Measures of sow development, both body weight and backfat, were taken throughout sow reproductive life. Both farms recorded age and body weight at first insemination, body weight at day 112 of pregnancy and body weight at weaning. On farm A also backfat wasmeasured (P2method) at first insemination, at day 112 of pregnancy and at weaning. Based on body weight and backfat, the protein content of sows on farm A was estimated according to the formula