Many studies show that ambient temperatures outside the normal range can negatively affect the health and performance of chickens, but there is little comparable research in turkey poults. Moreover, most chicken studies focus on extreme heat stress -- for example, 7-10°C (about 13-18°F) above an upper limit of 30-32°C (about 86-90°F).
But what about the effects of mild or moderate heat stress on turkey poults, especially negative effects that are not immediately apparent to the producer?
A recent study used "point-of-care" diagnostic technology to measure key plasma metabolites in turkey poults, showing that even minor differences in ambient temperature can affect blood chemistry and potentially impact performance.
Blood chemistry can change quickly in response to external stressors and health challenges in poultry, even before behavioral or clinical signs appear. Today, point-of-care analyzers can measure key hematologic parameters and plasma metabolites, providing objective data and real-time insight into bird health and performance. Some poultry producers already use such technology to speed disease diagnosis and support treatment decisions.
For turkeys, breeders provide brooding temperature guidelines and poults usually are able regulate their body temperature by 14 days of age. But even minor variations can cause stress. Most producers rely on subjective observations -- grouping behavior and noise -- to asses bird comfort. Maintaining optimal brooder ambient temperature and relative humidity can be a challenge, especially in cross-ventilated houses.
North Carolina State University researchers noted that blood chemistry has been used to measure thermal stress and identify health risk factors in broilers and layers. For brooding turkey poults, however, there was little data. They hypothesized that even minor changes in temperature and relative humidity would affect blood chemistry and influence performance of turkey poults.
"The goals of this study," the researchers stated, "were to investigate (1) the effect of mild temperature and humidity during brooding on the blood parameters of turkey poults, and (2) whether brooding temperature and humidity were associated with increased incidence of flip-over, dilated cardiomyopathy, mortality, and overall performance...."
This study explored the effect of mild changes in temperature (intervals of 3°C [5.4°F]) and relative humidity (RH 5-15% difference) on poult blood analytes and performance from 1 to 35 d of age. It also assessed how these brooding conditions affected early mortality and heart function.
The researchers obtained 2,240 one-day-old, Hybrid converter turkey hens from a commercial hatchery and distributed them into 16 rooms (140 per room at a density of 11 birds/m2 [1 sqft/bird]). Rooms were totally enclosed, with separate heating, lighting, and ventilation controls. Researchers provided water and feed ad libitum and used a standard commercial lighting program.
The 35-day experiment consisted of four treatments:
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Control -- 32°C (89.6°F), 60%RH
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Cold stress (CS) -- 29°C (84.2°F), 60%RH
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Heat stress (HS) -- 35°C (95.0°F), 60%RH
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Heat stress plus humidity (HHS) -- 35°C (95.0°F), 75%RH
To compensate for poult growth and increasing stocking density, the researchers lowered temperatures for all treatments 2°C (3.6°F) the first week and 1.5°C (2.7°F) each week thereafter by means of automatic controls. They kept relative humidity (RH) constant "as much as possible," but acknowledged some variability given the limitations of manually adjusted ventilation.
For point-of-care whole blood analysis, the researchers used i-STAT1 (Abbott Point of Care Diagnostics). Subsequent plasma analysis used sandwich ELISA (MyBiosource). Together their analysis measured more than two dozen analytes.
The researchers found that brooding treatment affected blood pH, partial carbon dioxide (pCO2), potassium (K), and sodium (Na). Poults under HS and HHS had higher pH and K, and lower pCO2 and Na in the blood.
"These changes," the researchers state, "suggest an attempt by the poults to cool down by increased water intake and panting. Furthermore, by the end of the experiment more birds in these two (heat stress) treatment groups had distended crops, (possibly due) to increased water intake also."
The researchers point out that blood pH is one of the most relevant parameters for survival: "Based on the (higher) pH values (for HS and HHS treatments), it is likely that some of the turkeys might have used different mechanisms, such as decreased feed intake to avoid additional heat production and to bring their body back to balance, rather than to grow. Still, the birds were able to co-op with the environment and survive."
They also note that warmer brooding temperatures generated higher ketone levels, indicating an off-feed situation, and promoted reduced cardiac ventricular contractility, suggesting weaker hearts. Higher temps also result in a higher incidence of pendulous crop.
However, given this study's relatively mild heat stress conditions, the researchers did not find significant changes in performance measures, including flip-over, dilated cardiomyopathy, mortality, and body weight.
What does this study mean for producers?
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Turkey producers can use point-of-care blood analysis to measure key poult blood analytes that respond to environmental conditions, particularly heat stress
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Key blood analytes for ambient temperature and relative humidity are acidity (pH), partial carbon dioxide (pCO2), potassium ion (K+), and sodium ion (Na+)
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Best tested poult brooding conditions were (1) initial temperature 32°C (89.6°F) with 60–70% relative humidity (RH), followed by (2) initial temperature 35°C (95.0°F) and 60–70% RH
The full paper, titled "Effect of brooding conditions on the blood chemistry and performance of turkey poults" can be found in Applied Poultry Research and online here.
DOI: 10.1016/j.japr.2024.100408
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