Serum Biochemical Assessment of Lactation Stress in High-Yielding Dairy Cows in Ogun State, South West Nigeria

High milk yield in dairy cattle is achieved at the cost of significant metabolic stress, particularly when dietary management fails to compensate for the nutrient demands of peak lactation. This study applied serum biochemical analysis to characterise lactation stress in high-yielding Friesian-Zebu crossbred cows at commercial dairy farms in Ogun State, South West Nigeria. Sixty cows with milk production above fifteen litres per day were classified as high-yielding and compared with forty moderate-yielding cows producing eight to twelve litres per day. Blood samples were collected monthly from calving to four months of lactation and assayed for non-esterified fatty acids, beta-hydroxybutyrate, insulin, glucose, total protein, albumin, and trace minerals. High-yielding cows demonstrated persistently elevated non-esterified fatty acids and beta-hydroxybutyrate throughout the first three months of lactation, indicating sustained negative energy balance. Insulin concentrations were lower in high-yielding cows, consistent with altered insulin sensitivity in peak lactation. Total protein and albumin declined progressively in the high-yield group, reaching values indicative of mild hypoproteinaemia by month three. Selenium and zinc were below reference thresholds in 40% of high-yielding cows. These findings highlight the multi-faceted metabolic challenge of sustained high milk production under South West Nigerian management conditions and support intensified nutritional monitoring and targeted supplementation for high-producing herds. Keywords: lactation stress, high-yielding cows, non-esterified fatty acids, negative energy balance, Ogun State.