Influence of sow, farrowing, and environmental factors on colostrum immunoglobulin G concentration in free-farrowing sows.

Colostrum is vital for neonatal piglets, with both quantity and quality determining survival and performance. Inadequate Immunoglobulin G content and insufficient intake are major risk factors for impaired health, growth and welfare. This study aimed to investigate the influence of sow-, farrowing-, and environmental-related parameters on colostrum immunoglobulin concentration. In total, 151 crossbred sows housed in free-farrowing pens were included. Sow-related data (parity, body condition score, backfat, gestation length, birth induction) and farrowing parameters (total piglets born, farrowing duration, obstetrical intervention, placental expulsion, litter and placental weight) were recorded. Ambient temperature and humidity were recorded within 24 h prior to farrowing. Colostrum samples were collected after the expulsion of the first piglet and analysed for IgG concentration using ELISA, with parallel measurement by digital Brix refractometry. Multiple linear regression with log-transformed IgG concentrations was performed, and Brix refractometry was evaluated using receiver operating characteristic (ROC) analysis. Brix values showed a moderate positive correlation with ELISA IgG (r = 0.66, p < 0.001). ROC analysis demonstrated good diagnostic performance of Brix refractometry for identifying poor-quality colostrum (IgG <50 mg/mL), with an optimal cut-off of 26.5%, an area under the curve (AUC) of 0.81 (95% CI: 0.73-0.89), a sensitivity of 72.5%, and a specificity of 80.2%. The final regression model (adjusted R2 = 0.377, p < 0.001) identified parity category, birth induction, and relative humidity during the 24 h preceding farrowing as significant predictors of colostrum IgG concentration. Compared with parity 1-2, geometric mean IgG concentrations increased progressively with parity, whereas birth induction was associated with lower IgG concentrations. In conclusion, Brix refractometry represents a practical and reliable on-farm method for identifying sows producing colostrum with low IgG concentrations. Furthermore, parity and relative humidity were significantly associated with colostrum IgG concentration in free-farrowing sows. The association between birth induction and colostrum IgG concentration was attenuated after adjustment for gestation length, but evidence of a trend towards an association remained, suggesting a potential relationship that warrants further investigation.