Blood gas parameters in dairy cow affected by subacute ruminal acidosis.

Subacute ruminal acidosis (SARA) may be a common and economically important problem for dairy cattle but clinical signs of SARA in a dairy herd can be subtle and easily overlooked. The diagnosis of SARA in a herd or a group, is difficult and the technique greatly employed is the measurement of ruminal pH in a subsample of cows. According several researchers rumenocentesis may be useful for the collection of rumen fluid for pH determination but this technique is often too difficult in field conditions. The aim of this trial was to study an alternative method of diagnosis of SARA, particularly by the evaluation of some hematological parameters, especially blood gas. During autumn 2007 twelve farms have been monitored: in all farms, twelve cows in early lactation, in good body condition and without clinical signs of disease were selected randomly from each herd, to perform rumenocentesis and obtain rumen fluid. At the same time blood samples for haemogasanalysis were obtained by jugular venipuncture from the same cows that had rumenocentesis. The herds were divided into three groups depending on the mean rumen pH: group A counted farms with average ruminal pH > 5.8 (normal), group B included farms with average ruminal pH between 5.6 and 5.8 (critical), and in group C, dairy farms presented an average ruminal pH < 5.6 (acidosis). Data were statistically analyzed by analysis of variance to verify the effect of the group. The three groups were homogeneous for average dry matter intake and all the animals were on absence of external clinical signs of disease. Blood bicarbonates, pH and partial pressure of CO2 didn't show significant differences but oxyhemoglobin (%O2 Hb), partial pressure of O2 (pO2), calculated and measured oxygen saturation (sO2c and sO2m) were significantly different. In particular %O2 Hb was 70.73±8.52, 66.25±8.95, 64.92±8.63 - pO2 was 41.18±5.03, 33.43±4.95, 34.67±5.01 mmHg - %sO2c was 76.70±7.97, 64.31±7.88, 66.57±7.84 - %sO2m was 70.80±8.64, 66.19±8.05, 64.96±8.95 in group A, B and C respectively. These data suggest that cow attended by SARA probably don't have any problem in acid-base equilibrium but this condition could be related with some problems in blood oxygenation status.