Heat stress reduces broilers’ growth rate
IT seems everyone is pre-occupied with finding ways to save themselves from possible dehydration due to the prevailing hot temperatures or heat wave — whatever you may choose to call it.
And true to their intentions, people are downing a lot of water and other beverages and staying in the shed during day.
Roadside vendors and those populating road intersections are making brisk business, as motorists and passengers alike, buy the precious liquid as they pass.
But from where I am standing, I do not seem to notice that kind of bee-hive among livestock farmers pushing to make life easier for their animals too.
Just like people, animals also need that water in abundance while a slight or outright adjustment to their feeding rota or even the living conditions may be the most welcome addition to the lavish water provisions.
The poultry sub-sector, for instance, is among the most vulnerable to high temperatures and is affected through many ways.
Heat stress is one of the key environmental stressors impacting poultry production worldwide with its negative effects on broilers and laying hens range from reduced growth and egg production to decreased poultry and egg quality and safety.
Once this happens, it means the farmer’s business will start bleeding and potential profits will decrease.
Naturally, heat stress poses a major problem to farmers in the poultry business, as it affects chickens’ performance and has vast potential to trigger huge economic losses.
This means that as the farmer frets over her safety from the raging high temperatures, she must also assess how her chickens are faring lest she sets herself up for huge losses that may even force her to abandon the project.
One thing farmers must realise is that chicken meat is currently one of the most important commodities with consumers treating it and eggs as key protein sources and a healthy alternative to red meat or other protein production systems.
Globally, the poultry industry is the source of chicken meat and eggs, which happen to be the most significant protein sources among animal foods.
It is a fact that the poultry industry has also not been spared from the destabilising effects of climate change, which is responsible for the current high temperatures that are not supportive of high performance and a decent welfare in chickens.
It is sad that chickens can only tolerate a narrow range of temperatures during heat stress.
The optimum temperatures for chickens and other poultry units’ well-being and productive performance — the thermoneutral zone — are between 18 and 22 degrees Celsius.
If farmers manage to keep their birds within this temperature range, that means the chicken will not need to use their energy on maintaining a constant body temperature, but for other productive purposes.
In their findings, researchers in poultry physiology and management Lara and Rostagno indicate that chickens’ feed consumption drops by five percent for every one-degree Celsius increase in temperature between 32 degrees Celsius and 38 degrees Celsius.
When the ambient temperature increases to 34 degrees Celsius, the mortality due to heat stress would be very high in broilers by 8,4 percent and the feed intake of the chicken decreases from 108,3g/bird/day at 31,6 degrees Celsius to 68,9g/bird/day at 37,9 degrees Celsius, the egg production would reduce by 6,4 percent.
Feed intake in broilers is reduced by 16,4 percent when they are subjected to chronic heat stress, and body weight is lowered by 32,64 percent.
Laying hens exposed to heat stress during 8-14 days, 30-42 days, and 43-56 days saw a decrease in egg production of 13,2 percent, 26,4 percent and 57 percent respectively.
Guided by these findings, farmers must appreciate the need to protect chickens from heat stress since it reduces feed efficiency, body weight, feed intake, and egg production, as well as an increase chicken mortality.
And owing to their inability to dissipate body heat production resulting from feather covering and limited sweat glands (Zhang et al., chi2017) chicken are most vulnerable to heat stress.
Heat stress always contributes to a series of physiological disturbances, including systemic immune dysregulation, endocrine disorders, respiratory alkalosis, and electrolyte imbalance, which affect the health and performance of the chickens.
To effectively understand and control environmental conditions causing the problem is always a part of heat stress management, which is crucial for ensuring animal welfare and achieving successful poultry production.
Most intervention strategies deal with heat stress through a wide range of measures, including environmental management, housing design, ventilation, sprinkling, and shading, among others.
It is also critical for farmers to intervene through effectively managing feeding strategies, nutrition and environmental factors to reduce the effects of heat stress. Intervention strategies can include dispensing pelletised diets with increased energy, higher fat inclusions, reduction of total protein, supplemental amino acids, higher levels of vitamins and minerals, and adjusting the dietary electrolyte balance. Nutrition is crucial, and the use of the right diets aids in attenuating heat stress in the birds.
But for the farmer to implement the strategies, there is need to correctly identify signs of heat stress in the birds lest one administers the wrong corrective measures to birds suffering from something different or that may even be healthy and not stressed at all.
There are animal-related factors such as body weight, feather coverage and distribution, dehydration status, metabolic rate, and thermoregulatory mechanisms that farmers can observe before moving to act.
They can also try to change the environment for the better by providing adequate ventilation and cooling systems and adjusting their nutrition to help lower the body’s metabolic heat output and keep electrolyte levels stable under high-stress, high-temperature circumstances.
High environmental temperatures are among the commonest environmental stressors for poultry production, causing significant economic losses in the industry.
Heat stress is the result of unsuccessful thermoregulation in the animals, as they absorb or produce a higher quantity of heat than they can lose.
It means that there is a negative balance between the net amount of energy flowing from the animal to the environment and the energy it produces.
Animals exposed to heat stress suffer hostile effects in terms of performance, which are widely known and include high mortality, lower growth and production and a decline in meat and egg quality.
The rule of thumb is that humidity in chicken runs should be kept between 45 and 75 percent alongside a temperature below 30 degrees Celsius.
Clinical signs of heat stress in layers and broilers include increased water consumption, reduced feed consumption, spreading of wings, lethargy or less activity and panting (breathing with open mouth.
In layers’ heat stress causes a reduction in nutrient and energy availability for egg production with clinical signs of heat stress including increased number of thin eggshells, reduced egg production and reduced egg size.
Post-mortem signs confirming heat stress include dry muscles, thick and dark-coloured blood and swollen kidneys.
To mitigate effects of heat stress, farmers can adjust feeding times, for instance, by giving them a third of their daily between 0600hrs and 1000hrs then take the food away during the hottest period of the day.
Give the remaining two thirds of the feeds between 1600hrs and 2100hrs.
Make sure there is plenty and cool drinking water (around 20 degrees Celsius is ideal).
Also protect drinking water from direct sunlight to keep it cool by using a roof over the tank or painting the tanks white to keep water cool.
Check quality of drinking water to prevent infection and acidify it to improve birds’ immune systems.