WINTER BONUS MAGAZINE 2026

Milk flocculation is primarily caused by calcium instability, often resulting from excessive potassium levels in pasture systems that lower milk pH. This issue is compounded by rumen pH fluctuations due to sudden dietary changes, as well as environmental stressors such as high temperatures and humidity. Calcium metabolism is heavily influenced by the balance of magnesium and potassium, with imbalances forcing the body to draw calcium from bone reserves, particularly in older cows. The staggers index (which reflects the potassium, calcium, and magnesium balance) is ideally between 1,8 and 2,2, but frequently exceeds this in spring and summer, increasing the risk of milk flocculation and making cows more susceptible to heat stress, as suppressed magnesium and calcium uptake can impair nerve function, muscle activity, and normal metabolic regulation. Poorly balanced soils and nitrogen- rich pastures further elevate potassium levels, intensifying the problem. The influence of potassium levels on protein stability of milk High dietary potassium levels negatively impact milk composition and stability, significantly reducing alizarol stability, milk protein, lactose, and milk urea nitrogen (MUN) levels. High levels of potassium intake decrease essential minerals such as calcium, phosphorus, and magnesium in milk, which are crucial for protein stability, but sodium and fat are unaffected. A study conducted by Prof. Robyn Meeske found that the kikuyu pasture used in their trial contained a high potassium concentration (5,2%), exceeding the recommended range for optimal milk protein stability. This high pasture potassium level was attributed to excessive soil potassium concentrations (>130 ppm), which are known to increase plant potassium uptake and negatively affect milk protein stability (Meeske et al., 2020). Acid-base balance of dairy cows and its relationship with alcohol stability and the mineral composition of milk Milk that is unstable in alcohol (unstable non- acid milk or UNAM) is associated with acid–base disturbances in cows, particularly respiratory alkalosis. Unstable milk samples show higher potassium and lower phosphate and calcium concentrations, which contribute to casein micelle instability and increased alcoholic instability. Metabolic alkalosis further affects milk stability by increasing bicarbonate excretion and elevating milk pH. Despite these alterations, common milk components such as fat, protein, lactose, and somatic cell count do not differ significantly between stable and unstable samples. Dietary andmineral influences on unstable non- acidmilk in Holstein cows A study by Pinheiro et al. (2022) investigated the occurrence of unstable non-acid milk (UNAM) in Holstein cows fed either sugarcane or corn silage. The authors reported that diet has a significant effect on milk stability, with sugarcane-based diets being more likely to induce UNAM compared to corn silage. The incidence of UNAM showed positive correlations with blood ionic calcium, glucose, and α S1-casein concentrations, while negative correlations were observed with lactose, phosphorus, and potassium levels. Cows fed sugarcane produced milk with higher fat and protein percentages, lower milk urea nitrogen (MUN) levels, and altered protein composition. Despite normal lactic acid concentrations, UNAM milk clots during alcohol stability tests, confirming that instability occurred independently of milk acidity (Pinheiro et al., 2022). High dietary potassium further contributes to milk instability. Elevated potassium intake disrupts mineral balance, negatively affects casein micelle stability, and increases the risk of alcohol-unstable milk, rendering it unsuitable for UHT processing (Pinheiro et al., 2022). Shade can increase the milk stability of dairy cows during summer Abreu et al. (2020) investigated the effect of natural tree shade on milk stability and acidity in lactating Holstein cows during the summer in subtropical conditions. The study found that the provision of natural shade significantly improved milk stability and composition under heat stress. Shaded cows maintain higher ethanol stability values, whereas unshaded cows show a marked reduction in milk stability. In addition, shaded cows produce milk with higher protein concentrations and lower titratable acidity compared to unshaded cows. Milk stability in previously unshaded cows takes approximately 14 days to recover after shade access is restored. Therefore, natural tree shade mitigates the negative effects of heat stress on key functional milk characteristics, enhancing milk suitability for processing while simultaneously supporting animal welfare in dairy systems. Practical recommendations Optimise pasture potassium: • Maintain pasture potassium levels between 3–4% on a dry matter basis. • Soil testing and monitoring • Adjust fertiliser strategy – avoid routine potassium application unless soil tests justify it. • Manage nitrogen applications – high nitrogen fertilisation increases plant potassium uptake. • Pasture species – some species like kikuyu, and ryegrass under high fertilisation accumulates more potassium • Manage soil potassium through practices such as silage production and pasture removal. www.agribonus.co.za Winter 2026 BONUS 15