Haemorrhage is a major challenge to the circulatory system and whole body homeostasis. Although the physiological responses to haemorrhage have been studied extensively in adults, there is still little known about those responses during the post-natal period. The goal of the present study was to investigate some of the cardiovascular and renal responses to severe haemorrhage during post-natal maturation. In addition, the present study aimed to elucidate the potential role of kappa opioid receptors in the cardiovascular and renal responses to severe haemorrhage. In order to achieve the goal of the study, two protocols were carried out in conscious lambs at two stages of post-natal maturation, one and six weeks. The first protocol investigated the cardiovascular effects of 30% haemorrhage and the associated changes in the arterial baroreflex control of heart rate. The second protocol investigated the effects of 30% haemorrhage on various parameters of renal function. Each protocol included a separate set of experiments to evaluate the role of endogenous activation of kappa opioid receptors after haemorrhage. Results from these experiments demonstrated for the first time the developmental variations in the cardiovascular and renal responses to severe haemorrhage. My results showed that the heart rate response to decompensatory haemorrhage is developmentally regulated in conscious lambs. In addition, my research results reveals underlying age-dependent variations in the arterial baroreflex control of heart rate after decompensatory haemorrhage. Also, my results indicated the importance of kappa opioid receptor activation in the decompensatory phase of response to haemorrhage and during the recovery phase early in life.