Association between metabolome and neutrophil count in intrauterine fluid after insemination in the mare

Abstract

Assessment of post-breeding endometritis is challenging in the mare. Correlation analysis of metabolite concentration in serum and intrauterine fluid with neutrophil count in intrauterine fluid after insemination was performed in 17 Spanish mares. After body condition score (BCS) was determined, a uterine edema score and intrauterine fluid diameter (IUF) were determined by ultrasonography at insemination and 8 hours afterwards, when a blood sample and low volume uterine lavage sample were collected. Neutrophils in the recovered fluid were counted using a Neubauer camera. In lavage supernatant fraction and in serum, metabolite determination by spectrophotometry was performed. Data were analyzed with PROC CORR (SAS) after log transformation of neutrophil count, oedema score and IUF. There was no association between edema or IUF at insemination and edema/IUF at lavage. The BCS tended to be positively associated with edema score (r=0.466, p=0.059) and IUF 8 hours after insemination (r=0.4562, p=0.066), but not at the time of insemination. Correlation analysis of BCS and neutrophil count did not reach significance (r=0.3928, p=0.118). Age tended to be positively associated with neutrophil count (r=0.4112, p=0.100) and was highly associated with urea concentrations in the IUF (r=6221, p=0.008). Edema at lavage was correlated with serum globulin concentrations (r=0.50911, P=0.03). The IUF was also correlated with serum albumin (r=0.5396, p=0.02),but no association with globulin was detected; instead IUF was correlated with serum glucose concentrations (r=0.4818, p=0.05). Neutrophil count was positively correlated with specific metabolites (cholesterol, urea, globulins), but not with glucose, triglycerides or albumin concentrations in the IUF. Neutrophil count was associated with serum globulin concentration (r=0.548, p=0.02), but no other correlations were found. The only metabolite that was correlated in serum and IUF was globulin (r=0.4777, p=0.05). Glucose and urea concentrations in the IUF were negatively associated with serum albumin (r= -0.6173, p=0.008 and r= - 0.4533, p=0.06 respectively). This is probably the first report showing an association between BCS and oedema score and intrauterine fluid after insemination, suggesting that in obese mares, clearance of physiological endometritis post-breeding is altered. The finding of the association between the oedema and neutrophil count with serum globulin concentrations, and the positive correlation of globulins in serum and uterine fluid suggest a systemic pro-inflammatory state that is present locally. Moreover, serum albumin was negatively correlated with glucose and urea in the uterine fluid. Overall, neutrophil count in low volume lavage obtained after breeding is consistent with the metabolome in uterine fluid and serum, and thus neutrophil count and serum globulin determination could be used as a diagnostic tool for post-breeding endometritis.