Nitrogen or Water Limitation to Grassland Growth during a Moderate Dry Season in the Humid Tropics

The aim of this work was to compare the effects of nitrogen and water shortage on grassland production during a moderate dry season in a tropical humid environment. The results of two experiments carried out in Guadeloupe (FWI) have shown that during dry spells, the reduction in growth of natural grasslands based on Angleton grass (Dichantium aristatum) is more easily corrected by nitrogen fertiliser application than by irrigation. This shows that it is not the availability of water, but that of nitrogen, which is limiting the primary production of Angleton grass, stands. This result is less clear for a pasture based on Pangola grass (Digitaria decumbens), a species introduced to improve forage production. Research experience in the field of water-plant-weather relations in a humid or sub-humid tropical environment cannot be extrapolated to animal production systems based on natural grasslands. The productivity of this forage resource is much more dependant on nitrogen availability, during periods of low rainfall or when water soil reserve is low

Effects of Fasting on Ingestive Behaviour of Sheep Grazing Grass or White Clover Monocultures

Effects of fasting sheep for 24 h (F), compared with controls (NF), on their ingestive behaviour and particle size in extrusa was investigated using oesophageally fistulated animals, grazing monocultures of Lolium perenne (G) or Trifolium repens (C). Bite masses tended to be lower on G than C and tended to increase with fasting (40, 64, 61 and 70 mg DM bite-1) for treatments GNF, GF, CNF and CF, respectively. Prehension rate was lower (52 vs. 69 bites min-1) and masticating rate was higher (106 vs.86 mastications min- 1) for G and C treatments, respectively. Over 24 h following fasting, NF animals grazed less (458 vs. 578 min 24 h-1) and ruminated less (276 vs. 348 min 24 h-1) than F animals. Particles in extrusa \u3c 0.18 mm were 48 vs. 55 %, for G and F, and 49 vs.54% for F and NF treatments

The importance of grasslands for animal production and other functions: a review on management and methodological progress in the tropics

The global importance of grasslands is indicated by their extent; they comprise some 26% of total land area and 80% of agriculturally productive land. The majority of grasslands are located in tropical developing countries where they are particularly important to the livelihoods of some one billion poor peoples. Grasslands clearly provide the feed base for grazing livestock and thus numerous high-quality foods, but such livestock also provide products such as fertilizer, transport, traction, fibre and leather. In addition, grasslands provide important services and roles including as water catchments, biodiversity reserves, for cultural and recreational needs, and potentially a carbon sink to alleviate greenhouse gas emissions. Inevitably, such functions may conflict with management for production of livestock products. Much of the increasing global demand for meat and milk, particularly from developing countries, will have to be supplied from grassland ecosystems, and this will provide difficult challenges. Increased production of meat and milk generally requires increased intake of metabolizable energy, and thus increased voluntary intake and/or digestibility of diets selected by grazing animals. These will require more widespread and effective application of improved management. Strategies to improve productivity include fertilizer application, grazing management, greater use of crop by-products, legumes and supplements and manipulation of stocking rate and herbage allowance. However, it is often difficult to predict the efficiency and cost-effectiveness of such strategies, particularly in tropical developing country production systems. Evaluation and on-going adjustment of grazing systems require appropriate and reliable assessment criteria, but these are often lacking. A number of emerging technologies may contribute to timely low-cost acquisition of quantitative information to better understand the soil-pasture-animal interactions and animal management in grassland systems. Development of remote imaging of vegetation, global positioning technology, improved diet markers, near IR spectroscopy and modelling provide improved tools for knowledge-based decisions on the productivity constraints of grazing animals. Individual electronic identification of animals offers opportunities for precision management on an individual animal basis for improved productivity. Improved outcomes in the form of livestock products, services and/or other outcomes from grasslands should be possible, but clearly a diversity of solutions are needed for the vast range of environments and social circumstances of global grasslands

SE 01. Critical analysis of grazing systems in antillean tropics

The Caribbean is characterised by limited rural zone, familial and mixed small farm units. Researchers and extension agents have promoted animal production improvement via forage intensification. It is based on technical choices frequently unadapted to the farming systems prevailing in the regions. Intensified grazing systems increase gastrointestinal parasitism impact, lead to herbage mass in excess and thus to bad management conditions and induce long term negative effects on the flimsy tropical ecosystem. A new research approach is proposed. It takes into account regional development objectives (needs for animal output improvement) as well as farmer’s circumstances (adapted technology transfer). Two experimental models are described in the French Antilles case: grazing systems with small ruminants and comparison of native and exogenous pastures. They are focused on the optimization of grazing systems, modelization of animal utilization and on gastrointestinal parasitism. Ecological impact and technical-economical results will be considered in these grazing systems