Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter | 28 Avian Clinical Biochemistry
Plasma glucose (mmol/l)
20
18
16
14
12
0 0°° 8°° 12°° 16°° 20°° 24°° 4°°
Time of day
FIGURE 28-2 Mean ( SEM) plasma glucose concentration as a function
of time in fasted racing pigeons. A cosine function y(t) is fitted to
the data: y(t) 16.26 1.55 • cos (0.2618t to 2.4646). The relevance of
the fit as judged by means of the multiple correlation coefficient was significant
(R 0.892, p 0.01). Reprinted with permission from Lumeij
et al . (1987b).
flights or to incubate eggs ( Blem, 2000 ). During migratory
flights, energy expenditure may be more than seven
times the basic metabolic rate for 3 to 5 days ( Battley,
2003 ). Lipid reserves in birds are stored as triglycerides,
which have a high caloric density and do not require water.
Storage of fat reserves may double the body mass in some
cases.
Starved birds go through three phases. The total duration
of the various phases depends on the size of the bird
and the amount of lipid reserves and may vary from a few
hours in hummingbirds to 5 months in emperor penguins
( Robin et al ., 1998 ).
In phase 1, food in the digestive tract and glycogen
reserves are used; in phase 2, lipids are metabolized; and
in phase 3, protein is used as a substrate for glucose synthesis.
Phase 2 of starvation is characterized by an almost
constant rate of body mass loss, a low respiratory quotient,
and steady plasma concentrations of uric acid and β
hydroxybutyrate. Although fatty acids provide the main
energy source, about 5% of the energy is provided by protein
breakdown, to generate citric acid intermediates, to
act as substrate for gluconeogenesis, and for production
of antioxidants ( Battley, 2003 ). When critical depletion of
fat stores is imminent, phase 3 of starvation is heralded by
lowering of plasma concentrations of β-hydroxybutyrate
and increased uric acid concentrations, reflecting a
decreased contribution of lipids to energy metabolism and
increased protein catabolism, respectively ( Fig. 28-3 ). The
refeeding drive is related to the attainment to a given energy
status rather than to a given duration of fasting or body
mass loss ( Robin et al ., 1998 ). The metabolic shift to an
increased protein breakdown is regulated by an endocrine
level, nmol·L 1 level, mmol·L 1 display song
Corticosterone Plasma b–OHB
Behavioral
index and
Body mass
Plasma uric
loss
g·kg 1·24h acid level,
1
3
2
1
0
1.0
0.8
0.6
0.4
90
60
30
0
1.8
1.2
0.6
0.0
24
18
12
6
0
mmol·L 1 Plasma
36 33 30 27 24 21 18
Body mass, kg
FIGURE 28-3 Changes in specific daily body mass, plasma uric acid,
corticosterone, and β-hydroxybutyrate (β -OHB), and behavior versus
body mass in spontaneously fasted emperor penguins (X SE; n 6).
Crosshatched bars represent periods of display songs. The behavioral
index was calculated as number of days an animal was active during
successive periods of fasting corresponding to a 2-kg loss in body mass.
Reprinted with permission from Robin et al . (1998) .
shift (elevated corticosterone concentration), after which
a further adrenocortical response to an acute stressor is
inhibited. The adrenocortical response typical for an emergency
situation is only reached when muscle protein is
dangerously low ( Jenni et al. , 2000 ) .
Mortality resulting from hepatic lipidosis has been
described in a wide variety of avian species ( James et al .,
2000 ; Wadsworth et al. , 1984 ) including, among others,
chickens ( Butler, 1976 ), turkeys ( Gazdinski et al. , 1994 ),