Aiming for top performance all summer long
The summer period is a welcome arrival for many, but for livestock it can be a time that adversely affects their performance, not just in the summer, but also into the following autumn and winter months. As animal performance increases, against a backdrop of changes in the climate with unpredictable weather; from extreme heat waves to high humidity days, it becomes a challenge to combat the issues associated with heat stress.
BY GRAZIANO MANTOVANI, MARK SCOTT AND BEATRICE PAYOUX, CARGILL R
ecognising the thresholds at which heat stress is triggered, as well as a better understanding of the behavioural and physiological factors affecting live- stock, has enabled Cargill to develop management
and nutritional programmes to support animals during spring and summer to keep animal performance on target.
Heat-stress threshold While it is tempting to attribute heat stress solely to high
temperatures, it is actually a combination of temperature and relative humidity that can cause problems. The temperature humidity index (THI) is taken as an industry benchmark for assessing heat stress in livestock systems.
Feeling the heat The most obvious signs of heat stress; animals will deviate from their usual routines. Like less time spent walking and eating. Cooler areas will be favoured, and outdoor farmed an- imals will look for shade. Lower feed intakes and physiological changes related to heat stress will lead to dips in fertility in breeding livestock, and milk, egg and weight gain reductions across species. Longer term effects on fertility, and even epigenetic effects on progeny, can be seen. While housed livestock is considered most at risk, those in outdoor systems can also be affected. And we also know that the consequences of heat stress can be experienced earlier in the season and extend for a much longer period than previously thought.
Heat stress in cows Recent dairy cow data, for example, has highlighted that fertility can be adversely affected from as low as THI 57. A study of 22,212 high yielding Holstein cows in 15 large-scale dairy herds in Germany, from 2013 to 2015, showed that when average daily THI exceeded 57 (for example 14°C at 60% relative humidity) oestrus activity reduced, leading to reduced submission rates and fewer inseminations. Reduced conception rates were also recorded from a THI 65, equivalent to 20°C at 60% relative humidity. If temperatures reach 22°C, then up to 20% of cows can miss a breeding cycle. And at 27°C this figure is estimated at 43%.
Thermal indicator of when THI impacts dairy cows. Humidity indicated here is 60%.
32 ▶ HEAT STRESS | MAY 2021
Heat stress in swine In pigs, heat stress is experienced when the outside temperature is higher than the pigs’ skin temperature coming from heat from conduction, between the pig and the floor, convection and radiation. The comfort zone temperature will depend on pig age and production phase. In breeding units, the consequences of heat stress will manifest themselves in a fall in fertility performance and this is seen at a lower critical temperature than had previously been thought. Figure 1 shows that feed intake in lactation sows starts to fall from 22°C. This in turn results in lower milk production leading to worse litter performance.
PHOTO: CARGILL
PHOTO: CANVA/MICHAEL JORDAN
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