Seasons, herd mobility and management drive feed intake and digestibility in grazing cattle in West African landscapes

Habibou Mohamed Assouma^1*Philippe LECOMTE²Pierre Hiernaux³Alexandre Ickowicz²Virginie Decruyenaere⁴Mélanie Blanchard²Coly WADE⁵Bérénice Bois²Christian Corniaux²Françoise Guichard⁶Jonathan Vayssières²

• ¹Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Institut National de la Recherche Agronomique (INRA), Montpellier, France
• ²CIRAD Departement Environnements et Societes, Montpellier, France
• ³pastoc, Caylus, France
• ⁴Centre wallon de Recherches agronomiques, Gembloux, Belgium
• ⁵ISRA-LNERV, DAKAR, Senegal
• ⁶Meteo France, Saint-Mandé, France

Estimating the daily diet of grazing cattle from available feed resources in pastoral and mixed crop-livestock systems in tropical West Africa remains a challenge. The objective of this study was to describe the relevance of cattle diet monitoring across the seasons to better assess the livestock-resources interactions in its local environment in the region. We analyzed seasonal profiles of the diet of grazing cattle in five sites distributed along the Sudano-Sahelian climate gradient from an arid to a sub-humid bioclimate. In the five sites (ranked from the driest to the wettest: Widou, Dahra, Niakhar, Koumbia, Kolda), the feeding behavior of grazing cattle was monitored and feces were collected monthly for one year to estimate dietary intake and digestibility. All the conserved dry samples (n = 1,186) underwent near infrared spectroscopy (NIRS) analyses. The resulting spectral data were compared with a large set of spectral reference data (n=4,138) to predict dry matter intake (DMvi_Fnir DM; g.kgMW-1) and digestibility (dMO_Fnir,%OM) using an updated NIRS "local calibration" procedure. Daily fodder intake ranged from 38.90±6.35 in the hot dry season to 83.86±8.73 gDM.kgMW-1.d-1 in the late wet season. Estimated diet organic matter digestibility ranged from 53.6±8.51% in the hot dry season to 74.3±3.52% in the early wet season. Estimated by aggregation, the total annual intake of a tropical livestock unit (TLU, i.e. a standard 250 kg live weight animal) ranged from 1,236 ± 255 kgDM.TLU-1.year-1 in Dahra to 1,560±142 kgDM.TLU-1.year-1 in Widou. This was well below the 2,281 Kg.DM annual estimate derived from a standard intake of 2.5% LW in DM. Taking digestibility into account, the summed annual metabolizable energy (ME) intake values ranged from 9,858 ± 2,077 Mj.TLU-1.year-1 in Dahra to 13,929 ± 2,345 Mj.TLU-1.year-1 in Koumbia. While important gaps appear during the dry season in some locations, this covered the annual basal maintenance requirements of a TLU, which, based on international standards, are estimated at 7,819 Mj.TLU-1.year-1 (21.4 Mj.day-1). This leaves ME at varying extend, to cover the needs for growth, milk production and reproduction.