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Complex interactions between livestock, trees and pasture occur in silvopastoral systems. Between trees and pasture, competition for soil resources (nutrients and water) occurs, becoming especially relevant when one of them is in scarce supply. Trees reduce light and water reaching the understorey layers according to tree density and canopy size. However, they may ameliorate extreme climatological features (reducing wind speed and evapotranspiration, and alleviating extreme temperatures), and improve soil properties, for example, deciduous tree litter may contribute to increased pH and soil nutrient concentrations. During tree establishment, there are generally negligible effects on pasture, irrespective of tree type. However, there is a decline in pasture production and nutritive value under shade with increasing tree age and higher stand density. Under the same conditions, deciduous trees affect pasture later (extinction point of pasture occurs at 85% of canopy closure) than evergreen trees (about 67% for Pinus radiata D. Don). This is mainly because deciduous trees have a leafless period that enables pasture recovery, and their litter smothers pasture less intensely because of its relatively fast decomposition. Silvopastoral studies conducted in New Zealand are reviewed to discuss these effects, and differences in the effects of evergreen and deciduous trees are shown using the examples of P. radiata, and Populus and Salix spp. respectively, which exist in many temperate countries. Future research needs are outlined.

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Conjugated linoleic acid (c9, t11 CLA) is a dietary fatty acid produced mainly by ruminant animals and exhibits promising health-promoting biological effects. For lipid fatty acid composition analyses, including CLA, lipids must be pre-treated so that the free and esterified fatty acids (triacylglycerols, phospholipids, etc) are available for determination. The most common treatments involve fatty acid methyl ester derivatives from relatively simple chemical reactions, but this becomes complicated when esterification of CLA is involved because of potential changes in its positional and geometrical isomers by reaction with certain reagents. In this review we explain concisely the advantages and disadvantages of the most popular methods (acid-and base-catalysed methods) generally employed for total fatty acid derivatization and their determination on a gas chromatograph. Based on our experiences we put forward the (trimethylsilyl)diazomethane method as an alternative and successful approach for ruminant tissue lipid determinations.