Relationships between hormonal and metabolic changes around parturition and colostrum yield and composition were investigated in 16 Landrace \u00d7 Large White primiparous sows. Blood samples were taken daily from d 105 of pregnancy to d 2 postpartum (with d 0 being the day of parturition). Colostrum samples were taken at the onset of parturition (T0), and then 3, 6, and 24 h later (T3, T6, and T24, respectively). Colostrum yield was calculated from the beginning of parturition until 24 h later by adding colostrum intake of individual piglets, which was estimated from their BW gain. Colostrum yield averaged 3.22kg. Four sows had very low colostrum production (1.10kg; n = 4), whereas the others produced between 2.83 and 4.64 kg of colostrum (3.93kg; n = 12). Compared with the high-colostrum-producing sows, the low-colostrum-producing sows tended to have greater plasma concentrations of progesterone during the 20-h prepartum and tended to have smaller plasma concentrations of prolactin 40 and 30 h before parturition. Sows with a low colostrum yield had greater plasma concentrations of glucose than sows with a high colostrum yield from d \u22129 to \u22122. At the onset of parturition, colostrum from lowproducing sows had greater percentages of DM, lipids, and GE, but less lactose, than that from high-producing sows. The Na:K ratio in colostrum during the 6 h postpartum was greater in low-producing sows than in high-producing sows, indicating that cellular junctions between epithelial mammary cells were less tightly closed. Concentrations of IgG in colostrum varied greatly between sows and decreased by approximately 80% between T0 and T24. Within high-producing sows, concentrations of IgG in colostrum at T0, T3, and T6 were negatively correlated with lactose concentrations in colostrum at the same times and were positively correlated with plasma concentrations of IGF-I measured from d \u22129 to 0. In contrast, no correlation was found between IgG concentrations in colostrum at any time and prolactin, estradiol-17\u03b2, progesterone, or cortisol. In conclusion, sows that produced a low yield of colostrum were characterized by a leaky mammary epithelium and reduced synthesis of lactose, related to delayed hormonal changes before parturition.<\/p>\n