SAFEGUARDING WELL-BEING OF FOOD PRODUCING ANIMALS
Location: Livestock Behavior Research
Title: Genetic variations alter production and behavioral responses following heat stress in two strains of laying hens
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 2012
Publication Date: N/A
Interpretive Summary: Heat stress is a condition in which an animal is exposed to a high temperature environment for an extended period of time. In laying hens, heat stress is a common problem, especially in warm climate areas. Previous studies have shown that when a bird is experiencing stress, including heat stress, egg production is dramatically reduced while incidences of mortality increase. Furthermore, it has been shown that the hens’ response to stressors is dependent upon their genetic background. The goal of the current research was to determine the genetic variation of the heat stress response in two strains of well studied hens. To achieve this, we separated half of our hens into two treatments; a control temperature at 24.3 °C and heat stress temperature at 32.6 °C for 2 weeks. The results showed differences in production values, as well as hormone and immune functions between heat stressed hens and their controls. Compared to Dekalb XL (DXL) hens, kind gentle bird (KGB) hens responded better to heat stress. These results are extremely beneficial to the scientific community in better understanding the role of genes in heat stress response. These data also provide evidence that is useful to egg producers to aid in selecting for hens with genetic backgrounds that are more capable of handling heat stress.
Heat stress is a problem for both egg production and hen well-being. Given a stressor, genetic differences alter the type and degree of hens’ responses and their adaptation. This study examined heat stress responses of two strains of White Leghorns: Dekalb XL (DXL), a commercial strain individually selected for egg production and kind, gentle bird (KGB), a strain selected on high group productivity and survivability. Ninety 28 wk old hens (48 DXL and 42 KGB) were randomly pair-housed by strain and assigned to hot (HOT) or control (CON) treatments for 14 days (mean: HOT = 32.6 °C, CON = 24.3 °C). Hens’ egg production (egg production, EP; egg weight, EW; and shell thickness, Sh-Th), behavior, physical variables (body weight, BW; relative ovary weight,OW; number of mature follicles; and crop fill weight), and hormone concentrations (plasma triiodothyronine, T3; plasma thyroxine, T4, plasma and yolk corticosterone concentrations, P-CORT and Y-CORT) were measured. At wk 1, EP (P < 0.0001) and EW (P < 0.001) were reduced (P < 0.05) in HOT hens compared to CON hens across both strains. Egg shell thickness was also reduced in HOT hens during the treatment (P < 0.01). In heat stressed hens, but not CON hens, EP, EW, and Sh-Th improved over time. Behaviorally, HOT hens drank (P < 0.01) and rested (P < 0.01) more and sat less often (P < 0.05) than CON hens. Comparing strains, DXL hens rested more (P < 0.05) and spent less time eating than KGB hens (P < 0.001). Body weight (P < 0.001) and OW were reduced in the HOT hens compared to CON hens (P < 0.05). The plasma T3 concentration was reduced in HOT hens, (P < 0.0001) but neither treatment nor strain affected concentrations of plasma T4, P-CORT, and Y-CORT. The results indicate that although heat stress reduces production and causes behavioral changes in both hen strains, genetic background shaped the nature and intensity of the response.