SPRING SUMMER BONUS MAGAZINE 2026

Understanding these relationships is critical for avoiding deficiencies or toxicities, even when dietary supply appears adequate. Understanding these relationships is critical for avoiding deficiencies or toxicities, even when dietary supply appears adequate. 1. Gastrointestinal absorption (in the rumen and intestines) This is where minerals are first absorbed into the body. Example: • High potassium (K) in lush pasture reduces magnesium (Mg) absorption in the rumen • This can lead to grass tetany 2. Transport proteins (minerals are present in the blood, but cannot be transported properly to where they are needed) After absorption, minerals are carried in the blood by specific proteins. Example: • High molybdenum (Mo) and sulphur (S) form compounds (thiomolybdates) that bind copper (Cu). • This prevents copper from attaching to its normal transport protein in the blood. 3. Cellular uptake (entry into cells) Minerals must enter cells to do their job. Example: • Excess iron (Fe 2+ ) competes with zinc (Zn 2+ ) for absorption in the intestine. Both minerals carry the same positive charge (2+), which allows them to use similar transport pathways (such as DMT1). • As a result, even when dietary zinc levels are adequate, high iron intake can reduce zinc absorption and limit the amount of zinc available to body tissues. 4. Metabolic pathways (inside the cell) Once inside the cell, minerals are used in biochemical reactions. Example: • Copper (Cu) and zinc (Zn) are both part of antioxidant enzymes. • Too much zinc can interfere with copper use in these enzyme systems. Key antagonistic interactions Calcium–phosphorus ratio • Optimal Ca:P ratio typically ranges from 1.5:1 to 2:1. • Excess calcium reduces phosphorus absorption. • Imbalances in this ratio can lead to milk fever (hypocalcemia). Iron interference • Excess iron reduces the absorption of copper, zinc, and manganese. • Common in water or soil contamination scenarios. Key synergistic interactions Vitamin–mineral synergy • Vitamin D enhances calcium and phosphorus absorption. • Vitamin E works synergistically with selenium in antioxidant defence. Sodium and potassium balance • Both are critical for maintaining osmotic pressure and acid-base balance. • Sodium and potassium regulate the movement of water in and out of cells. • Sodium (Na) is mainly found outside the cells (extracellular fluid). • Potassium (K) is mainly found inside the cells (intracellular fluid). • Sodium and potassium are classified as strong cations and play a major role in maintaining the cow’s acid–base balance. Diets high in Na and K increase the Dietary Cation Anion Difference (DCAD). Proper balance supports feed intake and milk production. Effect of rumen ph onmineral solubility and absorption Rumen pH plays a critical role in determining mineral solubility and ultimately their absorption. When rumen pH is within the normal range (approximately 6,0–6,8), most minerals remain in a soluble form, making them more available for absorption in the rumen or later in the intestines. However, when rumen pH drops (as in subacute ruminal acidosis), the solubility of trace minerals increases while certain macro minerals’ solubility decreases, disrupting normal microbial activity and reducing overall mineral utilisation. Conversely, at higher rumen pH levels, certain minerals, particularly trace elements like copper, zinc, and manganese, can form insoluble complexes, especially in the presence of antagonists such as sulphur or molybdenum, reducing their bioavailability. Organic vs inorganic minerals Organic minerals are minerals that are chemically bound to carbon-containing molecules (like amino acids), while inorganic minerals exist in their simple, non-carbon-bound forms as found in rocks, soil, or water. www.agribonus.co.za Spring/Summer 2026 BONUS 61