monogastrics

8/13/2019 Monogastrics

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MONOGASTRIS AND THE ENVIRONMENT


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Monogastrics and the Environment

The livestock sector has a key and growing role in the agricultural economy.Whereas the Green Revolution was a concerted political and scientific response torapidly growing populations, the Livestock Revolution currently underway in developingcountries is driven by growing incomes or the worlds emerging middle class. It is alsoan important determinant of human health and diet.

The livestock domesticated animals can divide into two groups. Theyare monogastrics and ruminant organism. A monogastrics organism has a simplesingle-chambered stomach, compared to a ruminant organism, which has a four-chambered complex stomach. Examples of monogastrics animals includeomnivores such as humans, rats and pigs, carnivores such as dogs and cats,and herbivores such as horses and rabbits. Herbivores with monogastrics digestioncan digest cellulose in their diet by way of symbiotic gut bacteria. However, their ability

to extract energy from cellulose digestion is less efficient than in ruminants.Herbivores digest cellulose via microbial fermentation (biochemistry). Monogastric

herbivores that can digest cellulose nearly as well as ruminants are called hindgutfermenters, while ruminants are called foregut fermenters. These are sub divided intotwo groups based on the relative size of various digestive organs in relationship to therest of the system: colonic fermenters tend to be larger species such as horsesand rhinos, and cecal fermenters are smaller animals such as rabbits and rodents.The great apes (bonobos, chimpanzees, gorillas, and orang-utans), in contrast tohumans, derive significant amounts of phytanic acid from the hindgut fermentation ofplant materials.

Monogastrics cannot digest the fiber molecule cellulose as efficiently as ruminants,though the ability to digest cellulose varies amongst species. A monogastric digestivesystem works as soon as the food enters the mouth. Saliva moistens the food andbegins the digestive process. After being swallowed, the food passes from theoesophagus into the stomach, where stomach acid and enzymes help to break downthe food. Bile salts stored in the gall bladder empty the contents of the stomach into thesmall intestines where most fats are broken down. The pancreas secretes enzymes andalkali to neutralize the stomach acid.

Recently, a number of studies have under scored the impact of livestock on theglobal environment, including anthropogenic climate change, nitrogen cycles, andphytomass appropriation .The areas of climate change, reactive nitrogen mobilization,and anthropogenic biomass appropriation and that curbing livestock sector growthshould be a major focus in environmental governance. The current environmentalimpact of livestock is large, but it can be significantly attenuated. Some counter vailingtrends are already in place that has the potential to reduce environmental impactdrastically, notably the shift to monogastrics and continued efficiency gains in theproduction of feed and livestock. These tendencies will help mitigate livestocks globalenvironmental impact to a larger extent. Although addressing excessive levels ofconsumption will help reduce environmental impact, there is a vast mitigation potentialon the production side. Addressing environmental impacts of livestock on the productionside may also carry important benefits for socially and economically disadvantagedlivestock producers in developing countries.
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Demand projections point to increases of global meat consumption of 68% and of

global milk consumption of 57% over the 2000 base period by 2030 (6) . Livestock areused to appropriate the majority of global phytomass captured by human activity, mostlyby converting vegetal material of no immediate other use by way of ruminant production.

Biomass appropriation does not necessarily imply a negative impact on the environment.In properly managed grass-based systems, grazing and mowing contribute to increasedecosystem productivity and biodiversity. The continuation of ruminant-based meatproduction systems into modern days, however, implies significant resource use and lowresource-use efficiencies when high-value feed is used. This is because of the inherentlylow feed conversion rates of ruminants and their long reproduction intervals, which entailthat more than one-half of dietary energy requirements in cattle production systems arefor maintenance (2) . In addition, because of the specifics of the digestive system ofcattle, sheep, and goats (foreguts), their production is associated with high levels ofmethane emissions, substantially contributing to climate change. The production ofmonogastric meat and eggs is associated with much lower emission intensities,phytomass appropriation, and reactive nitrogen. Global monogastric meat production hasincreased by 103% over the 1987 2007 period as opposed to an increase of 28% inruminant meat production (7) ; these trends are expected to continue into the future (6) .

Productivity growth, triggered by demand growth and resource scarcity, also hasthe potential to reduce phytomass appropriation per unit of product and emissionintensity. Measured in global protein output per standing livestock biomass, theproductivity of ruminant species (beef and sheep) has been stable over the past twodecades, whereas productivity of monogastrics (pig and poultry) grew at an annual rateof 2.3% (8) . Productivity increases in livestock have been brought about by the broadapplication of science and advanced technology in feeding and nutrition, genetics andreproduction, and animal health control as well as general improvements in animalhusbandry. Because livestock production relies increasingly on products of arable land,productivity increases in crop production also help in reducing the environmental impactthat can be attributed to livestock. Close to 90% of total crop production increase is theresult of productivity increase as opposed to area expansion (9) . This is indicative of thelarge role that advanced technology can play in reducing environmental impact,particularly in developing country agriculture and livestock production where there arelarge productivity gaps. Closing these gaps could substantially reduce aggregateenvironmental impact of livestock. Fig. 1 describes the aggregate of the land use oflivestock between 1961 and 2001. Globally, meat and milk production increased by 245%

and 70%, respectively, whereas total use of arable land increased by 30% and grazingland by less than 10% (2) .
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Addressing the dietary convergence and putting in place environmental and public healthpolicies to reorient consumption patterns on more sustainable paths would effectivelyreduce the sectors impact. Policies directly targeting dietary patterns are often resentedas interfering with very personal choices of how and what to eat; educational andawareness programs which promote healthy food choices have been shown to work in

some places (13 ) but are likely to be slow in yielding the desired impact.The extent and form of global environmental impact of livestock production, like in

the form of climate gas emissions, have developed in the absence of environmentalpolicies; in the livestock sector, such policies have mostly targeted water pollution andodour issues in industrialized countries and, to a certain extent, in emerging countries.Livestock production and consumption issues have not been a major focus ofenvironmental policies thus far, and it can be argued that such policies could correct formany of the environmental externalities through regulatory and market-basedinstruments (14 ). Such policies could alter production modes to much higher efficienciesand shift prices to levels that reflect a social value of resources and emissions. Given thelarge gaps between attainable and actually attained efficiencies and the vastconsumption growth potential in industrializing countries, a dual approach, targeting bothproduction systems and consumption trends, should be pursued to effectively bring downthe environmental impact of livestock.

References1. Delgado C, Rosegrant M, Steinfeld H, Steinfeld H, Ehui S, Courbois C (1999) Livestock to 2020: The

Next Food Revolution. Food, Agriculture and the Environment (International Food Policy ResearchInstitute, Washington, DC) Discussion Paper 28.

2. Food and Agriculture Organization, (2006) Livestocks Long Shadow: Environmental Issues andOptions (Food and Agriculture Organization,Rome).
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