Preliminary data on nutritional value of abundant species in supraforestal Pyrenean pastures

Abstract

The alpine pastures of the Pyrenees have been used as summer ranges for centuries and continue to be an important forage resource for livestock husbandry to this day. Some studies attribute high nutritional values to alpine pas- tures, but recent surveys have revealed weight-loss in animals summering in Pyrenean pastures. There is virtually no information available with regard to the nutritional value of the species which constitute Pyrenean summer pastures. Twenty-three of the most common species were analysed chemically to determine their nutritional value and their capacity to meet livestock requirements. Monthly samplings of uneaten plants were performed from June to September in plots where species were abundant. These samples were analysed to determine neutral detergent fiber (NDF), lignin (ADL), crude protein (CP), P, K and Mg content. In vitro dry matter digestibility (IVDMD) was calculated using the pepsin-cellulase method and metabolizable energy (ME) was estimated from it. On average, graminoids presen- ted higher levels of NDF and lower levels of the other nutrients when compared with forbs. Month effect was significant for ADL, CP, P and K. In these cases June was the month which differed significantly from other months. Crude protein, P and K contents diminished with maturity, whereas ADL and Ca levels increased. NDF, IVDMD and Mg values remained fairly constant throughout the summer in both botanical groups. This fact is noteworthy because it may provide a constant supply of ME for herbivores during the grazing period (July to September). Dicotyledoneous forbs meet livestock requirements of all the nutrients analysed except P during the grazing period. Graminoids are deficient in ME (mainly for sheep), P and Mg, and their CP content is slightly low for the requirements of sheep. When cattle and sheep diets are based mainly on graminoids, they could suffer a nutritional deficit in alpine Pyrenean pastures.