Heat Stress on Gastrointestinal Tract in Ruminants

The Effects of Heat Stress on the Gastrointestinal Tract

• Heat stress affects the gastrointestinal tract, specifically the rumen epithelium, which is essential for nutrient absorption, transport, short-chain fatty acid metabolism, and barrier protection.
• The effects of heat stress on the rumen epithelium can be explained by:
  • Reduced feed intake
  • Release of heat shock proteins and cytokines (inflammation mediators)
  • Disruption of the rumen and intestine barrier, leading to the translocation of toxins (endotoxins, mycotoxins) and unwanted metabolites (biogenic amines such as histamine) into the blood circulation.

Endotoxins

• Endotoxins are lipopolysaccharides (LPS), a part of the outer membrane of Gram-negative bacteria.
• The lipid A part is the toxic part of LPS.
• Endotoxins are released during lysis of bacteria and are always present in the rumen due to the presence of Gram-negative bacteria in an animal's microflora.
• The structure of LPS consists of polysaccharide (O-Antigen and Core oligosaccharide) and the toxic lipid A part.

Heat Stress Classification

• Heat stress can be classified based on temperature ranges:
  • Mild: 23°C ≤ 26°C
  • Moderate: 26°C ≤ 31°C
  • Severe: 31°C ≤ 37°C
  • Emergency: ≥ 37°C

Heat Stress Effects on Cow Health

• Heat stress can cause sub-acute rumen acidosis (SARA), leading to a massive increase in endotoxins concentration.
• The barrier prevents endotoxins from entering the circulation in healthy animals, but heat stress can impair this barrier, allowing endotoxins to reach the blood circulation and cause a strong inflammatory response.
• This response consumes a lot of energy, which the animal cannot use for growth, milk production, or reproductive performance.

Practical Management to Reduce Heat Stress Effects

Nutritional System in Hot Weather

• Water consumption is crucial:
  • Clean, fresh water should be provided in suitable quantities.
  • Cold water is preferred to stimulate and cool the cows.
  • Water troughs should be placed in shaded areas and cleaned regularly.
• Feedstuff should:
  • Be of good quality, rich in energy, protein, vitamins, and mineral elements.
  • Have increased energy, protein, and fiber content.
  • Include fat as an excellent way to increase energy content (but not exceeding 5-6% of dry matter).
  • Provide necessary protein, but not excessive (not exceeding 17%).
  • Include fiber for normal digestive functioning.
  • Include mineral elements and vitamins, especially sodium, potassium, magnesium, and vitamins C and A.

Other Practical Management

• Provide appropriate shade to lower body temperature and respiratory rate.
• Design animal houses with high roofs and gradual slopes to stimulate air flow and reduce thermal transfer.
• Avoid sunlight entering animal houses.
• Use fans and sprinklers to moisturize and evaporate the animal's surface, reducing body heat.
• Provide sufficient areas for feeding and drinking, and avoid crowding around barns.
• Provide sufficient amounts of non-concentrated feedstuff like hay.
• Increase food intake with small quantities, multiple times.
• Avoid high feed temperature and spoilage.
• Prevent fly infestation and feed infection.
• Increase food quantities during cool periods of the day.
• Separate small animals from large and pregnant females, and provide feed for each breed separately.
• Process grains before serving, such as crushing or grinding, and ensure complete mixing.