Dry matter production of plant communities and goat selection during dry season in rangelands of the northeastern Mendoza, Argentina

FUCILI, M.; PAEZ, S.A.; EGEA, A.V.; SALVA, J.S.; GUEVARA, J.C.,; ALLEGRETTI, L.I.

Gan Canaria

Conferencia; XI International Conference on Goats; 2012

To evaluate the relationships between productivity of plant communities and goat selection during the dry season (winter), seven females of a free-ranging Creole goats herd (n = 150) were fitted with GPS collars to record the grazing itineraries. Plant communities were determined by an unsupervised classification of a Landsat-5 satellite image and subsequent field corroboration. The positions corresponding to grazing were overlaid on the classified image to calculate the selection index (SI): ratio between the proportion of grazing positions within a plant community and the proportional area of that plan community. In 13 sites, the available dry matter production (DM) of the main forage species was estimated by the closest individual method. The record of height, average diameter and distance of the nearest individual along linear transects, allowed to determinate plant density of woody species and estimated the forage phytovolume by referring each plant to the ideal volume of a cylinder. Available production was harvested from 10 plants per species to determinate the relationship between phytovolume and DM production by linear regression. An ANOVA procedure was used to analyze differences in the DM production and in the SI. The relationship between DM production and SI was determined by linear regression. We identified 4 different plant communities: semi-closed woodlands of Prosopis flexuosa (Algarrobal), open woodlands of Prosopis flexuosa with Tricomaria usillo and Atriplex lampa (Algarrobal abierto), open woodlands of Tricomaria usillo (Usillar) and shrublands of Larrea divaricata (Jarillal). The DM production (kg ha-1) of Algarrobal abierto (363.25) was higher (P < 0.05) than that of Algarrobal (175.29), Usillar (172.50), and Jarillal (130.49). The SI of Jarillal (0.56) and Algarrobal (0.68) were lower (P < 0.005) than those of Algarrobal abierto (1.33) and Usillar (1.33). There was a positive relationship (r=56 P < 0.0001) between the SI and DM production. The DM production of the most selected communities had a great contribution of species that had been determined as preferred by goats in previous studies: 22% P. flexuosa, 22% A. lampa and 18% T. usillo in Algarrobal abierto and 50% T. usillo in Usillar. Concluding, during the dry season, the DM production could be considered one of the factors influencing the grazing behavior of goats that selected mainly the plant communities that offer greater amount of available forage, especially of preferred species.