Milk composition and growth in wild and captive Tasmanian bettongs, Bettongia gaimardi (Marsupialia)

A review of wombat diet and nutrition

In this review we investigated the diet and nutrition of wombats and highlight areas for future research. The low energy requirements of wombats, conservative foraging behaviours and burrowing lifestyle allow them to subsist on low-quality food. Furthermore, their digestive anatomy and physiology is well adapted for digesting the resources available in their habitats. All species feed predominantly on native grasses; however, the nutritional requirements of juvenile and aged wombats are largely unknown. Changes to food availability and grass species in wombat habitats may alter their diet and nutritional intake. Also, despite evidence suggesting that wombats can satisfy their water requirements via the food they eat, the minimum threshold of water content at which wombats will cease feeding is unknown. Other areas for future research include investigating factors that affect digesta retention times (such as age or lactation), and the development of a method to determine age, because unlike most other mammals, wombat teeth grow continuously, hence teeth cannot be used as a reliable predictor of age in wombats.

Marsupial and monotreme milk-a review of its nutrient and immune properties

All mammals are characterized by the ability of females to produce milk. Marsupial (metatherian) and monotreme (prototherian) young are born in a highly altricial state and rely on their mother’s milk for the first part of their life. Here we review the role and importance of milk in marsupial and monotreme development. Milk is the primary source of sustenance for young marsupials and monotremes and its composition varies at different stages of development. We applied nutritional geometry techniques to a limited number of species with values available to analyze changes in macronutrient composition of milk at different stages. Macronutrient energy composition of marsupial milk varies between species and changes concentration during the course of lactation. As well as nourishment, marsupial and monotreme milk supplies growth and immune factors. Neonates are unable to mount a specific immune response shortly after birth and therefore rely on immunoglobulins, immunological cells and other immunologically important molecules transferred through milk. Milk is also essential to the development of the maternal-young bond and is achieved through feedback systems and odor preferences in eutherian mammals. However, we have much to learn about the role of milk in marsupial and monotreme mother-young bonding. Further research is warranted in gaining a better understanding of the role of milk as a source of nutrition, developmental factors and immunity, in a broader range of marsupial species, and monotremes.

The hypothalamic-pituitary-ovarian axis and manipulations of the oestrous cycle in the brushtail possum

The main purpose of this review is to provide a comprehensive update on what is known about the regulatory mechanisms of the hypothalamic-pituitary-ovarian axis in the brushtail possum, and to report on the outcomes of attempts made to manipulate by hormonal means, these processes in the possum. Over the last 15 years, several unique features of possum reproductive physiology have been discovered. These include an extended follicular phase despite elevated concentrations of FSH during the luteal phase, and early expression of LH receptors on granulosa cells of small antral follicles, suggesting a different mechanism for the selection of a dominant follicle. The use of routine synchronisation protocols that are effective in eutherians has failed to be effective in possums, and so the ability to reliably synchronise oestrus in this species remains a challenge.

Consumption of milk by quokka (Setonix brachyurus) young

We investigated the consumption of milk by the young quokka using the stable isotope deuterium oxide. The volume of milk consumed increased from 1.6 mL day–1 at 55 days post partum to 32.5 mL day–1 at 165 days. The daily energy intake ranged from ~22 to 151 kJ day–1 during pouch life. The crude growth efficiency (grams of growth per millilitre of milk consumed) increased from an average of 0.35 to 0.46 g mL–1 in the early stages of pouch life, and then decreased to 0.24 g mL–1 during Phase 2b of lactation. The crude growth efficiency measured in our study indicates that quokkas are equally efficient in converting milk energy to body mass as other marsupials reported in the literature. Measuring milk intake with this method offers a non-toxic, minimally invasive alternative to other techniques for measuring milk consumption in marsupials, when milk is the only source of water intake.

Composition of the milk of the quokka (Setonix brachyurus)

We investigated the composition of the milk of the quokka between 70 and 300 days post partum. From 70 to 180 days, the mean concentration of protein in the milk was 63.5 ± 6.50 g L−1. The protein levels then began to increase, peaking at 120 g L−1 towards the end of lactation. The mean lipid and total solids content were 45.0 ± 6.50 and 175.0 ± 11.77 g L−1 from 70–180 days, increasing to 150 and 250 g L−1 after permanent pouch exit. In contrast, the total carbohydrate concentration of the milk decreased from 80 to 20 g L−1 at 150 days. The concentration of lactose started to decrease at 180 days from 30 to 10 g L−1, and galactose and glucose began to rise from 1 to 9 g L−1 and 0.5 to 4.0 g L−1, respectively. The milk lipid consisted mainly of long- and medium-chain fatty acids, with no short-chain fatty acids detected. The major fatty acids present were palmitic and oleic acids, followed by linoleic, trans-vaccenic and stearic acids. The percentage composition of oleic and stearic acids varied significantly during lactation. The composition of the milk of the quokka changed during lactation, coincident with the young reaching critical milestones in its development. This finding supports the hypothesis that the composition of the milk changes to meet the nutritional needs of the developing young.

Milk composition and growth in wild and captive Tasmanian pademelons, Thylogale billardierii (Marsupialia)

Changes in milk composition (total solids, carbohydrate, protein, lipid and calculated gross energy content) during lactation in three groups of wild (recently culled) and one captive group (fed ad libitum) of Tasmanian pademelon (Thylogale billardierii) were related to growth rates and body condition. The habitats of the three wild groups differed. Total milk solids were generally greater in the captive group but this difference disappeared in late lactation. Milk carbohydrates showed a general increase to mid-lactation in all groups, decreasing subsequently, but were always greater in the captive group. The captive group’s milk protein was always greater than those of wild Groups 1 and 2 but differed from wild Group 3 only in mid-lactation. Milk lipid concentrations started low in all groups; thereafter, the captive group had higher concentrations of lipid in mid-lactation but there were considerable differences between the groups in late lactation with Group 2 having the highest concentrations. Other than in the captive group there was little difference in energy content between early and mid-lactation. Growth rates of young differed between all wild groups, with the captive population exhibiting more rapid growth than all others. Thus, differences in milk composition resulting from different planes of nutrition can lead to differences in growth rates of marsupial young.

Fur Seal Adaptations to Lactation: Insights into Mammary Gland Function

The fur seal (Arctocephalus spp. and Callorhinus spp., members of the pinniped family) is a mammal with the unusual capability to modulate its lactation cycle by turning milk production on and off without the typical mammalian regression and involution of the mammary gland. Lactation has evolved from constraints arising from the spatial and temporal separation of infant nursing and maternal foraging as the mother gives birth and feeds the pup on land while acquisition of nutrients for milk production occurs at sea. The lactation cycle begins with the female fur seal undergoing a perinatal fast of approximately 1 wk, after which time she departs the breeding colony to forage at sea. For the remainder of the long lactation period (116-540 days), the mother alternates between short periods ashore suckling the young with longer periods of up to 4 wk of foraging at sea. Milk production continues while foraging at sea, but at less than 20% the rate of production on land. Fur seals produce one of the richest milk reported, with a very high lipid content contributing up to 85% of total energy. This feature serves as an adaptation to the young's need to produce an insulating blubber layer against heat loss and to serve as an energy store when the mother is away foraging at sea. This atypical pattern of lactation means mothers have long periods with no suckling stimulus and can transfer high-energy milk rapidly while on land to minimize time away from foraging grounds. The absence of suckling stimulus and milk removal during foraging does not result in the onset of involution with associated apoptosis of mammary secretory cells and a subsequent progressive breakdown of the cellular structure of the mammary gland. The mechanisms controlling lactation in the fur seal mammary gland have been investigated using molecular and cellular techniques. These findings have shed light on the processes by which the unique features of lactation in the fur seal are regulated.

Milk composition of the Tasmanian pademelon (Thylogale billardierii Desmarest) (Macropodoidea:Marsupialia) in captivity

This is the first study of milk composition in any member of the wallaby genus Thylogale. Milk samples (n = 44) were collected after oxytocin injection from 12 females carrying pouch young aged 2–30 weeks followed by sampling of the mothers until weaning by Week 39. The lactation period could be partitioned into early (Weeks 2–20), mid (Weeks 21–30) and late (>30 weeks) stages. Although milk concentrations changed little during lactation the energy content increased almost 4-fold from 540 ± 39 kJ (100 mL)–1 (mean ± s.e.) to 1908 ± 102 kJ (100 mL)–1. Carbohydrate concentrations decreased from 13.3 ± 0.1 g (100 mL)–1 (early lactation) to 10.9 ± 0.9 g (100 mL)–1 in mid-lactation, falling to 4.8 ± 0.9 g (100 mL)–1 in late lactation. Lipid increased from 6.3 ± 1.1 g (100 mL)–1 to 12.5 ± 4.1 g (100 mL)–1, reaching 31.4 ± 5.0 g (100 mL)–1 in late lactation. Protein increased from 3.3 ± 0.1 g (100 mL)–1 to 9.7 ± 1.6 g (100 mL)–1 in mid-lactation to 14.0 ± 1.5 g (100 mL)–1 in late lactation. This relatively high level of lipid and protein in late lactation may be the cause of the more rapid growth and, hence, shorter pouch life of the Tasmanian pademelon (Thylogale billardierii) compared with the well studied tammar wallaby (Macropus eugenii).

Changes in milk composition during lactation in the eastern barred bandicoot (Perameles gunnii) (Marsupialia:Peramelidae)

Perameles gunnii is a small to medium-sized omnivorous marsupial. We measured milk components from Week 4 until weaning at Week 8; these showed marked quantitative and qualitative changes. The milk produced in the early stages of lactation was dilute, ~28% solid (w/w). At four weeks carbohydrate, protein and lipids were also at low levels: 2.0 g (100 mL)–1, 4.5 g (100 mL)–1 and 3.1 g (100 mL)–1 respectively. At the mid-phase of lactation solids reached 36%, carbohydrate 5.5 g (100 mL)–1, protein 10.0 g (100 mL)–1 and lipids 8.5 g (100 mL)–1. The energy content of the milk at 4 weeks of lactation was 2.25 kJ mL–1 while at pouch vacancy it reached 8.86 kJ mL–1. At 8 weeks the pouch young was almost weaned and all the constituents but carbohydrates had increased significantly. We compared the milk components of the eastern barred bandicoot with those of other marsupial species and with the Wombaroo milk formula used by zookeepers and carers to hand-raise orphaned bandicoots. We found the milk formula to be deficient in both protein and lipid.