Influence of Amount
of Dietary Fat on Plasma Cholesterol Concentrations in African Grey
F. J. Bavelaar, MSc, MVR
Prof. Dr. Ir. A.C. Beynen
Department of Nutrition
Faculty of Veterinary Medicine
University of Utrecht, The Netherlands
African Grey parrot, atherosclerosis, plasma cholesterol concentration,
The incidence of atherosclerosis in African Grey parrots
is high. An important risk factor for atherosclerosis in humans is an
elevated plasma cholesterol concentration; this might also hold for
parrots. Plasma cholesterol levels in humans can be lowered through
dietary intervention. We studied the influence of diets with different
dietary fatty acid composition and fat content on plasma cholesterol
concentrations in African Grey parrots. Four groups of parrots were
fed 4 different diets according to a Latin-square design. There were
2 low- and 2 high-fat diets, and the diets contained either sunflower
oil or palm kernel oil as a variable fat source. Sunflower oil is rich
in the polyunsaturated fatty acid linoleic acid. Palm kernel oil is
rich in the saturated fatty acids lauric acid and myristic acid. Twenty
parrots were involved in the entire experiment. The high-fat diet with
palm kernel oil resulted in significantly higher plasma cholesterol
and phospholipid concentrations when compared with the other 3 diets.
The magnitude of the parrots’ cholesterolemic response to the amount
and type of fat in the diet appeared to be comparable to that reported
in humans. Thus, it is possible to influence plasma cholesterol in parrots
through dietary intervention.
Atherosclerosis is a common disease in parrots, especially
in African Grey and Amazones parrots.1 The incidence is considered to
be about 10%,1–3 but Bavelaar and Beynen4 found sudanophilic
staining in aortas of 84% of parrots presented for autopsy. In parrots,
atherosclerosis is mainly located in the beginning of the aorta and
the brachiocephalic arteries.1,5,6 The most common sign of atherosclerosis
is sudden death.7 However, there can be clinical signs such as hind
limb paresis, sudden collapses, dyspnea, and lethargy.1,7,8 The diagnosis
of atherosclerosis is rarely made in the living animal,1 and there is
no treatment for atherosclerosis in the parrot, which makes prevention
Regarding the development of atherosclerosis in parrots,
possible risk factors such as a high-fat diet, social stress, inactivity,
high plasma cholesterol, and high blood pressure have been suggested,1,3,7,9–11
but no experimental evidence is available. One of the most important
risk factors of human atherosclerosis is an elevated plasma cholesterol
concentration.12 Cholesterol might also be a risk factor in parrots,
assuming that they share similarities with budgerigars. Finlayson and
Hirchinson13 induced hypercholesterolemia and severe atheroma in female
budgerigars by feeding them a diet rich in cholesterol.
Diet composition is an important determinant of plasma
cholesterol concentrations in humans. Dietary saturated fatty acids,
as opposed to isoenergetic amounts of either carbohydrates or mono-
or polyunsaturated fatty acids, increase plasma cholesterol concentrations
in humans14,15 We are not aware of literature describing the influence
of diet on plasma cholesterol concentrations in parrots. Thus, this
experiment was designed to study the effect of the amount and type of
dietary fat on plasma cholesterol concentrations in African Grey parrots.
As mentioned above, African Grey parrots display a high incidence of
atherosclerosis, and dietary intervention would be expected to be most
effective in this species. It was anticipated that the results obtained
would contribute to the formulation and selection of appropriate diets
MATERIALS AND METHODS
Animals and Housing
A total of 30 African
Grey parrots (Psittacus erithacus) were used. The parrots were made
available by the Dutch Parrot Refuge (Nederlandse Opvang Papegaaien,
Veldhoven, the Netherlands) and were housed in groups in 4 aviaries.
Each group consisted of 7 or 8 birds. The parrots were of both genders,
with ages ranging from 3 to 41 years and body weight from 338 to 571
g. Before the experiment, all parrots had been fed the same diet (Nutribird
P15, Versele-Laga, Deinze, Belgium) for at least 2 months. The parrots
had been chipped for identification. The aviaries had an indoor and
outdoor space. Outside, the floor was covered with sand and inside with
wood shavings. Indoors, there was continuous light. Feed and water were
provided inside for ad libitum consumption and were refreshed daily.
The aviaries were cleaned weekly. Food consumption was recorded per
group per day. At the end of each dietary period (described subsequently)
all parrots were caught for the collection of blood samples and for
the determination of body weight. If a parrot had lost 15% or more of
its initial body weight, it was excluded from the experiment. Parrots
showing signs of sudden illness and those involved in fighting were
excluded as well.
The experiment was approved by the animal experiments
committee of the Faculty of Veterinary Medicine, Utrecht, the Netherlands.
The trial was performed from the beginning of February to the end of
May 2001. To eliminate any effects of animal baseline value, diet sequence,
and time, the experiment had a 4 x 4 Latin-square design. There were
4 dietary treatments and the 4 groups of parrots were randomly allocated
to the 4 diet orders. The first 2 experimental periods lasted 28 days
each, the third lasted 32 days, and the last period was 24 days. On
the last day of each experimental period, blood samples were collected
from the jugular vein of each parrot, and the birds were weighed. The
blood samples, ranging from about 0.1 to 1.5 mL, were collected in heparinized
tubes. Blood was centrifuged (10.000 x g, 10 minutes) and the plasma
was stored at -20˚C until
The experimental diets differed in fat content and fatty
acid composition. There were 2 low- and 2 high-fat diets with sunflower
oil and palm kernel oil as variable fat sources. To formulate the low-fat
diets, glucose was isoenergetically substituted for part of the variable
fat source in the high-fat diets. For the isoenergetic substitution,
the energy densities of glucose and fat were taken to be 17 and 39 kJ
gross energy per gram. The composition of the experimental diets and
their constant components are given in Tables 1 and 2. The diets were
composed so as to meet the assumed nutrient requirements of parrots.16
The diets were fed as extruded pellets.
Dry matter, crude protein, crude fiber, and crude ash
in the diets were analyzed according to the Weende analysis. Crude fat
was extracted from the feed with chloroform:methanol (2:1, v/v) as described
by Folch et al,17 and the extracted fat was weighed. For determination
of the fatty acid composition of the fat sources, the oils were saponified
using methanolic sodium hydroxide and the constituent fatty acids were
converted into their methyl esters using boronitrifluoride in methanol.
Fatty acid analyses were performed by gas-liquid chromatography using
a flame ionization detector, a Chromopack column (Fused silica, no.
7485, CP.FFAPCB 25 m x 0.32 mm, Chromopack, Middelburg, the Netherlands)
and H2 as carrier gas.18 The individual fatty acids are expressed
as weight percentage of total methyl esters. The fatty acid composition
of the fat sources (Table 3) and that of the other ingredients, as derived
from the Dutch Feedstuff Table 199919 and from the USDA nutrient database
(www.nal.usda. gov/fnic/foodcomp), were used to calculate the fatty
acid composition of the whole diets (Table 4).
Plasma total cholesterol, phospholipids, and triglycerides
were determined with commercial test combinations and the Cobas-Bio
centrifugal analyser (Roche Diagnostics, Basel, Switzerland). For the
cholesterol and phospholipid determination, Precinorm U (cat. nr. 171743,
Boehringer, Mannheim, Germany) was used as the control serum, and Precinorm
L (cat. nr. 781827) was used for the triglyceride determination. If
more than 150 mL plasma was available, high-density lipoprotein
(HDL) cholesterol was determined as soluble cholesterol after precipitation
of apoB-containing lipoproteins (cat. nr. 543004, Roche, Mannheim, Germany)
using the Cobas-Bio autoanalyser and Precinorm L as the control serum.
Low-density lipoprotein (LDL) cholesterol was calculated with the formula
of Friedewald et al20 as LDL-cholesterol (mmol/L) = total cholesterol
(mmol/L) - triglycerides (mmol/L)
/ 2.2 - HDL-cholesterol (mmol/L).
Individual parrots were considered as experimental units.
Data were used from 20 birds that had participated in the entire experiment.
Plasma lipid values and body weights were subjected to a univariate
analysis of variance. The plasma values were logarithmically transformed
so that they showed a normal distribution. Group, carry-over effect,
dietary treatment, and feeding period were used as fixed factors, and
the parrots as a random factor. If a significant (P<0.05) effect
of one of the fixed factors was observed by analysis of variance, a
least significant difference (LSD) test was then used to identify group
differences. The statistical analyses were performed with the computer
program SPSS (SPSS Inc, Chicago, IL).
Chemical Analyses of Diets
The results of the chemical analyses of the experimental
diets are given in Table 1. The low and high-fat diets contained about
69 and 193 g fat/kg, respectively. The fatty acid composition of the
variable fat sources is given in Table 3. As would be anticipated, the
palm kernel oil was rich in lauric acid and the sunflower oil was rich
in linoleic acid. The calculated fatty acid composition of the whole
diets is shown in Table 4. The high-fat diets resembled the variable
fats more closely than did the low-fat diets, in which the fatty acid
composition of the other ingredients had a greater impact.
Feed Consumption and Weight Changes
Of the 30 parrots, 20 animals finished the experiment.
Seven parrots were excluded because of unacceptable weight loss or illness,
one parrot escaped, one was removed because of fighting, and one parrot
was found dead. The mean daily feed consumption per animal was 39.3
g for the low-fat diet with sunflower oil, 36.7 g for the low-fat diet
with palm kernel oil, 31.1 g for the high-fat diet with sunflower oil,
and 34.7 g for the high-fat diet with palm kernel oil. Because the parrots
could not be fed individually, body weight served as an indicator of
individual feed consumption. The experimental diets had no differential
influence on body weight (P=0.32), but feeding period was associated
with a significant difference in weight (P=0.014); body weight was significantly
higher during the third period. Because there was no diet effect on
body weight, it is concluded that the parrots consumed equal amounts
of energy with the 4 diets and that there was no difference in palatability.
This conclusion is supported by the feed intake values given previously
and the calculated energy contents of the diets (Table 1).
The plasma values at the beginning of the experiment (n
= 30) were 8.39 ± 2.57 (range,
5.31–18.62) mmol/L for total cholesterol, 5.33 ±
1.00 (range, 3.48–8.49) mmol/L for phospholipids, and 2.27 ± 1.33 (range, 0.59–5.63) mmol/L for triglycerides.
The plasma values per dietary treatment are given in Table
5. No group effect and no carry-over effect were found. The diet had
a significant influence on plasma cholesterol concentrations (P=0.006).
The high-fat diet rich in saturated fatty acids lauric and myristic
acid, added in the form of palm kernel oil, produced significantly higher
levels of plasma cholesterol than did the other 3 diets.
Both dietary treatment and feeding period had a significant
influence on plasma phospholipid levels (P<0.001 and P=0.014, respectively).
Feeding the high-fat diet with palm kernel oil resulted in significantly
higher plasma phospholipid concentrations when compared with the other
3 diets. The first feeding period was associated with lower phospholipid
concentrations when compared with the other 3 periods. No significant
differences among the dietary treatments were found for plasma triglyceride
In many cases, there was not enough plasma to determine
HDL-cholesterol. Therefore, the statistical power was low, and it was
decided not to analyze the values for HDL-cholesterol statistically.
LDL-cholesterol was not determined but was calculated from HDL-cholesterol.
Therefore, no statistical analyses were performed for LDL-cholesterol
either. In general, HDL was the main cholesterol carrier in the blood
of the parrots; the average percentage of total cholesterol in HDL was
56%. Two parrots had LDL as the main cholesterol carrier, with this
lipoprotein providing 56% and 65% of the total cholesterol. Throughout
the experiment, the mean LDL to HDL cholesterol ratio in individual
parrots varied from 0.17 to 2.81.
Initial plasma lipid values and those seen in the course
of the experiment showed great inter-individual variation. During the
experiment, the lowest average plasma cholesterol concentration in an
individual parrot was 4.64 mmol/L and the highest value was 18.62 mmol/L.
Polo et al21 reported that the plasma concentration of cholesterol was
6.8 ± 0.7 (range, 5.8–8.2) mmol/L
for African Grey parrots fed a mixed diet. The plasma concentrations
of cholesterol found in this study are generally higher and show a much
greater range. Polo et al21 gave no information about the number of
birds examined, their age and gender, or their housing conditions. Researchers
believe that in middle-aged humans, the risk for coronary heart disease
is increased when plasma cholesterol concentrations are higher than
5.17 mmol/L (200 mg/dL)22 and that the risk increases progressively
above this concentration.23 All of the parrots in this experiment and
all of those studied by Polo et al21 had a plasma cholesterol value
higher than 4.64 mmol/L. It appears relevant to know at which level
an individual parrot should be considered hypercholesterolemic.
In birds on a cholesterol-free diet, the main carrier
of blood cholesterol is HDL.24–26 In general, the parrots in this experiment
also had HDL as main cholesterol carrier, but in 2 parrots, most plasma
cholesterol was carried in LDL. The LDL/HDL cholesterol ratios showed
great variation among the parrots. This ratio is of interest because
it is considered to be a risk factor for atherosclerosis in humans that
is more predictive than total cholesterol.27 A low ratio of LDL/HDL
cholesterol may prevent the development of atherosclerosis. Unfortunately,
we cannot conclude whether or not the experimental diets affected the
LDL/HDL cholesterol ratio in these parrots.
Plasma phospholipids are mainly transported by HDL particles.
Indeed, the high-fat diet with palm kernel oil significantly raised
phospholipids and also increased group-mean plasma HDL cholesterol concentrations.
In humans, plasma HDL cholesterol and triglyceride concentrations are
inversely related,28 but this was not seen in the parrots. However,
it should be noted that the parrots were not fasted before blood sampling
and thus may have been in different feeding states, increasing the variation
in plasma triglyceride concentrations.
The major objective of this experiment was to examine
the effect of amount and type of dietary fat on plasma total cholesterol
concentrations in parrots. Plasma cholesterol concentrations were found
to be significantly higher when the parrots were fed the high-fat diet
rich in saturated fatty acids (lauric and myristic acid) in the form
of palm kernel oil. No difference in plasma cholesterol was found for
the two low-fat diets versus the high-fat diet rich in the polyunsaturated
fatty acid linoleic acid (in the form of sunflower oil). It can be concluded
that, for low-fat diets, the type of dietary fat has no important influence
on plasma cholesterol concentration. However, when a high-fat diet is
given, polyunsaturated fatty acids versus saturated fatty acids may
lower plasma cholesterol concentrations in parrots. A high-fat diet
rich in polyunsaturated fatty acids may lower cholesterol to levels
seen for low-fat diets. Thus, both the amount and type of dietary fat
should be considered in relation to plasma cholesterol concentrations.
Mensink and Katan15 conducted a meta-analysis of 27 trials
in humans. They came up with a formula to predict the changes in plasma
cholesterol concentration when carbohydrates are replaced by fatty acids.
The equation is change in total cholesterol (mmol/L) = 0.039 ¥ (carbÆsat)
- 0.003 ¥
(carbÆmono) - 0.015 ¥ (carbÆpoly), in which (carbÆsat) refers to the isoenergetic replacement of carbohydrates by
saturated fatty acids, (carbÆmono)
to the replacement by monounsaturated fatty acids and (carbÆpoly) to the replacement by polyunsaturated fatty acids. The amounts
of carbohydrates and fatty acids and their replacements are expressed
as percent contribution to total daily energy intake. We have used the
equation of Mensink and Katan15 to predict the diet-induced differences
in plasma cholesterol in this study. The isoenergetic replacement of
glucose and fatty acids was expressed in terms of gross energy. The
analyzed amounts of macronutrients (Table 1) and calculated fatty acid
composition of the diets (Table 4) were used. Between the high-fat diet
with palm kernel oil and the low-fat diets with either sunflower or
palm kernel oil, the predicted differences in plasma cholesterol are
0.78 and 0.65 mmol/L, respectively. In this study, the measured differences
were 0.68 and 1.06 mmol/L, respectively. It would appear that the cholesterol
response to the amount and type of dietary fat in parrots is of the
same order of magnitude as that in humans, but the lower group-mean
cholesterol concentration for the low-fat diet with palm kernel oil
instead of the sunflower oil was unexpected.
In conclusion, this experiment shows that it is possible
to influence plasma cholesterol concentrations in parrots through the
composition of the diet. Dietary intervention might be an approach to
decrease the risk for atherosclerosis in parrots. To lower plasma cholesterol
in parrots, the diet should either have a low fat content or be rich
in polyunsaturated fatty acids. In pelleted parrot feeds, the fat concentration
ranges between 5% and 15%, whereas in seed diets, the fat content may
be much higher, but the proportion of polyunsaturated fatty acids is
often also high. To give a solid recommendation as to an appropriate
diet for parrots, more research is necessary. For the time being, it
would appear advisable to use diets with up to 10% fat in the dry matter.
We thank the Dutch Parrot Refuge for their cooperation
and the use of their parrots. Furthermore, we want to thank Hedwig Van
der Horst, DVM, for her assistance during the experiment, Jan Van der
Kuilen, Inez Lemmens, and Robert Hovenier for their analytical assistance,
and Eloy Cruz for extrusion of the diets.
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Table 1. The
Ingredients, Analyzed Composition, and Calculated Energy Contents of
Table 2. The
Ingredient Composition of the Constant Components in the Experimental
Low-Fat Palm High-Fat
Sunflower kernel Sunflower Kernel
Sunflower oil 15.0 — 132.0
Palm kernel oil — 15.0 —
1000.0 1000.0 1000.0 1000.0
Crude protein 154.8 158.5 181.4
Carbohydrates† 577.9 573.2 417.1
Gross energy‡ 16.2 16.2 19.0
*Glucose and the variable fats were exchanged on an energy basis so that
on a weight basis the amount of constant components in the high-fat
diets was greater than in the low-fat diets.
†Calculated as residual fraction.
‡The gross energy values (MJ/kg) used were as follows: protein 23.8; fat
39; carbohydrates 17.
Wheat middlings 52.9
Corn glutenmeal 92.5
Sugarbeet pulp, dehydrated 125.6
Soy beans, extracted 92.5
Molasses, cane 6.6
Yeast, dehydrated 19.8
Alfalfa meal, dehydrated 72.7
Trace-element premix* 10.6
Vitamin premix† 13.2
Table 3. Contents
of Selected Fatty Acids in the Variable Fat Sources
Table 4. Contents
of Selected Fatty Acids in the Experimental Diets
Fatty Acid Sunflower methylesters
acid 0.0 0.0
g/100g High fat Palm
Fatty acid Sunflower
methylesters Sunflower kernel
0.1 17.0 0.0 41.9
0.3 5.2 0.1 12.2
15.2 15.8 8.7 10.2
4.2 3.8 3.4 2.4
27.5 24.8 23.5 17.0
44.3 23.5 60.4 9.0
1.4 0.4 0.4
2.9 0.7 6.9 0.2
*P/S is the polyunsaturated to saturated fatty acid ratio. P is the sum
of C18:2 and C18:3 and S is the sum of C12:0. C14:0 and C16:0.
Table 5. Mean
Plasma Values of Total Cholesterol, Phospholipids, Triglycerides, High-Density
Lipoprotein (HDL) Cholesterol and Low-Density Lipoprotein (LDL) Cholesterol
for the Four
Low-Fat Low-Fat High-Fat High-Fat
Sunflower Oil Palm Kernel Oil Sunflower Oil Palm Kernel Oil
N mean ± SD N mean ± SD
N mean ± SD N
mean ± SD
20 8.15a ± 2.25 20 7.77b ± 1.93 20 7.43c ± 1.25 19 8.83abc ± 1.30
20 5.14d ± 0.64 20 5.15e ± 0.65 20 5.01f ± 0.47 20 5.74edf ± 0.70
20 2.37 ± 2.14 20 2.01 ± 0.65 20 1.68 ± 0.48 20 1.67
HDL-cholesterol1 12 4.49 ± 1.43 10 4.44 ± 0.95 13 4.10
10 5.85 ± 1.05
LDL-cholesterol1 11 3.19 ± 2.45 10 2.37 ± 0.95 13 2.61
10 2.44 ± 0.65