Summary
Report Summaries
Business Unit
PCA
MLA Program Area
MLA Sub Program
MLA Product Group
Productivity (On Farm)
Beef Productivity
Productivity Practices for Grassfed Cattle
Summary Title *
Developing profitable strategies for increasing growth rates of cattle grazing tropical pastures
Summary Content
The project was a collaborative effort between the Department of Primary Industries (Queensland), University of Queensland and MRC, and included a major grazing trial at Brigalow Research Station Theodore, pen and metabolism studies in Brisbane, and a collation of information on production and feed plans from some high-producing beef enterprises which were already achieving the target growth rate (Case Studies). The major emphasis in the research was on supplementary feeding strategies, although the Case Studies indicated that, within the large diversity of feed plans employed, several other approaches were appropriate including use of improved pastures and forage crops.
The project developed a series of growth response curves relating the liveweight responses of young, growing cattle to increasing amounts of various supplement types. Cottonseed meal and grains (sorghum and barley balanced for urea and minerals) were the predominant supplements used, and they were fed over a range of intakes up to 2% of body weight (2 kg/ 100 kg bodyweight). Supplements were fed throughout the year in order to gauge the effect of pasture (and diet) quality on the response to feeding. In general, growth rate increased linearly with increasing intake of supplement on forages of all qualities.
However, the response to feeding was very low during the main wet season period, greater during the wet/dry season transition phase, and highest when forage quality was low. For instance, feeding barley at 1% of bodyweight (1 kg/ 100 kg bodyweight) produced an additional gain of 0.1 kg/day on high quality, and 0.55 kg/d on low quality, forage diets. On the low quality forages, cottonseed meal gave a substantially higher response than barley at low-medium intakes, but in all other situations barley and cottonseed meal were comparable at similar intakes. The liveweight response to sorghum feeding was about one-third less than for barley when both grains were fed dry-rolled.
These responses were poorly predicted by the feeding standards and their associated models which appear inadequate for tropical grazing systems at present. More intensive investigations in pen feeding studies indicated that feeding supplements to cattle on low quality forages substantially increased growth of micro-organisms in the rumen, which, by virtue of their major role as a source of protein to the animal, translated to increased protein supply. It was further shown that the efficiency of production of this microbial protein was very low on these tropical pastures, but was markedly increased with supplementation; that is, the amount of microbial protein produced per unit intake of digestible plant material.
These studies also indicated that the greatest impediment to increasing growth rates of cattle, especially on higher quality pastures, was the substitution of supplement for pasture by the animal. Major increases in growth rate through supplementation on tropical pastures will require, therefore, strategies to reduce this substitution effect and to increase the efficiency of microbial protein production. The availability of well-defined response curves to some major supplement types, aligned with pasture quality, has provided producers with tools by which they can more confidently predict growth responses and make more objective, economic decisions about supplementation strategies than was previously possible. Further research is needed to fully exploit the potential of these supplements by reducing the inefficiencies of feeding.
