Abstract
The aim of this study was to investigate the effects of Fadrozole hydrochloride and recombinant human insulin-like growth factor I (rhIGF-I) on female-to-male sex reversal, hatching traits, and body weight of broiler chickens. On the third day of incubation, fertile eggs were randomly assigned to five experimental groups comprising (i) Fadrozole (0.1 mg/egg), (ii) rhIGF-I (100 ng/egg), (iii) Fadrozole (0.1 mg/egg) + rhIGF-I (100 ng/egg), (iv) vehicle injection (10 mM acetic acid and 0.1% BSA), and (v) non-injected eggs. Eggs in the rhIGF-I-injected groups showed the mode of hatching time at the 480th hour of incubation, 12 hours earlier compared to the other groups, with no statistically significant difference in mortality and hatchability. On Day 1 and 42 of production, 90% of genetically female chicks were masculinized using Fadrozole treatment, while 100% female-to-male phenotypic sex reversal was observed in the Fadrozole+rhIGF-I group. Fadrozole equalized the body weight of both genders, although rhIGF-I was effective on the body weight of male chicks only. Interestingly, combined rhIGF-I and Fadrozole could increase the body weight in both sexes compared to the individual injections (P<0.05). These findings revealed that (i) IGF-I-treated chicken embryos were shown to be an effective option for overcoming the very long chicken deprivation period, (ii) the simultaneous treatment with Fadrozole and IGF-I could maximize the female-to-male sex reversal chance, (iii) the increase in the body weight of masculinized chickens via Fadrozole could be equal to their genetically male counterparts, and (iv) the IGF-I effectiveness, specifically along with the application of aromatase inhibitors in female chicks, indicates that estrogen synthesis could be a stumbling block for the IGF-I action mechanism in female embryos.
Highlights
Sexual differentiation in the avian system is directed by the presence or absence of the W chromosome, similar to the Y chromosome in mammals [1]
Chicken embryos were treated with recombinant human IGF-I and Fadrozole, as a nonsteroidal antiaromatase reagent, on Day 3 of incubation
We evaluated the simultaneous and separate effects of these two compounds on female-to-male sex reversal and body weight on the Day 1 and 42 of production as well as the hatching traits
Summary
Sexual differentiation in the avian system is directed by the presence or absence of the W chromosome, similar to the Y chromosome in mammals [1]. Genetically male birds are homozygous (ZZ) and the females are heterozygous (ZW) [2,3]. Like in mammals, one or both of the chicken sex chromosomes carry genes which control the cellular decision-making process for gonad development, resulting in ovary development in ZW hens and testis in ZZ roosters [4]. The onset of gonadal sex differentiation in birds is sensitive to steroid hormones [5]. 17bHydroxysteroid dehydrogenase and aromatase enzymes which are responsible for the conversion of androgens to estradiol-17 b are only detectable in the female embryos’ gonads [7]. Estradiol can be detected from E9 to E15 in female chicken embryonic gonads by monitoring the production of estradiol-17b [8]
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