Abstract
Bovine neosporosis has emerged as a major cause of reproductive losses in dairy cattle worldwide, representing a relevant concern for animal welfare and health. The transition period in dairy cattle is characterized by physiological, metabolic and immunological changes. However, the specific humoral immune response against
Neospora caninum
has been only partially characterized during this critical period, raising the hypothesis that transition-associated physiological changes may influence the humoral response to chronic
N. caninum
infection. The aim of this study was to characterize changes in
N. caninum
-specific total IgG, IgG
1
/IgG
2
ratio, and avidity in serum samples from chronically infected Holstein heifers (n = 7) at prepartum, calving, and postpartum sampling times. Additionally, temporal profiles of NEFA, cholesterol, GOT, GPT; total proteins and albumin between chronically
N. caninum
-infected and seronegative Holstein heifers (n = 5) were described. Specific total IgG antibody levels declined progressively from prepartum to postpartum (p 1
/IgG
2
ratio was significantly reduced at calving compared to prepartum (p N. caninum
-infected Holstein heifers undergo measurable changes in humoral immune parameters across the transition period. Total specific IgG declined progressively from prepartum to postpartum, and the IgG
1
/IgG
2
ratio was transiently reduced at calving, indicating a shift in antibody subclass balance rather than a uniform decline across all IgG-related parameters. Antibody avidity remained stable throughout the sampling period. Noteworthy, this humoral response to
N. caninum
infection did not appear to modify the metabolic status characteristic of the transition period: significant serostatus × time interaction was observed for cholesterol, GOT, GPT, total proteins, or albumin. This indicates that the immunological changes associated with chronic
N. caninum
infection occur largely independently of the metabolic adaptations that dairy heifers undergo during the periparturient period, and do not appear to exacerbate the metabolic stress typically observed during this stage.