Valor nutritivo de las principales comunidades de pastos de los puertos de Góriz (Pirineo Central)

Resumen

Pyrenean summer pastures are an important feeding resource for extensive livestock production; however information on its nutritive valué is scarce. Chemical composition of seven types of pastures, quantitatively important in Central Pyrenees, their temporal variation and their capability to meet livestock nutritional requirements were measured. The influence of necromass (standing dead matter) and other structural components (proportion of graminoids and forbs) on chemical composition were also studied. At the beginning of each month, from June to September, samples were taken at random in ungrazed plots oíBromion erecti (BE), Nardion strictae (NS), Primulion intricatae (PI), Festucion gautieri (FG), Saponarienion caespitosae (SP), Festucion eskiae (FE) and Bromion-Nardion (BN) pasture communities. Contents of NDF, ADF, lignin, crude protein (CP), P, K, Mg and K were determined in laboratory. Potential digestibility (PD) and metabolizable energy (ME) were estimated from equations. On average, Primulion intricatae and Nardion strictae have the highest CP valúes but their PD and ME are the lowest. The lowest valúes for PB were obtained in Festucion gautieri and F. eskiae and the highest ME in Saponarienion caespitosae and Bromion erecti. PD and ME average valúes remain relatively constant during the vegetative period; however, CP and P content show a máximum at the beginning of summer, declining rapidly later. The proportion of forbs associates positively with an increase in P, K and PD content, and negatively with NDF. Necromass proportion is negatively correlated to K content and positively to NDF. Green/dead matter ratio correlates positively with PD content when its valué is lower than 2. The studied communities would meet cows and sheep PB, Ca and K requirements and only partially Mg, P and ME requirements. Mesophylous communities, as BE and PI, have higher nutritive valué than acidophylous communities, as NS and FE, coinciding with what was described earlier by other authors in the Pyrenean Range.