José Luis Repetto

Anaerobic Metabolism of the Agro-Pesticide Nitroxinil by Bovine Ruminal Fluid

Metabolism of three different agro-pesticides widely used in Uruguay, the insecticides imidacloprid and thiamethoxam and the antiparasite nitroxinil, by bovine ruminal fluid, as supply of anaerobic microorganims, was studied. Complete ruminal fluid was incubated with each of the agrochemicals in different conditions, varying time, nutrients, and nitroethane supplementation as methanogenesis modificator. Only biotransformation was detected for nitroxinil in some of the studied variables. In the optimized condition only one product was generated and the chemical structure of this main metabolite was elucidated using combined spectroscopies evidencing a structural motive unrelated with the products of the corresponding mammal biotransformation results of reduction, and substitution processes. The ruminal generation of the metabolite was confirmed. In order to employ this anaerobic microbial system as potential bioremediator of agrochemical-contaminated soils, the toxicity, against mammal cells, and the mutagenicity, using Ames test, of the product of biotransformation were studied. The lack of toxic effects encouraged us to propose the ruminal system as a plausible system for agrochemicals bioremediation.

Behaviour of cows fed a total mixed ration with different access time to fresh forage

ABSTRACT Nine lactating cows fed a total mixed ration (TMR) were assigned to three 3 × 3 Latin squares with 20-day periods to evaluate the effects of access time to fresh forage (FF) on behaviour and dry matter intake rate (DMIR). Forage (Lolium multiflorum) was cut daily and individually offered from 0800 h for 0 (T0), 4 (T4) or 8 (T8) hours of daily access, and a TMR was offered during the remaining time. Treatments had no effect on the average proportion of time spent eating or ruminating. However, the distribution of behaviours across time was different among treatments, with T4 and T8 cows spending a high proportion of the available time eating and achieving a high DMIR only when they had access to TMR. Additional research is warranted to identify strategies that increase the DMIR of TMR-fed cows when FF is progressively included in their diet.

Anaerobic Biotransformation ofN-oxide Containing Aromatic Heterocycles by Bovine Ruminal Fluid

Microorganisms of bovine rumen fluid have been studied as biocatalysts for the reduction of different N-oxide containing aromatic heterocycles, i .e. quinoxaline N 1 ,N 4 -dioxide, phenazine N 5 ,N 10 -dioxide, indazole N 1 -oxide, benzofuroxan and furoxan. In anaerobiosis, the microorganisms biocatalyzed the reduction of some N-oxides, quinoxaline and phenazine dioxides, to yield the corresponding heterocycle while in the case of benzofuroxans the heterocycle-opening, o-nitroaniline was generated as the unique product. Contrarily, the furoxan was not biotransformed in the studied conditions. The indazole N 1 oxide was biotransformed very slowly and incompletely in the corresponding indazole. Only one of the studied indazole N 1 -oxide derivative was completely converted to a new compound, different to the expected reduced indazole. For that, a semi-preparative scale biotransformation was performed and the new product was spectroscopically identified.