Money and credit are ubiquitous in actual economies, but there is an active theoretical debate on whether they are both necessary if they can both be used in all transactions. Recently, Gu et al. (2016) have shown that money and credit cannot be simultaneously essential and debt limits do not matter for the determination of real allocations in a class of monetary economies. In this paper, we revisit their irrelevance result in a monetary economy based on Lagos and Wright (2005), which exhibits a misallocation of liquidity that is common in search models of money. We show that monetary loans, which naturally require the use of both money and credit, implement Pareto superior allocations in which the size of debt limits matters.

Arsenic (As) is highly toxic element, even at very low concentrations in feed and drinking water. Its physiological role in poultry is well established, as it is essential for the synthesis of methionine metabolites including cysteine, even though it is a teratogenic and carcinogenic element. Paradoxically, recent studies have uncovered its nutritional value. The recommended amounts of As in poultry feed are between 0.012 and 0.050 mg/kg. Water is the primary route for the transfer of As and exposure of animals to its toxic effects. The available data on the impact of water contamination on the deposition of As in broiler tissues are rather scarce. The amount of As was 0.006-0.015 mg/kg in breast meat, 0.007-0.017 mg/kg in drumstick meat, 0.001-0.014 mg/kg in liver and 0.008-0.016 mg/kg in testicles of broilers at the end of a 42 day experiment after exposure to naturally contaminated drinking water. The toxic dose of As for poultry is between 40 and 50 mg/kg of poultry feed whereas the amount of 40 mg/kg leads to decreased egg production and the amount of 50 mg/kg leads to decreased feed consumption. Symptoms of chronic As exposure differ among individuals, populations and geographic regions, which suggests that there is no universal definition of symptoms associated with chronic As poisoning. Moreover, some individuals can tolerate high As, that is, levels that can be fatal for others. In wild birds, the content of As was the highest in meat of march hens (0.063 mg/kg), seagull muscle tissue (0.058 mg/kg), in meat from swans (0.022 mg/kg) and the white-tailed eagle (0.022 mg/kg). In this review, the essential role and toxicity of As in poultry nutrition is addressed with particular emphasis on its importance as a contaminant of poultry feed and products.

We propose a model in which money performs an essential role in the process of exchange, despite the presence of a multilateral clearing house that collects resources from and distributes them to anonymous agents. Money improves the functioning of the clearing house, simultaneously keeping the incentives to contribute and guaranteeing the fine-tuning of allocations.

The levels of essential microelements in poultry feed must be high enough to satisfy the birds' requirements, yet low enough to ensure the safety of both animal feed and meat and eggs for human nutrition. The essential role of vanadium (V), chromium (Cr) and nickel (Ni) in poultry nutrition is still under investigation, while their toxicity was well established a long time ago. Even though some feeds might represent a potential source of harmful amounts of microelements, the combination of relevant quality control programs in the animal feed industry, as well as the application of good production practices and the adequate education of nutritionists can substantially reduce the risks associated with overfeeding such minerals. The aim of this review is to give an overview of the role, importance and needs of poultry for V, Cr and Ni.