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The objective of this study is to characterize purebred Arab mares' milk through monitoring its physicochemical and microbiological composition during different lactation stages and to test its ability to coagulate. Sixteen purebred Arabian mares were selected among 45 mares with approximately the same foaling dates. Milk samples were collected once a week for each mare during 4 months of lactation and analysed in three replicates for physicochemical composition, nitrogen fractions, somatic cell count and total bacterial count. Coagulation assays were carried out in triplicates on fresh mare's milk using increasing doses of calf rennet, starter (Streptococcus thermophilus) and CaCl 2 . Arab mare's milk is characterized by an alkaline pH, low-fat and protein contents and high lactose content. The somatic cell and bacterial counts are very low, indicating good health status of mares. Fat and protein contents decreased as the stage of lactation progressed. However, as lactation number increased, fat level tended to increase while protein level tended to decrease. Clotting assays proved that it is possible to coagulate Arabian mare's milk using appropriate doses of calf rennet and starter, while respecting the coagulation procedures and parameters.

Food security issue is getting more attention in middle-income countries such as Tunisia after the revolution 2011, where many factors affecting its food security are multiplied. An econometric analysis of food security was done through the Vector Error Correction Model approach (VECM). The result of this approach shows that there is a significant long-term causality between the dependent variables and the explanatory variables. Some signs of variables like land under cereals assert the hypothesis of Ricardo’s land rent theory and also attract attention for the preservation of land fertility in climate change context. However, there is a short-term causal relationship between food security and independents variables like: land under cereals, inflation and food imports. These results confirm that the issue of food security in Tunisia is a question of threat in the short and long-term instability. So, it is important today to readjust some factors to ensure food security in Tunisia like controlling inflation and lowering the food importation as short-term measures and preserving and improving the fertility of land under cereals and adopting climate change as long-term measures.

Recent studies on agricultural water management in Tunisia report low water productivity for some of the currently widely cultivated crops such as durum wheat. The objective of this study is to estimate water productivity and marginal value of irrigation of durum wheat in central Tunisia. We develop a production function, in which the durum wheat irrigation revenue of farmers per hectare is expressed in terms of the used water volume in addition to other production factors. The function was estimated for a sample of durum wheat farms from Central Tunisia. Results show that 31.7% of the farmers were applying water volumes above the economic optimal volume (more than 2700 m 3 /ha). Moreover, 50% of the farmers were found to be applying less irrigation water than this optimal volume. Applying water above the optimal volume means that the benefit farmers obtain from each supplementary unit of irrigation water is lower than the market price of irrigation water currently applied in the region (0.110 TND/m 3 ). Then, water is wasted. However, using less water than the optimal volume means that farmers can make further supplementary irrigations and obtain more benefit from it (extra-yield). The study also shows that most of the farmers in the study area do not apply good practices with respect to irrigation scheduling and irrigation doses. Improving irrigation performance will largely preserve water resources and enhance food security in Tunisia.

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