Agriculture Reference
In-Depth Information
population, it is important to avoid competition
between feed for animals and food for humans.
Ruminants have a key role in converting
plant resources that humans cannot (or choose
not to) consume into high-quality human-edible
food. By virtue of the use by ruminants of cell
wall rich plant material, including grass, crop
residues and other by-products of farms and
industry, they do not necessarily compete
directly with humans for food. In fact, rumi-
nants augment the human food supply by
exploiting inedible biomass to produce high-
quality human-edible food. This ability to turn
human-inedible products into human-edible
products necessitates consideration of the basis
to express efficiency (Baldwin, 1984; Gill
et al
.,
2010; Wilkinson, 2011). In terms of total energy
or protein efficiency (efficiency of conversion of
feed energy or protein to energy or protein in ani-
mal products), cattle are usually far less efficient
than monogastrics (Table 2.1). Also, beef pro-
duction is less efficient than milk production. In
all cases, inputs exceed outputs when expressed
on a total basis. However, in ruminant produc-
tion systems, the efficiency when expressed on
a human-edible basis (efficiency of conversion of
human-edible energy or protein into energy or
protein in animal products) is quite different
from total efficiency. Ruminant systems are
inherently more efficient when compared with
non-ruminant systems on the basis of inputs and
outputs edible to humans (Reynolds
et al
., 2011).
The return on human edible energy and protein
inputs (Table 2.1) represents the contribution
ruminants make to the total human food supply,
with values of over 1 indicating that animals add
to the total human food supply (Baldwin, 1984).
Indeed, for dairy cattle, the human-edible effi-
ciency in all situations considered in Table 2.1 is
well over 1. For beef cattle, efficiencies on a
human-edible basis are more variable, with effi-
ciencies below 1 when diets contain a significant
amount of grain. Overall, increased use of feed
grains generally increases total efficiency (see
previous section), but decreases returns on
human edible inputs. Thus, cattle production
systems based on forages and food by-products
may well be net contributors of human-edible
food supply, even though overall efficiency at the
animal level may appear low. In contrast, cattle
production systems based on high amounts of
human edible products such as cereals may be
net extractors of human-edible food supply, even
though overall efficiency may appear high.
For dairy cattle, the above efficiency analysis
is for adult cows only. The amount of energy or
protein required in the period from birth to first
lactation is not included in most of the analyses
presented. If the amount of feed consumed dur-
ing the rearing phase is included in the calcula-
tion of efficiency, both total and human edible
efficiencies decline. In the Netherlands for exam-
ple, the return on human edible protein input
decreases from 4.38 (without rearing costs) to
3.38 (with rearing costs) (Dijkstra, unpublished
results). The feed costs to grow a calf from birth
until first lactation are considerable. Analogous
to the effect of dilution of maintenance when
production levels increase, the feed inputs for
rearing are diluted when cows produce more
milk and/or when an increase in longevity
(the productive period per cow) is achieved
(Van Vuuren and Chilibroste, 2013). For exam-
ple, the return on human edible protein input
including the rearing phase when culling cows
after their first lactation or after six lactations
is 2.04 and 3.74, respectively (Table 2.1;
Dijkstra, unpublished results). Thus, dilution of
feed inputs during the rearing phase increases
efficiency of milk production. Management
strategies to reduce involuntary culling need to
be optimized to improve efficiency. However, it
should be noted that milk and beef production
systems in many countries are closely interlinked,
as fattening of surplus calves from dairy farming
and culled dairy cows provide a significant
amount of beef. Feed efficiency and environmen-
tal impact of the full system (milk and beef) are
not necessarily enhanced when production level
or longevity of dairy cattle increases, since the
improvement of efficiency on the dairy side may
be party or completely offset by a decline in effi-
ciency on the beef side (Zehetmeier
et al
., 2012).
Finally, several studies have emphasized the
role of milk and beef in adequate nourishment
of humans. Animal products are relatively com-
plete, energy-dense, rich in high-value protein,
and important for the bio-available micronutri-
ents such as vitamin B-2, vitamin B-12, vitamin D
and zinc (FAO, 2011). Animal protein sources
are superior to plant proteins in cereal-based
diets as they provide a complete source of protein
