Impacts on Cows
Cows have evolved a range of mechanisms to off-load heat, but problems can occur if temperatures and humidity remain high. Heat load accumulation can occur when hot nights do not allow animals to recover.
At temperatures above 25 degrees Celsius, a cow begins to feel uncomfortable, reducing their ability to produce milk and get in-calf. Their health and welfare may also be affected. The increase in metabolic activity associated with high milk yields has added to the heat stress dairy farmers must manage in their herds.
Of the European dairy breeds, Brown Swiss and Jersey are least vulnerable to heat stress, then Ayrshire and Guernseys, followed by the Holstein-Friesian.
More information on the impact on heat and climate change on cows is available here.
Impacts on pasture
The combination of increased atmospheric carbon dioxide concentrations, higher temperatures, lower rainfall and increased climate variability will challenge some aspects of the current dairy feedbase, while benefiting others.
The overall challenge remains producing (and sometimes preserving) home-grown forage of a suitable quality to match the feed requirements of the herd at a suitably low price to meet farm business requirements. In all cases, the scale of the response will depend on the scale of any climate changes.
Temperatures during winter will be warmer and there will be fewer frosts in some regions, so pasture growth rates are likely to increase over winter. This may influence other decisions associated with calving time, grazing management, fertiliser (especially nitrogen) timing and amount and cutting times for hay or silage.
Feed gaps are likely to be more frequent, so feed purchasing and/or forage conservation activities may become more important as part of total farm management.
Future warmer and drier climate scenarios will alter the balance between the productivity and persistence of perennial grasses to support livestock production systems (Cullen et al). Heat tolerance and rooting depth are key factors and will influence a farmer's choice of species.
Depending on their dairy region, the following are some of the general pasture impacts farmers might see as a result of climate change:
- Winters will be warmer with fewer frosts. Pasture growth rates could be higher in winter in southern dairy regions and using nitrogen fertiliser during winter may become more effective
- Summer will be hotter, beginning earlier and finishing later - potentially causing heat/moisture stress over summer, while shortening the peak of spring growth and delaying the start of autumn. Short rotation pasture systems and winter fodder crops may become more attractive than irrigating pasture over summer
- Increased temperatures may make C4 pasture species like paspalum, kikuyu, maize and forage sorghum more competitive at the expense of the nutritious C3 species like ryegrasses
- Irrigation requirements will increase with higher temperatures and lower rainfall. Irrigation availability is likely to decrease, magnifying the impact on pasture production.
The impact of climate scenarios will affect regions differently:
- Those regions that are currently hot and dry (such as Moree and Wagga Wagga, New South Wales) will remain so, but existing pasture types at these locations based on a mix of C3 and C4 species appears to be quite resilient to the changes in climate.
- In other regions, hotter and drier conditions are likely to challenge the productivity and persistence of current pasture species, particularly where the current species are near the edge of their adaptive range (such as perennial ryegrass-based pastures at Hamilton and Terang in south-west Victoria).
- In cool temperate sites, perennial ryegrass production will increase in warmer and drier scenarios and its benefits in ease of management are likely to see it continue to be widely used. However, as the climate becomes warmer and drier, deeper rooted options such as tall fescue and phalaris may be integrated into the systems.
- Overall, increasing numbers of hot and dry days will challenge the persistence shallow rooted perennial grasses such as ryegrass. This will tend to favour the summer dormant species such as phalaris, however the trade-off between the ease of management of ryegrass with the persistence benefits of phalaris is likely to be amplified in many regions of southern Australia.
- Kikuyu is very reliant on summer rainfall to grow, so its production is highly susceptible to rainfall decline. In addition, low winter production will limit its adoption as feed grown through this period is valued a lot higher by farmers.
Impacts on farm water supplies
Climate change projections indicate farm water supplies will decrease due to lower rainfall, higher evaporation, changes in seasonal patterns and more frequent and longer droughts. These factors generally cause run-off to be reduced at more than double the rate of rainfall reduction.
Farmers who rely on surface run-off for irrigation or dairy supplies could face more severe water shortages. However, run-off estimates are not always reliable because run-off depends on timing and intensity of rainfall as well as rainfall amount.
If there is less rainfall and run-off, then reductions in the reliability of supply will vary but they are likely to be greatest where surface water use is already high and where climate change is predicted to have the largest impact on water availability. In the Murray-Darling Basin this would be the Murray, Goulburn-Broken, Campaspe, Loddon-Avoca and Wimmera regions.
By 2030 predictions, the availability of surface water in the Murray-Darling Basin will reduce by an average of 11%, 9% in the north of the Basin and 13% in the south.
Impacts on biosecurity
Future climate changes will influence the spread of livestock and pasture pests, disease and weeds. See the Biosecurity page for more on managing this risk.