A spatio-temporal analysis of forage availability and grazing and excretion behaviour of herded and free grazing cattle, sheep and goats in Western Niger

Abstract

Grazing itineraries of herded and free grazing cattle (n = 194), goats (n = 148), and sheep (n = 129) were monitored in a village territory over a 1-year cycle by direct observation of grazing and excretion behaviour and by parallel animal tracking using a Global Positioning System. During the study period, standing and litter biomass of spontaneous vegetation and crop residues was measured repeatedly on sample plots of fields (n = 16), fallows (n = 15) and rangeland (n = 8). Based on a land use map, a Geographic Information System on forage availability was produced for the territory and overlaid with the livestock grazing itineraries. The animals' behaviour at pasture was related to the forage mass encountered along their daily itineraries in order to analyse the spatial variation in behaviour as influenced by season, livestock species and herd management mode. Maximum daily itinerary lengths were 25 km in cattle, 20 km in goats and 21 km in sheep; itinerary length varied significantly between species, herd management modes and season. Animals spent between 456 and 625 min per day on pasture, the grazing day of cattle being longer than that of sheep and goats. Across seasons, all three species spent on average about 60% of the daily grazing time feeding, 20-26% walking and 12-20% resting. The forage mass encountered along the animals' itineraries was higher than the average amount of forage available in the area. Particularly during the late dry and the rainy season, herding increased the amount of forage on offer to grazing livestock. Throughout the year, 39% of the observed excretions occurred on cropland, 31% on rangeland, 20% on fallows and 10% in and around settlements; the spatial repartition of excreta deposits differed between herded and free grazing animals, with free grazing animals depositing a higher share of excretions on barren land. The obtained information on the variation of grazing and excretion behaviour with respect to ruminant species, land use type, forage supply, season and herd management can be coupled with quantitative data on feed intake and excreta deposition, in order to compute livestock-mediated nutrient budgets for Sahelian agro-pastoral land use systems.