Influencia de los diferentes sistemas de alimentación utilizados en las ganaderías de vacuno de Asturias sobre la producción y la composición de la leche

The traditional models of dairy cow systems in Asturias are based on the main forage crop culture, especially on maize due to its importance for dairy milk production. In the last decades, maize silage is the most used in the ration of dairy cow. However, the Asturian orography, characterized by an average slope upper to 20 per cent, there are areas where the maize crop cannot be cultivated. Furthermore the composition of cows diet varies throughout the year, because of the annual dynamic change of forage production and maize Italian ryegrass rotation. So, the crop area cannot always be associated with the ration. For this reason, the aim of this study was to identify the different feeding systems in dairy farms in Asturias. Also, the present study investigated the influence of theses feeding systems in milk production and composition, especially in fatty acid profiles. There were selected 16 dairy farms which were divided into four systems depending on the grazing situation and the percentage of area destined to maize culture. A survey was compiled four times in these farms for each season, since summer 2014 to spring 2015. The farmers were interviewed about production and feed offered to the cows in lactation, and feed and milk were sampled. The components of the ration were analyzed by cluster analysis to establish feeding systems. The results of milk composition were analyzed by ANOVA considering as main factors: feeding system, season and region. Additionally, these results were analyzed by principal components analysis, with the purpose to difference the feeding systems by milk composition. There were identified five feeding systems based in the ration composition: I) Grazing; II) aize silage; III) Grass silage; IV) Dry forage; and V) High concentrate. The results obtained show that the purchase of feedstuffs is associated with the percentage of fresh forage and maize silage. The purchase of forage off-farm was the lowest in system I and II. The maize silage system (II) was the highest in milk production and it spent less concentrate by kg of milk. Also, this system showed the highest proportions of protein, lactose, solids-non-fat in milk and urea. Besides, their fatty acid profiles were less unsaturated, with high proportions of fatty acids saturated and less amounts of stearic, vaccenic, oleic and alpha-linolenic acids. Fatty acid profiles of the systems identified as Grazing (I), Silage grass (III) and Dry forage (IV) were the highest proportion of unsaturated acids, such as, rumenic, vaccenic , oleic, alpha-linolenic and stearic acids.