Amino Acid Composition and Digestibility of Four Protein Sources for Dogs

Article (PDF Available)inJournal of Nutrition 121(11 Suppl):S64-5 · December 1991with 769 Reads 
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DOI: 10.1093/jn/121.suppl_11.S64 · Source: PubMed
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Amino Acid Composition and Digestibility
of Four Protein Sources for Dogs1
Veterinary Faculty, State University B43 Sart Tllman, 4000 Liege, Belgium
Indexing Key Words:
•symposium •dogs •dietary protein •protein di
Protein in dog diets can be either of animal source
or of vegetable origin. Dietary protein must supply 10
essential amino acids (EAA).Protein quality is depen
dent on the concentration of EAA and their availabi
lity. Quality is also influenced by digestibility. The
digestibility varies with processing and with the pres
ence of other components such as carbohydrates or
fiber. The purpose of the present study was to compare
amino acid (AA)composition and protein digestibility
in four diets containing four different protein sources.
Materials and methods. Three animal-protein
sources (lung, tripe, minced meat) and one vegetable-
protein source (soybean meal) were used. The lung,
tripe and minced meat were raw. They were incor
porated into a basic diet composed of cooked rice, corn
oil, minerals and vitamins. Four young adult Beagles,
two males and two females, were fed daily 550 kj me-
tabolizable energy (ME)/kg BW075. Protein was cal
culated to provide 20% of the ME. All four dogs were
fed the same diet during the same period. After a tran
sition period of 1 wk, each diet was tested during a 4-
wk period, at the end of which digestibility was mea
sured during 7 d. Feces were collected daily along with
food samples for analysis of dry matter (DM), ash and
ether extract (EE). The AA composition was deter
mined by capillary gas chromatography. Digestibility
of each protein source was calculated by difference,
assuming a digestibility for rice of 89% for DM, 91%
for organic matter (OM), 84% for crude protein (CP)
and 75% for EE. For corn-oil digestibility of DM, OM
and EE was estimated at 98%. Means among the pro
tein sources were compared by analysis of variance.
Results and discussion. Daily AA consumption
is given in Table 1. Difficulties were encountered in
the determination of the concentrations of Cys, Met
and Trp. Since the concentrations of the other AAs
were quite similar to reported data, these three values
have been taken from published data. The AA profiles
were similar in the four diets. Although soybean meal
is known to provide less sulfur-containing AAs, such
as Cys and Met, as well as His, the daily consumption
of these AAs with the diet based on soybean meal was
quite comparable to their consumption with the diets
based on animal protein. The diet based on lung, how
ever, provided less Met-Cys, His and Trp than the
other three diets. The concentration of Arg was low
in the diet with the minced meat. In the diet containing
tripe, concentrations of all AAs were fairly high, es
pecially the sulfur-containing AAs, due to the fact that
tripe was only washed so that the keratinized papillae
remained. The utilization of these AAs is, however,
assumed to be low since the proteolytic enzymes of
the dog and its intestinal microbes cannot digest kera
tin. The concentration of Leu was, on the contrary,
quite low in this diet. Regardless of these differences,
the concentrations of the EAAs in the four diets were
greater than the minimum requirements for mainte
nance according to the National Research Council (1).
They were still sufficient if the requirement was in
creased by 40% to compensate for impaired availabi
lity and digestibility (2). It should be noted that the
protein concentration in the diets was quite high (20%
1Presented as pan of the Waltham International Symposium on
Nutrition of Small Companion Animals, at University of California,
Davis, CA 95616, on September 4-8, 1990. Guest editors for the
symposium were James G. Morris, D'Ann C. Finley and Quinton
R. Rogers.
2To whom correspondence should be addressed: Veterinary Fac
ulty, State University B43 Sart Tilman, 4000 Liege, Belgium.
0022-3166/91 $3.00 ©1991 American Institute of Nutrition. J. Nutr. 121: S64-S65, 1991.
by guest on January 5, 2012jn.nutrition.orgDownloaded from
of the ME) to avoid any influence by protein deficiency
on digestibility and nitrogen balance.
Apparent digestibility coefficients of the compo
nents of the diets and the protein sources are given in
Table 2. The digestibility of DM was similar for the
diets based on animal protein and was ~90.36%. It
was significantly lower (P < 0.001) with the diet con
taining soybean meal (73.86%). The OM digestibility
was on average 3.31% units higher than the DM val
ues. High digestibility coefficients were observed for
CP (91.22%) and EE (96.79%) for the diets based on
animal protein. The corresponding figures were signi
ficantly lower (P < 0.001) when soybean meal was
When the digestibility of each protein source was
calculated by difference, coefficients differed only
slightly between protein sources and whole diet with
the animal proteins. For soybean meal the protein di
gestibility (CP) was rather low and similar to that of
the diet (76.33%) while DM and OM digestibility were
reduced to a large extent. The negative value for di
gestibility of EEis due to the low EEcontent of soybean
meal. Similar findings have been reported by Kendall
and Holme (3).
It appears from the present data that the three an
imal-protein sources did not differ to a large extent in
terms of AA profiles and digestibility. Animal protein
is generally well digested even if differences can be
found depending on the connective tissue (lung) or
carbohydrates (glycogen). Digestibility was lower in
the soybean-meal diet than in the animal-protein diets,
indicating that although the AA profile was compa
rable, the availability of the AA was lower in the soy-
Daily consumption of essential amino acids (EAA)
from four diets with different protein sources
Minced Soybean
Diet Tripe Lung meat meal Requirements'
Apparent digestibility coefficients of diets and
of protein sources1'1
Available amino acid based on 1985 NRC.
1Four dogs were fed each of the 4 diets.
2Abbreviations: CP, crude protein; DM, dry matter; EE, ether
extract; OM, organic matter; SED, standard error of the difference.
bean-meal diet. Proteins of plant origin generally have
a lower digestibility than animal proteins because plant
fiber or carbohydrates lower digestion due to a reduced
degradation rate of nutrients in the gut and an in
creased bacterial activity (4). In most commercial dog
foods both animal and vegetable proteins are used.
This combination raises the protein quality by com
plementation of EAA and increases the palatability of
the food (5).
The most interesting findings in the present trial
were the similarity in the EAA composition between
vegetable and animal protein, opposed to the reduced
digestibility of the vegetable protein. Further research
needs to be done with a lower level of protein in the
1. NATIONALRESEARCHCOUNCIL. (1985) Nutrient Requirements
of Dogs. National Academy Press, Washington, DC.
2. SHEFFY,B. A. (1989) The 1985 revision of the National Research
Council nutrient requirements of dogs and its impact on the
pet food industry. In: Nutrition of the Dog and Cat, pp. 11-26,
(I. H. Burger & J. P. W. Rivers, eds.), Cambridge University
Press, London.
3. KENDALL,P. T. & HOLME,D. W. (1982) Studies on the diges
tibility of soya bean products, cereals, cereal and plant by-pro
ducts in diets of dogs. /. Sci. Food Agrie. 33: 813-822.
4. MEYER,H. (1984) Nutrient digestibility and its relationship to
alimentary disorders in dogs. In: Nutrition and Behaviour in
Dogs and Cats, pp. 55-69, (R. S. Anderson, ed.), Pergamon Press,
5. BROWN,G. R. (1989) Protein in dog foods. Can. Vet. ]. 30: 528-
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