IMMUNITY : The Key to Productivity and Longevity
There are key factors that affect immune function in an animal. Immunity refers to an animal’s capacity to fight disease. When a cow is stressed, it produces cortisol, often referred to as the “stress hormone,” which is a powerful immune suppressant.
There are key factors that will affect immune function:
Body weight loss:
- Research has indicated that immune responsiveness decreases for many cows during the transition period.
- This decrease in immune function has been linked to inflammation, which is in turn associated with diseases such as mastitis and metritis.
- Elevated levels of fatty acids due to body weight loss — both pre- and post-calving—can lead to a decrease in liver function. This can be monitored by measuring
- NEFA (non-esterified fatty acid) levels in the blood during the transition phase.
Heat stress and acidosis:
- Both can lead to liver infl ammation and a subsequent decrease in immune function. This will lead to the increased production of free radicals and an oxidative imbalance.
- Research has demonstrated that the presence of toxins (especially DON, T-2) will lead to depressed immune function
WHAT IS OXIDATIVE STRESS?
Oxidative stress is the broad term that refers to impairment of immune function.
The production of free radicals leads to oxidative reactions, a normal defense mechanism in the dairy cow. If these oxidative reactions are out of control, then this represents an imbalance in the antioxidant capacity of the dairy cow.
Quench oxidants are enzymes that convert toxic compounds (free radicals) into less harmful or inactive end-products to prevent oxidative damage to cells. Supplying adequate levels of antioxidants may help minimize this situation.
Some of the key antioxidants are:
Tocopherols (vitamin E metabolites)Including adequate levels of vitamin E will improve immune status, especially when animals are under stress (transition period). Research would indicate that feeding excessive levels of vitamin E can create a pro-oxidant effect and create immune challenges for the cow.
Carotenoids (vitamin A precursors and metabolites)Provide adequate vitamin A (>100,000 IU/day). Chew et al. added beta-carotene and a low level of vitamin A (53,000 IU/day) and had a similar response to adding “high” levels of vitamin A (173,000 IU/day) in relation to mastitis and SCC.
Glutathione peroxydases (selenium)Selenium is a member of the glutathione peroxidase family of anti-oxidative enzymes that cause a reduction in oxidized molecules. Inorganic selenium (sodium selenite) is a very effective source of selenium, but producers may wish to incorporate organic selenium from a selenium-yeast source if there are antagonistic elements (iron, sulphur) in the water or feed that may inhibit selenium absorption. Organic selenium should be considered during the transition period and during periods of low DMI.
Trace minerals (copper, manganese, zinc)Copper: High levels of copper can become a potent pro-oxidant and raise concerns about the oxidative balance. Feeding proper but not excessive levels of copper is recommended. Use proper forage analysis to ensure that copper levels in the forages are not excessive.
Yeast cell wallMOS (mannanoligosaccharide) interferes with pathogen colonization by binding receptors on the surface of intestinal pathogens, thereby blocking pathogen adhesion to the lining of the gastrointestinal tract. Dietary ß-glucans have been shown to be directly immune-stimulatory, where activation is initiated in the intestinal epithelium. This stimulation is suggested to make the animal more prepared to handle infection.