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animals
Review
Land Use for Edible Protein of Animal
Origin—A Review
Gerhard Flachowsky 1, Ulrich Meyer 1, * and Karl-Heinz Südekum 2
1
Institute of Animal Nutrition, Friedrich-Loeffler-Institut (FLI), Federal Research Institute for Animal Health,
38116 Braunschweig, Germany; gerhard.flachowsky@fli.de
2Institute of Animal Science, University of Bonn, 53115 Bonn, Germany; ksue@itw.uni-bonn.de
*Correspondence: ulrich.meyer@fli.de; Tel.: +49-531-58044-137
Academic Editor: Frank Mitloehner
Received: 16 December 2016; Accepted: 13 March 2017; Published: 18 March 2017
Simple Summary:
The growing world population has led to a higher demand for more and better
quality food. In the future, there will be increasingly strong competition for arable land and other
non-renewable resources. Proteins of animal origin are very valuable sources of essential nutrients,
but their production consumes resources and causes emissions. The aim of this study was to calculate
exemplarily the land use for production of edible animal protein from different animal species and
categories in consideration of important influencing factors. Large differences were found with the
highest amounts per kilogram of body weight produced by broiler chickens and the lowest yields in
edible protein and the highest land need observed for beef cattle.
Abstract:
The present period is characterized by a growing world population and a higher demand for
more and better quality food, as well as other products for an improved standard of living. In the future,
there will be increasingly strong competition for arable land and non-renewable resources such as
fossil carbon-sources, water, and some minerals, as well as between food, feed, fuel, fiber, flowers,
and fun (6 F’s). Proteins of animal origin like milk, meat, fish, eggs and, probably, insects are very
valuable sources of essential amino acids, minerals and vitamins, but their production consumes
some non-renewable resources including arable land and causes considerable emissions. Therefore,
this study
´
s objective was to calculate some examples of the land use (arable land and grassland)
for production of edible animal protein taking into consideration important animal species/categories,
levels of plant and animal yields, the latter estimated with and without co-products from agriculture,
and the food/biofuel industry in animal feeding. There are large differences between animal
species/categories and their potential to produce edible protein depending on many influencing
variables. The highest amounts per kilogram body weight are produced by growing broiler chicken
followed by laying hens and dairy cows; the lowest yields in edible protein and the highest land
need were observed for beef cattle. This review clearly indicates that the production of food of animal
origin is a very complex process, and selective considerations, i.e., focusing on single factors, do not
provide an assessment that reflects the complexity of the subject.
Keywords:
food security; human-edible protein; land use; arable land; grassland; plant yield;
animal yield; co-products
1. Introduction
Food security is currently a pivotal phrase. Food security means meeting the demand of a growing
world population for food of plant and animal origin. The FAO (Food and Agriculture Organization of
the United Nations) [
1
] defined food security as “access to sufficient, safe, nutritious food to maintain
a healthy and active life”. This, in turn, is associated with a growing demand for limited natural
Animals 2017,7, 25; doi:10.3390/ani7030025 www.mdpi.com/journal/animals
Animals 2017,7, 25 2 of 19
resources such as land area, fuel, water, and minerals, and with elevated emissions of gases including
greenhouse gas (GHG) potential such as carbon dioxide (CO
2
), methane (CH
4
), nitrous oxide (N
2
O),
and other substances (e.g., nitrogen, phosphorus, trace elements).
At the end of October 2011, the seven billionth person was born. Sustainability in feed and food
production is a key challenge for agriculture as summarized recently in articles and monographs
(e.g., [
2
–
6
]). In the future, there will be strong competition for arable land and non-renewable resources
such as fossil carbon-sources, water [
7
–
9
], and some minerals such as phosphorus [
10
,
11
]. There will
also be competition for land use between feed, food, fuel, fiber, flowers, and fun (6 F’s concept; [
12
]),
as well as between areas for settlements and natural protected areas.
The balance between Planet (global resources and emissions), People (population all over the
world with adequate nutrition and social conditions), and Profit (money-making) in the so-called
3P-concept [
7
,
13
] is an important prerequisite for sustainable life and development on the earth.
Profit should not be the single objective of production. We have to find a balance between a careful
and sustainable use of limited resources on the one hand and low emissions with minimal local and
global consequences for later generations on the other hand.
According to the FAO [
14
,
15
], the human population will increase globally from above seven
billion currently to more than nine billion people in 2050, but the increase in the output of food of
animal origin is estimated to be about 70% [
16
]. Therefore, some authors propose a redefinition and
a rethinking of agricultural yield, and agriculture in general, from tons per hectare to people per
hectare [
17
,
18
] and increasingly demand sustainable animal agriculture [
19
]. The energy and protein
conversion efficiency from feed into food of animal origin is low and may range from 3% (energy—beef)
up to 40% (energy—dairy; protein—chicken for fattening) [
18
,
20
]. In some countries (e.g., USA)
between 67% (energy) and 80% (protein) of the crops are used as animal feed [
18
]. Feedstuffs such as
grass and other roughage which cannot directly be consumed by humans, co-products of agriculture
and of the food and biofuel industry may also contribute to a more efficient production of food of
animal origin. Especially with regard to ruminants, less potential human food should be fed to animals
in order to improve the proportion of protein output by animals relative to protein input [21].
These developments and complex connections present the following question: “Is there any need
for food of animal origin?” As some population groups (e.g., vegans) demonstrate, there is no essential
need for food of animal origin, but the consumption of meat, fish, milk, and eggs may contribute
significantly to meeting the human requirements of amino acids [
22
–
24
] as well as some important trace
nutrients (such as Ca, P, Zn, Fe, I, Se, and vitamins A, D, E, B
12
), especially for children and juveniles
as well as pregnant and lactating women [
25
,
26
]. Human nutritionists [
27
,
28
] have recommended that
about one third of the daily protein requirement (0.66–1g per kg body mass [
22
,
29
]) should originate
from protein of animal origin. Consequently, about 20 g of the daily intake of about 60 g protein [
30
]
should be of animal origin, which is lower than the present average consumption throughout the
world. Presently, there is an average consumption of animal protein (without fish and insects) of about
24 g per capita and day, ranging from 1.7 (Burundi) to 69.0 g (USA; Table 1). It is difficult to assess the
protein intake from fish. Avadi and Freon [31] estimate that half of the world´s population consumes
at least 15% of their animal protein from aquaculture.
Other reasons for consumption of food of animal origin are the high bioavailability of most
nutrients and their considerable enjoyment value. Such food is also considered to be an indicator of
standard of living in many regions of the world, and it is also determined by taste, odor, and texture,
as well as by geographic area, culture, ethics, and wealth. Further reasons for the higher demand
of food of animal origin in some countries are the increased income of the population [
32
] and the
imitation of the so-called “Western style of life”. Many developing countries continue to consume
more animal products than they produce. Therefore, they will continue to drive the world demand for
all agricultural products, including food of animal origin [
33
,
34
]. Wu et al. [
34
] estimated that with
exponential growth of the global population and marked rises in meat consumption, demands for
animal-source protein will increase by 72% between 2013 and 2050. Greater amounts of food of animal
Animals 2017,7, 25 3 of 19
origin require greater plant yields and/or more area for feed production, more animals and/or higher
animal yields, and an increase in agricultural trade.
Table 1.
Intake of milk, meat, and eggs as well as protein of animal origin per capita and year
1
and
portion (%) of total protein intake (global minimum-values; maximum-values and averages, as well as
German values for comparison; kg per capita and year: data base 2005; [15].
Food Minimum Average Maximum
Milk (kg per year) 1.3
(Kongo) 82.1 367.7
(Sweden)
Meat 2(kg per year) 3.1
(Bangladesh) 41.2 142.5
(Luxembourg)
Eggs (kg per year) 0.1
(Kongo) 9.0 20.2
(China)
Edible protein of animal origin
(g per capita and day)
1.7
(Burundi) 23.9 69.0
(USA)
Portion of animal protein as % of
total protein intake per capita
4.0
(Burundi) 27.9 59.5
(USA)
1
Total daily protein intake per person: Burundi 42.5 g, global average 85.7 g, USA 116.0 g;
2
Presumptive empty
body weight (meat plus bones).
On the other hand, changing the eating patterns [
35
] and eating fewer or no livestock products,
especially meat, is a possible solution to reduce the environmental impact of animal agriculture [
36
–
38
]
and to reduce the per capita land requirements [39,40].
Apart from resource needs, feed and food production causes emissions with a certain greenhouse
gas (GHG) potential, such as carbon dioxide from fossil fuel (greenhouse gas factor (GHF) = 1),
methane (GHF about 23) from enteric fermentation, especially in ruminants, and from excrement
management, as well as nitrogen compounds (NH
3
and N
2
O, GHF about 300; [
41
]) from protein
metabolism in the animals [
19
,
24
,
42
–
44
]. Apart from a lower input of limited resources along the
food chain, a low output of GHG, summarized as carbon footprints (CF) and expressed as carbon
dioxide equivalents (CO
2
-eq), and minerals such as phosphorus and some trace elements during feed
and food production are very important aims of sustainable agriculture. Presently, about 14.5% of
total human-induced global emissions, estimated at 7.1 Gt CO
2
-eq annually, come from the global
production of food of animal origin [
45
]. Therefore, as underlined by some authors [
43
,
46
,
47
], more
attention should be given to optimizing animal breeding [
19
,
48
] and animal health, reducing animal
losses, and developing low-emission diets using life cycle assessments (LCA) for all societies [49,50].
Land, especially arable land, is one of the most important limiting factors [
51
]. Only a small portion
of the approximately 13.4 billion ha global surface is available as arable land (about 1.5 billion ha,
or about 12% of the world’s land area [
24
,
52
]). This area could be extended to a degree (by about
120 million ha [
24
,
52
]), but some areas cannot be used because of limited water resources, forests,
urban settlements, environmental protection, deserts, mountains, and other factors. As a result of the
finite area of arable land and the increase in population, the area of arable land available per person
decreased from about 0.45 ha (1960) to about 0.25 ha (2010) and will further decrease to below 0.20 ha
per person after 2020 (Figure 1).
This situation and the increasing use of land for biofuel production [
53
], organic farming,
settlements, natural protected areas, and other purposes has consequences for feed and food production.
Because of the high need for limited resources, attention has been paid to the space needed for
animal production. Some authors have considered the land use, also described as land or area
footprint, for food of animal origin [
38
,
39
,
54
–
56
]. These authors proposed to distinguish between areas
(mostly arable land) that can also be used for purposes other than for feed production (6 F-concept:
food, feed, fuel, fiber, flowers, and fun) and typical feed areas (grassland or perennial crops).
Animals 2017,7, 25 4 of 19
Reynolds et al. [26]
analyzed the importance of animals in agricultural sustainability and food security.
Grassland and co-products of agriculture, food, and the biofuel industry do not need arable land and,
thus, do not contribute to food-feed competition between animals and humans. The human-edible
feed conversion efficiency (heFCE) [
57
,
58
] is defined as human-edible output via the animal products
(e.g., edible protein) divided by the potentially human edible input via feedstuffs and may contribute to
the calculation the feed need without competition to human nutrition. Van Zanten et al. [
59
] proposed
the calculation of land use efficiency of livestock systems to address the contribution of livestock to the
global food supply.
Animals 2017, 7, 25 4 of 19
animal products (e.g., edible protein) divided by the potentially human edible input via feedstuffs
and may contribute to the calculation the feed need without competition to human nutrition. Van
Zanten et al. [59] proposed the calculation of land use efficiency of livestock systems to address the
contribution of livestock to the global food supply.
Figure 1. Development of world population compared to arable land per inhabitant between 1960
and 2020 [52].
There is no reason to believe that the public interest in the use of limited resources and the high
emissions (i.e., CF) from the production of food of animal origin will diminish in the near future
because of the worldwide increase in land need and emissions. Therefore, the objectives of this paper
are (1) to make some model calculations for the land use and to propose land footprints (LF) for
production of food of animal origin, measured per product unit and/or as edible protein and (2) to
compare the data with selected references. Furthermore, some calculations to compare human-edible
protein output via food of animal origin with edible protein input are done.
Such data could be considered as a starting point for calculations of land use per inhabitant and
year (or lifespan), depending on, for example, the amount of protein consumption, protein sources,
and levels of plant and animal yields. Average values for plant and animal yields were used and
demonstrated the model character of present calculations. In the future, more details should be
considered to help determine the possible or necessary intensity level for feed and animal production
in order to have an available amount of food of animal origin for human beings. Alternatives to the
production of food of animal origin with minimal use of arable land, and with consideration of
grassland and co-products from agriculture and the food and fuel industries, should also be
considered.
The structure of this article is a combination of a review and author-based calculations, for which
references were selected based on presumed particular relevance in the context of the issues
discussed in this study A thorough review would have had the major message that previous attempts
to estimate land use for edible protein of animal origin had used very diverse variables and factors—
making sound conclusions impossible. For the same reason, a meta-analysis using an appropriate
statistical model could not be performed because different authors used different definitions for the
same term, and published data did not allow converting data to a common denominator. Without
this, however, a meta-analysis would have been subject to erroneous results.
2. Materials and Methods
2.1. Estimation of Human-Edible Fractions of Feeds
Food-producing animals, especially non-ruminants, consume plant protein which is also edible
by humans. Therefore, the proportion between edible protein input by animals and the output as
Figure 1.
Development of world population compared to arable land per inhabitant between 1960 and
2020 [52].
There is no reason to believe that the public interest in the use of limited resources and the high
emissions (i.e., CF) from the production of food of animal origin will diminish in the near future
because of the worldwide increase in land need and emissions. Therefore, the objectives of this paper
are (1) to make some model calculations for the land use and to propose land footprints (LF) for
production of food of animal origin, measured per product unit and/or as edible protein and (2) to
compare the data with selected references. Furthermore, some calculations to compare human-edible
protein output via food of animal origin with edible protein input are done.
Such data could be considered as a starting point for calculations of land use per inhabitant
and year (or lifespan), depending on, for example, the amount of protein consumption, protein
sources, and levels of plant and animal yields. Average values for plant and animal yields were used
and demonstrated the model character of present calculations. In the future, more details should be
considered to help determine the possible or necessary intensity level for feed and animal production
in order to have an available amount of food of animal origin for human beings. Alternatives to
the production of food of animal origin with minimal use of arable land, and with consideration of
grassland and co-products from agriculture and the food and fuel industries, should also be considered.
The structure of this article is a combination of a review and author-based calculations, for which
references were selected based on presumed particular relevance in the context of the issues discussed
in this study A thorough review would have had the major message that previous attempts to estimate
land use for edible protein of animal origin had used very diverse variables and factors—making
sound conclusions impossible. For the same reason, a meta-analysis using an appropriate statistical
model could not be performed because different authors used different definitions for the same term,
and published data did not allow converting data to a common denominator. Without this, however,
a meta-analysis would have been subject to erroneous results.
Animals 2017,7, 25 5 of 19
2. Materials and Methods
2.1. Estimation of Human-Edible Fractions of Feeds
Food-producing animals, especially non-ruminants, consume plant protein which is also edible
by humans. Therefore, the proportion between edible protein input by animals and the output as food
of animal origin are questioned (e.g., [
18
,
36
,
39
]). The human edible feed conversion efficiency (heFCE)
can be calculated on the base of human-edible output in the form of animal products divided by
potential human-edible input [
57
,
58
]. Such calculations can be done for edible protein (heP; see Table 2)
of feed, but also for edible energy (heE). The data shown in Table 2are used to calculate the heFCE.
Wilkinson [
57
] proposed values for the calculation of heFCE of rations for human-edible energy (heE)
and human-edible protein (heP): 80% for cereal grains, pulses, and soybean co-products; 20% for wheat
bran, sunflower, and rapeseed co-products and no heE/P (i.e., 0%) for grass, silages, and all other
co-products. Some values applied by Wilkinson [
57
] are disputable (e.g., for maize silage), because the
feeds are produced on arable land, which could alternatively be used for cultivation of plants with
high human-edible fractions (hef).
Table 2.
Crude protein content of some feeds [
60
] and their human-edible fraction (hef; in %) (taken
from Wilkinson [57]) and for three different estimation scenarios from Ert et al. [58].
Feedstuff Crude Protein
(g/kg DM 3)
Hef-Fractions
(% of CP)
Hef-Fractions (% of CP 2)
Low Medium High
Barley 125 80 40 65 80
Maize 106 80 70 80 90
Wheat 138 80 60 80 100
Soybeans 404 80 50 92 93
Rapeseed meal 406 20 30 59 87
Soybeans meal 513 80 50 71 92
Wheat bran 160 20 0 10 20
Maize silage 86 0 19 29 45
Others 10 0 0 0
1
Other co-products (e.g., sugar beet pulp; brewer’s grains; dried distiller’s grains with solubles, etc.) and roughages
(e.g., fresh grass; silages, hay etc.); 2Crude protein; 3Dry matter.
Some authors (e.g., [
21
,
22
,
52
]) consider the quality and digestibility of potentially human-edible
inputs (plant protein) to describe the nutritional value of proteins as the protein quality ratio (PQR).
Such calculations are based on the limiting amino acid in dietary protein, divided by the same
amino acid of the reference protein [
61
] or further derived equations [
24
,
52
]. This approach adds
further quality but also complexity to the estimation of heP which can make comparisons across
sources difficult.
2.2. Edible Fraction and Protein Content of Animal Products
The production of protein of animal origin is one of the most important goals of animal
husbandry [
5
,
38
,
55
]. Edible protein can be used to compare the efficiency of animal production
(e.g., milk, meat, eggs) and to assess the emissions per product [62].
Quantification of protein yield varies depending on some influencing factors. For example, milk
and eggs are clearly defined as food of animal origin and the yield can be measured (and expressed
as kg or L per animal or per day), and, therefore, it is relatively easy to use the yield of lactating and
laying animals for further calculations. The edible fraction of milk and eggs is almost 100% of the yield.
Only minor fractions are not consumed by humans (e.g., colostrum, milk samples at the beginning of
milking, egg membranes, and shells), which are not considered in further calculations (Table 3).
Animals 2017,7, 25 6 of 19
It is much more difficult to quantify and characterize the yield from the animal body after
slaughtering and processing. The following endpoints can be measured in the case of animals for
meat production:
•Weight gain of the animal (per day or per growing period) during the whole life span
•Weight gain of the animal without gastro-intestinal tract contents
•Empty body mass (or carcass weight; meat and bones; warm or cold)
•Meat (empty body mass minus bones)
•Edible fraction (meat plus edible organs and tissues)
•Edible protein (edible fractions of the carcass multiplied by their specific protein content)
Mostly, the term “meat” is used, but sometimes what is exactly meant by this term is not clearly
described (meat with or without bones). Peters et al. [
63
] introduced the term “hot standard carcass
weight” (HSCW) as the weight at the exit gate of the meat processing plant. The FAO [
24
] defines
meat from animals as fresh, chilled, or frozen meat with bones. The FAO data on meat are given in
terms of dressed carcass weight excluding offals and slaughter fats. The HSCW varies between 50%
and 62% of the live weight of cattle before slaughter, but it may vary between 50% in the case of
sheep up to 80% for turkeys [
38
,
42
,
63
,
64
]. Nijdam et al. [
38
] used the following killing-out percentages
(carcass weight as a percent of live weight): 53% for beef, 75% for pork, 46% for mutton, 70% for
poultry, and 40% for fish. The edible meat yield (retail meat of carcass), given by the same authors, is:
70% for beef, 75% for pork and mutton, 80% for poultry, and 100% for fish.
When it comes to the definition of “edible” fractions, large differences exist between countries, and
also between population groups within one country. Therefore, it is difficult to compare results from
various authors and to find out the actual protein yields. Regardless of the method used for calculations
of edible fractions, authors should always clearly describe how values were used and derived to allow
understanding and interpretation of results [
63
]. Another important factor for a reliable calculation of
protein yields of food of animal origin is the protein content of edible fractions as shown in Table 3.
Table 3.
Protein content of some edible land animal products/food by various authors (in g per kg
edible product).
Product/Food Authors Milk (Cows) Beef Pork Poultry Eggs
Flachowsky [65] 34 190 150 200 120
GfE 1[66–69]34 170–200 157
(129–178) n.d. 2121
(110–124)
Souci et al. [70]33.3
(30.8–37.0)
220 3
(206–227)
220 3
(195–240) 199 125
De Vries and de Boer [55] 30 190 190 190 130
Mekonnen and Hoekstra [71] 33 138 105 127 111
Andersen [72] 34 206–212 183–216 182–242 125
Lesschen et al. [73]434.4 206 156 206 119
Nijdam et al. [38] 35 200 200 200 130
USDA [74] 34 173 139 186 126
1Gesellschaft für Ernährungsphysiologie; 2no data; 3Muscles only; 4N-content x 6.25.
The results of specific studies (Table 3) as well as values from food tables [
70
,
74
] are, overall,
in agreement regarding the ranges of protein content in animal-based food: milk (between 30.8 and
37.0 g/kg), beef (170–227 g/kg), pork (129–240 g/kg), poultry meat (182–242 g/kg), and eggs
(110–130 g/kg). Much lower values for beef, pork, and poultry were used by [
71
] to calculate water
footprints for food of animal origin, resulting in very high values for some foods of animal origin
Animals 2017,7, 25 7 of 19
(e.g., [
71
,
75
]). The protein yield in the edible fractions of milk, meat, and eggs was calculated based on
our previous assumptions and data [65] (Table 3).
2.3. Animal Performances/Yields
Apart from the edible fractions and the protein content of edible fractions, the protein yield
per animal and day is also influenced by animal species and categories and by animal performance.
Table 4summarizes data about the animal species/categories and the performance of animals regarding
their expected yield of edible protein. This paper will consider edible protein of animal origin as the
main objective of animal husbandry. Furthermore, it is also easier to compare animal yields of various
forms of animal production based on animal protein yield [38,55,62].
Table 4.
Influence of animal species, categories, and performances on yield of edible protein
(without considering rearing periods and animal losses) [62,65].
Protein Source
(Body Mass)
Performance
(per d)
Dry
Matter
Intake
(kg per d)
Forage to
Concentrate
Ratio
(%, DM Basis)
Edible
Fraction
(% of Product
or Body Mass)
Protein in
Edible
Fraction
(g per kg)
Edible
Protein
Yield
(g per d)
Edible Protein
Yield
(g per kg Body
Mass and d)
Dairy cow
(650 kg)
2 kg milk
5 kg milk
10 kg milk
20 kg milk
40 kg milk
8
10
12
16
25
100
95/5
90/10
75/25
50/50
95 34
67
163
323
646
1292
0.1
0.25
0.5
1.0
2.0
Dairy goat
(60 kg)
0.5 kg milk
1 kg milk
2 kg milk
1
1.5
2
100
90/10
80/20
95 36
17
34
68
0.3
0.55
1.1
Beef cattle
(350 kg)
200 g ADG 1
500 g ADG
1000 g ADG
1500 g ADG
6.0
6.5
7.0
7.5
100
95/5
85/15
70/30
50 190
19
48
95
143
0.05
0.14
0.27
0.41
Growing/fattening
pig
(80 kg)
200 g ADG
500 g ADG
700 g ADG
1000 g ADG
1.5
1.8
2
2.2
30/70
20/80
10/90
0/100
60 150
18
45
63
90
0.22
0.56
0.8
1.1
Chicken for
fattening
(1.5 kg)
20 g ADG
40 g ADG
60 g ADG
0.06
0.07
0.08
15/85
10/90
0/100
60 200
2.4
4.8
7.2
1.6
3.2
4.8
Laying hen
(1.8 kg)
20% LP 2
50% LP
70% LP
90% LP
0.09
0.10
0.11
0.12
30/70
20/80
10/90
0/100
95 120
1.4
3.4
4.8
6.2
0.8
1.9
2.7
3.4
1Average daily gain; 2Laying performance.
The highest protein yields per kg body mass are from intensively produced growing and laying
poultry, followed by lactating ruminants and pigs. Growing ruminants (e.g., beef cattle, suckler calves)
show the lowest protein yield per kg body mass and day (Table 4). Table 4only shows data of animals
in the production phase. Yet, animal production is more complex and for more detailed and reliable
calculations, the breeding/reproduction phase should also be considered. If these phases are taken into
account, yields are lower and it also becomes evident that impaired reproduction or fertility—often
caused by poor nutrition and (or) diseases—is a major obstacle to more efficient resource use by
food-producing animals.
2.4. Plant Yields on Grassland (Perennial Crops) and on Arable Land
Apart from animal performance, information on plant yields should also be available for land use
calculations. The need for arable land is influenced by various factors such as
•Type of forage and crops from arable land and their yields
•Losses during harvest, preservation, and storage
Animals 2017,7, 25 8 of 19
•
Consideration of co-products of agriculture, food, and biofuel industries (such as straw,
solvent-extracted oilseed meals, dried distiller’s grains with solubles (DDGS) in animal nutrition)
•Animal species and categories, number of animals, and animal yields
•Diet composition; forage-to-concentrate ratio
The easiest way to incorporate plant yields is to calculate the land use on the basis of dry matter
(DM) yields, but a more specific characterization of feed (e.g., consideration of various plant species,
digestibility, protein yield, or energy yield expressed as digestible, metabolizable, or net energy) would
be helpful for a more accurate assessment. Energy and nutrient requirements for all food-producing
animals including horses across a wide range of performance levels can be found in documents from
the National Research Council of the USA (e.g., for dairy cattle: [
76
]) or in the recommendations of the
Society of Nutrition Physiology in Germany [66–69,77].
Three intensity levels (A—low, B—medium, and C—high) for plant yields on grassland
(perennial crops = roughage) and for arable land (cultivated crops = concentrate) were assumed for
further model calculations (Table 5). Low, medium, and high yield levels were considered. The assumed
plant yields (Table 6) were selected to show the influence of yield on the land needed per unit of animal
product. Higher plant yields are an important prerequisite for solving global nutrition problems [78].
Another point especially significant for ruminants is the digestibility or the feed value of roughage,
especially if grown under tropical conditions. Such climatic conditions are expected to result in
forage of low nutritive value and a high proportion of protective structures containing cellulose,
hemicelluloses, lignin, cutin, and other structural substances such as silica [
79
]. Tropical forage,
therefore, often has a low nutritive value and a high proportion of protective structures to protect
the plant against predation, i.e., herbivory. Additional factors, e.g., long warm nights promoting
respiration, warmer growth temperatures increasing lignification, and specific types of grasses in
the tropics (mostly C4-plants) are also responsible for the lower nutritive value of tropical plants.
As an example, the average digestibility of the dry matter of grass/legume mixtures as given by the
FAO [
24
] is 75% for Europe and 64% for Africa, and for conserved grass/legume mixtures, the values
are 71% for Europe and 54% for Africa. More country- and feed-specific values are available in specific
feed value tables (e.g., [80,81]).
In tropical areas, free ranging animals, mainly ruminants (e.g., cattle, goats, sheep, and deer),
consume grassland. They are able to select feed according to their preference [
82
] and may substantially
contribute to supplying food of animal origin under such conditions. No limited resources, such as
arable land and fuel, nor extra water supply, are needed for these animals. Future studies should
consider the plant yields (Table 6), the nutritive value of grassland and perennial crops, the methods for
increasing feed value by intensified plant breeding or the improvement in post-harvest methods before
and during storage, and the assessment of consumption of such feeds by ruminants. Lower plants
yields and variation in digestibility and feed intake should also be analyzed as they are additional
influencing factors on animal yields under tropical conditions.
In the present paper, further calculations were made taking into consideration the yields for
forage and concentrates (Table 6) grown under the same yield levels; however, in reality, it is also
possible to harvest forage with yield level B and concentrates with yield level C, or to import feeds from
regions with lower or higher yields. The significance of co-products for animal feeding is described
in Section 2.5.
Table 5. Assumed plant yields for further calculations (kg dry matter per ha and year).
Yield Level Grassland or Perennial Crops
(Roughage)
Arable Land or Cultivated Crops
(Concentrate)
A (low) 5000 2000
B (medium) 10,000 5000
C (high) 20,000 10,000
Animals 2017,7, 25 9 of 19
Table 6.
Model calculations for land use per kg of edible protein depending on animal
species/categories, plant yields, and animal performances (for forage to concentrate ratio see Table 4;
all concentrates from arable land, no co-products considered).
Protein Source Animal
Yield
Edible Protein Yield
(g/d)
Grassland or Perennial Crops
(m2/kg Protein) 1
Arable Land or Cultivated Crops
(m2/kg Protein)
A2B C A B C
Cow milk 2 kg per d 67 240 120 60 0 0 0
5 kg per d 163 120 60 30 15 6 3
10 kg per d 323 70 35 18 18 8 4
20 kg per d 646 38 20 9 30 12 6
40 kg per d 1292 20 10 5 50 20 10
Goat milk 0.5 kg per d 17 120 60 30 0 0 0
1 kg per d 34 80 40 20 22 9 5
2 kg per d 68 50 25 13 30 12 6
Beef 200 g ADG 319 630 315 160 0 0 0
500 g ADG 48 260 130 65 35 15 7
1000 g ADG 95 125 60 30 55 22 11
1500 g ADG 143 75 40 20 80 30 15
Pork 200 g ADG 18 50 25 12 300 120 60
500 g ADG 45 16 8 4 160 65 32
700 g ADG 63 8 4 2 140 55 28
1000 g ADG 90 0 0 0 120 50 24
Chicken meat 20 g ADG 2.4 8 4 2 100 4 20
40 g ADG 4.8 3 2 1 65 25 13
60 g ADG 7.2 0 0 0 60 25 12
Eggs 20% LP 41.4 40 20 10 220 90 45
50% LP 3.4 12 6 3 110 50 25
70% LP 4.8 5 2 1 100 40 25
90% LP 6.2 0 0 0 95 40 20
1
Some authors (e.g., [
63
]) calculated this without perennial crops in non-ruminant (pigs and poultry) feeding;
2Plant yields: Levels A (low), B (medium), and C (high); see Table 5;3Average daily gain; 4Laying performance.
Ruminants generally do not require grains or other concentrates because the microbial population
in the rumen is capable of digesting plant fiber and, after fermentation of the released sugars, delivers
energy to the ruminant animal. Ruminants are, therefore, able to produce edible protein of animal
origin (milk and meat) from permanent meadows and pastures. They are enabling a net output
of human edible protein and may contribute to meeting the human needs for food of animal origin
(e.g., [
83
–
85
]). Kratli et al. [
86
] pointed out that pastoralists are more efficient at producing food per unit
area of dryland than other forms of agricultural land use under the same conditions. Pastoralist systems
are also efficient users of resources such as manure [
87
]. Because of the high fiber content of forage
from grassland and the low animal yields, methane emissions and the CF per kg of edible protein may
be higher under such extensive conditions [
24
,
88
] and GHG mitigation measurements are, therefore,
very important [
43
–
45
,
89
]. On the other hand, it should be considered that permanent grassland has
a quantitatively significant potential for soil carbon sequestration [90,91].
2.5. Significance of Co-Products
Apart from roughages and grains, co-products from agriculture (e.g., [
60
,
92
,
93
]), food
production [
60
,
94
], and the biofuel-industry [
95
] are commonly used as animal feeds. Co-products
are by-products of main processes such as grain production (e.g., straw, stalks, husks) and processing
of raw products in the food industry (e.g., solvent-extracted oilseed meals from the vegetable oil
industry, bran from cereal grain processing, beet pulp or bagasse from the sugar industry, and animal
co-products from milk, fish, or meat processing) or from the biofuel industry (e.g., DDGS, rape seed
cake and meal, as well as cakes and meals from other oilseeds). According to the FAO [
24
], between 10%
and 50% of the estimated concentrate feed comes from co-products in various global regions [
96
].
In some countries, up to 100% of concentrate may be co-products.
Animals 2017,7, 25 10 of 19
Co-products are used in various amounts and proportions in animal diets. Cereal straws and
other co-products rich in plant cell-walls are mostly characterized by a low digestibility and are, thus,
poor in energy and protein delivery. They are fed to ruminants with low animal yields or just to meet
their maintenance requirements. For high yielding ruminants, they can only be considered as a source
of fiber. Normally, they are not used in the feeding of non-ruminants.
In co-products from the food and fuel industry, the concentration of those nutrients not used
for processing is two to three times higher than that found in the original product (e.g., protein in
the case of DDGS). They can be used as valuable sources of protein, minerals, and other nutrients
depending on the source material and the chemical or physical processing, without causing any LF.
In the future, more grain will be used for food and fuel and more co-products could be available
for animal nutrition [
21
,
85
,
97
] or other purposes. Additional details about the nutritive value and
utilization of co-products from the biofuel industry in animal nutrition were recently compiled by the
FAO [95].
Co-products of agriculture and of the food/fuel industry can be used to replace concentrates and
forage from grassland. Based on plant yield level B (Table 5), we assumed for model calculations that
agricultural co-products (e.g., cereal straw) may replace 10%, 20%, or 30% of forage from grassland or
other sources in all diets, and co-products from the food or biofuel industry may replace 15%, 30%
or 45% of concentrate without any land use in the model calculations of all animal diets.
2.6. Animal Feeding
The roughage-to-concentrate ratio is of special importance in ruminant nutrition (Table 4).
Ruminants need a certain portion of forage (i.e., structural fiber) for overall health and to sustain normal
rumen fermentation processes [
98
]. The concentrate portion in ruminant diets increases with higher
animal yields (Table 4) because of higher energy and nutrient requirements of such animals and limited
feed intake capacity [
68
,
76
], but a certain level of forage is also required to keep animals healthy. Higher
ruminant yields require more concentrates and more arable land; however, the land requirements
can be decreased by the strategic and intensified use of co-products. Special attention must be paid
to feeding of potential human edible feeds to ruminants, such as cereal grains and pulses [
18
,
99
].
Typically, non-ruminants are fed with concentrates or co-products from the food or biofuel industries
(Table 4). Animals with lower yields or mature animals (e.g., pregnant, non-lactating sows) may
also consume certain amounts of forage in their diets. However, it is nearly impossible to include
forage in the diets of higher performing non-ruminant animals without drastically compromising
performance [39].
3. Results and Discussion
3.1. Animal Species and Protein Yields
Table 6shows the calculated results of yields from perennial crops, arable land (yield levels A, B,
and C; Table 5), and animals (Table 4) based on the animal species/categories, whereas Table 4shows
the forage-to-concentrate ratios. Co-products from the food and biofuel industry were not considered
as feeds in the calculations of Table 6. Animal species, animal yields, and plant yields were the most
important influencing factors on land use.
Lower plant yields (levels A and B) require more area per unit of edible protein, especially in the
case of perennial crops. Higher ruminant yields increase the arable land use because of the higher
energy density in the diets, but decrease the need for roughage/grassland. Beef cattle produce lower
protein amounts (Table 4) and need much more land per unit of edible protein than dairy cows (Table 6).
Only small amounts of forage were used for non-ruminants with lower yields. Higher animal
yields from non-ruminants result in a decreased need of arable land per kg of edible protein (Table 6).
Non-ruminants need a much greater area of arable land compared to that of ruminants because of the
higher concentrate portion in their diets (Table 4). More detailed calculations, which would have gone
Animals 2017,7, 25 11 of 19
beyond the scope of this study, are necessary to consider growing and reproductive periods for cows,
sows, and laying animals as well as animal losses.
In the following paragraph, our data is compared with selected references. De Vries and de Boer [
55
]
reviewed 16 LCA studies and found—in agreement with the present calculations (Table 6)—that
the production of 1 kg of beef or 1 kg of edible beef protein required the most land and had the
highest global warming potential followed by the production of 1 kg of pork, chicken, eggs, and milk.
There was a similar ranking on the basis of edible protein (beef > pork > chicken > milk > eggs; Table 7).
De Vries and de Boer [
55
] did not distinguish between grassland and arable land, however, this is
important to compare total land use with arable land use of ruminants and non-ruminants.
Table 7.
Land use per livestock product or protein (in m
2
/kg product and m
2
/kg protein; n= 16; [
55
]).
Food of Animal Origin Land Use (m2/kg Product) Land Use (m2/kg Protein)
Milk 1.1–2.0 33–59
Beef 127–491 144–258
Pork 8.9–12.1 47–64
Chicken meat 8.1–9.9 42–52
Eggs 4.5–6.2 35–48
1Suckler cows with calves.
Nguyen et al. [
100
] calculated the land use of beef produced in different systems and expressed
land use per kg of slaughter weight at the farm gate. One kilogram of slaughter weight is approximately
equal to about 100 g of edible protein (Tables 4and 6). The total land use varied, depending on the
production system, between 16.5 and 42.9 m
2
/year (between 0 and 36.9 m
2
of grassland and between
6.0 and 16.5 m
2
of cropland). The values per kg of edible protein varied between 165 and 430 m
2
and
are similar to values in Table 7. In agreement with data from Table 6, the largest area of arable land
(cereal grains, soybean) was needed for the highest weight gain, whereas more extensive feeding
systems resulted in lower weight gains, longer feeding periods, and more grassland use.
3.2. Grassland and Arable Land
Arable land is needed for food production, industrial raw materials, or the other F
´
s, like fuel,
fiber, flowers, and fun [
12
]. Therefore, animal nutrition will be forced to use human-inedible biomass
from grassland or co-products from the food and fuel industries to a much greater extent.
On a global scale, grassland could be an important potential source for ruminant nutrition.
Sustainable intensification of ruminant farming requires a development of grassland-based forage
production [
84
]. Sustainable grassland management includes avoiding overgrazing and a strategic use
of manure to maintain or improve productivity of the swards.
Nijdam et al. [
38
] analyzed numerous LCA and considered both total land use and the portion
which is grassland (Table 8). The calculated values for the land use (m
2
) per product and per kg of
protein show a large range and cover all the data shown in Tables 6,7and 9. Apart from the total
land use, the authors also determined that the grassland portion produced 1 kg of products or 1 kg of
protein by ruminants per m
2
. The results demonstrate that a better description of conditions used for
calculations (such as plant and animal yields, use of grassland and arable land, as well as co-products in
ruminant feeding and slaughtering and protein yields of assessed food of animal origin) are necessary
to allow for the comparison of the results of various studies and to draw more reliable conclusions.
Animals 2017,7, 25 12 of 19
Table 8. Land use (both total and grassland) per kg product and per kg edible protein [38].
Food of Animal Origin
(Number of Studies)
Total Land Use
(m2/kg Product)
Proportional Grassland Use
(m2/kg Product)
Total Land Use
(m2/kg Protein)
Milk (14) 1–2 1 26–54
Beef; allover (26)
Industrial systems (11)
Suckler herds (8)
Extensive pastoral systems (4)
7–420
15–29
33–158
286–420
2–420
2–26
25–140
250–420
37–2100
75–143
164–788
1430–2100
Mutton (5) 20–33 18–30 100–165
Pork (11) 8–15 Not applicable 40–75
Chicken meat (5) 5–8 Not applicable 23–40
Eggs (5) 4–7 Not applicable 29–52
Table 9.
Model calculations for the land use per kg edible protein depending on animal species/categories,
plant yields, animal performances, and co-products from the agriculture, food, and fuel industries
(see Tables 3–5for further details).
Protein Source Animal
Yield
Edible Protein Yield
(g/Day)
Grassland or Perennial Crops
(m2/kg Protein)
Arable Land or Cultivated Crops
(m2/kg Protein)
Plant Yield Level B 1
Replacement by Co-Products (%)
10 20 30 15 20 45
Cow milk 2 kg per d 67 108 96 84 0 0 0
5 kg per d 163 54 48 42 5 4 3
10 kg per d 323 32 28 24 7 6 5
20 kg per d 646 16 14 12 11 10 8
40 kg per d 1292 9 8 7 17 14 11
Goat milk 0.5 kg per d 17 54 48 42 0 0 0
1 kg per d 34 34 28 21 8 6 5
2 kg per d 68 20 18 14 10 8 6
Beef 200 g ADG 219 280 250 220 0 0 0
500 g ADG 48 115 105 90 13 10 8
1000 g ADG 95 54 48 42 19 15 12
1500 g ADG 143 36 32 28 26 21 16
Pork 200 g ADG 18 22 20 18 102 84 65
500 g ADG 45 7 6 5 55 46 36
700 g ADG 63 4 3 3 47 39 30
1000 g ADG 90 0 0 0 42 35 28
Chicken meat 20 g ADG 2.4 4 3 3 34 28 22
40 g ADG 4.8 2 2 1 21 18 14
60 g ADG 7.2 0 0 0 21 18 14
Eggs 20% LP 31.4 18 16 14 76 63 50
50% LP 3.4 5 5 4 42 35 28
70% LP 4.8 2 2 1 34 28 22
90% LP 6.2 0 0 0 34 28 22
1
Plant yields: Levels A (low), B (medium), and C (high); see Tables 3and 5;
2
Average daily gain;
3Laying performance.
3.3. Co-Products
As mentioned earlier, the feed sources may remarkably influence the calculation of the land use
per kg of product or edible protein. There has been a long discussion about the land area considered for
co-products when used in animal nutrition. Some authors consider a part of the area (20%–50%) used
for growing the main product (e.g., cereals, oilseeds) as an area for the co-product. However, in other
studies, land use was not considered for growing co-products at all [
21
,
58
,
101
,
102
]. In accordance with
this concept, co-products may replace forage and/or concentrates in the diets without any additional
LF as shown in Table 6in comparison to Table 9.
Calculations in Table 9show examples when up to 30% of grassland areas and up to 45% of arable
land areas are replaced by straw or other low quality roughages and by co-products from the food and
Animals 2017,7, 25 13 of 19
fuel industries, respectively. Such conditions should be considered if the land uses of various protein
sources are compared. Extensive examples for the accepted uses of co-products in farm animal diets
were recently summarized in the literature [
58
,
95
]. Ertl et al. [
58
] demonstrated that wheat bran and
sugar beet pulp as sole concentrates for dairy cows supported a daily milk production of more than
20 kg per cow under Austrian conditions.
The results of field studies (Tables 7and 8) and our model calculations (Tables 6and 9,
Tables 10 and 11)
clearly show that the study or calculation conditions should be carefully described
to allow appropriate understanding and interpretation of data.
Table 10.
Calculation to the net protein contribution of milk production to the human food chain under
consideration of various amounts of co-products in concentrate (on the basis of the data in Tables 2and 4).
Milk Yield Total
DM-Intake
Concentrate
Intake
Co-Products in
Concentrate
Human Edible
Protein Input
Human Edible
Protein Output
Proportion
Output to Input
(kg per d) (kg/d) (kg DM/d) (%) (g/d) (g/d) (g/g)
2 8 0 0 0 67 -
5 10 0.5 100 18 163 20
10 12 1.2 100 196 323 3.4
20 16 4.0 50 2262 646 2.4
40 25 12.5 25 31450 1292 0.9
1
50% concentrate wheat bran; 50% dried sugar beet pulp;
2
25% concentrate wheat bran; 25% dried sugar beet pulp;
30% concentrate as cereals; 10% soybean meal; 10% rapeseed meal;
3
12.5% concentrate wheat bran; 12.5% dried
sugar beet pulp; 50% concentrate as cereals; 15% soybean meal; 10% rapeseed meal (see Table 2; hef-fractions by [
57
]).
Table 11.
Calculation of the net protein contribution of food of animal origin to the human food chain
without co-products and under consideration of 50% of concentrate based on co-products (based on
data of Tables 2and 4).
Protein for
Human
Alimentation
Animal
Yield
DM
Intake
Concentrate
Intake 1
Co-Products in
Concentrate 2
Human Edible
Protein
Input 3Output 4
Proportion
Output to Input
(per d) (kg/d) (kg DM/d) (kg DM/d) (g/d) (g/d) (g/g)
Cow Milk 20 kg 16 4 0
2
493
262 646 1.3
2.4
Beef 1000 g
ADG 57 1.05 0
0.52
130
70 95 0.7
1.3
Pork 700 g
ADG 2 1.8 0
0.9
224
127 63 0.3
0.5
Chicken 60 g
ADG 0.08 0.08 0
0.04
10
67.2 0.7
1.2
Eggs 70% LP 60.11 0.1 0
0.05
12
74.8 0.4
0.7
1
80% cereals; 20% protein sources (soybeans, rapeseed);
2
50% co products; 30% cereals; 20% protein sources
(soybeans, rapeseed);
3
see Table 2; (hef-fractions by [
57
]);
4
see Table 4;
5
Average daily gain;
6
Laying performance.
3.4. Human Edible Protein
The human edible protein yield was calculated by dividing the protein output per edible animal
product by the edible protein intake and denoted protein score. Values >1 indicate a net yield in human
edible protein, whereas values <1 demonstrate a protein loss via animals. Table 10 shows the effects
of milk yield and required concentrate amounts on the human edible protein input and the output
per cow as well as the protein score (as defined above; [
57
,
58
]). The higher the milk yield and the
higher the protein intake from edible concentrate, the lower the protein score. In agreement with the
calculated data (Table 10), Ertl et al. [
58
] calculated protein scores between 1.40 and 1.87 for milk for
the potentially human-edible plant protein for 30 Austrian dairy farms with average daily milk yields
between 20 and 25 kg.
Animals 2017,7, 25 14 of 19
Table 11 evaluates protein sources for the production of food of animal origin. In the first case, no
co-products are used in the diets; in the second case, 50% of concentrate are consumed as co-products,
mainly wheat bran, and sugar beet pulp. The data show that in addition to the lower need of arable
land (see Table 9), the protein score for all protein sources is higher if co-products are used in animal
feeding. Except milk, the protein scores for all food of animal origin are <1 without co-products as part
of concentrate (Table 11).
4. Conclusions
Arable land use per unit product or protein of animal origin depends mainly on animal species
and categories, animal production system, plant and animal yields, use of grassland, and the portion
of co-products in animal rations. The results presented here show that a clear and precise description
of study conditions and/or the basis of calculations is an inevitable prerequisite to allow for a fair
comparison of results concerning land use. More complex calculations, considering characteristics of
efficient use of limited resources and the reduction of emissions, seem to be helpful to find and specify
optima in the production of food of animal origin. Pertinent references are mentioned for further details.
The following aspects and measurements should be considered in future calculations [103]:
•Use of arable land (i.e., competition between various users [2,12])
•Comparison of output of human edible protein with input via feeding (should be >1 [57,58])
•Efficient use of water for feed and animal production [9,75]
•Minimization of the use of fuel and other limited natural resources in the food chain [13,14]
•Utilization of permanent grassland and co-products from agriculture and industry [21,60]
•
Reduction of greenhouse gas emissions per product or per kg of edible protein and along the
whole food chain [41–45]
•Plant and animal breeding as the starting points of the human food chain [48,78]
•Evaluating the potential of edible insects as protein sources for food and feed [49,104]
•Calculation of land use per inhabitant considering eating patterns of the population [17,35]
•
Reduction of food wastage (presently equal to about 1.4 billion ha land or 30% of the world’s
agricultural area [105,106]
The production of food of animal origin is a very complex process, and selective
considerations, i.e., focusing on single factors, do not provide an assessment that reflects the complexity
of the subject. Cooperation of animal scientists (e.g., nutritionists, geneticists, animal keepers/farmers,
veterinarians, etc.) with scientists working along the food chain in the fields of plant and feed science,
ecology, and economy contributes to improved problem solving and to developing improved and
resilient LF. In summary, the production of more food for more people with fewer resources and
emissions is one of the most important challenges for all of those involved in feed and food science
and production.
Author Contributions:
The idea for the manuscript was developed by Gerhard Flachowsky. He was the principal
organizer of the work and drafted the manuscript. Ulrich Meyer and Karl-Heinz Südekum contributed to
the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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