Abstract
Background:
Anadara granosa clam shell powder, as a natural aromatase blocker (NAB), may inhibit the conversion of testosterone to estradiol (E2). It triggered the feedback mechanism of follicle-stimulating hormone (FSH) secretion. The mechanism potentially accelerated the development of ovarian follicles and the first egg-laying age.

Aim:
This study aimed to evaluate the effect of A. granosa clam shell powder as an NAB on egg production (particularly age at first egg), number of ovarian follicles, egg quality, FSH, and E2 levels in laying hens.

Methods:
It was a completely randomized study of 30 laying hens of 14 weeks of age classified into three treatment groups: T0 (control), T1 (basal feed + 1 g of A. granosa clam shell powder as NAB), and T2 (basal feed + 2 g of A. granosa clam shell powder as NAB). The chickens were treated for 30 days and raised in a battery coop. The egg production parameters, namely age at first egg, number of eggs, and egg-laying percentage (production percentage). Blood samples were drawn on days 0, 7, and 30 and analyzed using enzyme-linked immunosorbent assay to establish FSH and E2 levels. At the end of the treatment, one laying hen at the age of first egg with the highest productivity from each group was slaughtered using the halal method to observe ovarian follicle characteristics. The number of ovarian follicles, egg production, and number of ovarian follicles were collected and analyzed descriptively.

Results:
The NAB supplementation (T1 and T2) could increase the number of ovarian follicles, especially small white follicles (SWF), small yellow follicles (SYF), and hierarchical follicles (F1) as compared to T0. The laying hens in T1 and T2 began to lay eggs earlier (117 days) than those in T0 (126 days). The egg production percentage of T1 and T2 increased faster and reached 50% at 128–129 days of age. The egg weight and the yolk color of T1 and T2 were significantly different (p < 0.05) from those of T0. The NAB supplementation (T1 and T2) on day 7 could significantly increase the FSH level compared to T0. The inter-column E2 hormone level on days 7 and 30 showed that treatments T1 and T2 were significantly different from T0.

Conclusion:
NAB supplementation accelerated the onset of egg production in laying hens without decreasing egg quality, increased the number of ovarian follicles, especially SWF, SYF, and hierarchical follicles (F1); improved egg quality, including egg weight and yolk color; and increased FSH and E2 hormone levels in laying hens.

Key words: Egg production; Egg quality; Natural aromatase blocker; Number of ovarian follicles; Reproductive hormone.