Short- and long-term dynamics of the physiological and behavioral response to heat stress and thymol supplementation in Japanese quail

Context- and scale-dependent effects of thymol bioactivity on biological networks: contributions from quail under heat stress

“…Similarly, apparent contradictory effects of thymol have also been reported regarding feed intake. On one hand, the inclusion of thymol in the diet of pigs [74], poultry [15,[75][76][77][78], and specifically female quail in the short-term quail [45] can promote reduced feed intake. On the other hand, several studies evaluating the long-term effects of thymol supplementation have shown that feed intake was unchanged after chronic thymol supplementation (>3-weeks) in growing broilers [42,73], adult laying hens [44] and Japanese quail [63,79], as observed in the Joint and Prior, but not in the Post, strategies.…”

“…The first day of the experimental period, females were randomly assigned to a control basal diet (Basal; 16 birds) or to a chronic dietary supplementation with 6.25 g of thymol/kg of feed (see preparation in S1 Appendix) that was supplied accordingly to one of three strategies Prior, Joint or Post strategy (16 birds in each strategy, see details described in the following paragraphs). At day 14 of the experimental period, half of the birds within each of these dietary groups were maintained at standard environmental temperatures (no heat stress; NHS, 23.6 ± 0.1°C) or were submitted to a chronic cyclic heat stress (HS) protocol induced by daily increasing the environmental (room) temperature from 23.6 ± 0.1°C to 34.2 ± 0.1°C between 8-17 h, over a 23-day period, according to [45] (see details in S2 Appendix). Finally, at day 37 of the experimental period, birds were euthanized.…”

“…Birds under these conditions will be referred to as "Joint-NHS" or "Joint-HS", depending on the environmental temperature they were exposed to. This supplementation strategy with thymol has previously shown beneficial influence on physiological and behavioral variables of adult female quail [45]. Additionally, as stated in the introduction, supplementation protocols in a joint strategy-like fashion are the most frequently found in literature regarding supplementation with phytogenic compounds in poultry under heat stress [14,[52][53][54].…”

“…Precedent studies in poultry and other farm animals have mainly focused on experimental designs aimed at evaluating one of two types of supplementation strategies. Specifically, those in which thymol or other phytogenic supplementation was initiated either prior to (appealing for potential preventive effects) or simultaneously with heat stress exposition [14,45,[52][53][54]. For example, adult Japanese quail exposed to chronic cyclic heat stress and previously supplemented with thymol, showed a heterophil/lymphocyte ratio similar to their control non-stressed counterparts [53].…”

“…As can be noted from the above descriptions, through various mechanisms and biochemical pathways, both thymol supplementation and heat stress have the capacity to influence some of the same traits (e.g., antioxidant system, somatic maintenance). Moreover, both factors separately and together have time-dependent effects on traits such as feed intake [21, 45], and antioxidant enzymes synthesis. For example, short-term exposure to thymol in fish [36] can induce a pro-oxidant effect with a decrease in antioxidant enzymes synthesis, while, in the long-term the contrary has been observed in mice [37].…”