We examined the effect of route of delivery on brown adipose tissue (BAT) function and thermoregulation in lambs born either vaginally at term or by cesarean section close to term. Immediately after birth, lambs were placed in a warm (30 degrees C; WD) or cool (15 degrees C; CD) ambient temperature, and measurements of colonic temperature, plus heat production (i.e., oxygen consumption and carbon dioxide production), were recorded for 6 h. Over the first 30 min of life, colonic temperature remained constant in vaginally delivered lambs and was lower in the WD group. Following cesarean section delivery, colonic temperature declined rapidly, a response that was greater in the CD group. Cesarean section-delivered lambs had an increased reliance on shivering thermogenesis and restored colonic temperature after 2 h, and by 6 h these parameters were higher than in lambs born vaginally. Irrespective of delivery, temperature, plasma thyroid hormone concentrations and norepinephrine content of BAT were lower in lambs born by cesarean section compared with those born vaginally. Plasma cortisol concentrations and epinephrine content of BAT were greater in lambs born by cesarean section. The amount of uncoupling protein and level of guanosine 5'-diphosphate binding in BAT were higher in vaginally delivered than in cesarean section-delivered lambs, and for each group mean values were greater for CD than WD lambs. Cesarean section delivery results in altered thyroidal, adrenal, and sympathetic activity, which appears to have a marked influence on BAT function, thereby contributing to distinct differences in thermoregulation compared with lambs born vaginally.

We investigated the influence of restricted maternal nutrition between 28 and 77 d of gestation on placental weight and appearance, and on fetal weight and conformation. Single-bearing ewes were fed either twice [i.e. controls (n = 19)] or half [i.e. nutrient-restricted (n = 28)] their energy requirements from 28 to 77 d of gestation, after which all ewes were fed to fully meet the energy requirements for maintenance and pregnancy. Close to term (145 +/- 1 d) placental weight was higher in the nutrient-restricted group [nutrient-restricted, 416.3 +/- 12.6 g; controls, 347.4 +/- 17.6 g (p < 0.01)], as was the abundance of everted placentomes. There was no significant difference in total fetal weight, or weights of individual organs between groups, but crown-rump length was significantly greater in lambs born to nutrient-restricted ewes [nutrient-restricted, 50.4 +/- 0.4 cm; controls, 48.2 +/- 0.6, cm (p < 0.01)]. Fetal to placental weight ratio was lower in the nutrient-restricted group [nutrient-restricted, 9.51 +/- 0.23; controls, 10.81 +/- 0.39 (p < 0.01)]. A stronger relationship between the total weight of the fetal component of the placental and fetal weight was observed in controls (r2 = 0.50) than in nutrient-restricted ewes (r2 = 0.18). In conclusion, maternal nutrient restriction over the period of rapid placental growth results in a larger placenta and altered placental to fetal weight ratio if ewes are subsequently fed to requirements for the remainder of gestation.

We investigated the influence of restricted maternal nutrition between 30 and 80 d gestation on placental growth. Singleton-bearing ewes were fed on either 0.6 (i.e. nutrient restricted) times their energy requirements or 2.25 times this amount (i.e. controls) up to 80 d gestation, when their placentas and fetuses were sampled and analysed. Nutrient-restricted ewes lost body condition score but not body weight and had lower plasma thyroid hormone concentrations than controls, but there were no differences in plasma glucose, non-esterified fatty acids or 3-hydroxybutyrate concentrations between groups. There was no effect of maternal nutrient restriction on fetal weight, conformation or organ weights with the exception of brain weight which was lower in nutrient-restricted ewes. Nutrient restriction had no effect on total placental weight, or proportion of inverted placentomes, but was associated with an increased abundance of small placentomes and decreased weight of the fetal but not maternal components of the placenta. Fetal cotyledons from nutrient-restricted ewes also had a lower DNA but higher haemoglobin concentration than those sampled from controls. The plasma concentration of triiodothyronine in umbilical cord plasma was also increased in fetuses from nutrient-restricted ewes. In conclusion, maternal nutrient restriction during early-mid gestation is associated with a smaller placenta.

We investigated the influence of maternal nutritional enhancement during the second half of gestation on prolactin receptor (PRLR) abundance in fetal brown adipose tissue (BAT) and liver close to term (i.e. 141-144 d gestation). Ewes were provided with 100% (i.e. control; n = 8) or 150% (i.e. well-fed; n = 7) of their metabolic requirements from 80 to 144 d gestation. Crude plasma membranes were prepared from fetal BAT and hepatic tissue, and individual molecular weight isoforms for the long and short forms of the PRLR were detected by immunoblotting. Mitochondrial preparations were prepared from BAT to measure the amount of the BAT-specific mitochondrial uncoupling protein-1 and its thermogenic activity (i.e. guanosine 5'-diphosphate binding). Fetuses sampled from well-fed ewes were heavier (controls, 3927 +/- 196 g; well-fed, 4783 +/- 219 g; p = 0.01) but possessed less BAT per kilogram body weight (controls, 5.92 +/- 0.43 g/kg; well-fed, 3.85 +/- 0.19 g/kg; p = 0.001), which had a greater uncoupling protein-1 abundance (controls, 56 +/- 5% of reference; well-fed, 78 +/- 9% of reference; p < 0.01) and higher thermogenic activity (controls, 157 +/- 41 pmol guanosine 5'-diphosphate per milligram mitochondrial protein; well-fed, 352 +/- 36 pmol guanosine 5'-diphosphate per milligram mitochondrial protein; p < 0.01) than controls. Multiple isoforms of the long and short forms of the P1LR were detected in all tissues. BAT from well-fed fetuses had a higher abundance of the 15-kD isoform of the long form of the PRLR (controls, 1.6 +/- 0.4 densitometric units; well-fed, 16.3 +/- 2.0 densitometric units; p < 0.001). This isoform was not detected in hepatic tissue. Maternal nutrient intake had no effect on any other isoforms of the PRLR in BAT or liver. In conclusion, increasing the quantity of feed provided in late gestation acts to promote fetal weight and BAT maturation, the combination of which will enhance neonatal viability.