Comparing the performance of fixed and flexible stocking rate strategies in the cattle industry of north Australia

Transcription

1 Comparing the performance of fixed and flexible stocking rate strategies in the cattle industry of north Australia Lester Pahl Queensland Dept. of Agriculture, Fisheries and Forestry Toowoomba, Queensland, Australia Joe Scanlan, Giselle Whish and Neil MacLeod

2 Outline of presentation 1. Briefly describe cattle properties in north Australia 2. Mismatch between cattle numbers and feed supply 3. Compare the performance of stocking rate strategies 4. Discuss how annual rainfall variability influences the performance of stocking rate strategies 5. Main findings

3 North Australia beef industry Large properties (6,000 km 2 ; 35,000 cattle) Native grasses are the main source of forage Rainfall is main driver of forage supply Annual rainfall is highly variable Mismatch between cattle and pasture Often results in poor outcomes

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13 ABC Rural Mon May 20, 2013 North Australia missed out on summer rain, and grass hasn't grown for cattle to eat

14 Cattle producers can potentially match stocking rates to forage supply but they don t!

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16 How best to manage stocking rates? Two approaches that can be used: 1. Fixed stocking constant, conservative stocking rate 2. Full flexibility stocking stocking rate adjusted in May, to achieve a particular utilisation rate of pasture (e.g. 20%) Simulation studies conclude that full flexibility achieves higher productivity and is more sustainable However, in these studies, stock come and go in large numbers without any costs or other barriers Recent review recommends that a constant light stocking rate is best for most cattle producers acknowledge that some annual change in stocking rates could improve performance, but the extent of change that is practical and beneficial is unknown

17 How best to manage stocking rate? What amount of change in stocking rates annually in response to changes in feed availability is optimal? No change? Full flexibility? Constrained flexibility? Limits constrain the extent stocking rates are changed: increases limited to 5, 10, 20, 30, 50, or 70% decreases limited to 5, 10, 20, 30, 40, 50, 60, 70, or 80% 54 combinations of these limits for increases and decreases in stocking rate Compared a total of 56 stocking rate strategies at 28 locations

18 Compared performance of strategies across north Australia The 28 locations cover the full range in mean annual rainfall and annual rainfall variability Mean annual rainfall ranged from 139 to 1602 mm Annual rainfall variability (%CV) ranged from 22 to 73 Compared performance when starting pasture condition was excellent (90% perennial grasses) or moderate (60% perennial grasses)

19 Model used GRASP pasture and animal production model Dynamic, point-based model that simulates pasture growth and animal production using daily climate records Simulation periods were 20 years Used the average of the 11 simulation periods, from 1890 to 2012 The starting stocking rate used with all strategies was the fixed stocking rate that maintained pasture condition during each simulation period

20 Explaining the performance of strategies Used decision-tree models to identify the variables that significantly (F-test) influenced pasture condition, stocking rates, and cattle live-weight gain/ha The variables were: Percent limits for annual increases in stocking rates Percent limits for annual decreases in stocking rates %CV of rainfall of locations Starting pasture condition

21 Results Pasture Condition The limits for annual increases in stocking rate had the greatest influence on percent perennial grass composition (pasture condition) over 20 years As the limits for annual increases in stocking rate rose, pasture condition declined Starting pasture condition had the next highest influence Average pasture condition over 20 years was highest when pasture started in excellent condition The limits for annual decreases in stocking rate had the third highest influence on pasture condition Pasture condition improved as the limits for annual decreases in stocking rate rose

22 % PG - % SR Results: Pasture Condition The %CV of rainfall had the 4 th highest influence on pasture condition The decline in pasture condition that is caused by high annual increases in stocking rate occurred to a lesser extent at locations with high %CV of rainfall When %CV of rainfall was high, so was the number of years when annual changes in pasture growth were much higher than annual changes in stocking rate 1450 R 2 = Percent co-efficient of variation in rainfall

23 Results: Cattle productivity Mean Annual Rainfall (mm) Stocking Rate (AE/100ha) 80 The %CV of rainfall had the greatest influence on stocking rates and live-weight gain/ha Categories of %CV of Annual Rainfall Mostly due to the decrease in mean annual rainfall that occurs as the %CV of rainfall increases R 2 = %CV of Annual Rainfall

24 Results: Cattle productivity Live-weight gain/ha (kg) Starting pasture condition had the next highest influence on stocking rates and live-weight gain/ha Categories of %CV of Annual Rainfall Excellent pasture condition Moderate pasture condition

25 Results: Cattle productivity The extent that SR can be increased each year had the next largest influence on SR and live-weight gain/ha achieved over 20 years The highest SR and LWG/ha were achieved by moderate annual increases in stocking rate (mostly 10, 20 and 30%), where higher annual increases were needed as %CV of rainfall increased Annual decreases in SR had the 4 th highest impact on SR and LWG/ha achieved over 20 years Higher annual decreases in SR where needed when annual increases in SR were high, and when %CV of rainfall was high

26 % PG - % SR Results: Cattle productivity When locations have large increases in pasture growth relative to increases in stocking rates between successive years, then strategies that allow large increases in stocking rate annually are needed to achieve the highest LWG/ha 1450 R 2 = Percent co-efficient of variation in rainfall

27 Results: Cattle productivity LWG/ha (kg) When locations have a high %CV of rainfall, chasing the highest LWG/ha comes at the cost of pasture condition E.g. Simpson Desert, with the highest %CV of Percent Perennial Grass Composition

28 Conclusions Rainfall variability in north Australia is high to very high Cattle SR are more likely to be adjusted in the dry season and carried through the next wet season Mismatch between demand for and supply of forage Relative performance of fixed stocking declines as %CV increases Full flexibility was amongst the worst performing strategies Best pasture condition achieved by fixed stocking, or 5% annual increases with 40% annual decreases in SR Highest cattle productivity achieved when annual increases in SR are 10 to 30%: 30% increases needed when %CV of rainfall is high

29 Conclusions Highest cattle productivity achieved at expense of pasture condition (trade-off) Need to sacrifice some LWG/ha if good pasture condition is to be maintained over 20 years and beyond Limits of 5-10% increases and 20-30% decreases in SR annually may be a good compromise between pasture condition and cattle productivity The extent of the sacrifice in LWG/ha increases as %CV of rainfall increases May be better to graze opportunistically when %CV of rainfall is high

30 Thank you very much for inviting me to participate in your conference