Animal Science Abstract
The nutritive value of five pasture species occurring in the summer grazing ranges of the Pyrenees
A. Marinas1, R. García-González1 and M. Fondevila2,A
ACorresponding author. E-mail: mfonde@posta.unizar.es
1Instituto Pirenaico de Ecología, CSIC, Apartado 64, 22700 Jaca, Huesca, Spain2Departamento de Producción Animal y Ciencia de los Alimentos, Universidad de Zaragoza, Miguel Servet 177, 50013 Zaragoza, Spain
Abstract
Five species of alpine pasture plants from the Pyrenees representing 3 botanical groups : grasses (Festuca eskia, Nardus stricta), forbs (Anthyllis vulneraria, Galium verum) and shrubs (Echinospartum horridum), were collected monthly from June to September and analysed for nitrogen (N) content, cell wall composition, in vitro enzymatic digestibility (DMDe) and volume of gas produced by microbial fermentation. Among the dicotyledenous varieties, A. vulneraria and G. verum showed the highest nutritive value whilst that of E. horridum was low due to high lignin content. Grasses showed moderate nutritive values in June rapidly decreasing thereafter. Nitrogen content and organic matter digestibility (OMDg) of A. vulneraria remained relatively constant through the sampling period whereas it abruptly decreased for remaining species from July. Gas production significantly differed among species during the first 48 h of microbial fermentation but not at later stages of fermentation. Collection date did not affect gas production before 24 h of incubation but significant differences were found thereafter with samples from June and July being more degraded than from August and September. Principal component analysis associated OMDg positively with N content and gas production and negatively with fibre content. Lignin proportion did not significantly correlate with gas production or with OMDg, suggesting that the degree of lignification is not the only factor affecting microbial fermentation but other factors such as lignin tissue locations may be involved. A. vulneraria has been revealed as very good forage with a high potential in extensive animal production systems. Both OMDg and DMDe methods seem more accurate than chemical analyses for evaluating forages at different stages of maturity.
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