The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

http://www.uco.es/zootecniaygestion/img/pictorex/01_10_22_grasa_1.pdf

Fat deposition, fatty acid composition and meat quality: A review

As renewed international efforts are needed to curb greenhouse gas emissions, the livestock sector can contribute its part. An important emitter of greenhouse gas, it also has the potential to significantly reduce its emissions. This report provides a unique global assessment of the magnitude, the sources and pathways of emissions from different livestock production systems and supply chains. Relying on life cycle assessment, statistical analysis and scenario building, it also provides estimates of the sector’s mitigation potential and identifies concrete options to reduce emissions. The report is a useful resource for stakeholders from livestock producers to policy-makers, researchers and civil society representatives, which also intends to inform the public debate on the role of livestock supply chains in climate change and possible solution.

Tackling climate change through livestock : a global assessment of emissions and mitigation opportunities

The State of Food and Agriculture

Poverty and Famines: An Essay on Entitlement and Deprivation

Enteric methane is formed during the microbial degradation of food in the rumen, and any variation in its production level is theresult of a change in the microbial ecosystem. Indeed the structure and / or activity of the microbial community determine the productionand, partially, the utilization of dihydrogen (the limiting substrate of methanogenesis). Methane is produced by a specializedgroup of microbes, the methanogens that represent only a small part of the microbial biomass and diversity in the rumen. There isno relationship between methane production and number of methanogens except where specific inhibitors of Archaea are used (vaccines,chemical additives); new studies suggest that the variations in methane production are more likely due to changes in the metabolicactivity of methanogens and / or changes in their diversity at the species or even strain level. The development of long-term mitigationstrategies requires a good understanding of the mechanisms involved in methanogenesis and needs to consider the microbialecosystem as a whole.

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Production de méthane et interaccions microbiennes dans le rumen

/pdf/effets-de-l-addition-de-matieres-grasses-non-protegees-a-la-5533isieuf.pdf

Effets de l'addition de matières grasses non protégées à la ration de la vache laitière sur la concentration et la composition chimique des bactéries et des protozoaires du rumen

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Effect of quality of hay given to mares around foaling on their voluntary intake and foal growth.

Feeding behaviour was measured in 12 multiparous dairy cows all day long during the first 5 weeks of lactation. These cows received corn silage ad libitum and concentrates representing 21 to 27% of total dry matter intake, depending on the week. During the first week of lactation, total eating and ruminating times were 364 and 426 min; eating and ruminating rates were 39.0 and 32.5 g DM/min. The feed intake increase during the first 5 weeks of lactation was accompanied by an increase in ruminating time (+ 22%) and eating rate (+ 26%). These two parameters were very sensitive to short-time decreases in DM intake. Animal variations of eating and ruminating rates, but not variations of total eating and ruminating times, were related to those of dry matter intake. Thus, animals which had the highest dry matter intake were those which had the highest eating and ruminating rates.

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Evolution des activités alimentaires des vaches laitières en début de lactation et liaison avec les quantités d'aliments ingérées

The aim of the current study was to analyse the environmental impacts of fattening bull systems using life cycle assessment (LCA). Three contrasting bull-fattening systems practised in France were compared. Diets H, MS and C differed by the nature of the forage consumed (hay, maize silage and wheat straw, respectively) and the proportion of concentrate, i.e. ground maize grain and soybean meal (0·51, 0·37 and 0·86, respectively) in the diets. Diet MS resulted in the lowest cumulative energy demand and in the highest acidification potential per kg of body weight gain (BWG). Eutrophication potential per kg of BWG was highest for diet C and the lowest for diet H. The relative contribution of eutrophication and acidification impacts by feeds and manure varied according to diet. The system using a hay-based diet resulted in the highest land occupation per kg of BWG and in the lowest impact per ha of land occupied for all impacts. It was found that the use of LCA, involving a multi-criteria assessment allowing the expression of results according to several functional units (kg of BWG and ha of land occupied) is essential to analyse the effectiveness of a pollution reduction strategy.

/pdf/life-cycle-assessment-of-three-bull-fattening-systems-effect-1o0hqmpl81.pdf

Michel Doreau

Papers

Production de méthane et interaccions microbiennes dans le rumen

Effets de l'addition de matières grasses non protégées à la ration de la vache laitière sur la concentration et la composition chimique des bactéries et des protozoaires du rumen

Effect of quality of hay given to mares around foaling on their voluntary intake and foal growth.

Evolution des activités alimentaires des vaches laitières en début de lactation et liaison avec les quantités d'aliments ingérées

Life cycle assessment of three bull-fattening systems: effect of impact categories on ranking