Indigestion in ruminant

Definitions

Lactic acidosis (ruminal acidosis or grain overload) is a metabolic disorder in ruminants caused by excessive accumulation of lactic acid in the rumen and bloodstream following rapid fermentation of highly fermentable carbohydrates. It leads to a sharp drop in ruminal pH (<5.6) and systemic acidosis

Forms

Acute ruminal lactic acidosis (acute acidosis / grain overload): rapid ingestion of large quantities of starches/ sugars → proliferation of lactate-producing bacteria (e.g., Streptococcus bovis, Lactobacillus spp.), marked lactic acid accumulation, rumen pH commonly <5.0,  leading to systemic illness and dehydration.

Subacute ruminal acidosis (SARA): recurrent or prolonged periods of moderately depressed rumen pH (commonly defined by many studies as pH <5.6 for extended periods), often insidious with reduced production, intermittent diarrhea, and usually occur at the herd level. 

Etiology & risk factors

• Main cause: sudden or excessive intake of highly fermentable carbohydrates (grains, finely processed concentrates, sudden diet changes).
• Rapid introduction or over-feeding of concentrates (poor adaptation).
• Inadequate effective fiber or long particle length in diet.
• Very fine grinding or pelleting of starch sources.
• High stocking density, feeding management
• Lack of feeding frequency or competition at the trough  (animals eat large meals).
• Water restriction (can exacerbate effects).
• Species/breed differences and age (young animals sometimes more susceptible).

Pathophysiology (how lactate accumulates and causes disease)

1.    Rapid fermentation of soluble carbohydrates → surge in short-chain volatile fatty acids (VFAs) and especially lactic acid produced by lactate-producing bacteria.

2.    Rumen pH falls (below ~5.5 for SARA; often <5.0 in acute cases). Low pH selects for lactate producers and suppresses lactate utilizers (e.g., Megasphaera elsdenii, Selenomonas spp.), generating a positive feedback loop.

3.    Osmotic and epithelial injury: lactic acid increases ruminal osmolarity → fluid shifts into rumen, dehydration; acidic damage to rumen mucosa (rumenitis) predisposes to translocation of bacteria (liver abscesses, bacteremia).

4.    Systemic effects: dehydration, metabolic acidosis, shock; cerebral effects (e.g., polioencephalomalacia) may follow from thiamine deficiency or rumenitis-related sequelae.

Clinical signs & sequelae

Acute (severe) cases

• Sudden anorexia, weakness, depression, ataxia, bloat or rumen distension, rumen stasis (no borborygmi), dehydration, tachycardia, rapid shallow respiration, recumbency, shock, sudden death in severe cases.
• Rumen fluid: very acidic, watery, often full of bacteria and debris; pH often <5.0.

SARA / subclinical forms

• Reduced feed intake and milk fat depression, loose feces or pasty feces, decreased rumination and cud-chewing, decreased milk yield, reproductive inefficiency, hoof problems (laminitis) and increased risk of liver abscesses. SARA may be largely subclinical at the individual level but causes herd-level economic losses.

Economic impact of lactic acidosis

·        SARA is especially insidious at the herd level: reduced milk fat, decreased feed efficiency, increased culling, hoof problems, and greater veterinary costs.

·        Acute cases carry higher mortality and treatment costs. Prevention and good feeding practice are typically far more cost-effective than treating outbreaks.

Diagnosis

History & herd context: sudden access to grain, recent diet change, feeding pattern.
Physical exam: dehydration, rumen atony and stasis
Rumen fluid analysis (most direct): rumenocentesis or rumen fluid collected by stomach tube to assess pH (lower than 505), odour, colour, motility of protozoa. Acidic pH (<5.0–5.5) is diagnostic when correlated with history.
Laboratory tests: CBC (hemoconcentration, leukocytosis if secondary infection), serum electrolytes and blood gas analysis (metabolic acidosis).
Herd-level diagnostic approaches for SARA: rumen pH profiling across high-risk cows, rumen bolus pH telemetry in research/advanced systems,

Treatment (clinical management)

Immediate (acute) treatment goals

1.    Restore circulation and correct dehydration / acid–base disturbances

o   Prompt IV fluids (crystalloids) to correct dehydration and improve perfusion.

o   Use blood gas/electrolytes to guide therapy.

2.    Reduce and neutralize rumen acidity

o   Oral/ruminal administration of alkaline buffers (e.g., magnesium hydroxide or sodium bicarbonate in warmed water) administered directly into the rumen to raise pH.

o   Reported ruminal magnesium hydroxide dose: e.g., 500 g per 450 kg animal diluted and administered into rumen solutions

3.    Rumen evacuation / lavage if large grain overload and severe: rumenotomy may be indicated in severe cases to mechanically remove grain and acids.

4.    Transfaunation / microbial restoration: restore rumen microflora using rumen fluid from a healthy donor (transfaunation) or using commercially available inoculants/rumen-adapted probiotics.

5.    Antimicrobials / anti-inflammatories: use selectively if there is systemic infection or to control secondary infections; NSAIDs can help control inflammation and endotoxemia. Avoid misuse of antibiotics that further disrupt rumen flora.

6.    Supportive care: thiamine (if neurologic signs), rumenotonic agents

7.    Treat sequelae (laminitis, liver abscesses)

Prevention & herd control

• Gradual adaptation to high-concentrate rations (stepwise increases over 2–3 weeks).
• Maintain adequate effective fiber (long-stem forage) to stimulate chewing and saliva production (natural buffer).
• Feeding management: frequent feeding, multiple smaller meals, ensure access to feed so animals do not eat large ‘binge’ meals; reduce competition at the bunk.
• Physical form of the diet: avoid excessively fine grinding; include particle size that promotes cud chewing.
• Dietary buffers: inclusion of sodium bicarbonate or other buffers at recommended levels for herds at risk. Studies support strategic buffering to reduce ruminal pH excursions.
• Feed additives: ionophores (where permitted) can reduce risk by modifying fermentation patterns; careful use of yeasts, direct-fed microbials and lactate-utilizing probiotics may reduce incidence — evidence varies and should be used as part of a broader plan.
• Monitoring: routine rumen pH monitoring in high-risk groups, track milk-fat depression and other production indicators; consider rumen pH boluses in research or intensive herds.

Complications

• Complications: laminitis, liver abscesses, rumenitis with bacterial translocation, peritonitis (if rumen wall damaged), polioencephalomalacia, chronic production losses and reproductive problems.

Prognosis:

Depends on severity and promptness of treatment.

·       Mild cases (SARA) can be reversed with management changes but cause production losses.

·       Severe acute acidosis can be fatal or lead to long-term sequelae despite treatment.