WINTER BONUS MAGAZINE 2026

Winter 2026 BONUS www.agribonus.co.za 4 Fortifying the frontline: The roles of vitamins A, D, and E in dairy cow immunity Hannah Gross – Technical Advisor: Dairy Vitamin supplementation in dairy cattle is not just essential to ensuring that they lead productive lives – it also plays a role in their immune function and is something to stay on top of with the current foot-and-mouth disease challenge in South Africa. Vitamin supplementation has become a regular part of the programme if you have livestock, and is a delicate art to balance, considering all of themineral, vitamin, and nutrient interactions that happen in the body. There is much research to support how vitamins are vital to immune function, particularly the fat-soluble vitamins A, D, and E. Vitamin A – the herd’s first line of defence 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 bodily 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 neutralise 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 defence 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 stabilised 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 prioritised 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