Haemoglobin and its functions in various organisms is well known; it increases the ability to obtain precious oxygen and it is crucial in aerobic performance. However, if high values of haemoglobin are always beneficial, why is there a large natural variation? This study investigated the effects of varying concentrations of haemoglobin on several stages in the lifespan of Red Junglefowl: egg production and hatching, chicken growth, haemoglobin and summit metabolism. Red Junglefowl were tested for fertility in both eggs laid and eggs hatched. The offspring were individually measured for whole blood haemoglobin concentration and tested for growth and summit metabolism. The results show that there is a difference in haemoglobin after two weeks of age and that growth differs at the same time. High Hb animals do not lay smaller nor fewer eggs than low line birds but their offspring are smaller at the same time as there is a difference in haemoglobin levels. There was also a difference in the summit metabolism between the lines, where the high line animals performed better. Importantly the increase in haemoglobin did effect the growth of the animals negatively, and this would imply that higher levels of haemoglobin is not detrimental to growth.