This study aimed to provide the performance, localization and expression of the epithelial calcium transporter channels Calbindin-D28k (Calb) and TRPV6, and of the morphology of the digestive and reproductive system of laying quail under heat stress (HS), and with methionine supplementation (MS). This study characterized the positivity (immunohistochemistry) and expression (real-time PCR) of calcium channels in the kidneys, intestine and uterus of 504 laying quails under different MS (100, 110 and 120%) and temperatures (20, 24, 28 and 32°C). The animals under HS (32°C) had lower villus height, villus:crypt ratio, and goblet cell index in the duodenum and jejunum, fewer secondary and tertiary uterine folds, smaller hepatic steatosis, and increased number of distal convoluted renal tubules (CT) positive to Calb, and increased positivity in proximal CTs. Deleterious effects of HS were minimized with MS for: duodenal crypts, number of goblet cells of the jejunum, number of uterine folds, decreased Calb positivity in intestines and kidney, increased positivity of Calb in the uterus and increased TRPV6 gene expression in the kidney (P≤0.05). Epithelial calcium transporters were altered due to less need for calcium absorption and reabsorption due to more calcium available with the MS, increasing egg production in HS and quality in termoneutrality (P≤0.05). MS further increased intestinal villus absorption area and height, increased steatosis, decreased Calb positivity in the intestine and kidney, increased uterine positivity of Calb, and increase Calb and TRPV6 expression in the kidney (P≤0.001) under thermoneutrality. It was concluded that the use of MS (120%) is justifiable in order to partially reverse the deleterious effects of HS on the production, in the epithelial calcium carriers, and in the digestory and reproductive morphology of laying quail.

23The aim of this study was to provide support for the performance, localization and expression of the 24 epithelial calcium transporter channels, calbindin-D28k (Calb) and TRPV6, and of the morphology of the 25 digestive and reproductive system of laying quails under heat stress, and with methionine 26 supplementation. Therefore, the present study characterized the positivity (immunohistochemistry) and 27 expression (real-time PCR) of calcium channels (Calb and TRPV6) in the kidneys, intestine and uterus of 28 504 laying quails that were submitted to different methionine supplementation (100, 110 and 120%) and 29 temperatures (20, 24, 28 and 32ºC). The animals under thermal stress had lower villus height, villus:crypt 30 ratio, and goblet cell index in the duodenum and jejunum, fewer secondary and tertiary uterine folds, 31 smaller hepatic steatosis, and increased number of distal convoluted renal tubules (CT) positive to Calb 32 (protein), and increased positivity in proximal CTs. The deleterious effects of heat stress were minimized 33 with methionine supplementation for the following variables: duodenal crypts, number of goblet cells of 34 the jejunum, number of uterine folds, decreased Calb positivity in intestines and kidney, increased 35 positivity of Calb in the uterus and increased TRPV6 gene expression in the kidney. Calcium transporters 36 were altered due to less need for calcium absorption and reabsorption due to more calcium available with 37 the supplementation, increasing egg production and quality. Methionine supplementation further 38 increased intestinal villus absorption area and height, increased steatosis, decreased Calb positivity in the 39 intestine and kidney, increased uterine positivity and Calb expression, and increased TRPV6 expression 40 in the uterus under thermoneutrality. This is the first study that describes the gene and protein expression 41 of calcium transporters in the intestine, kidney and uterus of laying quails, and concludes that the use of 42 methionine supplementation is justifiable in order to partially reverse the deleterious effects of thermal 43 stress on the production. 44 45 46 3 47 65Methionine, classified as an essential amino acid [9], is also the first limiting factor in poultry 66 feed, and is essential for the maintenance, growth, production, and development of feathers [10]. In 67 addition to the productive responses obtained with methionine supplementation in laying hens, studies of 68 the morphological analyses of the laying digestive and reproductive system of broilers and light birds 69 indicate favorable quantitative and qualitative changes, such as an increase in egg mass by 10%. [11,12], 70 decreased laying fat [13], increased eggshell thickness [14], and increased intestinal villi [15], which 71 provide and technically justify the improvement in zootechnical indexes of these animals with methionine 72 use [15][16][17][18]. 73Evaluating the existing literature [15][16][17][18], diets supplemented with methionine at levels above 74 NRC (Nat...