Pregnancy increases plasma leptin in nulliparous but not primiparous goats while lactation depresses it

Most dairy ruminants are still lactating during early pregnancy, which could induce hormonal adaptations different from those observed during pregnancy alone. The incidence of concomitant lactation and pregnancy on plasma leptin has not been studied, and physiological factors involved in its regulation have not been addressed in goats. We assayed leptinemia throughout the pregnancy-lactation cycle in nulliparous and primiparous goats, starting 165 days prior to parturition and finishing 59 days after. During the first half of pregnancy, primiparous goats were lactating. Lactating non-pregnant primiparous goats were studied in parallel. Plasma leptin increased (+49%) up to mid-pregnancy in nulliparous, but not in primiparous goats. Furthermore, leptinemia was similar between pregnant and non-pregnant lactating primiparous goats, suggesting a strong leptinemia down-regulation by late lactation. Plasma leptin decreased from mid-pregnancy to parturition, more markedly in nulliparous goats, and remained depressed during early lactation at a similar level in both female types. It was lower, at 130 days of pregnancy, in goats carrying two fetuses. The leptinemia down-regulation by late pregnancy was highlighted by the lack of plasma leptin increase after drying-off late-pregnant primiparous goats, while it strongly increased in non-pregnant goats. The observation of leptinemia increase only in nulliparous goats suggests that it is not an essential endocrine adaptation during early pregnancy. By contrast, in both female types, the low leptinemia during transition from late pregnancy to lactation, and during late lactation, may be important for the adaptations that occur during lactation such as the partitioning of energy and nutrients towards essential functions and/or hyperphagia.