Grazing patterns, energy extraction and livestock productivity in agro-pastoral production systems in Kibwezi, south-eastern Kenya
The primary energy pathways, energy intake, habitat exploitation patterns and feeding interaction of free ranging agropastoral herds (cattle, goats and sheep) in Kibwezi, a semiarid environment were investigated in two cycles of four consecutive grazing periods. The bites count and herd locations per area methods were used. The water balance and soil loss associated with key perennial grasses subjected to different levels of utilization were assessed using simulated rainfall. Using energy intake-digestibility constraint curves and a growth-consumption rate model, the optimal grass biomass at which energy intake and digestibility equilibrate were derived and the stability properties of the agropastoral system described, respectively. Also, the nature and extent of use of secondary land rights to access grazing resources and the factors affecting their application were analyzed by use of questionnaire and econometric techniques. These analyses aimed at contributing to enhanced livestock productivity in the agropastoral system. The animals exploited a wide array of plant species. Forage energy for cattle and sheep came primarily from herbaceous plants, while goats largely exploited woody plants. Enteropogon macrostachyus was the single largest energy pathway and accounted for over 30% of the total energy intake of cattle. The other important grass resources were Panicum maximum (9.9%) followed by Eragrostis superba (7.3%). Combretum exalatum and Duosperma kilimandscharica were the primary energy pathways that accounted for over 10% of total energy intake of goats with seasonal peaks of 18.5 and 17.2%, respectively. Sheep were largely mixed feeders, but Enteropogon macrostachyus (16.6%) and Blepharis integrifolia (10.3%) were the primary energy pathways. Energy constraint curves revealed that energy intake by cattle was optimized at 460,420,470 and 480 gm-2 of sward biomass, corresponding to 60.6, 64.3, 62 and 55.5 organic matter digestibility percentage for Enteropogon macrostachyus, Panicum maximum, Eragrostis superba and Chloris roxyburghiana, respectively. The animals had significantly different energy intake within and between seasons. All the animal species had a lower and higher energy intake in the dry and wet seasons, respectively. Energy intake more than doubled and tripled from the late dry to the late wet season, for sheep and goats, and cattle, respectively. All animal species recorded a negative energy balance only in the second late dry season. During this period, 100%, 100% and 67% of the cattle, sheep and goats in the ranch lost weight, respectively. While 50%, 67% and 33% of the cattle, sheep and goats in the agropastoral areas lost weight, respectively. Based on energy balance, goats maintained a superior position and thus were relatively hardier, followed by sheep and cattle. This was further evident given that 78%, 44% and 33% of the goats, sheep and cattle kidded, lambed and calved, respecti vel y. During the dry season, areas of concentrated drainage, river valleys, bottomlands and ephemeral drainage ways absorbed a greater feeding load, taking 57.1 to 60% of the grazing time by the animals. In contrast, areas of limited moisture concentration, the open sandy/clay plains, were mainly exploited in the wet season, and accounted for 52.6 to 55.6% of the grazing time. The trophic interaction patterns indicated that goats and cattle had a seasonal mean diet overlap index of less than 0.5 for all forage classes. Sheep and cattle, and sheep and goats had a seasonal mean diet overlap index of greater than 0.5 on grass and forbs, and browse and forbs, respectively. This suggested that during periods of resource scarcity, sheep and cattle or sheep and goats could become competitive feeders for same resources. Infiltration capacity for sites dominated by perennial grasses increased with increasing stubble height before levelling off towards the highest stubble height. A 50% removal of current growth was the upper limit above which runoffs and sediment loss from the grass stands increased rapidly. Aggregate stability, organic carbon and ground plant cover percentage were the most significant attributes that influenced infiltration capacity. Panicum maximum and Enteropogon macrostachyus stood out as the most suitable perennial grasses with favourable soil physical properties and infiltration capacity in the study area. From a growth-consumption rate model, a stocking rate of 7 TLUha-1 appears to be the upper limit in this agropastoral system, above which the system is destabilized during the growing period. Seventy percent of the households used secondary rights to secure pasture for their animals, particularly short term loans (64%) and exchange of bulls for ploughing (38%). Use of secondary land rights was positively and significantly influenced by increasing livestock per adult, smallstock to cow ratio, and small farm size per household. The amount of crop residue available and increasing grazing area per adult had a negative effect. Secondary rights gave households flexibility in dealing with pasture shortages during critical periods. Grazing management strategies that enhance a broadly stabilized energy extraction pattern and complementary trophic interactions, augmented by flexible secondary land rights, could be central to sustainable livestock production in such environments.