Agriculture Reference
In-Depth Information
and hormonal status of the animal. Maintenance
of body function has a high priority. This
requires in particular the supply of ATP via oxi-
dation and the supply of amino acids for obliga-
tory body protein turnover. The maintenance
requirements of animals are usually considered
fixed. High production levels will increase FCE
simply because the amount of metabolized feed
needed for maintenance processes is diluted
out (VandeHaar and St-Pierre, 2006), as dis-
cussed in the next section. The efficiency in
which absorbed nutrients are converted into
milk or meat also depends on the type of nutri-
ent absorbed. For example, the efficiency of use
of acetic acid appears to be lower than that of
most other absorbed nutrients, although acetate
may be used with higher efficiency if the supply
of glucogenic nutrients is high (Tyrrell
et al
.,
1979). To reflect such variation in efficiency, in
various feed evaluation systems the efficiency
with which metabolizable energy is converted
into net energy depends on feed metabolizability
(the ratio of metabolizable energy to gross
energy), although the effect of metabolizability
on this efficiency may well be considerably
smaller than assumed in present feed evaluation
systems (Strathe
et al
., 2011).
Production Level and Efficiency
Production level is among the most significant
elements in cattle production that determine
FCE. An animal that eats more feed to support
greater production partitions a smaller portion
of feed towards maintenance needs and a
greater portion is transferred to the product
(milk, meat, etc.) (Fig. 2.2). This improvement in
productive efficiency is the classic dilution of
maintenance effect, by which the total resource
cost per unit of product is reduced (Bauman
et al
., 1985; VandeHaar and St-Pierre, 2006).
The nutrient requirement of cattle comprises a
basal, specific quantity needed to maintain the
400
300
200
100
0
0
3,000
6,000
9,000
12,000
Milk production (kg year
-1
)
Maintenance
Heat increment milk production
Milk
Faeces, urine, gas
Fig. 2.2.
Milk production level (kg fat and protein corrected milk per cow per year) and partitioning of feed
towards losses in faeces, urine and gases, maintenance needs, heat increment for milk production, and
milk production in dairy cattle. Values based on Feed into Milk system (Thomas, 2004).
