2003; Jackson and Linsley, 2004; Jackson et al., 2006), and a variety of dsRNAs with no sequence similarity can silence the same genes (Semizarov et al., 2003).
       Once established, the effects of dsRNA may persist in some kinds of organisms, being transmitted to offspring. The instigating event is the initial combination of genetic elements with similar DNA sequences, but the silencing ef­fect may persist even in hybrids that retain a single copy of the gene.
       Furthermore, not all genes that are silenced remain so, nor are all plants grafted with tissues from silenced plants capable of acquiring the silenced phenotype. The science of infectious gene silencing is still young, leaving gaps in un­derstanding how the molecules are transmitted and main­tained, and in how the phenotype is regulated or reversed. If this or other epigenetic strategies for genetic modification are in time adopted, they must benefit from fundamentally new kinds of safety assessments in both their environmental and human health context. Importantly, these assessments should be conducted by competent researchers that are in­dependent of the developing industry.

6.3.2 Livestock breeding options
Technologies such as artificial insemination and embryo transfer, which are routine in industrialized countries have been successfully transferred and introduced in other parts of the world (Wieser et al., 2000). However, breeding tech­nologies are not exploited to the extent possible because animals are not adapted to local conditions, logistical prob­lems and poor support for breeding services and informa­tion management (Ahuja et al., 2000). There is scope to further develop conventional breeding technologies, in par­ticular through North-South cooperation. To be effective at meeting development goals breeding policies, programs and plans need to be location specific (Kurup, 2003; Chacko and Schneider, 2005).
       Thus far the impact of genomics in livestock agriculture is limited to the use of transgenic animals such as chick­ens and cattle to produce pharmaceutical or therapeutic proteins in eggs and milk (Gluck, 2000). Genomics for diagnostics and animal vaccine development, and in feed production and formulation (Machuka, 2004) may fur­ther boost the livestock industry, although the competition from alternative sources will probably be strong (Twyman et al., 2003; Chen, 2005; Ma et al., 2005). Moreover, all these new technologies create safety risks and may not always increase  sustainable production.  Hence,  applica­tions should be thoroughly evaluated to ensure that they do  not  also   undermine  development  and  sustainability goals.
         There are currently no transgenic food animals in com­mercial production and none likely in the short term (van Eenennaam, 2006). Over the next 10-50 years there is some potential for development and introduction of transgenic animals or birds with disease resistance, increased or higher nutritional value meat or milk production, or as biofacto-ries for pharmaceuticals (Machuka, 2004). The science and technology is available, but the barriers include regulatory requirements, market forces and IP, safety concerns and consumer acceptance, i.e., the same range of issues as de-

scribed for crops (Powell, 2003; van Eenennaam, 2006; van Eenennaam and Olin, 2006).
       Responding to the increased demand for livestock prod­ucts without additional threats to the environment is a ma­jor challenge for agriculture and for AKST. One option for satisfying the additional demand for animal protein is to use meat from monogastric animals (pigs and poultry) and eggs. Feed conversion rates and growth for monogastric animals are better than for ruminants, which is one reason why the increasing demand for meat tends to be met with chicken and pork. This development may be positive with regard to the direct pressure on (grazing) land caused by ruminants, but has resulted in the establishment of large pig and poultry production units which are often placed in peri-urban areas. Large volumes of animal feed are produced elsewhere and transported, while disposal of waste from these large units has become an environmental issue (FAO, 2006). Although these large livestock farms may generate some employment opportunities, the capital required excludes most small-scale farmers. One approach to increase the total efficiency and sustainability of the intensive livestock production sys­tem is area-wide integration, i.e., the integration of produc­tion with cropping activities. The main objective is to link these specialized activities on a regional scale to limit their environmental damage and enhance social benefits (LEAD, 2000).
        Recent   outbreaks   of  diseases,   including  some  that threaten human as well animal health, highlight the need to scrutinize large livestock units and their sustainability in wider terms with regard to environment and health (Stein-feld et al., 2006).
        For small-scale farmers in rural areas, local markets will remain the primary outlets for their products. These local markets may also provide opportunities for processed prod­ucts. However, processing of meat and livestock products into high value niche produces for distant markets might be economically attractive. Some associated risks include the required investment in marketing for a successful enterprise may decrease the "additional" product value. In addition, rural processors may not be able to meet the quality stan­dards to compete for distant urban or export markets (ILRI, 2006).
         Further extension of grazing land to produce meat from ruminants is not a sustainable way to meet the grow­ing demand for meat and livestock products (Steinfeld et al., 2006). Therefore, pastoralists and rangelands livestock keepers will only benefit from an increased demand for live­stock products if they are able to improve their present pro­duction systems by efficient use of existing resources, i.e., breed improvement (Köhler-Rollefson, 2003) improvement of animal health and disease control (Ramdas and Ghotge, 2005), of grazing regime and pasture management, includ­ing the planting of fodder trees, and if possible supplemen­tary feeding during times of limited grazing. Where there is potential for mixed farming, policies need to facilitate the transition of grazing systems into mixed farming systems in the semiarid and subhumid tropics through integrating crops and livestock (Steinfeld et al., 1997).