Summary
The Australian beef industry is primarily a grass-based industry, utilising a wide range of native and improved pasture systems, which vary greatly across the country. In 2001-2002, grassfed beef made up nearly 70% of total beef production in Australia (Gleeson et al 2003). However regardless of location, seasonal variations in rainfall distribution often result in significant fluctuations in pasture quality and quantity, which impact on a range of production traits including growth, fertility and survival (Entwistle, 1983; Winks, 1990; McCosker et al, 1991; Dixon et al 1996).
In addition, low soil fertility in some regions influences pasture quality and animal nutrient status (Miller et al, 1997), further influencing cattle performance. Optimising production requires that the physiological needs of the animal are matched with available nutrients, and for most environments and regions, particularly in Northern Australia, there is a seasonal imbalance between supply and demand. Supplementary feeding represents one, but not the only option, available to bridge the gap between nutrient supply and demand, since there are also a range of other management strategies (Holroyd et al 1988; McCosker et al 1991; Fordyce and Entwistle, 1992; Braithwate and de Witte, 1999) which can be used in breeder herds to minimise the need for additional nutrient inputs. Nutritional supplementation to enhance production or to supply specific limiting nutrients is a widely used management tool across broad sections of the industry and the literature on supplements and traditional supplementation techniques and strategies is voluminous (eg Winks, 1984; McLennan et al 1981,1991; Lindsay, 1984; Dixon et al 1996, Leng, 2003).
Common supplement delivery methods include loose dry mixes, incorporation of supplements in energy sources such as molasses (eg urea-molasses-M8U) and compressed blocks incorporating various nutrients with salt, molasses and binding agents. However, in some of these traditional supplementation systems, particularly those containing non-protein nitrogen (NPN, usually urea) and phosphorous (P) sources, irregular and variable intakes of supplements have often occurred where some animals over-consume, some under-consume, and others reject the supplement, leading to considerable variations in production responses (Entwistle and Knights, 1974; Nolan et a,l 1974; Dove, 1984; McLennan et al, 1981, 1991; Dixon et al, 1997).
This variability is caused by a number of factors, including animal behaviour effects such as previous exposure to supplements, dominance and temperament, and location of blocks in a grazing area (Petherick et al, 1998). Supplement factors including poor palatability, and/or poor attractiveness of some supplement ingredients for example phosphorus, and in the case of compressed blocks, lick block hardness can also influence acceptability and levels of intake (McLennan et al, 1981). These restricted intake problems can be severe under some extensive grazing situations, leading to poor efficiency of utilisation, lower than anticipated production responses and higher costs.
