Abstract Advances in genetics, nutrition, health, and management have greatly increased the prolificacy and metabolic demands of modern sows. As litter size and growth rate continue to rise, the energy requirements of lactating females often exceed their capacity for voluntary feed intake. When this occurs, sows mobilize body reserves to sustain milk production, which can compromise future reproductive performance, longevity, and efficiency. Traditional measures of lactation feed efficiency (LFE) based solely on feed intake and litter growth overlook this body catabolism component. The present retrospective study aimed to evaluate LFE using a framework that integrates milk energy output and sow body composition changes. Data were collected from 899 females (481 gilts and 418 sows) housed in a commercial 10,000-head farm equipped with automated Gestal Quattro Opti lactation feeders. Individual feed deliveries were recorded daily, and changes in body weight, backfat thickness, and loin depth were measured from farrowing to weaning. Females that maintained or gained either backfat, loin depth, or both tissues in lactation were considered low catabolism, and females that lost both tissues were considered high catabolism. Litter growth rate (g/d) was calculated as the difference between litter weight at weaning and litter weight after cross-fostering, divided by lactation length. Litter growth rate was then used to estimate milk energy output (4.92 × litter gain − 90 × litter size), and females were considered as low milk producing when milk energy output was below average within parity and high milk producing when milk energy output was above average. Females were then categorized into four LFE groups within parity as: Selfish (low milk, low catabolism), Inefficient (low milk, high catabolism), Super (high milk, low catabolism), or Martyr (high milk, high catabolism). Both Martyr gilts and sows lost significantly more weight and body tissue compared to Inefficient and Selfish groups (Table 1; P 0.05). Super and Selfish females had lower initial backfat and loin depth but lost little backfat or increased lean tissue through lactation compared to Martyr and Inefficient ones. Inefficient sows consumed the least feed, whereas Super sows had the highest intake (P 0.05). Gilts and sows from all groups were loaded with similar number of pigs as their teat counts. Martyr and Super females achieved increased litter growth and piglet survival from cross-foster to weaning compared to Inefficient and Selfish counterparts. No significant differences were observed among efficiency categories in subsequent reproductive performance. These findings indicate that LFE assessments must account for sow body tissue mobilization to avoid misleading conclusions. Incorporating body composition into LFE evaluation may enhance selection and management strategies supporting precision feeding and sustained sow productivity. Further research is warranted to validate this approach and its repeatability across multiple lactation cycles, farms, and nutritional programs.
Veldhuizen et al. (2026) studied this question.