N: 1110-5623 (Print) – 2090-0570 (Online) EFFECT OF ACUTE HEAT STRESS CONDITIONS ON EGG PRODUCTION, EGGSHELL QUALITY, INTESTINAL CALCIUM TRANSPORT AND CALBINDIN OF THE LAYING HENS

One hundred and fifty Hy-line layer hens, 40 weeks of age were used to study the impact of hot climate on egg production, eggshell quality, intestinal calcium transport and calcium binding protein concentration of the laying hen. Birds were randomly allocated to two experimental groups equally, the 1st group, that served as a control, was reared at room temperature under thermoneutral condition which ambient temperature was 25±1ºC, while the second group was subjected to 40±1ºC for 5 days (4 hrours daily). Egg production, eggshell quality, serum concentrations of calcium, phosphorous, thyroid, aldosterone and estrogen hormones as well as acid phosphatase and alkaline phosphatase activities were estimated. Calcium binding protein concentration and the transport of radioactive calcium ( 45Ca) across the duodenal were also measured. The results indicated that egg weight, hen-day egg production and eggshell quality were inversely related to high temperature peroids. Serum calcium, calcium binding protein, phosphrous and alkaline phosphatase values were significantly lowered in heat stressed birds. The highest values for serum acid phosphatase and duodenal calcium transport were recorded for heat-treated hens at the 5th days of heat stress period. Thyroid and estrogen hormones unlike aldosterone hormone concentrations declined under hot climates. In conclusion, the present study recommends avoiding exposure to heat stress conditions because of its negative impact on the level of blood calcium and intestinal calbindin-D28k and the consequent decrease in the egg production rate and the deterioration of the eggshell quality