Heat Stress in Poultry: Physiological Impacts and Nutritional Mitigation Strategies

/in ,

Introduction

Poultry are homeothermic animals with a normal body temperature range of 41–42°C. Under optimal thermal conditions, typically defined as the thermal neutral zone (18–22°C), birds can maintain their core temperature without expending additional energy. However, deviations from this range, particularly during brooding when higher ambient temperatures are necessary, impose significant physiological and behavioural adjustments. Environmental temperatures exceeding 25°C are sufficient to induce heat stress in poultry, which has profound effects on health, performance, and welfare.

Indicators of Heat Stress in Poultry

Behavioural Adaptations:
Poultry exposed to elevated temperatures exhibit distinct behavioural changes, including:

  • Reduced feed intake
  • Increased water consumption
  • Panting
  • Decreased mobility
  • Elevation of wings to expose less-feathered areas for heat dissipation

Physiological Responses:
Heat stress triggers several physiological disruptions, including:

  • Oxidative Stress: Resulting in impaired gut funtion, increased susceptibility to disease, and reduced growth rates.
  • Disturbance of Acid-Base Balance: Characterized by respiratory alkalosis and metabolic acidosis, negatively impacting production performance.
  • Immunosuppression: Evidenced by reduced antibody production and lowered white blood cell counts.

These alterations collectively compromise gastrointestinal functionality, reduce nutrient absorption, and increase intestinal permeability. Dysbiosis, characterized by a decline in beneficial microbiota and a concurrent rise in pathogenic populations, can lead to necrotic enteritis.

Neuroendocrine Changes:
Heat stress activates neuroendocrine pathways that elevate blood glucose levels and respiratory rates. These adaptations, while aimed at coping with hyperthermia, reduce growth efficiency and reproductive performance.

Nutritional Strategies for Mitigating Heat Stress

To counteract the adverse effects of heat stress, several dietary modifications can be employed:

  1. High-Energy Diets:
    Incorporating fats, which generate less metabolic heat compared to proteins and carbohydrates, enhances energy availability without exacerbating heat production.
  2. Pelletized Feed:
    Feeding pelletized diets can improve feed intake and nutrient utilization under heat stress conditions.
  3. Gut Health Enhancement:
    Indirect nutritional strategies, such as the inclusion of prebiotics, probiotics, organic acids, exogenous enzymes, and essential oils (e.g., oregano and thyme), can bolster gut integrity and mitigate the deleterious effects of heat stress.
  4. Supplementation of Vitamins, Minerals, and Phytochemicals:
    Specific nutrients with antioxidant and immune-supportive properties have proven effective:
Supplement Beneficial effect of heat stressed birds: Recommended dosage
Vitamin E Antioxidant; enhances lymphocyte proliferation 100-250mg/kg
Vitamin A Antioxidant and improves immunity
Vitamin C Reduces oxidative damage and boosts immunity 200-250mg/kg
Zinc Is associated with the antioxidant defense system, immune function, and skeletal development 40-60mg/kg organic Zn

 
Selenium Vital component of proteins which are different parts of enzymes in physiological processes. 0.15 – 0.3mg/kg
Electrolytes Higher range of dietary electrolyte balance (DEB): 200-300mEq/kg (use of Sodium Bicarbonate and Potassium Chloride)
Phytochemicals · Lycopene (found in tomatoes)

· Resveratrol (found in grapes, berries)

· EGCG (green tea extract)

· Curcumin (extracted from turmeric)

· Other with antioxidant properties:  Thymol, Carvacrol, Cinnamaldehyde, Silybinin and Quercetin.

 ·      Lycopene 200-400mg/kg

·      Resveratrol (300-500mg/kg)

·      EGCG 300-600mg/kg)

·      Curcumin 100-150mg/kg
Osmolytes · Betaine (increase water-holding capacity of the cells, thus preventing dehydration)

· Taurine (antioxidant action)

 Betaine: 0.05-0.2%

 

Taurine: 5g/kg feed

 

Conclusion

Through targeted dietary interventions, poultry producers can alleviate the detrimental effects of heat stress, safeguarding poultry health, welfare, and productivity. The adoption of these strategies provides a holistic approach to enhancing thermotolerance and maintaining performance under challenging environmental conditions.

Reference

Wasti, S., Sah, N., & Misha, B. (2020). Impact of Heat Stress on Poultry Health and Performances, and Potential Mitigation Strategies. Animals, 10(1266).

 

Importance of feed intake in commercial layer systems

/in

 By Herman Rossouw, technical advisor,  AFGRI Animal Feeds

The feed component of the average poultry production system makes up 70% of all expenses. Given the sharp increase in feed prices these past three years, there is renewed focus on the consumption and effectiveness of rations. In March this year, the average layer meal was 80% more expensive than in the corresponding month in 2020. In comparison, the price paid to producers for a dozen eggs rose by only around 30% in the same period. But what does optimal daily feed intake per hen in commercial egg production systems look like? The answer is somewhat complex.

Factors affecting feed intake
Excessive feed intake leads to financial losses because it adds to the feed bill and leads to health problems such as fatty liver; if the hen ingests too little feed, she will not be ingesting the nutrients she needs for optimal production and health.

A multitude of factors affect feed intake. These include temperature, humidity, water intake, housing density (competition for feeding space), diseases, stress, feed particle size, energy density of the feed, age and weight of the hen, as well as breed.

Each feed company has its own range of layer rations that differ in terms of nutrient density and energy composition – in other words, the optimal daily feed intake per hen will vary. Communication between the feed company and the producer regarding the theoretical and actual intake of a ration is therefore key.

Temperature and particle size
Hens tend to ingest less feed in the warm summer months, making it difficult to keep the actual intake in line with the theoretical intake. A more nutrient-dense feed will help to support hen production and bodyweight maintenance in summer. In this regard, management practices such as midnight feeding may assist in stimulating intake. Moreover, there are a number of supplements on the market that may help to alleviate heat stress.

Feed particle size – and more specifically changes in particle size – can quickly suppress or overstimulate hens’ feed intake. Not only will hens consume less feed if it is too fine, but such feed may also create dust in houses and lead to respiratory infections in hens and workers. Coarse particles, on the other hand, will stimulate feed ingestion, leading to selective feeding habits with hens selecting to eat the coarse particles (usually maize) first, leaving the finer particles (vitamins, minerals, enzymes and the like) behind.

With the latter in mind, it is important in especially older production systems, which still make use of manual feeding, that the hens clean out the feeders before new feed is added. To accomplish this, more daily feedings can be allowed rather than filling up the feeders in the mornings only.

Feed according to age
Although hens’ ration intake can be controlled to some extent, their physiology must be kept in mind. Young point-of-lay hens will not consume the same amount of feed than 60-week-old hens. Hence, rations and management practices need to be adjusted accordingly.

AFGRI’s Optilay Peak ration is specifically formulated for young point-of-lay hens that are physiologically unable to achieve intakes of 110 to 120g/hen/day. Once hens reach a physiological age at which they can comfortably ingest 110g/hen/day, the ration can be switched to Optilay 20.

‘To measure is to know’ is one of my favourite sayings and is very apt when it comes to feed levels and ultimately feed intakes. Daily feed intake per hen per day is the best way to identify problems early on, either with regard to the feed, hens or management practices.