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Abstract
Heat stress is one of the most detrimental confrontations in tropical and subtropical regions of the world, causing considerable economic losses in poultry production. Propolis, a resinous product of worker honeybees, possesses several biological activities that could be used to alleviate the deleterious effects of high environmental temperature on poultry production. The current study was aimed at evaluating the effects of propolis supplementation to Japanese quail (Coturnix coturnix japonica) diets on the production performance, intestinal histomorphology, relative physiological and immunological parameters, and selected gene expression under heat stress conditions. Three hundred one-day-old Japanese quail chicks were randomly distributed into 20 wired-cages. At 28 d of age, the birds were divided into 2 temperature treatment groups; a normal at 24°C (C group) and a heat stress at 35°C (HS group). The birds in each group were further assigned to 2 subgroups; one of them was fed on a basal diet without propolis supplementation (-Pr subgroup) while the other was supplemented with propolis (+Pr subgroup). Production performance including body weight gain, feed intake and feed conversion ratio were measured. The intestinal histomorphological measurements were also performed for all treatment groups. Relative physiological parameters including body temperature, corticosterone hormone level, malondialdehyde (MDA) and free triiodothyronine hormone (fT3), as well as the relative immunological parameters including the total white blood cells count (TWBC’s), heterophil/lymphocyte (H/L) ratio and lymphocyte proliferation index, were also measured. Furthermore, the mRNA expression for toll like receptor 5 (TLR5), cysteine-aspartic protease-6 (CASP6) and heat shock proteins 70 and 90 (Hsp70 and Hsp90) genes was quantified in this study. The quail production performance was significantly (P<0.05) impaired by HS treatment, while Pr treatment significantly improved the quail production performance. The villus width and area were significantly (P<0.05) lower in the HS compared to the C group, while Pr treatment significantly increased crypts depth of quail. A negative impact of HS treatment was observed on the physiological status of quail; however, propolis significantly alleviated this negative effect. Moreover, quail of the HS group expressed lower immunological parameters than C group, while propolis enhanced the immune status of the quail. The relative mRNA expression of TLR5 gene was down-regulated by HS treatment while it was up-regulated by the Pr treatment. Furthermore, the positive effects of propolis in HS-quail were evidenced by normalizing the high expressions of CASP6 and Hsp70 genes when compared to the C group. Based on these results, the addition of propolis to quail diets as a potential nutritional strategy in order to improve their performance, especially under heat stress conditions, is recommended.
Highlights
Japanese quail (Coturnix coturnix japonica) is considered one of the locally available and a cheap sources of poultry meat [1]
The results of the present study indicate that dietary propolis supplementation can alleviate the negative effects of heat stress on the growth performance, intestinal histomorphometry, physiology and immunity of Japanese quail
The plasma corticosterone and body temperature were decreased in the quail that were fed with propolis, indicating that propolis decreases the stress indicators in quail exposed to heat stress conditions
Summary
Japanese quail (Coturnix coturnix japonica) is considered one of the locally available and a cheap sources of poultry meat [1]. Quail meat is renowned for its dietary properties like highquality protein and low-caloric content, and its valuable taste to consumers [2,3]. It is a preferable experimental animal model for its unique characteristics and advantages over other species of poultry, which include early attainment of sexual maturity and short generation interval which normally produce several generations in a year [4]. It is indicated that exposure to acute heat stress causes a substantial impairment in the gut formation, intestinal epithelial integrity and villus morphology in laying hens [14]. It has been reported that poultry exposure to stress conditions, including heat stress, could have differential influences on the expression pattern of some genes such as apoptotic and heat shock proteins [15,16,17]
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