Colostrum and milk production in sows housed in free-farrowing versus crated systems under tropical conditions: Associations with sow metabolic state, oxidative stress, and piglet survival

Modern prolific sows experience substantial metabolic demands while nursing large litter, often leading to fat mobilization and oxidative stress. This study investigated the impacts of farrowing systems (free-farrowing pens vs. crates) and lactational backfat loss on colostrum yield, milk production, metabolic indicators (serum insulin, IGF-1, NEFA), and plasma MDA levels, in 76 crossbred sows raised under tropical conditions. From farrowing to weaning, sows were monitored for backfat loss, farrowing duration, litter traits, piglet preweaning mortality, and metabolic profiles. All sows received routine treatment with anti-inflammatory and antibiotic medications to manage postpartum uterine infection and inflammation, and to reduce the severity of health issues under tropical conditions. Sows were measured for backfat thickness, loin muscle depth, and their lactational loss, along with metabolic state, and oxidative stress profiles from farrowing to weaning. On average, sows lost 28.6 % of backfat and 15.9 % of loin muscle during lactation, with no differences between housing systems. Sows in free-farrowing pens produced more colostrum (5.6 vs. 5.0 kg; P = 0.035) and exhibited higher IGF-1 levels on day 1 postpartum (P = 0.018). NEFA concentrations tended to be higher at weaning in free-farrowing sows (P = 0.070), while insulin, MDA, and milk yield did not differ between groups. Preweaning mortality tended to be higher among piglets from free-farrowing sows than those from crated sows (24.7 % vs. 16.6 %, P = 0.074). Sows with high backfat loss produced more milk during both days 3–10 and 10–17 of lactation (P < 0.05), and colostrum yield was positively associated with subsequent milk production. Total preweaning mortality from days 0–21 was higher among piglets born to sows with moderate backfat loss (26.2 %) compared to those with low backfat loss (15.6 %, P = 0.037), but not different from those with high backfat loss (20.5 %, P = 0.263). In summary, the housing system influenced early lactation metabolism, with free-farrowing enhancing colostrum production and IGF-1 secretion, potentially due to increased physical activity and reduced stress, which may improve mammary blood flow and support hormonal regulation. High backfat loss was linked to greater milk output and reflected increased energy demand. These findings highlight the need for tailored management strategies, based on individual body condition and farrowing environment, to support sow metabolic status, oxidative resilience, and piglet survival in tropical production systems.