Oestrone sulphate levels in plasma of sows as a basis for prediction of litter size at term

Abstract

This study examines relationships between litter size at term and plasma levels of oestrone sulphate in sows between days 22 and 33 after mating. In 1948 animals tested, significant ( P<0.0001) correlations were found between litter size and levels of oestrone sulphate in plasma collected from sows on days 22–29 of gestation. Of four correlations examined, a rising exponential function (not forced through the origin) yielded the lowest root mean square residuals. Maximum levels of oestrone sulphate in plasma of 23 unmated sows were 1.9 n M; only five sows farrowed with oestrone sulphate values below this level. Plasma oestrone sulphate levels which were derived to identify sows with a <5% likelihood of farrowing exceeded 1.9 n M, actual values being dependent upon the number of days lapsed between mating and blood sampling. The results of this study indicate that, by specifying the day of blood sampling, measurement of oestrone sulphate levels in plasma collected from sows between days 22 and 29 after mating can be used to provide early identification of non-pregnant animals, prediction of litter size in sows which are pregnant, and diagnosis of low fecundity in the short term.