The greater egg surface area in the control group might be related to larger eggs having a greater surface area and an elongated shape (Akram etal.,2013). The egg shell density was greater in the thermoneutral group compared to the heat-stressed groups and this may be due to the greater egg size overall in the thermoneutral group. Sezer (2007) found that the egg shell density decreased as shell weight decreased and egg weight increased. The deteriorated shell quality in the present trial may be partially attributed to a decreased Ca level in plasma. It has been
recorded that estimated level of plasma Ca was significantly decreased in the laying hens confined to high temperatures. In addition, former reports concluded that Ca uptake by epithelial cells in the duodenum was decreased by exposure to high ambient temperatures (Mahmoud etal.,1996).