Background and Aim: Pelung cockerels (Gallus gallus gallusGallus gallus gallus [Linnaeus, 1758]) are different from other native cockerels in that they have a long and unique voice, in addition to their tall, large, and sturdy body with a relatively heavy body weight (BW). The sound quality of pelung cockerels is affected by the structure of the syrinx and their large and strong chest muscles. The performance of the chest muscles, and subsequently its voice, is influenced by the hormone testosterone. The shell of blood clams (Anadara granosa Linnaeus, 1758), a saltwater bivalve is known to contain a natural aromatase blocker (NAB) capable of blocking the aromatase enzyme from converting testosterone to estradiol. This generates consistently high levels of testosterone. This study aimed to determine the effect of blood clam shell powder (BCSP) as an NAB on the growth, pectoralis muscle performance, and testes of pelung cockerels.

Materials and Methods: The study design was a completely randomized design, with 16 pelung cockerels aged 40–56 weeks divided into four treatment groups: T0 (control); T1 (BCSP [A. granosa] 0.9 mg/kg BW); T2 (zinc sulfate [ZnSO4] 0.9 mg/kg BW); and T3 (testosterone 3 mg/day). The animals were acclimatized for 7 days and then given dietary treatments for 56 days. The measurement of the comb, wattle, and chest circumference (CC) of pelung cockerels was performed on days 0, 14, 28, 42, and 56. At the end of the treatment, the pelung cockerels were sacrificed and the data of the pectoralis muscle weight (PMW), testis weight (TW), and area of the pectoralis muscle (APM) were measured. Samples of pectoralis muscle and testes were taken and fixed in 10% neutral buffer formalin for histology. The proliferating cell nuclear antigen (PCNA) was identified by immunohistochemical staining. To measure fascicle area (FA), myofiber area (MA), and enumerate, the fascicle myofibers (NM) histology preparations were stained with hematoxylin and eosin (H and E). Testicular preparations were stained with H and E to measure the diameter of the seminiferous tubules (DST) using ImageJ software.

Results: The growth performance on day 56 showed significantly (p < 0.05) higher differences of CC in T1 compared to T2 and T0, in T1 and T3 compared to T0, and in T3 and T2 compared to T0. Pectoralis muscle results, that is, FA, NM, MA, and PCNA-positive cells, showed that cockerels on treatment T3 had significantly higher results than other treatments, T1 was significantly different from T2 and T0, and T2 was significantly different from T0. In addition, the TW and DST measurement of cockerels on treatment T3 were significantly reduced (p < 0.05) than the other treatment groups.

Conclusion: The oral administration of BCSP in the role of a NAB at a dose of 0.9 mg/kg BW for 56 days improved the growth performance and pectoralis muscle, especially the CC, FA, NM, MA, and PCNA-positive cells parameters, but did not affect the PMW, APM, and testis of pelung cockerels. The administration of testosterone at 3 mg/day for 56 days contributed to the decrease in TW and DST, as well as atrophy of the seminiferous tubules of pelung cockerels.

Keywords: growth performance, muscle, natural aromatase blocker, pelung, testis.