Morphological changes in the lungs and air sacs of the Japanese quail (Coturnix japonica) exposed to heat stress

Abstract

The Japanese quail presents a potential protein food security alternative in rural sub-Saharan Africa because of its small size and easy husbandry. The nutritional and therapeutic value of its meat and egg makes it an interesting and better choice than chicken in some parts of the world. In addition, researchers used Japanese quail as an animal model of human genetic and developmental disorders because of its short generational interval. However, global warming threatens its welfare by propagating heat stress. The physiological response of Japanese quail under heat stress causes negative performance and sometimes instant mortality. Hence, in this study, lung of the quail under heat stress was microscopically examined as it is the most important organ for survival under heat stress. All other organs depend on the lungs for oxygen, and it is also the most crucial in evaporative cooling. A total of 38 Japanese quail were used in this study. A pilot study was conducted that used eight quails, to ensure the possibility of survival under the proposed experimental temperatures. Afterwards, 30 quails were randomly allocated — based on initial body mass— to five groups of six quails each. The control groups (CT and CT2) were maintained at a thermoneutral temperature of 25°C throughout the experiment while acute heat stress group (AH) were maintained at 38°C for 24 hours only. The chronic heat stress groups (CH1 and CH2) were maintained at 35°C for seven days and 28 days respectively. Body mass, cloacal temperature, and respiratory rate of quails were measured daily to monitor health and detect any serious ill health from heat exposure. Food and water were provided ad libitum. At the end of the experiment, all quails were terminated using an overdose of anaesthetic and lungs were harvested and processed for microscopy. Lung weight, volume and size were measured before sampling. Tissue samples were processed, and sections were cut with a microtome and stained with Mayers H&E, new pentachrome stain and Gomori’s one-step trichrome stain. Other tissue samples were triple immunolabelled with anti-α-SMA and Collagen 1 antibody and DAPI nuclear stain. Tissue samples were also processed for scanning and transmission electron microscopy. No significant difference in body mass, cloacal temperature, respiratory rate and lung parameters was found in heat-stressed quails compared with control. However, microscopic examination revealed blood congestion and excessive leakage of blood into airway of lungs in heat-stressed groups compared with the control. In addition, there was structural damage to parenchyma and blood vessels, which incites an inflammatory response causing deposition of collagen fibres in some areas of the lungs in heat-stressed groups. Interestingly, these effects occur in a time-dependent pattern. The most impact is seen in AH and CH1 groups while CH2 shows signs of recovery. In conclusion, Japanese quail lung was negatively impacted by heat stress, which can lead to instant mortality or long-term reduction of performance. Despite the evidence from this study suggesting that Japanese quail can adapt to the effects of heat stress if it survives the initial impact, a conscious effort must be made to alleviate or remove heat stress for quality outcomes.