Fortifying the Frontline: The Roles of Vitamins A, D, and E in Dairy Cow Immunity

Vitamin A – the herd’s first line of defense:
Since the FMD virus and other pathogens will often enter through weaknesses in the mucosal barriers, these tissues must be maintained. The precursor for Vitamin A (β-Carotene) is found in fresh green roughages. It is either converted into active Vitamin A (retinol) for many body functions such as vision, growth and reproduction, or it remains as β-Carotene and functions as an antioxidant. β-Carotene can embed itself in cell membranes, where it behaves like a biological shield to neutralize oxidative stress that can cause damage to tissues during periods of high production. When it comes to FMD, Vitamin A behaves like a gatekeeper to maintain the epithelium (skin) and linings of the mouth, gut and lungs. It helps to provide the first line of defense against any entering virus.

A Vitamin A deficiency will make itself evident in increased incidences of respiratory problems, rough or dull coats and “night blindness” when cows are hesitant to move around in low light. During calving, retained placenta and birth of blind or weak calves are also signs of this deficiency. Injectables providing bioavailable Vitamin A for deficient or high-risk cows (like transition cows pre-calving) provide your immediate tactical strike against deficiency, while a sustained patrol through stabilized Vitamin A from mineral licks or mineral packs mixed into feed provides daily maintenance levels of Vitamin A. At the end of the day, your greatest reserve is fresh green pasture roughages since they are the best source of β-Carotene, so your most vulnerable animals (transition cows and calves) should be prioritized to receive the freshest roughages. Vitamin A deficiency is usually most prevalent during drought cycles.
 
Vitamin D – the immune commander:
If Vitamin A is building the barriers, then Vitamin D trains the soldiers for when there is a breach! Vitamin D3 is synthesized in the skin when the specialized sterols in the skin are exposed to the Ultraviolet light from the sun. This vitamin is not yet biologically active until it has been transported to the liver and then to the kidneys, where it is converted to the hormone calcitriol. Calcitriol is critically important for calcium absorption and strong bones, but new research also suggests it has an important effect on immunity and cell differentiation.

Specifically with transitional cows, which have such high demands on their bodies, cows will lose much of their stored Calcium to their milk and can suffer milk fever. Cows struggling with this low calcium effectively have a low immune status and are vulnerable to secondary infections. It is critical to help the cow replenish her bone reserves and to keep her internal defenses strong.

Vitamin D also induces macrophages (immune cells) to produce antimicrobial peptides, which will prime the immune system by regulating neutrophils and monocytes, enabling the body to kill pathogens more efficiently. Should a virus, like FMD, breach the Vitamin A-reinforced membranes, Vitamin D has the immune system's strike force ready to respond. In a time where we are more conscious of antibiotic resistance, Vitamin D is a helpful tool to maintain the welfare, health and longevity of your dairy herd.

When this commander is missing in action, a Vitamin D deficiency presents itself in cows with stiff gaits and swollen or painful joints due to slowed bone mineralization. In calves, there will be a higher prevalence of rickets and in milking cows, you would see a metabolic collapse during the transition period – milk fever. Vitamin D-deficient herds will also have sluggish immune systems, failing to respond to “normal” infections and vaccinations. To combat this deficiency, ensure that the animals are spending enough time in direct sunlight and fortify their diets with Vitamin D3 through mineral premixes – it must be protected against oxidation as it can degrade when stored in hot, damp conditions. An injectable concentrated form of bioavailable Vitamin D will bypass the rumen and prime the macrophages, best to inject 1-2 weeks before calving. Vitamin D needs magnesium to be a part of the reaction where it is converted into calcitriol, so if your commander seems to be failing despite Vitamin D supplementation, then it could be worth double-checking your herd’s magnesium levels to see if your commander is missing its radio!

Vitamin E – the cellular shield:
While Vitamin D commands the troops, Vitamin E and Selenium provide the armour that keeps the troops from being destroyed in battle. Vitamin E must be provided through the diet in fresh green roughage, and since it is highly heat- and oxygen-sensitive, concentrations decrease drastically when the roughage is cut for hay or fermented for silage. It works as an antioxidant to protect the fatty membranes of cells.

Vitamin E removes harmful free radicals and works together with Selenium, which forms part of an enzyme, to destroy toxic residues released by pathogens when they die, before they can destroy body cells. White blood cells, which are immune cells, neutrophils and macrophages, use oxidative bursts to kill pathogens (like the FMD virus). The Vitamin E and Se shield protects cells from being damaged by their own weapons.

You can see this clearly during calving, Vitamin E levels naturally decrease at this time and leave the cow open to infection. Maintaining high enough levels of Vitamin E and Selenium through the dry period can reduce the incidence of clinical mastitis. Through high-quality feed or strategic injection protocols, it is important to keep the cellular shield intact so that the immune system is not just equipped, but is resilient enough to survive the fight – you can protect the milk quality, as well as longevity and welfare of your cows.

If your shield is starting to look a bit rusty, the Vitamin E and Se deficiency will yield white muscle disease in calves, an increase in incidences of retained placenta and metritis in freshly calved cows, and immune-compromised cows that tend to spiral quickly from minor infections to clinical cases of mastitis.
 
Strengthening the cellular shield is critical to defending against deficiencies and can be done through supplying sufficient fresh green roughages, and supplementing orally through mineral licks or through mineral premixes in your TMR or dairy concentrate. A strategic protocol of preemptive bioavailable Vitamin E and Selenium injections will go a long way to boosting blood levels of Vitamin E 21 days before calving and strengthening that cellular shield before the battle of birth.

Conclusion:
In the face of the Foot-and-Mouth Disease challenge that the ruminant industry at large is battling, the answer does not just lie in high-energy rations. The freshness factor of your green roughages is important for your Vitamins A and E, as they start to oxidise when being cut for hay or turned into silage. Regularly checking the quality of your roughages will make sure that you are informed on whether to begin supplementing vitamins. If your cows spend less time in the sun, such as when they are housed in a shed or have limited time to graze (e.g. under TMR conditions), then they may not synthesise enough Vitamin D to meet their immune system requirements. The requirements of Vitamin D in high-producing cows can sometimes be higher than what they can synthesise naturally due to the fast calcium turnover. It is crucial to ensure that the mineral packs included in your ration are calibrated accordingly.

There are also a variety of injectable products on the market that will supply organically bound vitamins, like A and E with Selenium, directly into the bloodstream, which is helpful when rumen function decreases when the cow is under stress. These tactical strikes will provide a boost of bioavailable vitamins to the cows, but do not replace a sustained defense strategy. Balanced rations, that include the necessary ratios of micronutrients like Vitamins A, D and E, and good management will help you to build and maintain a herd that is fortified, internally commanded and shielded cellularly to ensure the biological resilience needed to withstand modern disease pressures.

If you require any additional information regarding vitamin inclusion in dairy feeds or have any further questions, please do not hesitate to contact your local technical advisor or one of our dairy product managers to ensure that you are up to speed – www.deheus.co.za/meet-out-team.