Chronic heat stress and prenatal development in sheep: II. Placental cellularity and metabolism1

Abstract

Aspects of placental protein and energy metabolism were examined in pregnant ewes subjected to either thermoneutral (TN, 18 to 20 degrees C, 30% humidity, n = 7) or hot (H, 30 to 40 degrees C, 40% humidity, n = 5) temperatures through mid and late gestation. Fetal and placental weights and total content of protein, RNA, and DNA were reduced (P less than .001) in H ewes. Placental protein and RNA concentrations (mg/g) were not different, and DNA concentrations were slightly greater (P less than .1), in H vs TN ewes. Thus, heat seemed to greatly reduce total cell number and placentome size and only slightly decrease cell size. Ratios of RNA to DNA indicated a reduced capacity for protein synthesis in H placenta. However, in vitro fractional rates of protein synthesis in tissue slices from the fetal and maternal placenta and from the myoendometrium were not different between TN and H ewes. The H ewes had greater placental protein concentrations of hydroxyproline and glycine, perhaps suggesting a greater collagen content. In vitro oxygen consumption of fetal placenta, but not of maternal placenta or myoendometrium, was lower in H than in TN ewes. This lower oxygen consumption was partially due to a lower Na+,K+ ATPase-dependent oxygen consumption.

Gestational Heat Stress Alters Postnatal Offspring Body Composition Indices and Metabolic Parameters in Pigs

“…B) Respiration rate presented as breaths per minute (bpm) was elevated as a result of postnatal HS ( P< 0.001) in addition to the detection of a postnatal treatment by time interaction ( P< 0.01). C) Skin temperature was increased in pigs subject to postnatal HS compared to thermal neutral [30] counterparts ( P< 0.001) in addition to detection of a postnatal treatment by time interaction ( P< 0.001). A gestational by postnatal treatment interaction was observed in skin temperature ( P  = 0.05) whereby gestational treatments exposed to HS during the second half of gestation had higher skin temperature (0.5°C) under HS conditions but lower skin temperature under TN conditions (0.3°C) compared to HSTN and TNTN gestational treatments.…”

“…B) Respiration rate, breaths per minute (bpm), is elevated in HS compared to thermal neutral [30] postnatal treatment ( P< 0.001), and a postnatal treatment by time interaction was also observed ( P< 0.001). C) Skin temperature was elevated as a result of postnatal HS ( P< 0.001) in addition to a postnatal treatment by time interaction ( P< 0.001).…”

“…B) Circulating insulin concentrations were elevated in pigs from dams exposed to heat stress (HS) conditions during the first half of gestation compared to those from dams gestated in thermal neutral [30] conditions during the first half of gestation ( P =  0.01). Different letters indicate P< 0.05.…”

“…To accomplish this, pregnant gilts were exposed to four different environmental conditions during gestation, and resulting offspring were then exposed to thermal neutral [30] or HS environments during postnatal growth and development for either 24 h or 5 weeks.…”

Evidence for placental compensation in cattle

“…Despite this high priority status of the conceptus, the prenatal growth trajectory remains extremely sensitive to environmental and maternal challenges. Thermal stress is known to compromise fetal development, caused by both decreased uterine blood flow (Reynolds et al, 2006) and placental function (Early et al, 1991). Heat stressed cows also have a reduced dry matter intake (Tao et al, 2011), which at least partly contributes to intrauterine growth retardation of the fetus.…”