Serum amyloid A and TNF$\alpha$ in serum and milk during experimental endotoxin mastitis

A cross-over study was conducted to investigate the effect of intramammarily infused lipopolysaccharide (LPS) on the acute phase reaction in early (EL) and in late (LL) lactation. Nine cows received intramammary injections of 100 µg of Escherichia coli 0111:B4 LPS during EL and LL. The severity of each cows systemic and local signs and change in milk appearance were recorded and scored throughout the experiment. Systemic and local signs were found to be more serious in EL cows. Tumor necrosis factor $\alpha$ (TNF$\alpha$) was detected in milk but not in serum. Serum amyloid A (SAA) concentrations increased both in serum and in milk. The milk TNF$\alpha$ concentrations peaked at 8 h post-challenge (PC). SAA concentrations started to increase at 8 h PC, and peak concentrations were seen at 32 and 48 h PC in milk and serum, respectively. The milk TNF$\alpha$ and SAA seemed to be correlated, being on average higher in EL. Serum SAA concentration was not correlated with milk TNF$\alpha$ or SAA, nor with the severity of local or systemic signs, but was correlated with changes in milk appearance