Contradictory results has been found on the effects of soybean supplementation and conjugated linoleic acid (CLA) content in milk on feeding systems based on fresh forage The objective of the study was to evaluate the effect of a dietary supplement with different quantities of extruded whole soybean on the production and composition of milk, and CLA concentration or their isomers in Jersey cows under pasture conditions. Twenty-one Jersey cows were randomly assigned into 3 groups of 7 animals each. The cows were supplemented with a dietary concentrate (5 kg d -1 ), and each group received one of the three next treatments: control without soybean (0-SB), with extruded whole soybean at 0.5 kg d -1 (0.5-SB) or at 1 kg d -1 (1-SB). The basic diet was a pasture composed of Lolium perenne (70%), Trifolium repens (25%) and other species. The duration of the study was 75 d. Milk production (p = 0.706) and protein production (p = 0.926) were not affected by treatments. Fat (p = 0.015) and protein (p = 0.045) content as well as fat production (p = 0.010) were lower in the 1-SB group. There was no effect of the inclusion of extruded soybean on total CLA content (p = 0.290) or the content of cis-9, trans-11 (p = 0.582), trans-10, cis-12 (p = 0.136) and cis-10, cis-12 (p = 0.288) isomers. However, concentrations of all isomers were affected by the nutritional quality of the pasture, with low values observed at greater maturity stages of pasture.Additional key words: CLA; dairy cows; grazing; milk quality. ResumenEfecto de la suplementación con concentrado de soja entera extrusionada en vacas Jersey en pastoreo sobre el contenido de ácido linoléico conjugado en la leche El efecto de la suplementación con soja en sistemas de pastoreo sobre el contenido de ácido linoléico conjugado (CLA) en leche es contradictorio. El objetivo de este estudio fue evaluar en vacas Jersey en pastoreo, el efecto de la suplementación de un concentrado con diferentes cantidades de soja entera extrusionada sobre la producción de leche y su composición, especialmente sobre el contenido en CLA y sus isómeros. 21 vacas Jersey fueron divididas al azar en 3 grupos de 7 animales cada uno. Los animales fueron suplementados con un concentrado (5 kg d -1 ) y a cada grupo se le asignó uno de los tres siguientes tratamientos: control sin soja (0-SB), con 0.5 kg d -1 de soja (0.5-SB) y con 1 kg d -1 de soja (1-SB). La base de la alimentación fue el pasto, compuesto mayoritariamente por Lolium perenne (70%) y Trifolium repens (25%). La duración del estudio fue de 75 días. La producción de leche (p = 0.706) y la producción de proteína (p = 0.926) no se vieron afectados. Los porcentajes de grasa (p = 0.015) y proteína (p = 0.045) y la producción de grasa (p = 0.010) fueron más bajos en el grupo 1-SB. Las cantidades de soja no modificaron los contenidos de CLA total (p = 0.290) y de los isómeros cis-9, trans-11 (p = 0.582), trans-10, cis-12 (p = 0.136) y cis-10, cis-12 (p = 0.288), pero si fueron afectados por la calidad nutritiva del pasto, observándose meno...

The distribution of conjugated linoleic acid (CLA) in dairy products commercially available in Chile is poorly understood. This study aimed to assess the content of CLA in dairy cow products from Chile and the effect of processing fresh milk into dairy products. Samples of raw milk were categorized into two groups based on the animal feeding system utilized by the dairy farm: 1) grazing based systems (Los Lagos region); and 2) housing systems using total mixed ration (TMR) diets (Los Angeles region). Simultaneously, commercial samples of condensed milk, powdered milk, butter and Gouda cheese were analyzed. Furthermore, samples of raw milk and processed products (powdered and sweetened condensed milk) were also analyzed. Dairy farms based on grazing systems had higher levels of CLA in raw milk than TMR farms. In addition, average values of CLA were 1.72 g 100 g −1 of total fatty acids, in spring milk in the Los Lagos region, and 0.42 g 100 g −1 in summer milk, in the Los Angeles region. Similarly, the CLA content of dairy products was higher than that of raw milk. Milk processing affected the transferring of CLA from fresh milk into the final products. Sweetened condensed milk presented lower CLA values than raw and powdered milk. In conclusion, this study indicates the importance of the production systems to the CLA content as well as the effects of milk processing into dairy products. To sum up, more research is needed to elucidate the exact effect of the processing conditions of dairy products on the CLA content.

INTRODUCCIÓN El ácido linoleico conjugado (ALC) se ha reportado como el ácido graso más benéfico para la salud humana (1). De los 20 a 28 posibles isómeros posicionales y geométricos del ALC solo cis-9, trans-11 y trans-10, cis-12 han sido reportados con actividad biológica en el ser humano (2). El isómero cis-9, trans-11 (C18:2) ó ácido octadecadienóico, es el producto intermedio de la biohidrogenación ruminal del ácido linoleico por acción de la bacteria Butyrivibrio fibrisolvens). Este isómero también puede ser sintetizado en los tejidos de la glándula mamaria por la enzima Δ-9 desaturasa a partir de ácido vaccénico (TVA-trans-11 C18:1), otro intermediario en la biohidrogenación ruminal del ácido linoleico y α-linolénico (cis-9, cis-12, cis-15 C18:3) (3). La Δ-9 desaturasa también se encuentra en el intestino delgado y tejido adiposo de los rumiantes y humanos (4), sugiriendo que podría ocurrir síntesis endógena en estos tejidos. El isómero cis-9, trans-11 es considerado desde el punto de vista biológico como el más importante por sus efectos anticancerígenos en modelos de tejido en ratas y en humanos (5). El isómero cis-9, trans-11

At present, there is limited and contradictory information about the effects of the use of canola (Brassica napus) seed as supplement on the contents of conjugated linoleic acid (CLA) in milk of grazing cows. The objective of this study was to evaluate the effect of a dietary supplement with canola seed on the production and composition of milk, and CLA concentration in Chilean Black Friesian cows under pasture conditions. Three experiments were done. Experiment 1: control group was fed 5 kg d -1 of commercial concentrate without canola (0-TC1) and treatment group that was fed 3.75 kg of commercial concentrate plus 1.16 kg of whole canola seed (1.16-TC1). Experiment 2: Control group was fed 8 kg d -1 commercial concentrate without canola (0-TC2) and treatment group that was fed 6.2 kg of commercial concentrate plus 1.2 kg of ground canola seed (1.2-TC2). Experiment 3: control group was fed 6 kg d -1 commercial concentrate without canola (0-TC3) and treatment group was fed 6 kg of commercial concentrate with 20% of whole canola seed (1.2 kg d -1 , 1.2-TC3). The duration of each experiment was 60 days. No differences in milk production and quality were observed among the experimental groups in every assay. The CLA isomers trans-10, cis-12 and cis-10, cis-12 were higher than those normally found in the scientific literature. There was no effect of the inclusion of canola seed on total CLA content or the content of cis-9, trans-11, trans-10, cis-12 and cis-10, cis-12 isomers.