Veterinary Public Health: Heat Stress Effects on Gastrointestinal Tract

The Effects of Heat Stress on the Gastrointestinal Tract

• Heat stress affects the gastrointestinal tract, particularly in ruminants, by:
  • Reducing feed intake
  • Releasing heat shock proteins and cytokines
  • Disrupting the rumen and intestinal epithelium barrier
• This disruption can lead to the translocation of toxins (endotoxins, mycotoxins) and unwanted metabolites (biogenic amines like histamine) into the blood circulation

Endotoxins

• Endotoxins are lipopolysaccharides (LPS) found on the outer membrane of Gram-negative bacteria
• The lipid A part of LPS is the toxic component
• Endotoxins are released during bacterial lysis and are always present in the rumen due to the presence of Gram-negative bacteria

Temperature Ranges and Cow Health

• Different temperature ranges can affect cow health, including:
  • Mild heat stress: 23°C - 26°C
  • Moderate heat stress: 26°C - 31°C
  • Severe heat stress: 31°C - 37°C
  • Emergency heat stress: ≥ 37°C

Heat Stress and Sub-Acute Rumen Acidosis (SARA)

• Heat stress can lead to SARA, which can cause a massive increase in endotoxin concentration
• In healthy animals, the barrier prevents endotoxins from entering the circulation, but heat stress can impair this barrier, leading to an inflammatory response

The Inflammatory Response

• Heat stress can trigger an inflammatory response, characterized by the release of:
  • Cytokines (histamines)
  • Acute phase proteins (haptoglobin)
  • Heat shock proteins
  • LPS-binding protein
• 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:
  • Provide clean, fresh water in suitable quantities
  • Offer cold water to soothe and stimulate the cows
  • Ensure easy access to water with shaded areas and umbrellas to protect from direct sunlight
• Feedstuffs:
  • Provide high-energy, protein-rich feed
  • Increase energy, protein, and fiber in the diet
  • Add fat to the diet (up to 5-6% of dry matter) from sources like oily seeds
  • Limit protein content to 17% or less in hot weather
  • Provide fiber for normal rumen functioning
  • Add mineral elements and vitamins, especially sodium, potassium, magnesium, and vitamins C and A

Other Practical Management Strategies

• Ensure appropriate shade to lower body temperature and respiratory rate
• Design animal houses with high, sloping roofs to stimulate air flow and reduce heat transfer
• Avoid direct sunlight entry into animal houses
• Use fans with sprinklers to moisturize and evaporate the animal's surface, reducing body heat
• Provide sufficient feeding and drinking areas, and avoid crowding
• Offer non-concentrated feedstuffs like hay and sweet clover hay
• Increase food intake with small quantities, multiple times a day
• Avoid high feed temperature and spoilage, and prevent external parasites
• Separate small animals, large animals, and pregnant females, and provide breed-specific feed
• Process grains before serving, such as crushing or grinding, and ensure complete mixing of foodstuffs

This quiz covers the effects of heat stress on the gastrointestinal tract in ruminants, including reduced feed intake and protein release. Designed for undergraduate students in the second stage of veterinary public health studies.