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Chapter ten: Post-partum
and provides non-shivering thermoregulatory benefits (Trumble et al. 2010). The majority of long-chain MUFA mobilized is directed to milk synthesis and the mother may
preferentially use PUFA and SFA for her own metabolism. The proportion of long-chain
MUFA in milk increases late in lactation in several species. The MUFA delivered in
milk may help pups establish a thermoregulatory blubber layer with optimal characteristics for energy density and thermoregulation.
The accessibility of pinnipeds when lactating onshore has allowed the use of cutting-edge techniques to study the metabolic adaptations associated with lactating while
fasting. In some cases, tracer techniques have been used to study metabolism in lactating
pinnipeds that have not been used in any other wildlife species. These studies demonstrate a remarkable ability to maintain metabolic homeostasis despite extraordinarily
high rates of energy mobilization and loss. For example, the combined energy loss for
metabolism and milk production in lactating elephant seals is nearly six times the predicted standard metabolic rate for a mammal of similar size (Crocker et al. 2001). Many
of the metabolic features that enable these feats of high-energy expenditure fasting are
also found in non-lactating conspecifics, but several studies have revealed important
alterations of maternal metabolism and physiology associated with lactation. These
alterations include changes in the release of hormones that regulate metabolism and
evidence for changes in the tissue responses to regulatory hormones. These studies also
provide evidence that metabolic features are strongly impacted by the amount of body
fat, or adiposity, of lactating females. For example, lactating females release less insulin
and exhibit reduced glucose clearance when compared to fasting pups. These changes
can vary directly with the depletion of adipose tissue reserves while lactating. So in contrast to humans and most mammals, where being fat is associated with reduced insulin sensitivity, seals appear to develop more diabetic-like features as they deplete their
body reserves while lactating. Similarly, responses to metabolic hormones like glucagon,
which typically increases production of sugars from stored body protein and release of
fatty acids from blubber, are altered in direct relation to depletion of body fat (Crocker
et al. 2014). Responses that would hinder the ability to continue fasting and producing
milk, like releasing insulin and making sugars from muscle or vital organs get downregulated, while responses that facilitate milk production and fasting, like enhanced
lipolysis, get upregulated. This represents a remarkable example of metabolic adaptation
for rapid reorganization of systemic and tissue metabolism to provide appropriate nutrients to the mammary gland, while protecting mothers from harmful effects of lactating
while fasting.
10.2.2.3 Mammary gland physiology
One aspect of pinniped lactation physiology that has received recent attention is the
unique physiological requirements of the mammary gland. The mammary gland of all
mammals undergoes a complex set of changes during lactation that includes proliferation
and differentiation of cells, secretion and ultimately the death and regression of mammary
cells after weaning in a process known as involution. The unusual composition of pinniped milk and the ability of the otariid mammary gland to sustain function despite long
interruptions in suckling provide an important comparative model with which to better
understand the regulation of involution in other species.
The milk sugar lactose has been detected in only trace concentrations in phocid milk
and is absent from the milk of otariids and odobenids. From the perspective of lactating
while fasting, the lack of carbohydrates in milk helps pinnipeds avoid the use of proteins from vital organs for carbohydrate synthesis. However, the low levels of milk lactose
Chapter ten: Post-partum
and provides non-shivering thermoregulatory benefits (Trumble et al. 2010). The majority of long-chain MUFA mobilized is directed to milk synthesis and the mother may
preferentially use PUFA and SFA for her own metabolism. The proportion of long-chain
MUFA in milk increases late in lactation in several species. The MUFA delivered in
milk may help pups establish a thermoregulatory blubber layer with optimal characteristics for energy density and thermoregulation.
The accessibility of pinnipeds when lactating onshore has allowed the use of cutting-edge techniques to study the metabolic adaptations associated with lactating while
fasting. In some cases, tracer techniques have been used to study metabolism in lactating
pinnipeds that have not been used in any other wildlife species. These studies demonstrate a remarkable ability to maintain metabolic homeostasis despite extraordinarily
high rates of energy mobilization and loss. For example, the combined energy loss for
metabolism and milk production in lactating elephant seals is nearly six times the predicted standard metabolic rate for a mammal of similar size (Crocker et al. 2001). Many
of the metabolic features that enable these feats of high-energy expenditure fasting are
also found in non-lactating conspecifics, but several studies have revealed important
alterations of maternal metabolism and physiology associated with lactation. These
alterations include changes in the release of hormones that regulate metabolism and
evidence for changes in the tissue responses to regulatory hormones. These studies also
provide evidence that metabolic features are strongly impacted by the amount of body
fat, or adiposity, of lactating females. For example, lactating females release less insulin
and exhibit reduced glucose clearance when compared to fasting pups. These changes
can vary directly with the depletion of adipose tissue reserves while lactating. So in contrast to humans and most mammals, where being fat is associated with reduced insulin sensitivity, seals appear to develop more diabetic-like features as they deplete their
body reserves while lactating. Similarly, responses to metabolic hormones like glucagon,
which typically increases production of sugars from stored body protein and release of
fatty acids from blubber, are altered in direct relation to depletion of body fat (Crocker
et al. 2014). Responses that would hinder the ability to continue fasting and producing
milk, like releasing insulin and making sugars from muscle or vital organs get downregulated, while responses that facilitate milk production and fasting, like enhanced
lipolysis, get upregulated. This represents a remarkable example of metabolic adaptation
for rapid reorganization of systemic and tissue metabolism to provide appropriate nutrients to the mammary gland, while protecting mothers from harmful effects of lactating
while fasting.
10.2.2.3 Mammary gland physiology
One aspect of pinniped lactation physiology that has received recent attention is the
unique physiological requirements of the mammary gland. The mammary gland of all
mammals undergoes a complex set of changes during lactation that includes proliferation
and differentiation of cells, secretion and ultimately the death and regression of mammary
cells after weaning in a process known as involution. The unusual composition of pinniped milk and the ability of the otariid mammary gland to sustain function despite long
interruptions in suckling provide an important comparative model with which to better
understand the regulation of involution in other species.
The milk sugar lactose has been detected in only trace concentrations in phocid milk
and is absent from the milk of otariids and odobenids. From the perspective of lactating
while fasting, the lack of carbohydrates in milk helps pinnipeds avoid the use of proteins from vital organs for carbohydrate synthesis. However, the low levels of milk lactose