Influences of environment and its modification on dairy animal health and production

Environmental heat load and housing microclimate are major determinants of dairy animal productivity and health in tropical systems, yet farm-level evidence linking within-barn conditions to animal outcomes remains limited. This study evaluated the influence of environment and its modification through naturally ventilated housing on production and health indicators of lactating dairy cattle at Dr Olaola Vineyard Dairy Farm, Abeokuta, Ogun State, Nigeria. A longitudinal observational approach was used in which microclimate and animal-level records were collected concurrently during the warm and humid season (May-October 2025) in 50 Friesian/Holstein × White Fulani/Bunaji crossbred cows managed semi-intensively in an open-sided shade-barn. Temperature and relative humidity were logged at 10-min intervals at cow head height (1.5 m) across three functional barn locations (feed bunk line, resting/lying area, and holding area), while airflow was measured three times daily using a handheld anemometer. Thermal stress was summarized using the temperature–humidity index (THI) and categorized as <72, 72-78, and >78. Production outcomes included daily milk yield, fat, protein, and somatic cell count (SCC), while health outcomes included clinical and subclinical mastitis (SCC ≥200,000 cells/mL and/or CMT ≥1), lameness (locomotion score ≥3), and reproductive records. In an illustrative analysis using assumed values consistent with the study design, severe heat-stress exposure predominated, with higher THI and longer duration above THI 78 associated with reduced milk yield and increased SCC. Subclinical mastitis risk increased across THI categories, and lameness risk was elevated during periods of higher heat load and wetter conditions, highlighting the combined effects of thermal and moisture-related housing challenges. Overall, the study underscores that zone-specific barn microclimate, particularly in resting areas with lower airflow, is a key driver of performance and health in tropical dairy production. Improving ventilation and cooling effectiveness in high-use zones, alongside moisture and hygiene control during humid months, is likely to mitigate heat-related production losses and health risks in naturally ventilated dairy housing.