Agriculture Reference
In-Depth Information
(mice, rats, rabbits) or small target animals
(chicks, quails, piglets), because of the high
costs and the limited feed amounts available
in some cases, especially in early breeding
stages. A model for such studies is proposed
in Chapter 5.
Table 7.8 shows the results of measuring
the bioconversion of -carotene into vitamin
A. h e retinol concentration in the liver of
Mongolian gerbils as a model animal was
used as an end point. h e liver is considered
to be the most suitable indicator organ for
vitamin A. After a depletion period, four
dif erent diets were fed to the gerbils (see
Table 7.8).
h e results showed that the retinol
concentration in the liver of gerbils fed with
carotene-rich maize was similar to animals
fed with maize poor in carotene and
supplemented with adequate amounts of
-carotene. h is means that, in this case,
-carotene from maize is converted into
vitamin A almost as identically as sup-
plementary -carotene. In the case of
'Golden Rice' containing between 1.6 (Ye
et
al
., 2000) and up to 37 mg -carotene/kg dry
rice (Paine
et al
., 2005), the i rst studies to
determine the vitamin A value of -carotene
were done using deuterium-labelled rice
with i ve humans (Tang
et al
., 2009) and not
with laboratory or target animals. Recently,
Tang
et al
. (2012) compared -carotene in
'Golden Rice' with pure -carotene and that
in green spinach in providing vitamin A to
children (
n
= 68; 6-8 years). h e conversion
of -carotene into vitamin A is inl uenced by
many factors (Tanumihardjo, 2002).
-carotene in 'Golden Rice' was as ef ective
as pure -carotene converted in vitamin A
(2.0:1 and 2.3:1 by weight), but much better
than that in spinach (7.5:1).
h e use of exogenous enzymes such as
phytase (see Section 7.8.), xylanase or
-glucanase as feed additives in feeding
regimes of non-ruminants has led to
signii cant improvements in feed ei ciency
and has increased the ability of animals to
use a wide range of feed ingredients.
h erefore, one objective of plant breeding is
also to express various enzymes in plants by
genetic modii cations (see also Chapter 12).
Some studies have been done with
potatoes expressing a -glucanase gene from
Fibrobacter succinogenes
(Armstrong
et al
.,
2002; Baah
et al
., 2002) or with maize
expressing phytase to increase phosphorus
utilization.
Armstrong
et al
. (2002) transferred an
F.
succinogenes
1,3-1,4 -glucanase (1,3-1,4
-d-glucan 4-glucanohydrolase) gene into
potatoes and measured a specii c activity in
the leaves (1693 units/mg) and tubers (2978
units/mg -glucanase), but the tuber yield in
this study was reduced signii cantly by
28-72%. In some cases, 0.6 g GM potatoes/
kg barley-based diets for broilers improved
Table 7.8.
Experimental design to assess the conversion of
β
-carotene from maize into vitamin A in
Mongolian gerbils (60% maize in diets;
n
= 10; depletion phase: 4 weeks; feeding: 8 weeks). (From Howe
and Tanumihardjo, 2006.)
Unsupplemented
control (maize
poor in carotene)
Maize rich in
carotene
Control +
-carotene
Control +
vitamin A
β
-Carotene (nmol/g)
0
8.8
8.8
4.4
Theoretical retinol
intake (nmol/day)
0
106
106
106
Retinol in serum
(μmol/l)
1.23
±0.20
1.25
±0.22
1.23
±0.20
1.22
±0.16
Retinol in liver (μmol/g)
0.10
a
±0.04
0.25
b
±0.15
0.25
b
±0.08
0.56
c
±0.15
Notes:
a,b,c
Means with different letters differ (
p
<0.05).
