Effect of heat stress on production, physiological, and metabolic parameters in three varieties of laying hens

Abstract

The needs for food with a growing world population have increased genetic selection for a more efficient bird, affecting parameters such as resistant to diseases and/or heat stress. Laying hens are affected by heat stress conditions (HS), and differences in production parameters (PP) as well as survivability have been observed. Different approaches have been used to increase thermotolerance in layers and broilers such as heat conditioning, manipulation of diet composition and feed deprivation, but usually these adjustments are not easy to apply and tend to require trained personnel. In this research a series of studies was done to evaluate productive, physiological and metabolic parameters, and the effect of addition of excess dietary vitamin D3 as a management adjustment in three varieties of laying hens (Hy-Line^® Browns, W98, and W36) exposed to HS. In general, the three strains responded in the same manner to HS (thermal panting, respiratory alkalosis, increase in fat metabolism, reduction of feed intake, intestinal calcium uptake (CaT), egg production (EP), reproductive hormone levels, and increase in liver expression of heat shock protein-70), but there were differences in the degree of the response being elucidated. The W36s were more resistant to HS in term of survivability, but PP were highly affected in this strain. The W36s expressed the highest rate of CaT, but calcium utilization (CaU) was greatly affected with a reduction in eggshell quality (EQ). Brown birds expressed the worst performance in survivability and PP during HS. W98 birds showed an intermediate mortality rate but expressed along with the W36s the highest PP during HS. However, the W98s showed the least reduction in EQ during HS. Vitamin D3 during HS was able to improved survivability, EP and CaT; however, CaU was not improved, as was noted by a poor EQ in white birds. Identification of gene markers involved in the development of thermotolerance in birds may provide a low-cost solution to be included in breeders selection programs.