Agriculture Reference
In-Depth Information
vital functions and minimum activities (mainte-
nance requirement) of the animal plus extra
nutrients to support the cost of growth or lacta-
tion. Thus, upon an increase in production level,
less feed resources per unit product are required.
This is illustrated in Figs 2.3 and 2.4. In Fig. 2.3,
requirements of energy per unit of milk as a
function of production level in dairy cattle are
shown using a net energy (NE) system (the
Dutch NE for lactation system; Van Es, 1978)
and a metabolizable energy system (the UK Feed
into Milk system; Thomas, 2004). Similarly, the
requirements for metabolizable protein per unit
of milk in the Dutch (Van Duinkerken
et al
.,
2011) and UK (Thomas, 2004) systems are
shown in Fig. 2.4.
Because the maintenance energy require-
ment is assumed not to change as a function of
production, whereas the daily energy require-
ment increases as milk yield increases, the pro-
portion of total energy used for maintenance is
reduced. For example, upon an increase in
annual fat and protein corrected milk (FPCM)
production from 6000 to 10,000 kg per cow, the
energy requirements per kg milk (MJ kg
−1
FPCM)
are reduced by 16% and 19% in the Dutch and
UK systems, respectively (Fig. 2.3). Similarly, as
described more extensively in Chapter 11 of this
topic, Capper
et al
. (2009) and Capper (2011)
showed that modern, high-production level
dairy and beef cattle practices require consider-
ably fewer feed resources than low-production
level systems several decades ago. Average
annual milk production in the USA increased
from 2074 kg per cow in 1944 to 9193 kg per
cow in 2007 and feed input per kg milk was
reduced by 77% at the 2007 level compared
with the 1944 level. Average daily growth rate
of beef cattle in the USA increased from 0.75
(1977) to 1.08 (2007) kg per head, and feed
input per kg gain was reduced by 19% at the
2007 level compared with the 1977 level.
Although maintenance requirements are gener-
ally assumed to be proportional to metabolic
body weight, it should be noted here that some
organs or tissues, in particular visceral organs,
have high metabolic rates and are responsive to
altered nutrient intake (Baldwin
et al
., 1985).
Possible differences in weights of those organs
or tissues or in their response to altered nutri-
tional states and production levels may actu-
ally lead to some variation in maintenance
energy requirement. The partial efficiency
of converting ME to NE in dairy cattle appears
14
12
10
8
6
4
3,000
5,000 7,000
Milk production (kg FPCM year
-1
)
9,000
11,000
13,000
Dutch NE system
UK ME system
Fig. 2.3.
Efficiency of conversion of net energy (NE) or metabolizable energy (ME) (MJ) into milk (kg fat
and protein corrected milk (FPCM) per cow per year) according to the Dutch NE system (van Es, 1978)
and the UK Feed into Milk system (Thomas, 2004).
