Dietary supplementation with folic acid has been shown to improve reproductive performance in sows (Lindemann 1993). However most studies have been for one cycle only and few have examined the effect of supplementation over several parities.

One hundred and thirty four crossbred sows ranging in parity from 2 to 4 were selected at farrowing and randomly allocated to two dietary treatments of low and high supplemental folic acid (0 and 10 g per tonne, Roche Products Ltd.). Treatments were applied for the following three lactations and post weaning periods, two full pregnancies and to day 30 of the pregnancy following the third lactation. The diet fed contained barley, wheat, soyabean meal and meat and bone meal with nutrient levels of 14.0 MJ DE/kg and 1.02% lysine. Sows were individually penned throughout with restricted feeding in pregnancy (2.2 kg/day increasing to 2.5 kg/day in the final month), and ad libitum in lactation (approx 5.0 kg/day) and post weaning (approx 3.4 kg/day). Blood samples for determination of plasma and red cell folate were taken from 14 sows per treatment on days 4, 50 and 110 of one cycle. These were determined by a microbiological assay (modification of methods of Scott et al 1974 and Wilson and Home 1982).