Effect Of Diet Formulation With Net Energy On The Laying Performance Of Heat-stressed Laying Hens

This study has evaluated the effects of different energy allowance on egg production, eggquality and blood responses of laying hens at higher ambient temperature. A completelyrandomized experimental design with a2×2factorial arrangement (diet and temperature),each with4replicates of12laying hens (Hy-line Variety Brown,48-wk-old), was applied.Diets were formulated to satisfy ME or NE requirements, respectively. Temperaturetreatments were24±2and32±2oC. The NE value of feed ingredients and experimentaldiets was calculated at a discount of ME, as described by Leeson et al. Experimental durationwas5weeks.At the end of the experiment, feed intake, laying production and egg weight wererecorded on a per-replicate basis, and feed to egg ratio was calculated. Also measured wereplasma contents of intermediary metabolites, such as glucose, triglyceride and urate.Parameters of egg quality were determined at4wk for three consecutive days after theexperiment began, including eggshell weight, eggshell strength, eggshell thickness, yolkweight, yolk color, Haugh unit and albumen height. Results are as follows:Laying performance: Feed intake (P <0.01), egg production (P <0.01), laying rate (P <0.05), body weight (P <0.01) and egg mass (P <0.01) of laying hens were all significantlydecreased by higher temperature. Feed to egg ratio had a marginal increasing trend (P=0.081)as temperature increased. At the first week of this experiment, egg weight of NE-allowedlayers was significantly higher than did ME-satisfied hens (P <0.05). A significant interactionwas observed between temperature and age for feed to egg ratio (P <0.05), but not betweentemperature and diet for any production trait.Egg quality: Parameters of egg quality were hardly affected by diet and temperaturetreatments as well as their interactions, except that egg weight was significantly decreased (P<0.01) by heat exposure.Blood parameters: Plasma level of urate was significantly altered by temperaturetreatment (P <0.01) and its interaction with diet (P <0.05). Plasma contents of triglycerideand glucose didn’t exhibit any significant change.In conclusion, heat stress has a detrimental effect on laying performance and egg quality of hens, which can not be alleviated by diets formulated on a NE basis. The application ofdietary NE allowance in layer production needs to be investigated further.