Fetal and maternal fluid balance in sheep during hyperthermia with and without water deprivation

Abstract

SUMMARYOur aim was to determine the efFect of maternal hyperthermia, both with and without maternal water deprivation, on fetal fluid balance. Seven pregnant ewes (131.8 + 1.0 days gestation) were studied during a control period and periods of maternal heating (MH,(42)(43)(44) stimulates ewes to drink substantially more than under normal conditions, thereby decreasing their plasma osmolality; water transfer to the fetus may increase, thereby decreasing fetal plasma osmolality. When drinking water is unavailable, maternal hyperthermia and associated dehydration may decrease water transfer to the fetus. Thus, the fetus becomes not only hyperthermic, but also hyperosmotic and possibly hypovolaemic. Matemal hyperthermia, irrespective of the availability of drinking water, decreases production rates of lung liquid and urine in the fetus.

Fluid Balance in Ruminants: Adaptation to External and Internal Challenges

“…It is therefore not surprising that the death rate of Merino sheep fetuses living in the hot arid regions of Australia is high. 28 Pregnant ewes 29 and goats 18 drank in excess during heat stress, particularly when the water was warm (35°C). The reason for the excessive drinking is not known, but a lack of the normal inhibitory signals from the oropharyngeal tract appears to occur and may be related to the lack of cooling effect of the warm water.…”

Feto‐Maternal Relationships in Goats During Heat and Cold Exposure

“…During heat exposure these species also showed a decrease in the feto-maternal temperature difference. The decline in the feto-maternal gradient during short-term heat stress could be the result of fetal thermal inertia alone (Morishma et al 1977;Andrianakis & Walker, 1994;Schröder & Power, 1994), but rises in uterine and/or umbilical blood flow have been reported (Morishima et al 1977;Cefalo & Hellegers, 1978;Dickson & Harding, 1997), which alone or jointly would increase fetal heat loss (Schröder et al 1988) and lead to a decrease in feto-maternal gradient. Thus goat fetuses, similar to those of sheep and baboons, appear to be protected from intra-uterine hyperthermia by a mechanism or mechanisms which result in a decrease in the feto-maternal gradient.…”