Summary
Strategies tested were:
(i) moderate stocking (LSR), stocked at the recommended long-term carrying capacity (c. 8 ha/ Animal Equivalent (AE));
(ii) heavy stocking (HSR) run at twice the long term carrying capacity (c. 4 ha/AE),
(iii) variable stocking (VAR), with an annual stocking rate adjustment based on available pasture at the end of the growing season (range: 4-12 ha/AE),
(iv) variable stocking (SOI) with an annual stocking rate adjustment based on the Southern Oscillation index and available pasture at the end of the dry season (range: 4-12 ha/AE), and
(v) rotational wet season spelling (R/Spell) with an intermediate level of stocking (1.5 x long-term carrying capacity, c. 6 ha/AE) in a 3-paddock system.
Trial management was conducted in close consultation with a grazier advisory committee. Good rainfall in the first 4 years was followed by 5 consecutive below-average years. Pasture biomass consequently varied 5-fold over the 9-year trial period. In the VAR and SOI, stocking rates were initially very high (c. 4 ha/AE) but were later reduced to c. 10 ha/AE. In the R/Spell stocking rates were also reduced in November 2004 to c. 10 ha/AE due to the combined effects of an ill-timed fire and drought. Stocking rates had to be cut by c. 30 % in the HSR in 2005 due to reduced carrying capacity arising from overgrazing.
Pasture utilisation rates were initially low in all treatments ( 70%) in the HSR. Annual live weight gain per head declined as pasture utilisation rate increased: average annual LWG/hd was consistently higher under LSR (126 kg/hd) than under HSR (96 kg/hd). Consequently, after 2 years on the trial, lighter-stocked cattle were 50-100 kg heavier, in better condition, and received better meatworks prices than those from heavily-stocked paddocks.
In contrast, LWG/ha was greatest in the HSR with production in the wetter period being almost twice that in the LSR (27.8 versus 15.5 kg/ha/yr). However, this difference narrowed markedly as rainfall declined and the impacts of heavy grazing emerged, and average annual LWG/ha over the whole trial period was 23.2 and 15.2 kg/ha for HSR and LSR, respectively. Importantly, HSR cattle had to be maintained with drought feeding in dry years. In the first four years, HSR had far higher annual gross margins than the LSR strategy ($3,522 versus $1,895 per 100ha). However, HSR gross margins were consistently negative during the latter five years of the trial (average of -$1,527 /100 ha) due to poor animal performance and greater costs.
In contrast, LSR gross margins stayed positive in all years irrespective of rainfall and, as a result, accumulated cash surplus per 100 ha over the nine years was substantially higher for LSR than HSR ($17,410 versus $10,112). For the VAR and SOI strategies, higher stocking rates in the 4-year wet period of the trial produced more profit than LSR, but this advantage was neutralised by poor LWG and selling losses in the initial year of the 5-year dry period. In contrast to the HSR strategy, however, the reduced stocking rate for VAR and SOI strategies during the subsequent 4 years resulted in a return to positive annual gross margins. Annual gross margins for the R/Spell strategy tended to track those of LSR, being slightly higher in the wetter period and slightly lower in the drier period. As a result, after 9 years, there was no increase in accumulated cash flow from applying VAR, SOI or R/Spell strategies above that achieved by moderate stocking. All these strategies, in turn, were more profitable than HSR.
