Agriculture Reference
In-Depth Information
which vary among feeds and diet composition. If there is no correction for endogenous
losses, the true digestibility of dietary amino acids is underestimated, hence the term
'apparent' digestibility. Correction for basal endogenous losses allows the estimation
of a standardized digestibility value, and correction for both basal and ingredient-
specific losses allows the estimation of a 'true' digestibility value. Because approaches
for the estimation of ingredient-specific endogenous amino acid losses are limited,
cost prohibitive and invasive, there is currently insufficient data available to estimate
'true' ileal amino acid digestibility in commonly used swine feed ingredients. Therefore,
standardized ileal digestibility values, derived from apparent digestibility values corrected
for basal ileal endogenous losses only, are used routinely in the formulation of swine
diets. The main benefits of using standardized over apparent ileal digestibility values
are that measures of standardized ileal digestibility are largely independent of dietary
protein contents and are additive in mixtures of swine feed ingredients. These concepts
are outlined in more detail in Stein et al. (2007).
6.4.2
Determinants of amino acid requirements
Maintenance
The main determinants of amino acid requirements for maintenance include the basal
intestinal endogenous amino acid losses, which are related to the level of feed intake, and
to the skin and hair amino acid losses, which are a function of the metabolic body size
(BW 0.75 ) (Moughan, 1999; NRC, 2012). Amino acid composition of skin and hair has been
reported by Van Milgen et al. (2008). The amino acid profile of the intestinal endogenous
losses in sows is assumed to be similar to that of the growing-finishing pig (NRC, 2012).
These profiles are related to ileal lysine losses, which are unique for gestation (0.522 g/kg
dry matter intake) and lactation (0.292 g/kg dry matter intake), and which are used to
calculate the intestinal losses for each of the essential amino acids. The ileal intestinal
endogenous losses are increased by 10% to include the contribution from large intestinal
losses. In addition to these physical amino acid losses, minimum amino acid catabolism
also contributes to maintenance amino acid requirements. However, insufficient literature
is available on amino acid catabolism associated with body maintenance functions. For
this reason, when deriving estimates of amino acid requirements for maintenance, NRC
(2012) applied an inefficiency factor taking into account the use of dietary amino acids
to meet the requirements for physical amino acid losses, which also reflect amino acid
catabolism. Given that amino acid losses related to skin and hair are rather small in sows,
maintenance requirements for amino acids during gestation and lactation differ mainly
on the basis of feed intake, with lactating sows consuming two to three times as much as
gestating sows (Table 6.4). It is noteworthy to mention that for gestating sows fed a diet
containing greater levels of fiber, endogenous amino acid losses may be slightly higher,
thereby increasing maintenance requirements.
Gestation protein pools
Amino acid requirements for gestation are defined by the amino acid composition of the
maternal body and the four major dynamic protein pools that are associated directly with
Search WWH ::




Custom Search