65 Australian Beef - the Leader Conference Genetics of adaptive traits KC Prayaga 1 , NJ Corbet 1 , JM Henshall 2 , HM Burrow 3 Cooperative Research Centre for Beef Genetic Technologies 1 CSIRO Livestock Industries, PO Box 5545, Rockhampton MC, Qld, 4702 2 CSIRO Livestock Industries, Locked Bag 1, Armidale, NSW, 2350 3 CRC for Beef Genetic Technologies, UNE, Armidale, NSW, 2351 Summary A focus on the genetics of adaptation in cattle is regaining importance primarily because of the need to produce consistent beef eating quality, which is often easiest to deliver from cattle breeds that are poorly adapted to tropical environments. Tick counts, worm egg counts, rectal temperatures, coat colour and coat scores have been studied as indicator traits of tropical adaptation. However, these traits are dificult to measure and poorly understood at a genetic level. Projects conducted through the Cooperative Research Centre for Cattle and Beef Quality (Beef CRC) recorded these adaptive traits in two distinct tropical breeds managed at several different northern Australian sites with varying levels of stressors typical of tropical environments. Genetic analyses of the data are underway at molecular and quantitative genetic levels. This paper presents preliminary results on the heritability of various adaptive traits and discusses possible relationships between them. Introduction Tropical adaptation can be deined as an animal’s ability to survive, grow and reproduce in the presence of endemic stressors of tropical environments (e.g. parasites, diseases, hot climates, poor seasonal nutrition). The economic implications for production systems due to the lack of adaptation include production losses, mortalities, treatment costs (where treatment is feasible) and marketing issues, for example associated with the presence of chemical residues in beef resulting from treatments to control parasites. The Beef CRC has investigated several of these adaptive traits in tropical beef cattle in northern Australia. Adaptive Traits The cattle tick, Boophilus microplus, is a single host tick of Asian origin prevalent in tropical climates worldwide. Ticks not only reduce growth and reproduction, but they harbour disease agents, transmitting Babesia bovis, B. bigemina and Anaplasma marginale. To manage ticks, cattle producers use resistant breeds (Bos indicus) or crossbreds (B.indicus x B.taurus) or, where feasible, undertake acaricide treatments. In Australia, ticks are distributed around the northern coastal areas as far south as the Queensland – NSW border, where they are contained by a quarantine boundary at a cost of >A$7 million p.a. (White et al., 2003). Haematobia irritans, known as buffalo ly in Australia and horn ly in north and south America, is another important tropical ectoparasite affecting beef production. Resistance to ectoparasites is generally measured as the number of ticks (Wharton et al., 1970) or lies (Bean et al., 1987) on one side of the animal as a result of natural infestation. Buffalo ly lesion scores, recorded on a 1-10 scale, have also been used to measure resistance to buffalo ly infestation. The number of worm eggs per gram of faeces (Roberts and O’Sullivan, 1950) is used as a measure of resistance to endoparasites (gastro-intestinal helminths or worms, predominantly Haemonchus, Cooperia and Oesophagostomum spp.). The impact of parasite-borne tropical diseases is measured by the incidence and intensity of a wide range of diseases such as ephemeral fever (Australia) and trypanosomiasis (Africa). Thermoregulation is a crucial factor for survival and production of cattle in tropical climates. Manifestations of effective thermoregulation include sleek coat, high sweating capacity and reduced metabolic heat production. Zebu cattle are well known for these attributes. Coat scores recorded on a 1 (extremely short and sleek coat) to 7 (very woolly coat) scale (Turner and Schleger, 1960) and rectal temperatures recorded under conditions of heat stress are used as measures of heat tolerance in cattle. Genetic parameters The moderate to high heritabilities of adaptive traits from earlier northern Australian studies (Table 1) indicate these traits have a strong genetic component, providing ample scope for selection to improve them. However, they are dificult to include in genetic evaluation systems because of the dificulty of measurement.