Feeding Studies with Secondgeneration GM Plants (Output Traits) with Food-producing Animals - Animal Nutrition with Transgenic Plants - page 103

feed conversion and reduced ileal digesta
viscosity (Baah et al ., 2002). h e authors
concluded that there might be potential for
using transgenic potatoes to deliver
enzyme(s) to improve poultry production,
but that it might be necessary to improve
the specii c activity and/or the level of
expression of the enzyme in the potato
tuber in order to achieve consistent results.

et al ., 2002). As a consequence, most of the
organically bound P passes through the
digestive tract and can be found in
considerable amounts in the faeces of those
animals, and may contribute to environ-
mental pollution in regions with high animal
concentrations.
Apart from the supplementation of
animal diets with inorganic P sources to
meet the P requirements of animals, or to
supplement microbially synthesized phytase
as feed additive (Wodzinski and Ullah, 1996;
see Chapter 11) to the diets, there are also
some opportunities in plant and animal
breeding to improve P availability, such as:
 Reduction of phytate synthesis in plants
via plant breeding to create low phytate
hybrids such as maize, barley, rice or
soybeans (Spencer et al ., 2000a,b; Raboy,
2002).
 Expression of phytase in plants and a
higher bioavailability of phytate P (Chen
et al ., 2008; Gao et al ., 2012).
 Expression of phytase in digestive juice
of non-ruminants (Golovan et al .,
2001a,b; Cho et al ., 2006).
In a study with pigs (Spencer et al ., 2000a,b),
low phytate maize showed the same results
as traditional maize supplemented with 2 or
1.5 g inorganic P/kg feed, but a signii cantly
lower P excretion (Table 7.9).
Gao et al . (2012) tested a phytase trans-
genic maize, an Aspergillus niger -derived
phytase expressed in the endosperm of the

7.8 Phytate and Phytase

Balance and feeding studies are necessary to
demonstrate the ei cacy of enzymes
expressed in plants or to show the higher
phosphorus (P) availability in plants with
lower phytate content. Phytate (phytic acid)
is one of the most important inhibitors of P
availability in various plants. Phytic acid
is a hexa-phosphorus-acid ester of the cycle
alcohol inositol and it is called d-myo-
inositol-(1,2,3,4,5,6)-hexakis dihydrogen
phosphate. Six P atoms and some bivalent
major and trace elements (e.g. Mg, Ca, Fe,
Zn, Cu) can be found in phytic acid (Johnson
and Tate, 1969). About 50-80% of the total
P content is present in many seeds as
phytate P (Eeckhout and De Paepe, 1994;
Rodehutscord et al ., 1996). Most cereal
seeds contain only low concentrations of the
specii c enzyme phytase and non-ruminants
(pigs, poultry, humans) do not express
phytase in their digestive tract, or only in
very small amounts (Yang et al ., 1991; Angel

Table 7.9. Conventional and low-phytate maize (78.5% of the mixture) in the feed of fattening pigs. (From
Spencer et al ., 2000a,b.)

Control Low-phytate maize

Parameter (0.3 g of available P/kg) (1.7 g of available P/kg)

Inorganic P supplement - + - +

P content (g/kg)
29-73 kg live weight 5.4 d 5.4 d 3.4 3.4

73-112 kg live weight 3.2 4.7 3.2 4.7 e

Feed intake (kg/day) 2.23 a 2.50 b 2.53 b 2.51 b

870 b 900 b 880 b

Live weight gain (g/day) 730

3.05 a 2.87 b 2.81 b 2.85 b

Feed per gain (kg/kg)

P excreted (g/kg) 4.6 a 8.9 c 3.8 b 8.8 c

Strength (4th metacarpal bone, kg) 79.3 a 138.5 b,c 132.2 b 153.9 c

53.5 a 60.1 b,c 59.3 b 61.2 c Ash content (% in 4th metacarpal bone)

Notes: a,b,c Different letters in one line indicate signifi cant differences ( p <0.05); d +2.0 g P/kg; e +1.5 g P/kg.