Changes of acute-phase proteins, glucose, and lipid metabolism during pregnancy in lactating dairy cows

The study aimed to evaluate the effects of different stages of lactation (0 to > 300 d) and pregnancy (0 to > 180 d) on serum amyloid A (SAA), C-reactive protein (CRP), glucose, total cholesterol (TCho), and triglyceride (TG) concentrations in dairy cows of different breeds. Thus, 40 healthy multiparous cows (10 Holstein, 10 Simmental, 10 Brown, and 10 Modicana) were randomly selected, and blood samples were collected once every 60 d for 1 year. Overall, SAA and CRP serum concentrations progressively increased and became more variable along the lactation, peaking at > 240-300 d, and then decreased in the last period (> 300 d). Along pregnancy, SAA and CRP initially increased, with the highest concentrations at > 60-120 d, and then decreased until the last phase of pregnancy (> 180 d). However, lactation and gestation phases did not significantly affect SAA and CRP when all the cows were analyzed together. A significant and positive correlation was observed between SAA and CRP both along lactation (r = 0.89; p<0.0001) and pregnancy (r = 0.91; p<0.0001). Breeds only showed differences in CRP levels along gestation (p = 0.0102), due to a peak registered at 0-60 d in Holstein cows. In pregnant cows, glucose was positively correlated with SAA (r = 0.43; p = 0.0017) and CRP (r = 0.42; p = 0.0019). Hence, these significant and positive relationships reflect the physiological adaptations of the dairy cows along both gestational and lactational dynamics, suggesting that these proteins may also be involved in non-pathological processes. In this perspective, this study established that the obtained response markedly varies among healthy individuals along lactation and gestation and thus that the physiological range of acute-phase proteins (APPs) is wide; this makes it difficult to use these proteins as a marker of different physiological reproductive and productive periods.