Subacute rumen acidosis in Italian dairy herds: occurence and diagnostic tools

Subacute rumen acidosis (SARA) represent one of the most important metabolic disorders in intensive dairy farms that affects rumen fermentations, animal welfare, productivity and profitability. Many are the factors that can increase the possible occurrence of SARA in dairy farms and in particular in intensive dairy farms: food type, food administration modality, rumen ability in absorbing short chain fatty acids (SCFA), year period, ingestion frequency, dry-lactation transition period and others conditions able to contribute to the SARA onset. SARA is possibly under diagnosed because of lack of pathognomonic signs, diurnal fluctuations in rumen metabolism, and problems in obtaining representative rumen fluid samples. Clinical signs of SARA include decreased dry matter intake (DMI), laminitis, rumenitis, liver abscesses, pulmonary bacterial emboli and, furthermore, displacement of the abomasums, mastitis and metritis, low fertility. These problems are linked to rumen pathology because of the exceptional osmotic capacity shown by the rumen and the increase in the adsorption rate of ruminal products, which may have toxic and vasomotor effects. Considering the above statement it is impractical to base the diagnosis of SARA only on the outcome of a clinical sign, but the only way to obtain an early and correct diagnosis is to observe and correlate multiple aspects of the condition: a thorough collection of the history in the farm; evaluation of the diet; evaluation of the ruminal fluid. The determination of ruminal pH is a key factor for the diagnosis of SARA. Different methods are available for the collection of rumen fluid for pH analysis. According several researcher rumenocentesis may be useful for the collection of rumen fluid for pH determination. A group of at least 12 cows (early or middle lactation) is defined as having SARA when more than 30% of them show a ruminal pH lower than 5.5. Anyway rumenocentesis remains a mildly invasive diagnostic method so it results hardly used by freelancer veterinarian and poorly accepted by farmer. A practical need for Veterinarians and Food practitioner, is to have a simple and economic method of diagnosis of SARA, in order to implement in a timely manner the appropriate corrective diet, eliminate the causes of arrival of this disorder and avert the danger of progress in the same very high levels. In response to these requests, the aim of this PhD thesis, was to lead three different studies related to each other but, in order to evaluate the occurrence of subacute rumen acidosis in intensive Italian dairy herds to determine the relationship among diet composition, ruminal pH and short chain fatty acids (SCFA) concentration, to evaluate the effect of the subacute ruminal acidosis on some blood parameters in lactating dairy cows and finally to evaluate the effects of rumenocentesis on the health and welfare status of lactating dairy cows, evaluated by physical examination, blood analysis, milk production and superficial temperature on the area of rumenocentesis using infrared thermography. Trial 1: The aim of the present study was to study the occurrence of subacute rumen acidosis in intensive Italian dairy herds and to determine the relationship among diet composition, ruminal pH and SCFA concentration. Ten commercial dairy herds were investigated; twelve cows in good body condition, between 5 and 60 DIM and without clinical signs of disease were selected randomly from each herd, to perform rumenocentesis and obtain rumen fluid. Ruminal pH was determined immediately after sampling and concentration of SCFA in ruminal fluid was determined on samples after storage. We further studied the effects of rumenocentesis on animal health. Our data confirm the extreme validity of this technique as ruminal sampling. Results were subject to ANOVA and correlation analysis using SIGMA STAT 2.03. The results indicated the presence of SARA in 3 herds (more than 33% cows with rumen pH < 5.5), a critical situation (more than 33% cows with rumen pH < 5.8) in 5 farms and a normal rumen pH condition in 2 herds. In particular dairy herds show an average SCFA concentration of 150, 145, 123 mmol/L for low pH, critical pH and normal pH herds, respectively. The differences among diet composition were not significant even if herds with SARA showed a light discordance between initial composition and residual feed. In the affected herds it was not possible to understand the exact causes of SARA. Animal management seems to be one of the most important factor in developing SARA, including total mixed ration preparation. Trial 2: The aim of this study was to evaluate the effect of subacute ruminal acidosis on some blood parameters in lactating dairy cows. The study was carried out on ten highly productive farms, stationed in different zones throughout northern Italy. In all farms, ruminal fluid was collected through rumenocentesis from 12 dairy cows in early lactation, and ruminal pH was measured with a pH meter. Blood samples for hematochemical and hematological profiles were obtained from the same cows that had rumenocentesis performed by jugular venipuncture. 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 (risk), 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 Bonferroni test was applied to determine statistical significances between the three groups. Statistically significant differences (p < 0.05) were observed for various parameters. It was concluded that during subacute ruminal acidosis in dairy cows, modifications of the concentrations of some blood parameters can be observed. Trial 3: The aim of this study was to evaluate the effects of rumenocentesis on the health and welfare status of lactating dairy cows, evaluated by physical examination, blood analysis, milk production and superficial temperature on the area of rumenocentesis using infrared thermography. Two groups of 6 cows either underwent ruminocentesis (GA) or sham (GB) procedures. Data were statistically analyzed by analysis of variance to verify the effect of the group. No effect was observed on white blood cell count, haptoglobin, total protein, and electrophoretic fractions between GA and GB groups. Milk yield was not affected by rumenocentesis. On the region of rumenocentesis in group GA, skin temperature increased 1.0°C immediately following rumen fluid collection, returned to the baseline after 48 h, and remained constant till the end of the study. This study suggested that ruminocentesis used to diagnose subacute ruminal acidosis has no negative impact on animal health and welfare of lactating cows.