Colostrum management is crucial for enhancing the immune response against enteropathogens and the survival of dairy calves during the first few weeks of life. However, few physiological studies have investigated the dynamics of general and specific immunoglobulin G (IgG) content in cow milk during early lactation stages, particularly in that of crossbred Gir × Holstein dairy cows, the most predominant dairy cattle population in tropical countries, such as Brazil. Therefore, this study evaluated the effects of parity and milking order on the volume and quality of colostrum, transition milk, and mature milk in crossbred Gir × Holstein cows using three traditional on-farm tests. The dynamics of IgG in the mammary secretions and the specific antibody levels against enteropathogens were also determined using sandwich enzyme-linked immunosorbent assay (ELISA) during the early stages of lactation. Fifty healthy Gir × Holstein cows were divided into two groups based on parity number, i.e., primiparous (n = 18) and multiparous (n = 33). They were monitored from the first to the 43rd milking. The colostrum volume and quality were evaluated using a colostrometer, Brix refractometer, and Colostro Balls after the first milking, in addition to the colostral IgG levels measured using sandwich ELISA as a reference standard. On-farm tests showed that the colostrum samples obtained from Gir × Holstein cows exhibited an optimal colostrum quality based on the literature criteria, regardless of parity number; however, the IgG mass was higher in the colostrum of multiparous (201 ± 67.03 g) cows than in that of primiparous (144 ± 32.40 g) cows. The volume and composition of transition and whole milk were also assessed at the second to ninth, 11th, 13th, 15th, 29th, and 43rd milkings. Multiparous cows produced higher volumes of transition milk than primiparous cows. In addition, multiparous cows exhibited a higher total solids percentage in their postpartum mammary secretions than primiparous cows. A higher percentage of inhibition of specific antibodies against Escherichia coli K99 was observed in the blood serum of multiparous cows than in that of primiparous cows. The volume and composition of mammary secretions changed over time; milk production increased, whereas total solids, total IgG, and specific antibody levels against most enteropathogens decreased, regardless of parity. Additionally, an association between parity and time was observed with respect to milk yield, the Brix score (%), and specific antibody levels against the Clostridium perfringens alpha toxin in mammary sections and against coronavirus and rotavirus in blood samples. This association indicated higher values in multiparous cattle than in primiparous cattle at specific time points. In conclusion, this study reveals postpartum time-dependent changes in the physiological and immunological components in the mammary secretions and blood of crossbred Gir × Holstein cows from the first to the 43rd milking. These results will contribute to the development of future research in Gir × Holstein-specific neonatology, which is genetically adapted to tropical and subtropical countries.
