Controverses liées à l’élevage

L’élevage est accusé de générer une pollution et une charge sur les ressources terrestres très importantes. La question est complexe, les défenseurs de l’élevage accusant ses détracteurs d’oublier la complexité des relations élevage/milieu : entretien des territoires, maintien de milieux ouverts, contribution à la fertilisation organique des cultures végétales, captation de carbone, valorisation d’aliments non consommables par les humains et de déchets agricoles, importance des produits animaux dans les pays en développement, etc.
Pour les questions plus spécifiquement liées à la souffrance animale comparée des systèmes d’élevage et des systèmes de production végétale, voir la page Agriculture et souffrance animale

1. Impact écologique de l’élevage
2. Comparaison élevage / herbivores sauvages

3. Publications sur l’efficience de l’élevage dans sa contribution à l’alimentation humaine.
4. Publications sur l’importance de l’élevage et des produits animaux dans les pays en développement.



Impact écologique de l’élevage

L’impact de l’élevage sur l’environnement est souvent mis en avant : il occupe beaucoup d’espace, il est susceptible de porter atteinte au sol, notamment en cas de surpâturage, s’il utilise des cultures végétales, ce sont des surfaces supplémentaires utilisées, responsables de déforestation, les ruminants émettent du méthane, le résultat étant qu’au niveau mondial, l’élevage est responsable de 10 à 18% des émissions de gaz à effet de serre, 14,5% étant un chiffre souvent repris.
Cependant, il semble que, correctement mené, l’élevage puisse participer à la protection des sols, retarder la désertification, et qu’il y ait de fortes disparités dans les émissions de gaz à effet de serre liées à la production animale : les systèmes les plus performants émettant moins de GES, avec un facteur 10, voire plus, par rapport aux moins performants. En conséquence, dans les pays développés, la contribution de l’élevage aux émissions de gaz à effet de serre est plutôt de l’ordre de 5 à 8%.

The Water Footprint of Diets: A Global Systematic Review and Meta-analysis
Harris et al.
Advances in nutrition, 2019
https://academic.oup.com/advances/advance-article/doi/10.1093/advances/nmz091/5564833?searchresult=1&fbclid=IwAR3sZL7XQ–ldhwkFkCTb7U6_DiKZrbV7slEE47Vivts-ZkHQCSAAt4Vj3U

Foods of animal origin are major contributors to the green WFs of diets, whereas cereals, fruits, nuts, and oils are major contributors to the blue WF of diets. “Healthy” dietary patterns (425 estimates) had green WFs that were 5.9% (95% CI: −7.7, −4.0) lower than those of “average” dietary patterns, but they did not differ in their blue WFs. Our review suggests that changes toward healthier diets could reduce total water use of agriculture, but would not affect blue water use.

Environmental footprints of beef cattle production in the United States
Rotz et al.
Agricultural systems, 2019
https://www.sciencedirect.com/science/article/pii/S0308521X18305675

Life cycle environmental impacts of U.S. beef cattle production were determined.
•Annual carbon emission was 243 ± 26 Tg CO2e (21.3 ± 2.3 kg CO2e/kg carcass weight).
•Annual fossil energy use was 569 ± 53 PJ (50.0 ± 4.7 MJ/kg carcass weight).
•Blue water consumption was 23.2 ± 3.5 TL (2034 ± 309 L/kg carcass weight).
•Reactive nitrogen loss was 1760 ± 136 Gg N (155 ± 12 g N/kg carcass weight).

Agricultural and forestry trade drives large share of tropical deforestation emissions
Pendrill et al.
Global environmental change, 2019
https://www.sciencedirect.com/science/article/pii/S0959378018314365

Depending on the trade model used, 29–39% of deforestation-related emissions were driven by international trade. This is substantially higher than the share of fossil carbon emissions embodied in trade, indicating that efforts to reduce greenhouse gas emissions from land-use change need to consider the role of international demand in driving deforestation. Additionally, we find that deforestation emissions are similar to, or larger than, other emissions in the carbon footprint of key forest-risk commodities. Similarly, deforestation emissions constitute a substantial share (˜15%) of the total carbon footprint of food consumption in EU countries. This highlights the need for consumption-based accounts to include emissions from deforestation, and for the implementation of policy measures that cross these international supply-chains if deforestation emissions are to be effectively reduced.

Pastoralism may have delayed the end of the green Sahara
Brierley et al.
Nature, 2018
https://www.nature.com/articles/s41467-018-06321-y

The model indicates that the system was most susceptible to collapse between 7 and 6 ka; at least 500 years before the observed collapse. This suggests that the inclusion of increasing elements of pastoralism was an effective adaptation to the regional environmental changes. Pastoralism also appears to have slowed the deterioration caused by orbitally-driven climate change. This supports the view that modern pastoralism is not only sustainable, but beneficial for the management of the world’s dryland environments.


Les prairies, sous certains climats, notamment semi-aride ou méditerranéen, pourraient se révéler meilleurs puits de carbone que les forêts, notamment grâce à une meilleure stabilité face aux incendies.

Grasslands may be more reliable carbon sinks than forests in California
Dass et al.
Enviromental research letter, 2018
https://iopscience.iop.org/article/10.1088/1748-9326/aacb39

Although natural terrestrial ecosystems have sequestered ~25% of anthropogenic CO2 emissions, the long-term sustainability of this key ecosystem service is under question. Forests have traditionally been viewed as robust carbon (C) sinks; however, extreme heat-waves, drought and wildfire have increased tree mortality, particularly in widespread semi-arid regions, which account for ~41% of Earth’s land surface. Using a set of modeling experiments, we show that California grasslands are a more resilient C sink than forests in response to 21st century changes in climate, with implications for designing climate-smart Cap and Trade offset policies. The resilience of grasslands to rising temperatures, drought and fire, coupled with the preferential banking of C to belowground sinks, helps to preserve sequestered terrestrial C and prevent it from re-entering the atmosphere. In contrast, California forests appear unable to cope with unmitigated global changes in the climate, switching from substantial C sinks to C sources by at least the mid-21st century.

Des méthodes complexes d’agro-pastoralisme sont susceptibles d’apporter des rendements importants et de la stabilité aux systèmes de production, du moins dans certaines conditions. L’exemple de la culture du riz associée à l’élevage de canards et de poisson dans le sud de l’Asie est assez bien étudié. Il n’y a pas forcément compétition entre la production végétale et la production animale, il peut y avoir synergie.

Complex rice systems to improve rice yield and yield stability in the face of variable weather conditions
Uma Khumairoh et al.
Nature scientific reports, 2018
https://www.nature.com/articles/s41598-018-32915-z

The integration of azolla, fish and ducks has been shown to create robust systems that maintain high yields under heavy rainfall […] We show that the introduction of additional elements into the rice cropping system enhanced the adaptive capacity to extreme weather events across four locations and three cropping cycles. The complex system showed both static and dynamic stability, and had the highest reliability index, thereby outperforming the conventional and organic monoculture systems. The complex rice system design provides a promising example for resilience towards the impacts of climate change on rice production and for safeguarding food security in Asia and beyond.

The water footprint of different diets within European sub-national geographical entities
Vanham et al.
Nature sustainability, 2018
https://www.nature.com/articles/s41893-018-0133-x

For all 43,786 analysed geographical entities, the water footprint decreases for a healthy diet containing meat (range 11–35%). Larger reductions are observed for the healthy pescetarian (range 33–55%) and healthy vegetarian (range 35–55%) diets.

Water foodprint diets Vanham 2018

Managing the global land resource
Pete Smith
Proceedings of the Royal Society B, 2018
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2017.2798

The main finding from this and other studies examining dietary change and waste reduction is that tackling demand, particularly the current and projected overconsumption of livestock products, greatly reduces pressure on land and creates the ‘headspace’ for other versions of global agriculture and food production to be accommodated. Demand management, through improving human diets and reducing waste, is therefore a policy target that would provide multiple benefits

Attention, article à lire avec un oeil très critique les arguments sur le climat, notamment. Les arguments portant sur les émissions de gaz à effet de serre de l’élevage sont à évaluer.

Domestic Livestock and Its Alleged Role in Climate Change
Albrecht Gatzle
Intertech Open, 2018
https://cdn.intechopen.com/pdfs/63148.pdf

we expose important methodological deficiencies in IPCC and FAO (Food Agriculture Organization) instructions and applications for the quantification of the manmade part of non-CO2-GHG emissions from agro-ecosystems. However, so far, these fatal errors inexorably propagated through scientific literature. Finally, we could not find a clear domestic livestock fingerprint, neither in the geographical methane distribution nor in the historical evolution of mean atmospheric methane concentration.

Une publication sur l’importance des effets de l’élevage et de son éventuelle suppression sur les émissions de GES aux Etats-Unis. Supprimer l’élevage aboutirait à plus de production agricole (+23%), mais à une plus mauvaise adéquation avec les besoins nutritionnels, notamment un moins bon rapport nutriments/énergie, et seule une part des émissions liées aujourd’hui à l’élevage seraient supprimées, aboutissant à un résultat absolu faible en matière de diminution des émissions de gaz à effet de serre :

Nutritional and greenhouse gas impacts of removing animals from US agriculture
White & Hall
PNAS, 2017
https://www.pnas.org/content/114/48/E10301?ijkey=bf6636e1d050e0e6f158c7442614312aad538c1a&keytype2=tf_ipsecsha

Livestock recycle more than 43.2 × 109 kg of human-inedible food and fiber processing byproducts, converting them into human-edible food, pet food, industrial products, and 4 × 109 kg of N fertilizer. Although modeled plants-only agriculture produced 23% more food, it met fewer of the US population’s requirements for essential nutrients. When nutritional adequacy was evaluated by using least-cost diets produced from foods available, more nutrient deficiencies, a greater excess of energy, and a need to consume a greater amount of food solids were encountered in plants-only diets. In the simulated system with no animals, estimated agricultural GHG decreased (28%), but did not fully counterbalance the animal contribution of GHG (49% in this model). This assessment suggests that removing animals from US agriculture would reduce agricultural GHG emissions, but would also create a food supply incapable of supporting the US population’s nutritional requirements.

Comparative analysis of environmental impacts of agricultural production systems, agricultural input efficiency, and food choice
Michael Clark & David Tillman
Environmental research letter, 2017
https://iopscience.iop.org/article/10.1088/1748-9326/aa6cd5/meta

Further, for all environmental indicators and nutritional units examined, plant-based foods have the lowest environmental impacts; eggs, dairy, pork, poultry, non-trawling fisheries, and non-recirculating aquaculture have intermediate impacts; and ruminant meat has impacts ~100 times those of plant-based foods. Our analyses show that dietary shifts towards low-impact foods and increases in agricultural input use efficiency would offer larger environmental benefits than would switches from conventional agricultural systems to alternatives such as organic agriculture or grass-fed beef.

Certaines méthodes de planification de pâturage semblent pouvoir améliorer encore l’efficacité de l’élevage et sa capacité de régénération des sols. Il n’est pas certain cependant que celles-ci soient généralisables, le résultat dépendant potentiellement du climat, de l’état pédologique initial, de la motivation et de la compétence des éleveurs, etc.

Potential of grassland rehabilitation through high density-short duration grazing to sequester atmospheric carbon
Chaplot et al.
Geoderma, 2016
https://manuscript.elsevier.com/S001670611630060X/pdf/S001670611630060X.pdf

However, in this paper we use a transparent, data-driven model, to show
that even if yield gaps are closed, the projected demand will drive further agricultural expansion. There are, however, options
for reduction on the demand side that are rarely considered. In the second par t of this paper we quantify the potential for
demand-side mitigation options, and show that improved diets and decreases in food waste are essential to deliver emissions
reductions, and to provide global food security in 2050.

Très grandes disparités d’efficacité de l’élevage à travers le monde. Les systèmes les plus performants émettent considérablement moins de GES que les moins performants. A production égale, il serait sans doute possible de diminuer considérablement les émissions de gaz à effet de serre liées à l’élevage, si les systèmes les moins performants étaient mis à niveau :

Biomass use, production, feed efficiency and greenhouse gases emissions from global livestocks systems
Herrero et al
PNAS, 2013
https://www.pnas.org/content/110/52/20888

Bovine GHG efficiency Herrero et al, 2013

The water footprint of the EU for different diets
Vanham et al.
Ecological indicators, 2013
http://ayhoekstra.nl/pubs/Vanham-et-al-2013a.pdf

Water foodprint diets Vanham 2013

Water use by livestock: A global perspective for a regional issue?
Doreau et al.
Animal frontiers, 2012
https://academic.oup.com/af/article/2/2/9/4638620

 

  • estimations of water use to produce 1 kg of beef range from 3 to 540 L of H2O or H2O equivalents for the life cycle assessment approach and from 10,000 to 200,000 L of H2O for the water footprint.
  • Ultimately, water scarcity depends on blue water use. Decreasing the contribution of livestock to water scarcity can be achieved by decreasing feed irrigation. Livestock farming also has positive impacts on the environment related to water use.

 

The price of protein: Review of land use and carbon footprints from life cycleassessments of animal food products and their substitutes
Nijdam et al.
Food Policy, 2012
https://static1.squarespace.com/static/56b97a017c65e4826a4a549c/t/59de84fa80bd5e963fd1912b/1507755259253/Nijdam+et+al%2C+2012+-+The+price+of+protein.pdf

In a general conclusion it can be said that the carbon footprint of the most climate-friendly proteinsources is up to 100 times smaller than those of the most climate-unfriendly. The differences betweenfootprints of the various products were found mainly to be due to differences in production systems.The outcomes for pork and poultry show much more homogeneity than for beef and seafood. This is lar-gely because both beef and seafood production show a wide variety of production systems.Land use (occupation), comprising both arable land and grasslands, also varies strongly, ranging fromnegligible for seafood to up to 2100 m2ykg1of protein from extensive cattle farming. From farm to forkthe feed production and animal husbandry are by far the most important contributors to the environ-mental impacts.

Land use Nijdam 2012

 

Comparaison élevage / herbivores sauvages

The Rise of the Anthroposphere since 50,000 Years: An Ecological Replacement of Megaherbivores by Humans in Terrestrial Ecosystems?
Hervé Bocheren
Frontiers in ecology and evolution, 2018
https://pdfs.semanticscholar.org/a36f/7c75a9fab91f86f256ff512a1e784298761b.pdf

Megaherbivores fulfilled a number of important ecological functions in terrestrial ecosystems and behaved as ecological engineers since 300 million years until around 12,000 years ago. These essential ecological functions include opening vegetation cover, selective seed dispersal and nutrient recycling and spreading. Thanks to these effects, megaherbivores change the vegetation structure where they live, with cascading effects on smaller herbivores and also on climate. The late Pleistocene extinction strongly impacted the megaherbivores almost all over the world and led to the loss of these important ecological functions in terrestrial ecosystems. These functions were partially restored by agriculturist humans through an ecological replacement that occurred through an ecological shift within the species Homo sapiens. A better understanding of the differences and similarities between the ecological impacts of megaherbivores and those of agricultural humans should help to predict the future of terrestrial ecosystems.

Une publication suggérant des émissions de méthanes assez proches entre les ruminants de la fin du pléistocène et les ruminants actuels (voir plus bas, Hristov 2012, pour un résultat comparable sur l’Amérique du nord).

Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget
Smith et al.
PNAS, 2016
https://pdfs.semanticscholar.org/abe6/8110246a30c715613f509da6b8f8ecd92282.pdf

CH4 emissions since pleistocene

 

L’un des problèmes liés à l’élevage concerne les émissions de méthane des ruminants. Mais il y avait, dans les régions d’élevage, des ruminants sauvages avant l’apparition de l’élevage, qui émettaient déjà du méthane. La question est de savoir si les émissions liées à l’élevage sont disproportionnées par rapport aux émissions sauvages historiques. Cette publication suggère qu’elles sont relativement proches.

Historic, pre-European settlement, and present-day contribution of wild ruminants to enteric methane emissions in the United States
Hristov
American Society of Animal Science, 2012
https://pdfs.semanticscholar.org/a9a0/8cf4be0b758ac14921e8c27a1a9c9a58a4a3.pdf

Overall, enteric CH4 emissions from bison, elk, and deer in the presettlement period were about 86% (assuming bison population size of 50 million) of the current CH4 emissions from farmed ruminants in the United States.

Agricultural net primary production in relation to that liberated by the extinction of Pleistocene mega-herbivores: an estimate of agricultural carrying capacity?
Christopher E Doughty & Christopher B Field
Environmental research letters, 2010
https://iopscience.iop.org/article/10.1088/1748-9326/5/4/044001/meta

Mega-fauna (defined as animals > 44 kg) experienced a global extinction with 97 of 150 genera going extinct by ~ 10 000 years ago. We estimate the net primary production (NPP) that was liberated following the global extinction of these mega-herbivores. We then explore how humans, through agriculture, gradually appropriated this liberated NPP, with specific calculations for 800, 1850, and 2000 AD. By 1850, most of the liberated NPP had been appropriated by people, but NPP was still available in the Western US, South America and Australia. NPP liberated following the extinction of the mega-herbivores was ~ 2.5% (~1.4 (between 1.2 and 1.6) Pg yr − 1 of 56 Pg C yr − 1; Pg: petagrams) of global terrestrial NPP. Liberated NPP peaked during the onset of agriculture and was sufficient for sustaining human agriculture until ~ 320 (250–500) years ago. Humans currently use ~ 6 times more NPP than was utilized by the extinct Pleistocene mega-herbivores.

 


Efficience de l’élevage

Les animaux d’élevage convertissent une alimentation végétale en divers produits animaux : des aliments, des fertilisants, des matières utilisées en habillement, d’autres matières utilisées dans l’industrie…
La conversion du végétal vers l’animal a un certain rendement. En calories brutes, il est forcément inférieur à 1 : les animaux consomment plusieurs calories végétales pour restituer une seule calorie animale.
Mais le rendement ne peut pas se limiter à une question de calories : parce que les produits animaux ne sont pas que cela (notamment, du point de vue alimentaire, ils apportent une série de nutriments que les végétaux n’apportent pas (la conversion n’est pas que quantitative, elle est aussi qualitative) : acides aminés semi-essentiels, meilleur équilibre général des acides aminés, acides gras à chaine longue, rétinol, vitamine D3, vitamine K2, etc.).
De plus, en fonction du type et du mode d’élevage, l’alimentation végétale des animaux d’élevage est plus ou moins largement impropre à la consommation humaine. Le résultat étant que plusieurs études suggèrent que, si l’on considère le rapport protéines animales produites sur protéines végétales consommables par l’homme consommées, la production  animale peut avoir un rendement supérieur à 1 (auquel il faut donc ajouter la production de sous-produits listés ci-dessus).

L’élevage est souvent accusé de dépenser beaucoup d’eau. Cette publication suggère que passer à une alimentation plus végétale permet d’économiser de l’eau verte, mais le gain est faible ou nul pour les eaux bleues. La question est alors de savoir s’il est judicieux de comptabiliser les eaux vertes (eaux de pluie) qui arrosent les prairies d’élevage.

 

L’efficience nette de conversion des aliments par les animaux d’élevage : une nouvelle approche pour évaluer la contribution de l’élevage à l’alimentation humaine
Laisse et al.
INRA, 2019
https://productions-animales.org/article/view/2355#

Efficience nette protéique corrigée elevage Inra Laisse 2019

Livestock: On our plates or eating at our table? A new analysis of the feed/food debate
Mottet et al.
Global food security, 2017
https://www.sciencedirect.com/science/article/abs/pii/S2211912416300013

 

86% of the global livestock feed intake in dry matter consists of feed materials that are not currently edible for humans
•Contrary to commonly cited figures, 1 kg of meat requires 2.8 kg of human-edible feed for ruminants and 3.2 for monogastrics
•Livestock consume one third of global cereal production and uses about 40% of global arable land
•Livestock use 2 billion ha of grasslands, of which about 700 million could be used as cropland
•Modest improvements in feed conversion ratios can prevent further expansion of arable land dedicated to feed production.

Net food production of different livestock: A national analysis for Austria including relative occupation of different land categories
Ertl et al.
Die Bodenkultur: Journal of Land Management, Food and Environment, 2016
https://www.degruyter.com/downloadpdf/j/boku.2016.67.issue-2/boku-2016-0009/boku-2016-0009.pdf

The results of this study clearly show that due to their dif-ferent digestive systems, ruminants (except in intensive growing-fattening bull systems) consume only small pro-portions of feedstuffs that are in direct competition with human foods as compared with monogastric animals.

An approach to including protein quality when assessing the netcontribution of livestock to human food supply
Ertl et al.
Animal, 2016
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/FCFCDF7166AA557F0BD776222DCD63EF/S1751731116000902a.pdf/an_approach_to_including_protein_quality_when_assessing_the_net_contribution_of_livestock_to_human_food_supply.pdf

Efficience nette protéique corrigée elevage laitier Autriche Ertl 2016

Global food supply: land use efficiency of livestock systems
van Zanten et al.
The international journal of life cycle assessment, 2016
https://link.springer.com/article/10.1007/s11367-015-0944-1

The LUR for the case of laying hens equaled 2.08, implying that land required to produce 1 kg HDP from laying hens could directly yield 2.08 kg HDP from human food crops. For dairy cows, the LUR was 2.10 when kept on sandy soils and 0.67 when kept on peat soils. The LUR for dairy cows on peat soils was lower compared to cows on sandy soils because land used to grow grass and grass silage for cows on peats was unsuitable for direct production of food crops. A LUR <1.0 is considered efficient in terms of global food supply and implies that animals produce more HDP per square metre than crops.

 


Importance et problématiques de l’élevage dans les pays en développement

Leveraging human nutrition through livestock interventions: Perceptions, knowledge, barriers and opportunities in the Sahel
Dominguez-Salas et al.
ISI journal, 2019
https://cgspace.cgiar.org/handle/10568/103751

There was agreement among stakeholders on the importance of livestock and ASF to improve human nutrition, and on the prominent disconnect whereby livestock interventions often neglect human nutritional goals, due to the complexity of impact pathways and the multiple roles of livestock in livelihoods.

Eggs in early complementary feeding and child growth: A randomized controlled trial
Ianotti et al.
Pediatrics, 2017
https://escholarship.org/content/qt9gq0c883/qt9gq0c883.pdf?t=oww21v

RESULTS: Mothers or other caregivers reported no allergic reactions to the eggs. Generalized linear regression modeling showed the egg intervention increased length-for-age z score by 0.63 (95% confidence interval [CI], 0.38–0.88) and weight-for-age z score by 0.61 (95% CI, 0.45–0.77). Log-binomial models with robust Poisson indicated a reduced prevalence ofby 0.63 (95% confidence interval [CI], 0.38–0.88) and weight-for-age z score by 0.61 (95% CI, 0.45–0.77). Log-binomial models with robust Poisson indicated a reduced prevalence of stunting by 47% (prevalence ratio [PR], 0.53; 95% CI, 0.37–0.77) and underweight by 74% (PR, 0.26; 95% CI, 0.10–0.70). Children in the treatment group had higher dietary intakes of eggs (PR, 1.57; 95% CI, 1.28–1.92) and reduced intake of sugar-sweetened foods (PR, 0.71; 95% CI, 0.51–0.97) compared with control.
CONCLUSIONS: The findings supported our hypothesis that early introduction of eggs significantly improved growth in young children. Generally accessible to vulnerable groups, eggs have the potential to contribute to global targets to reduce stunting.

The effect of egg supplementation on growth parameters in children
participating in a school feeding program in rural Uganda: a pilot study
Baum et al.
Food and nutrition research, 2017
https://foodandnutritionresearch.net/index.php/fnr/article/view/1202/4491
Methods
: Children (ages 6–9; n = 241) were recruited from three different schools located
throughout the Kitgum District of Uganda. All participants in the same school received the same dietary intervention: control (no eggs (0 eggs); n = 56), one egg five days per week (1 egg; n = 89), or two eggs five days per week (2 eggs; n = 96). Height, weight, tricep skinfold thickness (TSF), and mid-upper arm circumference (MUAC) were measured monthly over 6 months.
Results
: Following six months of egg supplementation, participants receiving 2 eggs had a
greater increase in height and weight compared to the 0 eggs and 1 egg groups (P < 0.05). In addition, participants receiving 1 egg and 2 eggs had a significantly higher (P < 0.05) increase in MUAC at six months compared to 0 eggs.
Conclusion
: These results suggest that supplementation with eggs can improve parameters of
growth in school-aged children participating in school feeding programs in rural Uganda.

The consequences of replacing wildlife with livestock in Africa
Hempson et al.
Nature scientific reports, 2017
https://www.nature.com/articles/s41598-017-17348-4

Our analyses reveal pronounced herbivore biomass losses in wetter areas and substantial biomass increases and functional type turnover in arid regions. Fire prevalence is likely to have been altered over vast areas where grazer biomass has transitioned to above or below the threshold at which grass fuel reduction can suppress fire. Overall, shifts in the functional composition of herbivore communities promote an expansion of woody cover. Total herbivore methane emissions have more than doubled, but lateral nutrient diffusion capacity is below 5% of past levels. The release of fundamental ecological constraints on herbivore communities in arid regions appears to pose greater threats to ecosystem function than do biomass losses in mesic regions, where fire remains the major consumer.

Milk Matters. A Literature Review of Pastoralist Nutrition and Programming Responses
Sadler et al, 2009
https://eeas.europa.eu/sites/eeas/files/milk_matters_a_literature_review_of_pastoralist_nutrition_final_may09.pdf

This review highlights the ongoing problem of child malnutrition in pastoral areas of sub-Saharan Africa, particularly during drought years when access to milk is significantly reduced. It discusses the importance of milk and milk products in the diets of pastoralists and the critical contribution it makes to improving dietary quality for women and young children. There are many challenges however to ensuring a sufficient and constant supply of milk in pastoral communities. These include the impact that more frequent drought and animal disease has on milk supply and the increasing trend of settlement and commercialization in some areas.

Meat Supplementation Improves Growth, Cognitive, and Behavioral Outcomes in Kenyan Children
Neumann et al.
The journal of nutrition, 2007
https://academic.oup.com/jn/article/137/4/1119/4664672

Findings from the 3-country Nutrition Collaborative Research Support Program (NCRSP) study in Egypt, Kenya, and Mexico during the mid 1980s stimulated the study reported here. The NCRSP longitudinal observational study of “energy intake and human function” found positive associations between meat intake and physical growth, cognitive function, school performance, physical activity, and social behaviors, particularly in the Kenya study.
[…]This is the first randomized, controlled feeding intervention study with meat supplementation to show a causal set of positive relationships between meat and milk intake and important functional outcomes in children: improved cognitive performance; increased high levels of PA; increased initiative and leadership behaviors; and increased MAMA. Milk supplementation resulted in improved linear growth in younger and already stunted children. Compared with the Control group, all supplemented groups improved overall weight gain, suggesting a chronic energy deficit and inadequate energy intake for any catch-up growth.