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The nutritional value of ryegrass-white clover leaf protein concentrate : a thesis presented in partial fulfillment [sic] of the requirements for the degree of Doctor Philosophy in Biochemistry at Massey University
Leaf Protein Concentrate (LPC ) , which was manufactured from a
mixture of Ryegrass and White Clover (Lolium perenne and Trifolium
repens) at the Ruakura Agricultural Research Centre , was evaluated
as a possible protein source for feeding to chickens . The
nutritional value of LPC was compared to that of soybean meal ( SBM ) .
LPC was shown to have a lower nutritional value than SBM in the
growth trials . The addition of methionine or cystine to the
diet containing LPC improved both food utilization and weight
gain of the chickens . These growth parameters showed the
greatest improvement when 2 g methionine/kg diet was added to the
LPC diet. The additional quantity of 2g methionine/kg diet was
similar to the amount of sulphur amino acid contributed by LPC to
the d i e t ; 1.8 g sulphur amino acid from L PC /kg diet. When an
equivalent amount of cystine (1.6g) to methionine , on a sulphur
basis , was added to the LPC d i e t and fed to chickens , it was shown
to support the same amount of growth and maintain a similar food
utilisation level as additional methionine . LPC contributed only
0.6g cystine/kg of diet . As this was much lower than the added
cystine and/or methionine , it was concluded that the availability
of cystine in the whole diet was reduced by the presence of LPC
rather than the lack of availability of cystine in LPC alone .
The following information was also obtained : -
(i) Pancreatic hypertrophy and increased pancreatic enzyme
activity (trypsin and chymotrypsin ) occurred due to feeding the
LPC diet .
(ii) The invitro exhaustive enzyme digestibility study
indicated that while the overall digestibility of LPC was approximately
6% lower than that of SBM, none of the individual amino acid
digestibility estimates i n LPC diverged markedly from the mean . All
LPC amino ac ids were released equally by enzyme hydrolysis .
(iii) In contrast to the invitro findings , the in vivo
mean amino acid availability estimates for the ingredient LPC
(as measured in the excreta) were lower than the corresponding
SBM estimates by approximately 1 5% . The cystine availability
estimate for the ingredient LPC was only 5 1 . 2% in terms of corrected
amino acid availability ( CAAA), and 1 1 . 9% in terms of apparent
amino acid availability ( ApAAA). By comparison the cystine
availability estimates for the ingredient SBM were 80 . 8% CAAA and
7 5 . 7 % ApAAA. When the diets containing LPC or SBM were assayed
by the same technique , the differences in the amino acid availability
estimates were markedly reduced . The availability estimates of
cystine in the LPC diet were still lower than the other amino acid
availability estimates for the LPC diet . These however were only
8-10% lower than the corresponding estimates for the SBM diet.
(iv) The mean amino acid digestibility estimates, derived
by analysis of the ileal contents of chickens fed with the LPC d i e t
were 26% lower than those for chickens fed the SBM d i e t s . The
cystine digestibility estimates for the LPC d i e t was approximately
45% lower than the corresponding cystine digestibility estimate for
the SBM diet. These results indicated that digestion and/or
absorption of the LPC diet was probably being retarded as compared
with the SBM diet.
(v) Supplementation of the LPC diet with the antibiotic , Neomix ,
gave an improvement in growth and an increase in the mean amino acid
availability ( measured by excreta analysis ) of approximately 7%.
This indicated that the gut microflora were influencing the nutritional
value of LPC .
Feeding the LPC diet in comparison to feeding the SBM diet also
tended to increase the level of c1 9 cyclopropane fatty acid in the
excreta. This indicated that feeding the LPC diet was influencing
the nature and/or activity of the microfloral population .
The physiological and metabolic effects of feeding r aw soybean
meal and/or trypsin inhibitors , which have been reported in the
literature, included pancreatic hypertrophy , increased pancreatic
proteolytic enzyme activity , retardation of ileal protein
digestibility and.an influence by gut microflora . Each of these
factors were characteristic of chickens fed the 1PC diet. It
was therefore concluded that the additional need for cystine or
methionine by chickens fed the 1PC diet , was due to the presence
of trypsin inhibitors in the 1PC .
It was demonstrated, by feeding 1 - (methyl 14c) methionine that
phenolic compounds were being methylated . However the need for
detoxification of aromatic compounds , which required methionine
(as a methyl donor ) and /or arginine ( ornithine ) , could not explain
the growth depression experienced by chickens fed the unsupplemented
The feeding of 1- (methyl 14c) methionine in conjunction with the
1PC diet also indicated that the digestibility of methionine was
not being hindered during the digestive process by preferential
binding with other compounds in the 1PC diet.
I t was concluded from the result s of this study that 1PC adequately
supplemented with methionine , could b e a useful addition to the
range of ingredients available for use in poultry feeds.