GENERAL INTRODUCTION CHAPTER 1 General Introduction The aim of breeding programs is to improve production and biological efficiency. Large differences exist between breeds for most bioeconomic traits as a result of different selection goals in different breeds (Gregory et al. 1982; Cundiff et al. 1986). Hence selection of the most suitable breed should be done before selection within that breed (Van Vleck et al. 1992). However, production potential cannot be fully expressed unless animals are highly adapted to their production environment (Frisch 1997). The greatest gains are achieved when genotypes are matched to management systems, environments in which they will produce, and to markets for which they are destined (Frisch 1997). Beef production contributed $7.8 billion to the Australian economy in 2005-06 (ABS 2007). The domestic market is Australia" s largest beef market, while 1apan and Korea are Australia" s largest premium export beef markets. Australia is the world" s largest beef exporter, contributing 25% of total beef traded at a value of $3.9 billion to the economy (ABS 2005). The most important pre-purchase considerations for beef consumers are the amount and distribution of fat, lean meat colour, fat colour and appearance, and freshness. Post-purchase, tenderness is the most important factor, followed closely by flavour and juiciness (Egan et al. 2001). In response to domestic and 1apanese market demands for consistency of beef eating quality, the Beef Cooperative Research Centre (Beef CRC) was formed in 1993 to examine genetic and non­ genetic factors influencing beef quality from breeding through to consumption. One of the key issues was the large proportion of beef coming from tropical, subtropical and semi-arid regions of northern Australia. In 2004, Queensland held 420/0 of Australia"s 27.5 nlillion cattle, while New South Wales and the Northern Territory held 21 % and 160/0 respectively (ABS 2006). Queensland contributed 42% of total cattle slaughtered in 2003-04 (ABS 2005). Of the total GENERAL INTRODUCTION 666,000 head of cattle in Australian feedlots in March 2004, Queensland held nearly half of these (ABS 2005). Though the percentage of cattle finished in feedlots and slaughtered In northern Australia can vary significantly from year to year due to drought conditions. Brahman is the predominant breed in northern Australia. The tropical and subtropical climates, poor nutrition and extensive management systems under which Bos indicus breeds have evolved has increased their tolerance to those environments through selection pressure (Nogueira 2004). Hence, Bos indicus can thrive where Bos taurus cannot. The superior adaptation of Brahmans has meant their role in northern Australian beef production systems has continued to grow, particularly since the 1970s. More than 500/0 of the national herd is now estimated to have some Brahman genes (Bindon 2002). A consequence of selection pressure for adaptation has been reduced productivity and precocity (Nogueira 2004). Brahmans have a reputation for poor carcass and meat quality, poor performance in feedlots, and poor fertility relative to Bos taurus breeds and Bos indicus x Bos taurus crossbreds. Crossbreeding allows the complementary blending of breed characteristics - adaptation with productive and reproductive traits. Commercial cattle producers have been using tropically adapted straightbreds, crossbreds and composites in an effort to overcome some of the shortcomings of straightbred Brahmans for beef quality, feed efficiency and fertility, while maintaining adaptation characteristics in their breeding herds. There are many studies that examine Brahman x Bos taurus crosses relative to Bos taurus performance in temperate environments, one of the most well known and comprehensive research projects being the ongoing Germplasm Evaluation Program conducted at the USDA Meat Animal Research Center at Clay Center, Nebraska (Cundiff et al. 1998; Cundiff et al. 2001). However, there are few studies examining economically important traits of Brahmans relative to Bos taurus x Brahman in tropical and subtropical environments. Where studies on Brahmans and Brahman crossbreds 2 GENERAL INTRODUCTION have been conducted in tropical and subtropical regions of other parts of the world, temperature extremes and rainfall patterns differ significantly to northern Australian environments. Furthermore, cattle production systems, finishing regimes, processing practices and markets differ significantly between other countries and Australia. Therefore, the purpose of this thesis was to compare the performance of tropically adapted crossbred and composite cattle with straightbred Brahmans for economically important production and reproduction traits under tropical and subtropical conditions in northern Australian using typical commercial beefproduction practices. This research used data generated from the Beef CRC's Northern Crossbreeding Program and Project 2.3. This research was limited to northern Australian beef production systems, excluding the live export cattle trade, but has application in parts of the world that use Brahman and tropically adapted crossbreds and composites in their beefherds. Chapter 2 examInes the literature on beef cattle production including genetic and environmental influences on carcass and meat quality, feed efficiency and fertility of Brahmans, Brahman crossbreds and tropically adapted composites. To achieve the overall research aim, Chapters 3 and 4 examined carcass quality and meat quality (objective and sensory palatability) characteristics of straightbred Brahmans relative to Brahman crossbreds when finished on pasture and in feedlots, to domestic and export market weights. Chapter 5 examined differences in feed efficiency and feeding behaviour of straightbred Brahmans relative to Brahman crossbreds when finished in a feedlot to export market weights. Economic pressures focus animal selection on carcass and meat quality, and feed efficiency characteristics. Genetic antagonisms exist between yield and feed efficiency traits and fatness traits. As fatness is believed to be positively associated with fertility in females, selection for higher retail beef yield or feed efficiency may have detrimental effects on replacement female fertility. This may be 3 GENERAL INTRODUCTION exacerbated under the stressors of northern Australian beef production environments. To detennine if there was a relationship between fatness and fertility, Chapter 6 examined the phenotypic relationships between scanned subcutaneous fat measurements and weight at the start of mating and reproductive success in straightbred Brahmans and tropically adapted composites. Finally, Chapter 7 provides a general discussion on the use of Brahman crossbreds and tropically adapted composites relative to straightbred Brahmans in northern Australia. Recommendations are made with specific relevance to beefindustry application in Australia. 4 LITERATURE REVIEW CHAPTER 2 Literature Review 2.1 Introduction This literature review examines traits of economic importance to beef production in Australia. It reviews genetic and non-genetic influences on carcass quality, meat quality (including objective and sensory palatability), feed efficiency, feeding behaviour and female fertility, with specific reference to Brahmans, Brahman crossbreds and tropically adapted composites relevant to this study. Because ofthe limited Australian research on several traits of interest, many studies from other beef producing countries have been sourced. Some dairy cattle references have been used when there was insufficient beefresearch on particular fertility traits. 2.2 Beefquality 2.2.1 Importance to beefindustry The beef cattle industry is one of Australia's major agricultural industries. A total of 8.9 million cattle and calves were slaughtered during 2004-05, producing 2.16 million tonnes of pasture- and grain-finished beef, and raising more than $6.7 billion (ABS 2006). Of these, 420/0 were slaughtered in Queensland. Despite declining consumption of beef, the domestic market remains the largest single market for Australian beef, commanding 37% of total grain fed beef production (ABS 2005). Australia is the world's largest beef exporter contributing 250/0 of the total beef traded in 2003-04, worth $3.9 billion to the economy (ABS 2005). Japan is Australia"s most important premium export beef market, consuming 438,500 tonnes (20.3%) of the total beefproduced in Australia in 2004-05. The USA is Australia"s largest importer ofmanufacturing beef, consuming 17.1 % in the same period, while Korea is the third largest export market, 5 LITERATURE REVIEW consuming 5.2% (ABS 2006). In the mid-1980s, the USA realised the potential of the Japanese and Korean beef markets and became a major competitor with Australia. Since then Australian beef producers have been under increasing pressure to become consumer-driven, focussing on the consistent supply ofquality beefto maintain market share. Consumers base purchase decisions on two main factors. These are visual appearance including amount and distribution of fat (marbling fat and subcutaneous fat), lean meat colour, fat colour and appearance, and eating quality including tenderness, flavour and juiciness (Egan et al. 2001). A review by Egan et al. (2001) concluded leanness was the most important factor influencing purchase decisions of domestic consumers, with a preference for lean steaks and minimal marbling. While domestic consumers select lean beef in the supermarket, they