Rumenocentesis and rumen fluid analysis

• Rumen fluid sampling can be a useful aid in the diagnosis of nutritional problems in dairy cows, most notably sub-acute rumen acidosis (SARA) at a herd level.
• The correct selection of animals, and timing of sampling is critical in achieving an accurate diagnosis.
• Results should be evaluated in conjunction with other clinical signs.
• May also be of use in the individual animal suspected of having acute rumen acidosis eg secondary to cereal overeating.
• Samples can be obtained by stomach tube, but are most frequently collected by rumenocentesis.

Uses

Advantages

• A quick and straightforward means of assessing rumen fluid, and measuring pH.

Disadvantages

• Both orogastric sampling and rumenocentesis are invasive and cause a degree of pain for the animal, although a small study by Mialon et al (2012), concluded rumenocentesis was no more stressful for the animal than handling and restraint.
• The same authors considered the technique to be ethically justified as a diagnostic procedure but consideration would need to be given as to the ethics of a the procedure when used as a routine monitoring tool.

Technical problems

• The correct animal selection is critical.
  • Atkinson (2017) suggests sampling six animals more than 3 weeks calved, who should be adapted to the ration, and six cows 1-3 weeks calved who are still adapting to the milking cow diet.
• Timing of the sample needs to be planned carefully in relation to concentrate feeding in order to obtain the pH readings at their lowest.
  • Two hours post concentrate feed is suggested for non Total Mixed Ration (TMR) herds, and four hours post fresh feed is offered in fully TMR herds. Herds utilising out of parlor feeders etc can pose further problems and should be assessed on an individual basis.
• Provides a 'Snapshot' of information and hence must be interpreted with caution.
• Potential for hemorrhage and/or peritonitis at site of rumenocentesis

Alternative techniques

• Samples may also be taken via orogastric tubing, with the use of a weighted rumen fluid collection kit (eg Selekt rumen fluid collection kit, Nimrod animal health) Transfaunation.
  • This method is quicker and less invasive, however Shen et al (2012), showed statistically significant differences in fermentation parameters of collected rumen fluid, related to depth of insertion of tube. Numerous authors have shown a higher pH in the cranio dorsal rumen, which they attributed to saliva flow.
  • Saliva contamination of the sample will act as a buffer and may invalidate pH readings.
  • Potential for causing esophageal trauma/rupture when passing stomach tube.

Time required

Preparation

• 15 - 20 minutes to restrain the animal, aseptically prepare the site, insert local anesthesia Local anesthesia: overview a minimum of 5 minutes before needle insertion.
  • Mialon et al (2012), however concluded that local anesthesia does not reduce the stress levels of animals subject to the procedure.
• 5 minutes to insert needle and withdraw sample. Air/collected sample may need to be used to flush the needle if it clogs with fibrous material during sampling.

Decision taking

Criteria for choosing procedure

• Herd suspected of suffering SARA, or for routine nutritional monitoring.

Risk assessment

• Potential of injury to the operator by kicking, crushing against handling system or needlestick injuries.
• Potential of rumen wall laceration by sampling needle, due to rumen movements or inadequate restraint. This can be mitigated by use of a long needle.