Trace element nutrition in the tropical zebu cattle type. Lessons from the Gilgel Gibe catchment, Ethiopia

Abstract

In the tropics, cattle are majorly dependent on natural pastures growing on poor soils and as a result prone to trace element deficiencies. This work investigated several aspects of trace element nutrition in zebu (Bos indicus) cattle, the most widely used cattle type in the tropics. Through several trials conducted at the Gilgel Gibe catchment, Ethiopia, we aimed to study factors influencing the flow of trace elements from soil to plant and grazing zebu cattle, and to investigate the impact of trace element status on health, production and trace elements in animal products. Overall, trace element, e.g., Cu, deficiencies were widely prevalent. Environment and certain grazing strategies were intimately related and affected trace element supply whereas cattle type affected trace element status. The effect of trace element status on trace elements in animal products was obvious, whereas the impact on health and production was less clear-cut. Key words: trace elements, minerals, cattle, zebu, Bos indicus, Ethiopia, tropics Introduction and objectivesThroughout the animal kingdom, a certain dietary supply of trace elements (e.g. copper (Cu), zinc (Zn), selenium (Se)) is known to be essential for optimal health (Bender, 2007). In the early days of trace element research in farm animals, numerous studies confirmed their importance for cattle, as supplementation of these elements alleviated elusive symptoms (e.g. claw malformations, muscle skin lesions, diarrhoea) and improved production (McDowell & Arthington, 2005). Following these trials, authors around the globe reported shortages in some trace elements as well as excess in others in natural pastures, indicating an omnipresent risk for trace element imbalance in grazing cattle (Abdelrahman et al., 1998;Mortimer et al., 1999; Govasmark et al., 2005a,b). Indeed, the 1 This is the report of PhD research carried out at Ghent University, under the supervision of prof. dr. ir. Geert Janssens.afrika focus -Volume 27, Nr. 1 [ 88 ] grazing cow is part of the trace element flow from soil to plant and animal and back, and the bovine trace element status is directly influenced by this flow, although many indirect factors are yet to be unravelled (Suttle, 2010). Furthermore, studies investigating the effects of trace element supply on body functions (e.g., immunity: Spears, 2000;Weiss & Spears, 2006;Spears & Weiss, 2008) as well as on production (Ward & Spears, 1997;Engle & Spears, 2000) often produce conflicting results. Additionally, few studies investigated the impact of trace element supply under practical farming conditions (Wichtel, 2003). Finally, the influence of the established trace element status in the animal (e.g deficient, optimal, in excess) on trace element concentrations in edible tissues and milk, is not well understood (Garcia-Vaquero et al., 2011;Rey-Crespo et al., 2013).In tropical areas, poor grasslands remain the primary bottleneck for optimal cattle production (McDowell & Arthington, 2005) and several environmental characteristics (e.g. parent material...