), fetal fluid (80.4±10.0 vs. 90.4±10.6 g), and placental efficiency (fetal weight/placental weight; 0.60±.04 vs. 0.55±.05) did not differ (P>.10) for GHS vs. GTN (respectively). The ratio of male to female fetuses was similar (P>.10) for GHS (1.3±.3) and GTN (1.6±.3). 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). The conclusion was 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. Research was supported by the National Pork Board.

Keywords: fetal development, gestation, heat stress