This study investigates the effects of early age conditioning (EAC) and linseed (Linum usitatissimum) supplementation (LS) on the biochemical and haematological parameters of broiler chickens exposed to chronic heat stress and coccidiosis. Hypoproteinaemia, a significant metabolic characteristic of coccidiosis, was addressed by EAC and LS through their influence on metabolic balance and stress response mechanisms. Chronic heat stress typically reduces protein synthesis, yet EAC and LS helped maintain protein levels by mitigating stress-induced cortisol secretion and protein catabolism. Both treatments significantly reduced cholesterol and triglyceride levels, crucial markers of metabolic health under thermal stress, and increased blood glucose levels, improving homoeostasis disrupted by coccidiosis. The treatments also normalised cholesterol and triglyceride levels in untreated infected chickens, mitigating the adverse effects of coccidiosis on lipid homoeostasis. Urea levels, a byproduct of protein degradation, were increased at the end of the rearing period, indicating enhanced proteolysis without adverse effects on renal function. The observed increase in blood pH suggested a beneficial effect of EAC and LS in preventing acid-base imbalances caused by heat stress and coccidiosis. Additionally, EAC and LS improved fluid balance and mineral concentrations, enhancing Na+ and K+ levels, crucial for maintaining homoeostasis under heat stress. In haematological changes, such as reduced haemoglobin levels and erythrocyte counts, were mitigated by EAC and LS. EAC reduced haematocrit and blood viscosity, improving circulation and thermolysis. The treatments' combined effects significantly increased erythrocyte counts, countering reductions caused by coccidiosis and enhancing overall health. The reduction in leukocyte counts at T3 in treated groups indicated a localised and effective immune response against parasites, highlighting the anti-coccidia, anti-inflammatory, and healing properties of linseed. EAC and LS also promoted red blood cell maturation and increased mean corpuscular volume (MCV), suggesting enhancing resilience and health status in broilers under stress conditions. These findings provide valuable insights into the potential of EAC and LS to enhance the health and performance of broiler chickens under challenging environmental conditions, offering practical strategies for improving poultry management and welfare.