maize–soybean diet, to 1146 U, for a semi-
purified soybean diet. Piglets given a
maize–oats–soybean meal diet required
only 380 U of phytase to release 1 g of P
(Hoppe et al., 1993).
The P-releasing power of microbial
phytase and wheat phytase are very
different. Eeckhout et al. (1992b) compared
the efficacy of 500 U of wheat middlings
phytase and natuphos (microbial phytase)
in 13 kg piglets. Although both phytase
sources increased digestibility of P and Ca,
the microbial phytase was 74% more
efficient. The increased effectiveness of the
microbial phytase was attributed to its
ability to retain activity at lower pHs than
wheat phytase. The additional benefit of
microbial phytase was that there was 27%
less P found in the faeces compared with a
maize–soybean meal–heated wheat middl-
ings diet (i.e. no phytase activity) without
microbial phytase supplementation.
Eeckhout et al. (1992c) conducted the
same experiment with 50 kg pigs. As a
result, pigs given 500 U kg^1 of microbial
phytase had 0.035% (20% of requirements)
more absorbable P. There was no evidence
from Eekhout et al. (1992c) to suggest that
the efficiency of microbial phytase is
affected by pig weight between 13 and
50 kg. Over a broader range in liveweight
and physiological status, phytase efficacy
does change (Kemme et al., 1997) (Table
19.5). All pigs in this experiment were
given identical diets containing Ca 6.2 g
kg^1 , total P 4.8 g kg^1 and phytate P 3.7 g
kg^1 with an intrinsic phytase activity of
120 FTU kg^1. This table shows how stage
of pregnancy and liveweight influence the
amount of P released by phytase.
Mroz et al. (1994) showed the import-
ance of feeding level and feeding frequency
on the apparent digestibility of phytate P, N
and Ca in grower pigs (45 kg) given supple-
mentary phytase (800 U kg^1 ). Phytase
increased the apparent total tract digesti-
bility of DM OM, CP, Ca, total P and all
amino acids except cysteine and proline.
Increasing the feeding level from 2.3 to 2.8
times maintenance improved the retention
of N, Ca and P, and increasing the feeding
frequency from once to seven times per day
increased the ileal digestibility of phytic
acid and some amino acids. This experi-
ment highlights how difficult it is to
interpret and compare results between
experiments as there are a large number of
factors influencing the efficiency of supple-
mentary phytase.
In summary:● Pigs are less susceptible to dietary anti-
nutritional factors than broilers and are
less likely to show an economic
response to enzyme supplementation.
Of the classes of pig, it is the piglet that
stands to benefit most from enzyme sup-
plementation. Multienzyme supple-
ments tend to be more effective than
those with single activity.
● Microbial phytase can increase P avail-
ability, Ca + N retention and decrease P
excretion in young pigs. The efficiency
of phytase is affected by diet, feeding
level, feeding frequency, source and
amount of phytase and the physiological
state of the pig.Feed Enzymes in Aquaculture
Aquaculture has been relatively slow to
adopt feed enzyme technology. This is
possibly due to its reliance, until recently,
on fish meal as the sole or major source of
protein, especially for carnivorous species.
Fish meal is highly digestible and meant
there was little to be gained by adding
either protease or carbohydrases.
Yet, in recent years, the world catch of
wild fish has begun to decline and alterna-
tives to fish meal protein have been sought.414 D.I. Officer
Table 19.5.Effect of physiological status of a pig on
the efficiency of P release (g) with the addition of
500 FTU kg^1 phytase.
Physiological status g Extra digestible P
Lactating sows 1.03
Grower/finishing pigs 0.83
Sow (end of pregnancy) 0.74
Piglets 0.66
Sows (mid-pregnancy) 0.32
Kemme et al.(1997a).