No abstract

Ruminal pH in dairy cows follows a diurnal fluctuation; low values are indicative of subacute ruminal acidosis and are associated with alterations of rumen fatty acids concentrations. The objective of the present study was to prospectively study the associations between ruminal pH and the rumen fluid concentrations of short, medium, and long chain fatty acids, under field conditions during the first half of lactation in 53 Holstein cows of a dairy farm. Ruminal fluid was obtained by rumenocentesis, which was performed at 30, 90, and 150 days in milk (DIM). Ruminal pH was measured immediately after collection with a portable pH meter, whereas gas chromatography was used for the determination of ruminal fatty acid concentrations. Mixed linear regression models were used for data analysis. The prevalence of cows with low ruminal pH (≤5.5) was 45.3%, 54.7%, and 66.0% at 30, 90, and 150 DIM, respectively. The concentrations of acetic, propionic, butyric, valeric, isovaleric, caproic and linoleic acids were negatively associated with ruminal pH values, whereas the acetic to propionic ratio was positively associated with rumen pH. Under field conditions and naturally occurring low ruminal pH cases, ruminal concentrations of most fatty acids are negatively related with ruminal pH values

Subacute ruminal acidosis (SARA; implying a rumen fluid pH between 5.5 and 5.0), is one of the most important metabolic diseases of dairy cows. In this study, the effect of SARA and rumen fluid pH on milk yield and composition was assessed in dairy cows under field conditions, with repeated measurements in the same cows, at different stages of lactation. Rumenocentesis was performed in 83 Holstein cows of a commercial herd at 30, 90, and 150 days in milk (DIM). Rumen fluid pH was measured on-site using a portable pH-meter. Milk yield was also recorded at the same days. Milk samples were analyzed for fat, protein, lactose and total solids content. For the statistical analysis, mixed linear regression models were used. Prevalence of SARA was 48.2%, 53.8% and 65.3% at 30, 90 and 150 DIM, respectively. There was a significant negative effect of SARA and decreased rumen fluid pH on milk fat content; SARA was associated with a decrease of milk fat content by 0.22%, while a one-unit increase of rumen fluid pH, even within the normal range, was associated with a 0.28% increase of milk fat content and 0.44% increase of milk total solids content. There was no effect of SARA on milk yield or protein, lactose and total solids content. In conclusion, under field conditions, SARA and decreased rumen fluid pH reduce milk fat content.

Subacute or subclinical ruminai acidosis (SARA) is one of the most important metabolic diseases of dairy cows, characterized by a decrease in pH of rumen fluid below 5.5 (up to 5), certain hours after feeding. SARA is commonly found in intensive livestock production systems; so far, its prevalence has been studied only in few countries and was found to be particularly high. The disease is caused by a decrease in rumen pH below normal level, due to an excessive increase of rumen volatile fattyacids (VFA) concentration. The increased concentration of VFA could be due to diets rich in easily fermentable carbohydrates or slow absorption of the VFA by the rumen wall, due to maladjustment in high energy diets. Finely chopped feeds that do not adequately stimulate mastication and rumination, resulting in less production of saliva that acts as a buffer of the rumen fluid pH, seem to play an important role in the etiology of the disease. The diagnosis of SARA, based on its definition, is established by rumen pH determination, at specific time intervals after feeding. Continuous pH data acquisition can be obtained, for research purposes only, by rumen cannulation and immersion in rumen fluid of a pH-meter that continuously transmits pH data to a computer. Alternatively, the pH-measuring device can be inserted orally into the rumen in a bolus form, which is also a transmittersending the pH data continuously to a computer. The latter method is very promising for clinical practice, but, unfortunately, is currently too expensive. It is easier and more affordable for practitioners to obtain a rumen fluid sample by either using a rumen tube or, preferably, by performing rumenocentesis, by which rumen fluid free of "contaminating" saliva is collected. Rumenocentesis is safe, easy to perform and more accurate than rumen tubing. The impact of SARA in dairy cows includes,amongst others, reduction of milk production, milk fat content depression, laminitis and, therefore, lameness, liver abscesses formation and, therefore, caudal vena cava syndrome, increased culling rate without any obvious cause etc. SARA treatment and prevention is mainly based on management and dietary measures that eliminate the causes of the disease.

Subacute ruminal acidosis is a major issue in dairy cattle and a definite diagnosis is only established by measuring the rumen fluid pH, most credibly collected by rumenocentesis. However, due to its invasive nature, there is still some debate whether it is a safe method or poses risks for cows’ health and welfare. The aim of the study was to retrospectively evaluate the safety of rumenocentesis as a technique to obtain rumen fluid in dairy cows. Results were derived from 2 studies. In study 1, rumenocentesis was performed in 153 Holstein cows from 12 herds, once, between 10 and 90 days in milk (DIM). In study 2, 83 Holstein cows from a dairy farm were repeatedly subjected to rumenocentesisat 30, 90 and 150 DIM. From the 83 cows that were initially enrolled, 8 were culled before the end of the study for reasons irrelative to rumenocentesis; therefore, 236 rumenocenteses were actually performed in study 2 (3 times in 75 cows, twice in 3 cows and once in 5 cows). All cows were monitored for 10 days after rumenocentesis for presence of complications. In addition, daily milk yield was automatically recorded for each cow in study 2 to detect any possiblepost-rumenocentesis short-term reduction of milk yield. Minor only complications were recorded in 7 cases: in 4/153 (2.61%) and 3/236 (1.27%) rumenocenteses in studies 1 and 2, respectively. Small diameter abscesses in 6 cows (3 in study 1 and 3 in study 2) and a larger one in 1 cow in study 1 were observed. The 3 small abscesses in study 2 were all recorded after the 1st rumenocentesis, at DIM 30. All 7 cases were resolved spontaneously within two weeks. Moreover, short-term daily milk yield of study 2 cows was not affected by rumenocentesis. The conclusion is that rumenocentesis is a safe technique to collect small volume of rumen fluid for SARA diagnosis, which does not compromise cows’ health and welfare when appropriately performed.