Foetal mortality in moderately zinc-deficient rats is strictly related to the process of parturition: effect of maternal essential fatty acid supplementation.

1. Although disrupted parturition and high foetal losses have previously been reported in pregnant rats maintained on zinc-deficient diets this is the first report to differentiate between the effects of reduced Zn intake and the effects of reduced food intake on the outcome of pregnancy in the rat. 2. Rats maintained on a 0.5 mg Zn/kg diet for the last 7 d of gestation or on a 5 mg Zn/kg diet throughout gestation did not consume significantly less food than rats given 10 or 20 mg Zn/kg diets except during the last 2d of gestation. Pair-feeding of Zn-adequate rats (20 mg/kg) to those given low-Zn diets for the last 2 d of gestation did not affect the outcome of pregnancy in these rats. 3. In the rats maintained throughout gestation on 5 mg Zn/kg or on 0.5 mg Zn/kg in the last 7 d of gestation, parturition onset and duration were not significantly altered. Foetal survival was very significantly reduced but only from day 22 onwards; before the onset of parturition, foetal survival was not significantly affected by Zn deficiency during gestation. 4. Subcutaneous injection of evening primrose (Oenothera biennis) oil into rats throughout gestation enhanced foetal and neonatal survival in rats given 5 mg Zn/kg but reduced foetal survival in rats given 0.5 mg Zn/kg in the last 7 d of gestation. 5. The results suggest three points: (1) subtotal Zn deficiency during gestation in the rat jeopardises foetal survival at parturition without affecting the onset or duration of parturition, (2) foetal death in rats maintained on Zn-deficient diets occurs only in relation to parturition itself, (3) provided that Zn intake near term is at least 5 mg/kg, supplemental essential fatty acids (evening primrose oil) will reduce foetal mortality during parturition and in the neonatal period.