The first few weeks of 2018 have seen temperatures in eastern Australia rise to levels well above average. Hot temperatures challenge livestock as well as challenging people. With another month of summer still to come, its unlikely the heat will ease that much. So it’s worth taking some time to think about how you may help your livestock cope a little better.
Hot weather is an issue for livestock welfare and for livestock productivity. Cattle generally have a core body temperature of around 390C. There many be some slight fluctuations, but in general cows work pretty hard to maintain the core temperature.
As well as generating heat from their metabolism and from movement, environmental influences also impact on the cows temperature. Hot conditions either from air temperatures, solar radiation – and direct sunlight, relative humidity, air flow and the length of time hot conditions persist all impact on the heat load of cattle.
In general, cattle have developed strategies to off load excessive heat. However, when temperatures and humidity are very high it becomes much more difficult for cattle to cope. If cattle don’t have an opportunity to off load heat, they will start to become stressed and may die.
Cattle off load heat in various ways. Drinking cold water absorbs heat and helps lower the animal’s temperature. Heat can also be conducted from the animal to the ground by lying down. Standing in water is an obvious way of transferring heat.
The effect of shade on livestock is just as important. Work by Dairy Australia has shown that cows with access to shade receive 50% less solar radiation than exposed cattle. The movement of air through branches helps the transfer of heat from cattle to the atmosphere and will further reduce the heat load.
When cattle can access shade they tend to rest until the cooler parts of the day before grazing. I recently read some research that showed cattle prefer shade over water in hot conditions and they actually spend more time resting and less time chewing their cud as temperature rises.
Without shade cattle will camp close to dams and water supplies. They will often group together just to get some shade from their heard mates. While this does provide a little shade, it also means more heat absorption from the close contact with other animals. Where they can cattle will look for places where there may be a breeze to help provide some air flow and allow heat to be transferred from their bodies.
In practical terms, along with access to sufficient good quality water, providing cattle with access to shade is probably the most effective method of helping them cope with hot temperatures.
Trees are a more effective option to provide shade for livestock than artificial structures. I’ve spent some time talking to researchers who have shown that trees not only reduce radiation on cattle. They also reduce the air temperature under the tree by around 10.
While that seems to be only a small reduction, it does mean that the ground under the trees is also much cooler. Cows can lay in the shade and transfer heat more easily than if they were in an exposed paddock.
Trees also cool the air around them through a process known as evapotranspiration. This is the process of water evaporating from the leaves of the tree. As this occurs it helps reduce the amount of radiant energy left to war the air. In some ways trees act as a natural air conditioner!
However there is a catch! Evapotranspiration is much more effective when a tree is growing well ad in good health. There is plenty of data that shows single trees, and trees in poor health are much less effective in this process. There is some research that suggests that heavily compacted or poorly aerated soil will reduce the amount of evapotranspiration is 75% lower than in healthy trees. Quite simply the tree can’t absorb enough water from the soil for the process to happen.
So what does this mean in practical terms? I reckon the first is that natural shade is vital. I guess a single tree is better than nothing. But for a big mob of cattle a single tree wont really do much. Having a big group of stock crowding around a tree will place a lot more pressure on that tree. The soil is likely to be more compacted and reduce the ability of the tree to absorb the water it needs.
I really think that in periods of hot weather, your cattle will be much more able to off load heat if you grazed them in paddocks with plenty of trees. If they can spread out they will find their shade, and spend less time standing in dams, which often results in fouled water. (This has its own set of problems!)
Longer term you may even consider planting more trees. More trees in places will take pressure off those old single trees, and will give you and your cattle some useful options to cope with the hot days in the future.
Lastly, excessive movement creates heat and prevents cattle from finding ways to off load the heat they have accumulated. Moving or working cattle should be done early in the day or later in the afternoon. This lets your cattle find some shade when its hot and avoids building up unnecessary heat.
Its important not to forget that water consumption (even with plenty of shade) will be much higher in hot weather. So make sure you check your water supplies regularly to make sure there is enough good quality water for all your cattle!
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