Leptin and the Adaptations of Lactation in Rodents and Ruminants

Abstract

Lactation markedly increases nutrient requirements in both rodents and ruminants. This is met mostly by increased food intake, but there are also adaptations to increase metabolic efficiency. Despite such changes, lactating animals usually experience periods of negative energy balance. This is not due to a physical constraint on food intake, at least in the rat. Leptin, a hormone secreted by adipocytes, plays an important role in the regulation of appetite and energy balance. During lactation, serum leptin concentration is decreased in both rodents and ruminants, and the nocturnal rise in concentration is lost in rats. Hypoleptinaemia in lactation is primarily a result of negative energy balance. There is also increased clearance of serum leptin, and the attenuation of the nocturnal rise in leptin in rats is at least partly due to the suckling stimulus. Hypoleptinaemia is not the major factor driving hyperphagia in lactating rats, but it probably facilitates the increased food intake. Leptin may play a more important role in this respect in lactating ruminants. Leptin is probably involved in other adaptations that increase metabolic efficiency during lactation. The ability of hypothalamic neuropeptides to respond to leptin does not appear to be altered by lactation in either rodents or ruminants. The reason why lactating animals do not respond to hypoleptinaemia with a further increase in appetite, thereby achieving energy balance, appears to be due to a failure to respond to changes in neuropeptides which mediate the effects of leptin.

Increased plasma leptin attenuates adaptive metabolism in early lactating dairy cows

“…The mammary demand for glucose is similarly extensive, with 85% of the whole animal supply devoted to lactose synthesis (Bell 1995). These nutritional challenges are compounded by the inability of dairy cows, unlike rodents, to increase voluntary feed intake in proportion to milk yield in EL (Bell 1995, Johnson et al 2001, Vernon et al 2002. The consequent energy insufficiency causes a reduction in leptin production even before significant depletion of fat depots occurs (Block et al 2001, Reist et al 2003, Janovick et al 2011.…”

“…In most mammals, the nutrient demands of lactation are met by a combination of increased voluntary feed intake and adaptive metabolism (Vernon et al 2002).…”

“…Adaptive metabolism refers to processes preserving metabolic homeo stasis during periods of energy insufficiency and includes mobilization of endogenous reserves, tissue-specific insulin resistance, and improved metabolic efficiency (Bell 1995, Vernon et al 2002, Boisclair et al 2006. The relative importance of increased feed intake vs adaptive metabolism in support of lactation varies across species.…”

“…This can be illustrated by comparing the mouse and the modern dairy cow, two species with similar milk energy output when expressed on a metabolic body weight basis (Prentice & Prentice 1988). After parturition, the lactating mouse meets a gradual increase in mammary nutrient demand nearly entirely by a matching increase in feed intake (Johnson et al 2001, Vernon et al 2002. By contrast, the modern dairy cow reaches near peak milk production within days of parturition in the absence of a compensating increase in voluntary appetite (Bell 1995, Block et al 2001, Reist et al 2003).…”

“…By contrast, the modern dairy cow reaches near peak milk production within days of parturition in the absence of a compensating increase in voluntary appetite (Bell 1995, Block et al 2001, Reist et al 2003). The energy deficit that follows can reach 30% of total energy requirements over the first month of lactation, necessitating sustained reliance on adaptive metabolism (Bell 1995, Vernon et al 2002. Accordingly, the modern dairy cow provides an opportunity to understand factors triggering adaptive metabolism in the context of lactation.…”