Early post-partum hematological changes in Holstein dairy cows with retained placenta

• Information on hematological changes associated with retained placenta are scarce.
• We retrospectively examined hematological changes associated with retained placenta.
• Neutropenia is associated with retained placenta in cattle.
• No changes of acute phase proteins are present when neutropenia occurs.
• Neutropenia may be a co-factor involved in the pathogenesis of retained placenta.

Retained placenta (RP) occurs frequently in dairy cattle but little is known about the pathogenic or prognostic role of the hematological changes in this disease. This retrospective study was designed to investigate the hematological changes associated with RP in the immediate post-partum period and to assess whether these changes are associated with an acute phase reaction. Data concerning hematology, acute phase proteins, markers of inflammation and serum biochemistry performed on cows at 3 ± 1 days in milk (DIM) from two intensive farms were extracted from the database of the ProZoo project, a research project aimed to investigate the relationship between genomic traits and bovine health and production. After application of restrictive inclusion criteria, data from 45 cows, 22 with RP and 23 controls, were statistically compared. RBC count, d-ROMs concentration, and AST activity were significantly higher in the RP group than controls. Conversely, neutrophils, thiol groups, and serum zinc concentration were significantly lower in the RP group than controls. In conclusion, although retained placenta has to be considered as a syndrome with multifactorial causes, neutropenia may be a co-factor involved in its pathogenesis. Further studies are needed to clarify whether neutropenia acts as a contributor in the pathogenesis of RP or if it is a very early consequence of the syndrome, preceding any other inflammatory changes in blood.