By feeding the composition of the present invention to pregnant mother sows, the percentage of the piglings as born from the mother sows but died at the farrow and during the breast-feeding period is lowered, the number of the piglings suffered from diarrhea during the breast-feeding period is lowered, and the weight of the grown piglings increased. Constitution: A feed composition containing at least one selected from the group consisting of sterilized bacterial cells, disrupted cell fragments to be obtained by mechanical disruption or enzymatic decomposition of the cells and cell wall component-containing fractions to be obtained by fractionation of the disrupted cell fragments is fed to pregnant mother sows so as to reduce the lethal percentage of piglings from the sows during birth or breast-feeding of them and to prevent the born piglings from having diarrhea thereby to promote increase of the weight of them during the breast-feeding period.
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