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Subacute Rumenal Acidosis (view source)
Revision as of 08:39, 27 August 2010
, 08:39, 27 August 2010→Diagnosis
==Diagnosis==
==Diagnosis==
Subacute ruminal acidosis is diagnosed on a group rather than individual basis. Measurement of pH in the ruminal fluid of a representative portion of apparently healthy animals in a group has been used to assist in making the diagnosis of subacute ruminal acidosis in dairy herds. Animal selection should be from high-risk groups, eg, in the first 60 days of lactation. Ruminal fluid is collected by rumenocentesis or stomach tube and can be measured in the field using wide-range pH (2-12) indicator paper, although a pH meter yields more accurate results. Twelve or more animals are typically sampled at ~2-4 hr after a grain feeding (in component-fed herds) or 6-10 hr after the first daily total mixed ration feeding. If >25% of the animals tested have a ruminal pH <5.5, then the group is considered to be at high risk of subacute ruminal acidosis. This type of diagnostic tool should be used in conjunction with other factors such as ration evaluation, evaluation of management practices, and identification of health problems on a herd basis.
Subacute ruminal acidosis is diagnosed on a group rather than an individual basis. Certain clinical signs may be suggestive, and there are a number of procedures that can be preformed to thlp make the diagnosis.
===Clinical Signs===
===Clinical Signs===
Clinically, SARA is characterised by:
Clinically, SARA is characterised by:
to SARA is recognised as impacting
to SARA is recognised as impacting
===Laboratory Tests===
Measurement of pH in the ruminal fluid of a representative portion of apparently healthy animals in a group has been used to assist in making the diagnosis of subacute ruminal acidosis in dairy herds. Animal selection should be from high-risk groups, eg, in the first 60 days of lactation. Ruminal fluid is collected by rumenocentesis or stomach tube and can be measured in the field using wide-range pH (2-12) indicator paper, although a pH meter yields more accurate results. Twelve or more animals are typically sampled at ~2-4 hr after a grain feeding (in component-fed herds) or 6-10 hr after the first daily total mixed ration feeding. If >25% of the animals tested have a ruminal pH <5.5, then the group is considered to be at high risk of subacute ruminal acidosis. This type of diagnostic tool should be used in conjunction with other factors such as ration evaluation, evaluation of management practices, and identification of health problems on a herd basis.
Milk fat depression is a poor and insensitive indicator of subacute ruminal acidosis in dairy herds. Cows and herds with severe subacute ruminal acidosis may have normal milk fat tests. Thus, it is vitally important not to exclude the diagnosis in a dairy herd that has a normal milk-fat test.
Rumenocentesis (see box) may be considered the definitive
test for the identification of SARA (Garrett and others
1999). It is a herd-based test and the selection of cows
for testing is critical, as is the time of sampling. As a
rule,12 cows should be sampled from the early lactation
group (this being the group most at risk from SARA). If
30 per cent of the animals tested have a pH equal to, or
below, the threshold, a diagnosis of SARA may be made
(Garrett and others 1999). In a herd solely fed a TMR, 12
recently calved cows (14 to 21 days calved) and 12 cows
at peak dry matter intake (60 to 80 days calved) should be
sampled; this gives an insight into the cause of the prob- J
lem - for example, is the problem associated with diet
formulation per se or is it associated with poor transitioning
in early lactation? Cows should be sampled four to
eight hours after access to fresh TMR.
Selection of cows in herds managed either on a
hybrid TMR or a component-based ration is more problematic
as the incidence of SARA is likely to be associated
with parlour concentrate feeding and substitution
effects. In such cases, it is advisable to sample cows
receiving different levels of concentrate, ensuring that
the amount of concentrate fed is recorded. Alternatively,
two groups of cows may be sampled: first, those cows
receiving maximal levels of concentrates and, secondly,
those cows that may be overfed in t-he early postpartum
period. Cows should be sampled two to three hours after
receiving any parlour fed concentrates.
===Other Tests===
===Other Tests===