Pregnancy and lactation challenge the homeostatic mechanisms of the body, especially those controlling the cardiovascular and fluid-regulatory systems. Although differences between species are substantial, most knowledge in this area comes from studies of humans and rats, the latter being the predominant animal model. Adaptations that help dairy goats and sheep to deal with their demanding lactation period have received less attention. Therefore this review is focused on these two species. The cardiovascular and fluid-regulatory systems are intimately linked to each other. The regulation of water and sodium turnover and the distribution of fluid between the different compartments in the body change during the course of pregnancy and during lactation. Extra water and sodium are needed for the foetus(es) and to support milk production. Blood volume and cardiac output increase, as does the blood flow to the uterus and the mammary glands, respectively. The heart rate increases to a varying extent depending on the species and stage of pregnancy, and the blood pressure may decline. After parturition the blood volume and cardiac output remain increased, while the heart rate declines, and during lactation these parameters stabilise at levels proportional to the milk production of the animal. Techniques such as radiotelemetry make it possible to monitor blood pressure, heart rate and motor activity continuously for long periods. Such measurements have provided new insights into the regulation of the cardiovascular system during pregnancy and lactation. Peptides such as vasopressin, angiotensin II (ANGII) and atrial natriuretic peptide (ANP) influence both the cardiovascular and fluid-regulatory systems, but the stimulus for their release and their effects on the target organs vary depending on the animal`s reproductive stage. By combining physiological, histochemical and isotope techniques it has been possible to gain further knowledge of the effects of these hormones on the fluid and cardiovascular regulatory systems in small ruminants, which is also presented in this short review.
Buy this Article