This study measured forage biomass production, diet quality, cattle liveweight gain, and economic performance of six forage types at 21 sites across 12 commercial beef cattle properties in the Fitzroy River catchment of Queensland during 2011–2014 (28 annual datasets in total). The forages were annual forage crops (oats (Avena sativa), sorghum (Sorghum spp.) and lablab (Lablab purpureus)), sown perennial legume-grass pastures (leucaena-grass (Leucaena leucocephala spp. glabrata + perennial, tropical grass (C4) species) and butterfly pea-grass (Clitoria ternatea + perennial, C4, grass species)), and perennial, C4, grass pastures. The sown forages resulted in 1.2–2.6 times the annual cattle liveweight gain per ha than perennial grass pastures. Annual cattle liveweight gain per ha, forage establishment and management costs, and cattle price margin (sale price less purchase price, $/kg liveweight) all influenced gross margin, however, none was an overriding factor. The average gross margins ($/ha.annum) calculated using contractor rates, ranked from highest to lowest, were: leucaena-grass pastures, 181; butterfly pea-grass pastures, 140; oats, 102; perennial grass, 96; sorghum, 24; and lablab, 18. It was concluded that the tendency towards greater average gross margins for perennial legume-grass pastures than for annual forage crops or perennial grass pastures was the result of the combined effects of lower average forage costs and high cattle productivity.

Abstract. The rumen degradability parameters of the diet selected by two to four oesophageal-fistulated Brahman steers grazing a range of tropical pastures were determined by incubation of extrusa in nylon bags suspended in the rumen of rumen-fistulated (RF) Brahman steers. The effective protein degradability (Edg) was determined by measuring the rate of disappearance of neutral detergent insoluble nitrogen (NDIN) less acid detergent insoluble nitrogen (ADIN) in the incubated extrusa. Six to eight RF steers also grazed each of the pastures along with the oesophageal-fistulated steers, to allow determination of key rumen parameters and rumen particulate matter fractional outflow rates (FOR). The seven pastures studied included: native tropical grass (C 4 ) pasture (major species Heteropogon contortus and Bothriochloa bladhii), studied in the early wet (NPEW), the wet/dry transition (NPT) and the dry (NPD) seasons; introduced tropical grass (C 4 ) pasture (Bothriochloa insculpta), studied in the mid wet season (BB); the introduced tropical legumes (C 3 ), Lablab purpureus (LL) and Clitoria ternatea (BP); and the temperate grass (C 3 ) pasture, ryegrass (Lolium multiflorum, RG). Using the measured particle FOR values in calculations, the Edg estimates were very high for both C 4 and C 3 species: 0.82--0.91 and 0.95--0.98 g/g crude protein (CP), respectively. Substitution of an assumed FOR (k p = 0.02/h) for the measured values for each pasture type did not markedly affect estimates of Edg. However, C 4 tropical grasses had much lower effective rumen degradable protein (ERDP) fractions (23--66 g/kg DM) than the C 3 pasture species RG and LL (356 and 243 g/kg DM, respectively). This was associated with a lower potential degradability and degradation rate of organic matter (OM) in sacco, lower in vitro organic matter digestibility (IVOMD) and CP concentrations in the extrusa, and lower ammonia-N and branched-chain fatty acid concentrations in rumen fluid for the tropical grasses. As tropical grass pastures senesced, there was a decline in Edg, the ERDP and rumen undegradable protein (UDP) fractions, the potential degradability and degradation rate of OM and the IVOMD. These results provide useful data for estimating protein supply to cattle grazing tropical pastures.

Context Phosphorus (P) deficiency occurs in beef cattle grazing many rangeland regions with low-P soils, including in northern Australia, and may severely reduce cattle productivity in terms of growth, reproductive efficiency and mortality. However, adoption of effective P supplementation by cattle producers in northern Australia is low. This is likely to be due to lack of information and understanding of the profitability of P supplementation where cattle are P-deficient. Aims The profitability of P supplementation was evaluated for two dissimilar regions of northern Australia, namely (1) the Katherine region of the Northern Territory, and (2) the Fitzroy Natural Resource Management (NRM) region of central Queensland. Methods Property-level, regionally relevant herd models were used to determine whole-of-business productivity and profitability over 30 years. The estimated costs and benefits of P supplementation were obtained from collation of experimental data and expert opinion of persons with extensive experience of the industry. The economic consequences of P supplementation at the property level were assessed by comparison of base production without P supplementation with the expected production of P-supplemented herds, and included the implementation phase and changes over time in herd structure. In the Katherine region, it was assumed that the entire cattle herd (breeders and growing cattle) grazed acutely P-deficient land types and the consequences of (1) no P supplementation, or P supplementation during (2) the dry season, or (3) both the wet and dry seasons (i.e. 3 scenarios) were evaluated. In the Fitzroy NRM region, it was assumed that only the breeders grazed P-deficient land types with three categories of P deficiency (marginal, deficient and acutely deficient), each with either (1) no P supplementation, or P supplementation during (2) the wet season, (3) the dry season, or (4) both the wet and dry seasons (i.e. 12 scenarios). Key results In the Katherine region, year-round P supplementation of the entire cattle herd (7400 adult equivalents) grazing acutely P-deficient pasture resulted in a large increase in annual business profit (+AU$500000). Supplementing with P (and N) only in the dry season increased annual business profit by +AU$200000. In the Fitzroy NRM region, P supplementation during any season of the breeder herd grazing deficient or acutely P-deficient pastures increased profit by +AU$2400–AU$45000/annum (total cattle herd 1500 adult equivalents). Importantly, P supplementation during the wet season-only resulted in the greatest increases in profit within each category of P deficiency, comprising +AU$5600, AU$6300 and AU$45000 additional profit per annum for marginal, deficient and acutely P-deficient herds respectively. Conclusions The large economic benefits of P supplementation for northern beef enterprises estimated in the present study substantiate the current industry recommendation that effective P supplementation is highly profitable when cattle are grazing P-deficient land types. Implications The contradiction of large economic benefits of P supplementation and the generally low adoption rates by the cattle industry in northern Australia suggests a need for targeted research and extension to identify the specific constraints to adoption, including potential high initial capital costs.

Context. Beef producers in northern Australia are continually presented with new technologies and opportunities to enhance beef production. They need to be able to accurately and efficiently assess the potential impact of alternative strategies on profitability, risk and the period of time before benefits can be expected. Aims. Our aim was to demonstrate the value of the farm-management economics framework for assessing alternative management strategies applicable to beef cattle enterprises in northern Australia. Methods. Beef cattle herd models incorporated into a farm-level partial discounted cash-flow framework were used to evaluate the potential effects of alternative management strategies on the performance of enterprises. This was undertaken using constructed, representative beef enterprises developed for the following three regions in Queensland: Central, Northern Downs and Northern Gulf, and the Katherine region of the Northern Territory. The analysis considered the expected response to change in the management of the base herd. Strategies that targeted (1) overall herd or property performance, (2) breeder reproductive performance, (3) steer growth rates, (4) alternative beef cattle marketing options, or (5) enterprise expansion were assessed. All of the changes considered to the current management strategy of the base herd and property were put forward by industry participants as potentially positive. Key results. The framework efficiently identified substantial differences in net benefits among strategies and allowed ranking of the alternatives at the property level. Strategies that improved profitability also generally increased management complexity and financial risk. While strategies that could substantially improve profitability were identified, many other strategies were likely to reduce profitability at the property level. Key insights were gained into the time taken to implement the strategies, the complexity of implementation, and the level of financial risk incurred. Conclusions. This study (1) demonstrated the appropriate framework to compare management options and support decision making, (2) efficiently indicated the potential range of outcomes, and (3) provided insight into the risks associated with development processes and technology adoption. Implications. This farm-management economics framework could be used to assess alternative strategies for individual beef enterprises and to guide appropriate adoption of technology.

Abstract. Estimates of microbial crude protein (MCP) production by ruminants, using a method based on the excretion of purine derivatives in urine, require an estimate of the excretion of endogenous purine derivatives (PD) by the animal. Current methods allocate a single value to all cattle. An experiment was carried out to compare the endogenous PD excretion in Bos taurus and high-content B. indicus (hereafter, B. indicus) cattle. Five Holstein-Friesian (B. taurus) and 5 Brahman (>75% B. indicus) steers (mean liveweight 326 ± 3.0 kg) were used in a fasting study. Steers were fed a low-quality buffel grass (Cenchrus ciliaris; 59.4 g crude protein/kg dry matter) hay at estimated maintenance requirements for 19 days, after which hay intake was incrementally reduced for 2 days and the steers were fasted for 7 days. The excretion of PD in urine was measured daily for the last 6 days of the fasting period and the mean represented the daily endogenous PD excretion. Excretion of endogenous PD in the urine of B. indicus steers was less than half that of the B. taurus steers (190 µmol/kg W 0.75 .day v. 414 µmol/kg W 0.75 .day; combined s.e. 37.2 µmol/kg W 0.75 .day; P < 0.001). It was concluded that the use of a single value for endogenous PD excretion is inappropriate for use in MCP estimations and that subspecies-specific values would improve precision.Additional keywords: rumen microbial protein, cattle.