Growth of the pouch young, tooth eruption and age determination in the Red Kangaroo, Megaleia rufa

Journal of Experimental Biology

Dawson

2006

SUMMARY Using red kangaroos Macropus rufus Desmarest, a large (>20 kg)marsupial herbivore, we compared the digestive capabilities of juveniles with those of mature, non-lactating females on high-quality forage (chopped lucerne Medicago sativa hay) of 43±1% neutral-detergent fibre (NDF)and poorer quality, high-fibre forage (chopped oaten Avena sativahay) of 64±1% NDF. On chopped lucerne apparent dry matter (DM)digestibilities by young-at-foot (YAF) red kangaroos (an age that would normally be taking some milk from their mother), weaned juveniles and mature females were similar (55–59%). On chopped oaten hay apparent DM digestibility was lower in the YAF (35.9±2.3%) followed by weaned(43.4±2.8%) and mature females (44.6±1%). The digestion of NDF and its components (mainly cellulose and hemicellulose) was lowest among the YAF followed by weaned and then mature females. The YAF and weaned kangaroos could not sustain growth on the poor-quality diet, and appeared to be at or near maximal gut fill on both forages; the values being 114–122 g DM for YAF and 151–159 g DM for weaned kangaroos. Mean retention times (MRT) of particle and solute markers were significantly longer for the YAF and weaned kangaroos on oaten hay than on lucerne hay, and DM intake (g d–1) was ∼50% lower on the oaten hay. In contrast, solute and particle MRTs in the mature females were not significantly affected by diet; they maintained DM intakes by increasing DM gut fill from 264±24 g on chopped lucerne to 427±26 g DM on chopped oaten hay. Clearly, the mature female kangaroos did not maximise gut fill on the high-quality forage,presumably as a consequence of their proportionally lower energy requirements compared with still-growing juveniles. Overall, we have provided the first mechanistic link between the physiological constraints faced by juvenile red kangaroos in relation to their drought-related mortalities, rainfall and forage quality.

Section: Experimental Animals Juvenilessupporting

confidence: 75%

“…They spend their first 6·months of life within a large well-developed pouch, a characteristic of macropodid marsupials Sharman et al, 1964). By 230-250·days, they permanently exit the mother's pouch, becoming a 'young-atfoot' (mass 4-5·kg).…”

Section: Introductionmentioning

confidence: 99%

Forage fibre digestion, rates of feed passage and gut fill in juvenile and adult red kangaroosMacropus rufusDesmarest: why body size matters

Journal of Experimental Biology

Dawson

2006

“…The diet of YAF kangaroos was supplemented with a ration of low lactose milk (Digestelact, Sharpe Laboratories, Sydney, Australia), the quantity of which was reduced over time until it was eliminated at normal weaning age. Juvenile red kangaroos on this diet regimen show growth and development patterns that are comparable to those raised on natural diets Sharman et al, 1964;Munn and Dawson, 2003). Food was withheld for 24·h prior to experimentation.…”

Section: Metabolism and Ventilation Experimental Animalsmentioning

confidence: 91%

Ventilation patterns in red kangaroos (Macropus rufusDesmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality

Journal of Experimental Biology

Dawson

Maloney

2007

SUMMARY Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos (Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25°C) and extreme (–5°C and 45°C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation,using predicted body mass scaling exponents for oxygen consumption (0.75),respiration rate (–0.25), tidal volume (1.0), ventilation rate (0.75)and oxygen extraction (0.0). At ambient 25°C, the juveniles' resting metabolic rate was 1.6 times that of the mature females (ml min–1 kg–0.75), accommodated by significantly higher levels of oxygen extraction of 21.4±1.8%versus 16.6±1.9% (P<0.05). At thermal extremes,juveniles showed typical mammalian responses in their ventilation, mirrored by that of adults, including higher metabolic and ventilation rates at ambient–5°C and shallow panting at 45°C. However, at thermal extremes the juvenile kangaroos needed to work harder than adults to maintain their body temperature, with higher rates of ventilation at ambient –5°C and 45°C, accomplished via larger breaths at –5°C and higher respiratory rates at 45°C.

“…800 mg (Sharman et al 1964;Frith and Calaby 1969). The tiny hairless neonate makes its way from the mother's cloaca to a large, well-developed pouch, characteristic of macropodid marsupials.…”

Section: Introductionmentioning

confidence: 99%

“…The tiny hairless neonate makes its way from the mother's cloaca to a large, well-developed pouch, characteristic of macropodid marsupials. By around 190 d old, at about 2 kg, the young is fully furred and ventures out of the pouch for short periods, returning regularly to the pouch, pre-sumably for warmth and safety (Sharman et al 1964;Frith and Calaby 1969). By 230-250 d old, the young red kangaroo permanently leaves the mother's pouch, becoming a young-at-foot (YAF; body mass 4-5 kg).…”

Section: Introductionmentioning

confidence: 99%

Endogenous Nitrogen Excretion by Red Kangaroos (Macropus rufus): Effects of Animal Age and Forage Quality

Physiological and Biochemical Zoology

Dawson²,

Hume³

2006

). Endogenous nitrogen excretion by red kangaroos (Macropus rufus): Effects of animal age and forage quality. Physiological and Biochemical Zoology, 79 (2), 424-436. Endogenous nitrogen excretion by red kangaroos (Macropus rufus): Effects of animal age and forage quality AbstractRed kangaroos (Macropus rufus) are large (>20 kg) herbivorous marsupials common to arid and semiarid Australia. The population dynamics of red kangaroos are linked with environmental factors, operating largely through juvenile survival. A crucial period is the young-at-foot (YAF) stage, when juveniles have permanently left the mother's pouch but still take milk from a teat in the pouch. Forage quantity and quality have been implicated in drought-related mortalities of juvenile kangaroos. Here we compared how forage quality affected nitrogen (N) intake and excretion by YAF, weaned, and mature, non-lactating female red kangaroos. On highquality forage ( chopped lucerne hay, Medicago sativa) low in neutral-detergent fiber (43% +/-1%) and high in N (2.9% +/-0.1%), YAF and weaned kangaroos had ideal growth rates and retained 460-570 mg dietary N kg(-0.75) d(-1). But on poor-quality forage ( chopped oaten hay, Avena sativa) high in neutral-detergent fiber (64% +/-1%) and low in N (0.9% +/-0.1%), YAF and weaned kangaroos could not sustain growth and were in negative N balance at -103 +/-26 mg and -57 +/-31 mg N kg(-0.75) d(-1), respectively. Notably, the YAF kangaroos excreted 64% of their truly digestible N intake from forage as nondietary fecal N (NDFN). By weaning age, the situation had improved, but the juveniles still lost 40% of their truly digestible N intake as NDFN compared with only 30% by the mature females. Our findings support field observations that forage quality, and not just quantity, is a major factor affecting the mortality of juvenile red kangaroos during drought. ABSTRACTRed kangaroos (Macropus rufus) are large (120 kg) herbivorous marsupials common to arid and semiarid Australia. The population dynamics of red kangaroos are linked with environmental factors, operating largely through juvenile survival. A crucial period is the young-at-foot (YAF) stage, when juveniles have permanently left the mother's pouch but still take milk from a teat in the pouch. Forage quantity and quality have been implicated in drought-related mortalities of juvenile kangaroos. Here we compared how forage quality affected nitrogen (N) intake and excretion by YAF, weaned, and mature, nonlactating female red kangaroos. On high-quality forage (chopped lucerne hay, Medicago sativa) low in neutral-detergent fiber ( ) and high in N ( ), YAF and 43% ‫ע‬ 1% 2.9% ‫ע‬ 0.1% weaned kangaroos had ideal growth rates and retained 460-570 mg dietary N kg Ϫ0.75 d Ϫ1 . But on poor-quality forage (chopped oaten hay, Avena sativa) high in neutral-detergent fiber ( ) and low in N ( ), YAF and 64% ‫ע‬ 1% 0.9% ‫ע‬ 0.1% weaned kangaroos could not sustain growth and were in negative N balance at mg and mg N kg Ϫ0.75 Ϫ103 ‫ע‬ 26 Ϫ57 ‫ע‬ 31 d Ϫ1 , respectively. Notably,...