by Dr Pooja BhardwajMVSc (Pharmacology & Toxicology)
One of the greatest challenges to production facing poultry farmers in India is heat stress and the strain that it causes to the bird. Climatic conditions in India are such that there is intense radiant energy for an extended period of time. Poultry create a large quantity of metabolic heat and accumulates additional heat from radiant energy. Heat production and accumulation, coupled with compromised cooling capability because of environmental conditions, cause heat load in the bird to increase to the point that body temperature rises, intake declines, and ultimately the bird’s productivity drops. Birds are ‘heat stressed’ if they have difficulty achieving a balance between body heat production and body heat loss.
Consequences of Heat Stress
Management of heat Stress
The strategies to minimize the effects of heat stress can be achieved by:
1) Genetic modification by developing heat-tolerant breeds
2) External environment management: –
a) Improved nutritional management practices.
b) Physical modification of the environment (shading, cooling)
In this article, we will discuss the nutritional management of heat stress.
Improved nutritional management practices.
1) Feeding Strategies for Heat Stress
During hot weather, birds reduce feed consumption resulting in the deficiency of some nutrients. Manipulating the ration such as increasing energy intake should be done carefully and technically. Avoid using rancid fats & amino acids balance must be maintained by using vegetable protein sources rather than animal protein. Measure feed intake per day/per week regularly & adjust the level of critical nutrients according to intake. To encourage feed consumption during heat stress various feeding strategies can be employed like:
a) Feed Restriction: Feed restriction can be done to reduce the heat load when the ambient temperature is high. Gratification for 2 hours prior to the warmest period during the day to fix the FCR and reduce mortality without affecting body weight. One option is to complete the morning feeder cycle by 10:00 am. An additional advantage with this is the availability of calcium in the digestive system during shell formation at night and in the early hours of the morning, so-called ‘midnight snacks’ are a good tool to give hens extra feeding time in the cooler parts of the night. A good strategy to take an unnecessary heat load off the birds is to withdraw feed 8 hours prior to the anticipated time of peak temperature. One-third of the daily feed ration should be given in the morning and two-thirds in the late afternoon. Feeders should run empty at least once a day to enhance the appetite and to ensure that the fine particles of the feed (premixes, vitamins etc.) are consumed.
b) Free choice feeding: Poultry can adjust nutrient consumption by the need to select appropriate feed ingredients for physiological needs. Feed with the rough shape particles will have a longer retention time in the digestive tract so will generate heat slower during digestion. In addition, feed consumption as coarse particles encourage more water consumption than regular feed so that it can reduce the heat load to facilitate heat dissipation in evaporation. The feed texture should not be too fine. Oil/Molasses can also be used to avoid “dusty” feed and to increase palatability.
c) Wet feeding:
As shown in the flow chart (above) Prolonged panting causes increased CO2 loss & changes the acid-base balance in the body. Birds’ metabolism also gets affected due to respiratory alkalosis & dehydration.
To overcome this imbalance acidifiers & electrolytes can be supplemented in feed as wet feeding. This will also create optimal conditions for enzyme activity & digestion so that feed can easily be digested and absorbed, which will improve body weight gain and FCR.
Advantage of use of acidifier for wet feeding
• Liquid acidifier moistens the feed without compromising the sterility of the feed
• Acts as feed sanitizer
• Improves palatability of feed. Thus, improves voluntary feeding
• Improves digestion & absorption of feed by balancing the gut pH
d) Special Feed formula for summer
Increase dietary protein: In hot weather, the need for maintenance energy is much lower than at an ideal temperature and birds respond by less feed consumption. With the reduction in consumption, there is often a reduction in intake of essential nutrients such as protein, essential amino acids, minerals, and vitamins, which can result in reduced body weight and egg production. So, to ensure feed intake of essential amino acids & vitamins, it is recommended that the protein content of feed should be increased by 1-2 %. However, there is a possibility that increasing dietary protein might be detrimental to the bird as more heat is produced during its utilization and that may well overload heat dissipation mechanisms (i.e., panting, blood circulation etc.)
Therefore, improving the overall balance of the diet by amino acid supplementation appears to be more effective than increasing protein intake.
Increase nutrient density of the diet: To increase the energy content of the diet during hot weather, it is always recommended the use of supplemental fat. Dietary fat increases the palatability of feeds and reduces the amount of heat increment that is produced during its utilization in the body.
Feeding calcium carbonate or oyster shells: Calcium content of the diet should be adjusted according to the anticipated level of intake, such that each bird can consume the right amount per day. For laying hens, top dressing feed with oyster shell or large particulate limestone is beneficial and has the added advantage of stimulating feed consumption. Limestone and oyster chips may be provided at a rate of 625 g per100 hens.
Supplements (Minerals and Vitamins): Imbalances acid-base is very common in heat-stressed birds. Therefore, the inclusion of various compounds in the diet or water is a common practice to alleviate the adverse effects of heat stress. These include sodium bicarbonate, potassium chloride, calcium chloride, ammonium chloride and Research has proven that sodium bicarbonate at high temperature stimulates water and feed consumption & contributes to improved weight gain. Sodium bicarbonates can act as an alternative source of sodium & assist in maintaining a healthier living environment with better conditions. The addition of 8 g of sodium bicarbonate to the 100 liters of drinking water [or 35g per 25kg) can be useful in heat-stressed birds to stimulate water consumption.
Vitamin C rich diet
Any stressors like heat stress may increase the chickens’ need for vitamin C, since chicken is not able to synthesize enough vitamin C to meet increased physiological demands. Vitamin C plays crucial role in amino acid & mineral metabolism and synthesis of some hormones.
Vitamin C ameliorates heat stress-induced problems such as poor immunity, feed intake, weight gain, oxidative stress, rectal and body temperature, fertility and semen quality, carcass weight and mortality in birds. Supplementation of essential herbs like Ocimum sanctum, Withania somnifera, Emblica officinalis & minerals can also help to overcome heat stress.
Advantage of Vitamin C supplementation in feed
- Antioxidant: Ascorbic acid can scavenge free radicals and reduce oxidative stress. It is also protecting the fat-soluble vitamins A and E as well as fatty acids from oxidation.
- Immune System: Vitamin C makes the epithelial tissues in the mouth less permeable to bacteria. It also assists the white blood cells for proper function and so contributes in maintaining the immunity. Furthermore, it protects the immune system and reduces mortality in growing birds infected with IBD in a hot environment by protecting the lymphoid organs and bursal activity.
- Maintenance: Vitamin C helps in hydroxylation & maturation of collagen fibers. Collagen is integral part of bone, cartilage & blood vessels. So, better maturation of collagen helps to improve egg shell quality in layers & dressing percentage in broiler.
- Enhances iron absorption: Vitamin C improves the absorption of iron by converting Fe into its bioactive form, which intern increases the hemoglobin level in body & limit the respiratory alkalosis to an extent.
The availability of adlibitum clean, cool drinking water is very crucial during hot conditions. Any action which limits water intake will depress production.
The ideal drinking water temperature is 10-120C. Ensure there are enough drinkers with even distribution throughout the shed at the right height. Water tank should be filled in every 4 hours with fresh & cool water.
a) Use of Vitamin C in drinking water to avoid Heat Stress: Vitamin C in drinking water can lower rectal temperature during the day time in chickens. The secretion and release of corticosterone can be reduced by Vitamin C supplementation. Supplementation of honey @ 20ml per liter of drinking water can decreased the frequency of panting and heart rate. Honey contains phytohormones that play a role in muscle contraction and relaxation of the heart and lungs.
b) Advantage of water acidification in summer: Water quality frequently changes from season to season in each location or area depending on the source. In summer the decreased underground water level results into increased pH & total dissolved solids [TOSI in drinking water leading to high water alkalinity and hardness. It is advisable to monitor water composition every six months and not only when the producer experiences poor flock performance. In summer as water consumption also increased, there is maximum threat of water borne diseases. Chlorination is an ideal tool to achieve highest water sanitization, but for proper chlorination water pH should be kept in acidic range. By using acidifier in drinking water both the problems can be solved as organic acids balance water pH in 5-5.5 range and due to their bacteriostatic action ensures the safety of drinking water.
By understanding heat stress and taking steps to prevent it, you will be keeping your birds comfortable and still loving the sunshine.
Vitamin C is necessary for various biosynthesis [collagen, 1,25- dihydroxy vitamin D and adrenaline) as well as for regulation of diverse reactions [secretion of corticosterone, regulation of body temperature and activation of immune system). It has been reported that vitamin C enhances the antioxidant activity of vitamin Eby reducing the tocopheroxy radicals back to their active form of vitamin E. Adult poultry under normal conditions are able to synthesize vitamin C to meet the requirement. However, it has been reported that vitamin C requirement is higher during stress and several reports have documented a beneficial effect of supplementing poultry feed with ascorbic acid.
Ascorbic Acid also called vitamin C, had been very useful as a supplement in poultry diets under stress, particularly under heat stress. In view of the fact that ascorbic acid of tissue synthesis is not sufficient at periods of stress, and that diets do not usually contain vitamin C, the birds are liable to suffer from vitamin C deficiency, if rations are not supplemented with vitamin C. It has been observed that supplementation of diets with ascorbic acid at required levels, especially under heat stress, improves growth, egg production, egg shell strength, fertility within (male and females) and hatchability of poultry eggs. The depressant effect of high temperature on performance often compels the technique of supplementing poultry diets to ensure optimum production. Therefore, it is necessary to adopt effective measures to control heat stress and its adverse effects on livestock. Vitamin C alleviates the side effects of stress, thus increased heat tolerance in birds, and improved chickens’ response to cell functional immunity. Therefore, ascorbic acid could be included at the rate of 250mg/kg diet, 500mg/kg diet and 400mg/kg diet for day old chicks, Breeders or Layers and broiler chickens, respectively.