Serum from 88 pregnant sows and gilts was sampled 24 and 28 days after their first insemination or mating day. The oestrone sulphate (E1S) concentration in the samples was assessed with a commercially available radioimmunoassay kit modified for use with swine serum. The first aim was to test whether it was possible to predict litters of total number <10 piglets at term. The second aim was to compare the use of day 24 or day 28 samples, or of both, in this prediction.
Day 24 E1S levels were positively correlated with litter size at term (R2 = 0.26; p < 0.001). E1S levels on day 28 were correlated with the levels on day 24 in the same animals but could not be used for prediction of large or small litters. The odds ratio for a small litter size was 0.16 (p < 0.01). This means that odds for a litter size <10 piglets decreased by 84% when E1S levels increased by 1.0 ng/ml.
Keywords: sows, pregnancy, prediction, litter size, oestrone sulphate.