Compromised fetal growth has been associated with increased risks of mortality and morbidity at birth and in later life. Maternal diet is known to have a profound effect on fetal growth. Extensive sheep farming may lead to periods of acute undernutrition, e.g. after snowfall. In humans, ill health may reduce food intake temporarily. This study assessed the effects of acute nutrient restriction in mid-gestation on parameters of fetal growth.

All procedures were performed under the UK Animals (Scientific Procedures) Act, 1986. Welsh Mountain ewes of body condition score 2.0-2.5 were fed a complete pelleted diet providing 100 % of their maintenance requirements. The ewes were bedded on wheat straw, to provide minimum nutritional value, with free access to water. At day 83 of gestation, ewes were allocated to fed or nutrient restricted groups (NR). The concentrate ration of the NR ewes was reduced from days 83 to 85 and withdrawn completely between days 85 and 90. At day 90, half the ewes (NR: n = 7, fed: n = 8) were humanely slaughtered. The remainder (NR: n = 9, fed: n = 9) were fed their maintenance diet until slaughter at day 135 (term ~147 days). Upon removal, the fetus was given a fatal intracardial injection of sodium pentobarbitone. At each time point, data were analysed using Student’s unpaired t test with a level of significance of P < 0.05; data are presented as means ± S.E.M.

Fetal weight was unaffected by the mid-gestation nutrient restriction at both time points. At day 90, there was a tendency towards decreased weight of the fetal lung in the NR group, both as actual weight (fed, 27.1 ± 1.63; NR, 22.9 ± 0.93 g; P < 0.06) and as a percentage of fetal body weight (fed, 4.9 ± 0.25; NR, 4.3 ± 0.19%; P < 0.1). This was associated with a significantly decreased thoracic girth (fed, 17.4 ± 0.26; NR, 16.5 ± 0.34 cm; P < 0.05) and a reduced volume of uterine fluid (fed, 724 ± 49.6; NR, 530 ± 66.9 ml; P < 0.05). At day 135, the difference in actual lung weights between the groups was significant (fed, 116.4 ± 6.01; NR, 100.0 ± 3.18 g; P < 0.05).

Reduction in amniotic fluid volume imposes exaggerated trunk flexion on the fetus, narrowing the thoracic cavity and displacing the diaphragm upwards (Harding et al. 1991); this may limit the expansion of the lungs by lung fluid. Reduced amniotic volume is associated with fetal lung hypoplasia, which may lead to respiratory insufficiency at birth and is present in 14-20 % of neonatal autopsies (Sherer et al. 1990). In lambs, intra-uterine growth retardation is associated with impairments in respiratory function during early postnatal life (Joyce et al. 2001). The association of reduced fluid volume and thoracic girth with decreased lung weight in this study suggests that this chain of events occurred in response to the mid-gestation nutrient restriction, with potentially adverse consequences for the neonate.

This work was funded by The Wellcome Trust, BBSRC and SERAD.