H. Mohammadi - Department of Agriculture, Payame Noor University, Tehran, P. O. Box: ۱۹۳۹۵-۳۶۹۷, Islamic Republic of Iran.
Z. Ansari-Pirsaraei - Department of Animal Science, Sari Agricultural Sciences and Natural Resources University, Sari, Islamic Republic of Iran.

Hen aging is accompanied by a disruption of productive performance, namely, egg production. The current study was carried out to investigate how exogenous Growth Hormone (GH) and Testosterone (Ts) change diameters of hierarchal follicles, egg weight, and egg production performance of old laying hens in the late phase of production. To this end, ۱۶۰ HyLine W-۳۶ laying hens (aged ۷۳ weeks), were injected (single injection) with GH and Ts as follows: Treatment ۱: ۱۰۰ µL distilled water (control group); Treatment ۲: ۵۰۰ µg Ts kg-۱ Body-Weight (BW)+۵۰ µg GH kg-۱ body-weight; Treatment ۳: ۵۰۰ µg Ts kg-۱ BW+۱۰۰ µg GH kg-۱ BW, and Treatment ۴: ۵۰۰ µg Ts kg-۱ BW+۱۵۰ µg GH kg-۱ BW. The experiment had four replicates and ۱۰ birds in each replicate in a completely randomized design. The diameters of Small White Follicle (SWF), Large White Follicle (LWF), the First (F۱), Second (F۲) and Third (F۳) largest yellow follicles in treatment ۳ were significantly larger than in the control group, in the second week after the injection. Hen-Day Egg Production percent (HDEP), egg mass, and Feed Intake (FI) of treatment ۳ were significantly higher than all other groups, during the second week after the injection; besides, HDEP and FI in treatment ۴ were significantly more than in the control group. These results suggest that in old laying hen, GH and Ts may positively influence follicular diameters and egg production performance.

Egg parameters, Hen-day egg production, HyLine W-۳۶ laying hens