This study investigates the effect on performance, carcass and meat characteristics of increasing the forage level in the diet of fattening Tudanca young bulls using silage as the forage source as compared with a conventional ad libitum straw plus concentrate diet. Twenty two Tudanca young bulls were assigned to three different finishing diets: ad libitum grass silage plus ad libitum concentrate (GS-AC), ad libitum grass silage plus concentrate limited to a half of the intake of the ad libitum group (GS-LC), ad libitum barley straw plus ad libitum concentrate (Str-AC) and then slaughtered at around 11 months of age. GS-LC diet resulted in relation to GS-AC and Str-AC diets in lower (p≤0.05) average daily weight gain (750 vs 1,059 and 991 g/animal/day, respectively), lower (p≤0.05) carcass weight (133 vs 159 and 152 kg, respectively) and carcasses with slightly lower conformation scores. Although GS-LC diet allowed for a lower dependence on concentrate (372 vs 657 and 729 kg/animal, respectively), economic margin was similar for the two GS groups (-63.1 and -64.1 vs -91.8 €/head). The polyunsaturated/saturated fatty acid ratio was the lowest (p≤0.05) in GS-AC meat (the group showing the highest IMF levels) and the ratio n-6/n-3 was the highest (p≤0.05) in Str-AC meat. GS-LC meat showed higher collagen content and Str-AC meat presented higher cohesiveness, springiness and chewiness values. Results suggested that the substitution of straw by grass silage and the restriction of the concentrate level could be recommended for finishing young Tudanca bulls in indoors systems.

The aim of this work was to establish homogenous groups of cattle farms in the mountains of León, Spain, using the variables selected in a sister paper (this issue). Principal components analysis (PCA) was used to characterise and compare the different farms studied. Two classifications were established, the first taking into account the first seven axes selected by PCA, and the second by taking into account only the first two. A comparison of these systems led to the latter being selected. The final classification system involves eight groups based mainly on the orientation of production, size, productivity per breeding cow, and productivity per work unit.

This paper reports the f irst stage in the establishment of a farm classif ication system: the identif ication of classification variables. The aim of this work was to identify the variables most appropriate for characterising the cattle farms of the mountains of León, Spain, using multivariate and principal components analysis. The information used was obtained by surveying the cattle farms of the Montaña de Riaño (León) area from 1996-1998. The 35 variables taken into account in the principal components analysis refer to labour, the stock base, production, land use and farm economy. Seven principal components were found to explain 67.1% of the total variance.

ResumenSe estudió el efecto de dos sistemas productivos (semi-extensivo: pasto y concentrado en cantidad limitada o intensivo: paja y concentrado ad libitum) y dos edades de sacrificio (12 o 14 meses) (lotes 12SE, 14SE, 12IN y 14IN) sobre los parámetros productivos y la calidad de la canal de 33 teneros de raza Tudanca destetados con 5 meses. El consumo de concentrado desde el destete hasta el sacrificio fue de 368, 494, 1.198 y 1.493 kg MS/animal, respectivamente. El sistema productivo con concentrado ad libitum tuvo un efecto positivo sobre el peso vivo al sacrificio, el rendimiento y el peso de la canal. Estos parámetros también se vieron positivamente afectados por el incremento en la edad de sacrificio de forma que no se observaron diferencias entre los lotes 14SE y 12IN. El engrasamiento de la canal del lote 12SE fue inferior a los otros tres lotes, entre los cuales no hubo diferencias. El porcentaje de grasa diseccionable de la 6ª costilla y de grasa intramuscular fue superior en el sistema intensivo y no se vio afectado por la edad de sacrificio. El peso de la grasa perirrenal fue superior en los animales del sistema intensivo y se incrementó con la edad de sacrificio. Los animales del sistema semi-extensivo presentaron mayor eficiencia de utilización de la energía. Sólo se obtuvo un margen económico positivo en el sistema semi-extensivo (161 €/cabeza). Mientras que este margen aumentó con la edad de sacrificio en el sistema semi-extensivo, disminuyó en el intensivo.Palabras clave: Raza rústica, producción en pastoreo, crecimiento, engrasamiento, eficiencia productiva. Abstract Production system and slaughter age effects on performance, carcass quality and profit margin of the production of calves and yearlings from Tudanca breedThe effect of two production systems (semi-extensive: grass feeding and concentrate in a restricted quantity or intensive: cereal straw and ad libitum concentrate) and two slaughter ages (12 or 14 months) (12SE, 14SE, 12IN and 14IN lots) on performance, carcass quality and profit margin of 33 Tudanca calves weaned at 5 months of age were studied. Concentrate intake from weaning to slaughter was 368, 494, 1,198 and 1,493 kg DM/animal, respectively. Feeding with ad libitum concentrate and straw had a pos-

La finalidad del acabado de vacas de desecho de los rebaños lecheros es incrementar el peso de la canal y el engrasamiento. El incremento de peso debido al músculo es relativamente constante y la mayoría del incremento de peso conseguido a partir de los 30 días de acabado se debe a la deposición de grasa. El ritmo de ganancia de peso y la eficiencia de conversión del alimento disminuyen con el tiempo de acabado y su evolución depende de la raza, la edad y el estado inicial de condición corporal. Entre los factores que condicionan los resultados productivos y la calidad de