Final report on stream sediment, soil and forage chemistry as indicators of cattle mineral status in north-east Zimbabwe

Undernutrition is probably the main cause of low production and reproduction rata amongst grazing livestock in many developing countries, however, mineral deficiencies and imbalances in forages undoubtedly also have a negative effect Mineral deficiencies and excesses have been reported from most regions of the world, but the problem appears to be particularly severe in the tropics. For grazing livestock, deficiencies of CO, Cu, I, Fe, Mn, Se and Zn together with excesses of Cu, F, Mn and MO have been recognised as detrimental to health. As farming systems in developing countries progress and farmers are encouraged to seek higher levels of productivity from forage fed livestock, it will become increasingly important to correct for mineral deficiencies or imbalances in forage. Once the more limiting energy and protein deficiencies have been rectified, any method of identifying those areas particularly susceptible to mineral deficiencies will be of considerable value as it will permit the design and implementation of effective supplementation programmes which will lead to even higher levels of productivity. Clinical, pathological, biochemical, soil, water, plant, animal tissue and animal fluid analyses have all been used to diagnose trace element deficiencies and excesses in animals. Apart from some notable exceptions such as goitre resulting from iodine deficiency and dental mottling and skeletal deformities associated with excess fluoride, few deficiency or toxicity syndromes induced by anomalous intakes of trace elements are distinguished by specific clinical symptoms. Diagnosis of sub-clinical cases is complicated by the fact that many of the symptoms of mild and transient mineral imbalances, such as unthriftiness, subnormal growth and reproduction, may also be caused by energy and protein deficiencies and the effects of parasites. Diagnosis of sub-clinical cases must rely on chemical and biological analyses. Screening large numbers of animals for evidence of mineral deficiency without first recognising which areas to target, would be an expensive and laborious process and would probably be subject to variations due to season, climate and physiological status of the animal at the time of sampling. Soil and forage analyses have been used by previous workers in tropical regions to identify mineral deficiencies and toxicities in grazing livestock However, in many cases results tend to be equivocal and have to be interpreted with caution because of local variations in soil chemistry; uncertainties regarding the significance of extractable mineral concentrations in soils and variations in mineral concentrations between forage plant species and with forage maturity.