HEAL ▶▶▶TH Managing heat stress

Rising global temperatures and the undeniable fact that modern, highly productive poultry breeds are more prone to heat stress, is a challenge for the industry. Fortunately, innovative plant-based nutritional solutions now provide the opportunity to stabilise broiler and layer performance during hot weather.


2.00 1.95 1.90 1.85 1.80 1.75 1.70


1.89 *

0.20 0.15 0.10 0.05 0.00

Control IQs Control

odern poultry breeds are particularly suscepti- ble to warming temperatures because their in- sulating feathers, lack of sweat glands on the skin and a high body mass to body surface area

ratio make it difficult to lose heat. Additionally, in broilers, for example, the ability of a modern bird to tolerate heat has been further eroded by the fact that intensive genetic selec- tion – in the quest for a faster growth rate – has boosted metabolic activity. Heat stress is a physiological response to the combined ef- fect of high ambient temperature and the relative humidity of the air. Heat stress occurs if poultry are outside their ther- moneutral zone and struggle to regulate their body temper- ature. Birds that are too warm will increase their respiratory rate and divert blood away from the gastrointestinal tract towards their skin, comb and wattles in an attempt to cool down. They can also reduce their feed intake by as much as 20%. Clearly, this can have a catastrophic effect on both broiler growth and egg laying performance. Furthermore, heat stress also has adverse consequences for meat quality

Figure 1 - FCR and Gut integrity of birds fed IQs under heat stress (HS) conditions compared to Control.

FCR (d14 - 42) 0.25 FITC-dextran 0.23

0.17 *

and even increases the risk of poultry becoming contami- nated with food-borne pathogens, which represents an im- portant food safety issue, so the effective management of this environmental challenge is becoming increasingly important. Improved house design, including better insulation and ventilation, can help to mitigate the undesirable physiologi- cal effects of heat stress but building modifications can be prohibitively expensive. A variety of remedial nutritional steps can also be taken, depending on the local situation. These include ensuring an optimum drinking water temper- ature, the use of highly digestible feed proteins, choosing the right anticoccidial programme (as some anticoccidials decrease the capability to cope adequately with high ambi- ent temperatures), the use of appropriate electrolytes and/ or antioxidants and even the application of specific organic trace elements – but often these can be relatively ineffec- tive tweaks that will not necessarily address one of the fundamental physiological effects of heat stress in poultry.

Intestinal integrity compromised There is a strong link between heat stress and intestinal in- flammation with far-reaching consequences for intestinal barrier function. As evidenced by various research papers, heat stress compromises intestinal integrity, in conjunction with increased levels of pro-inflammatory cytokines, stress hormones (cortisol) and reactive oxygen species, leading to suboptimal nutrient uptake and poor performance. Indeed, intestinal mucosal barrier dysfunction, inflammatory re- sponses and an enhanced risk of bacterial translocation from the intestinal lumen into the bloodstream have all been identified as major symptoms in birds subjected to heat stress. Consequently, a number of feed additives known for their anti-inflammatory effects have been inves- tigated for their potential to reduce this heat stress-induced intestinal inflammation. For example, isoquinoline alkaloids (IQs) have been shown to boost growth in broilers due to their anti-inflammatory properties. It is logical, therefore, to try to assess their ability and potential to mitigate intestinal inflammation caused by heat stress.


Adapted from Kikusato et al., (2021) *significant difference vs. Control group (P < 0.05). HS conditions were 33°C from 14 d onwards. All measurements at 42 days of age.

34 ▶ POULTRY WORLD | No. 3, 2021

New studies In a recent trial at Tohoku University in Japan, 360 male Ross 308 broiler chickens were divided into two treatment groups – a control and a group fed a diet supplemented with a standardised blend of plant-derived IQs. The birds were kept under thermoneutral conditions until day 14. Thereafter, a 2×2 factorial design was used to determine the



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