Heat Stress Effects on Fetal Development during Late Gestation in the Ewe

Abstract

Forty-eight crossbred ewes were subjected to heat stress of short or long duration during the last third of gestation in a completely randomized design to determine the effects of maternal heat stress on lamb birth weight, lamb conformation and subsequent preweaning growth rate. Ewe treatments were spring range pasture, confinement on slotted floors in a heated room maintained between 28 to 38 C or in a slotted floor barn with feed intake equal to the feed intake of the 38 C housed ewes. Treatment exposure averaged 25 and 53 days for short and long duration, respectively. Lamb birth weights of heated, range and restricted fed ewes were 3.18, 4.57 and 4.16 kg, respectively. After adjustment for sex and multiple birth effects, birth weight of lambs from hot environment ewes were smaller (P<.01) for both durations of treatment. Lamb birth weights from heated ewes were smaller than those of lambs from restricted fed ewes (P<.05). Relative kidney and liver weights were greater in lambs from heated ewes (P<.05). Relative muscle weights and relative linear equivalent bone lengths were not different among ewe treatments. Lambs from heated ewes had 30 and 56-day weights similar to those of lambs from range and restricted fed ewe groups. Small Iambs resulting from maternal heat stress of 25 or 53 days duration are proportional dwarfs and occur independently of ewe level of nutrition. Department of Animal Science. 2Studies were conducted at the Dixon Springs Agricultural Center, Simpson, IL. The cooperation of Drs. M. E. Mansfield and D. Drori is gratefully appreciated.

Thermal Environment and Human Birth Weight

“…However, restricting heat stress exposure to mid-pregnancy still compromises growth compared to control animals (Galan et al, 1999), and exposure in only the "nal 25 days of the 145 day gestation period likewise produces intra-uterine growth retarded lambs (Brown et al, 1977). These "ndings indicate that two distinct factors may be involved in foetal growth retardation.…”

Late-gestation heat stress abatement on performance and behavior of Holstein dairy cows

“…7 2010). Intrauterine growth retardation of heat-stressed ewes during late gestation has been found to be independent of malnutrition (Brown et al, 1977). Finally, heat stress in ruminants effects on pregnancy are related not only to decreased blood flow to the uterus (Reynolds et al, 1985), but also to decreased placental size (Collier et al, 1982a) and function (Collier et al, 1982b;Bell et al, 1989).…”

Altered arterial concentrations of placental hormones during maximal placental growth in a model of placental insufficiency

“…This regime allows developmental or growth impairment to be attributed to the effects of chronic heat exposure. When TN ewes are fed the same feed intake of gestational age matched heat stressed ewes, heat stressed lamb birthweights are significantly reduced, while TN weights are unaffected (Cartwright & Thwaites 1976, Brown et al 1977. Furthermore, both groups of ewes consumed approximately 10·7 MJ per day, an amount greater than the estimated 10·5 MJ required metabolizable energy intake of pregnant ewes during the first 105 days of gestation (Subcommittee on Sheep Nutrition 1998).…”

“…Alterations in steroid and protein hormones of placental origin have been shown to occur in IUGR pregnancies, specifically progesterone and placental lactogen (PL) (Nisbet et al 1982, Westergaard et al 1984, Yanaihara et al 1984, Laurin et al 1987. Changes in hormonal profiles, placental functional capacities, and IUGR have been associated with changes in placental mass (Brown et al 1977, Bell et al 1987, Thureen et al 1992. The underlying associations made from such studies have been that these hormonal and fetal alterations are a result of reduced placental growth.…”