Three experiments were conducted on sows. In experiment I, Landrace gilts were fed ad libitum, from 10 weeks of age to puberty, diets containing either 2800 (LE), 3400 (ME) and 3900 (HE) Kcal DE/kg. Age at puberty was delayed in gilts fed LE and ME. Backfat thickness was significantly reduced in LE and ME groups. Puberty onset was more determined by age and backfat thickness than by weight. In experiment II, all gilts that had shown normal heat within 240 days of age, were inseminated on the second estrus and given the same diet as received during their growing period. Feed was restricted to 2.0 kg per day during gestation and was provided ad libitum in lactation. Gilts in LE and ME gained less weight and backfat during gestation than gilts in HE group. Gilts gaining more weight and backfat during gestation, with a resulting higher body weight and backfat thickness at parturition, lost more in lactation. Incidence of anoestrus after weaning was higher in the LE and HE groups. In experiment III, multiparous Landrace-Yorkshire sows from two herds were used. An extended weaning to remating interval and reduced number of piglets weaned was observed in first and second parity sows. Lower reproductive performance in one herd was related to an excessive loss of backfat in lactation and a low backfat level at weaning.

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