Blood Testosterone Concentration and Testosterone-induced Aggressive Behavior in Male Layer Chicks: Comparison between Isolated- and Grouped-Raising

Abstract

Testosterone (T) is known to induce aggressive behavior, mainly in male animals. Subcutaneous implantation of T-filled silastic tubes, rather than intramuscular injection of T, is generally recommended for long-term treatment using exogenous T. However, the effect of T implantation on chicken aggressive behavior has not been investigated. In addition, the concentration of T required to induce aggressive behavior or whether rearing conditions such as isolated-or grouped-raising affect T-induced aggressive behavior in chickens is not known. The present study aimed to examine the relationship between the lengths of T-filled tubes, blood T concentration, and aggressive behavior in group-and isolation-raised male layer chicks. The testes were bilaterally removed and silactic tubes of various lengths filled with crystalline T were subcutaneously implanted at 14 days of age. A social interaction test was performed to quantitatively assess chick aggressive behavior at 32 days of age. Comb weight and size were used to assess the activation of endogenous androgen receptors. Total aggression frequencies (TAF) and aggression establishment rate (AER) were used to evaluate aggressiveness. Significant positive correlations (P＜0.001) were observed between the comb parameters and plasma T concentration. In the isolation-raised chicks, the TAF and AER were high irrespective of the lengths of the implanted T tubes or the corresponding plasma T concentrations. However, in the group-raised chicks, the AER tended to differ between the T-implanted aggressors (P＝0.0902), and the AER significantly increased with implantation of 1.0-cm-long T-filled tubes (P＜0.05), which corresponded to approximately 47 pg/mL plasma T concentration. These results suggest that both grouped raising and approximately 47 pg/mL plasma T concentration are required for the induction of T-dependent aggressive behavior, and that isolationinduced aggressive behavior is T-independent in male layer chicks.

Effects of Testicular and Non-Testicular Testosterone on Territorial and Isolation-induced Aggressive Behavior of Male Layer Chicks

“…The R-I test was performed at 29 and 30 days of age and the SI test at 31 and 32 days of age. The TAFs and AER were calculated according to the protocols of Raihan et al (2017) and Yan et al (2019). The TAFs are defined as the sum of the frequencies of pecking, biting, kicking, threatening, and leaping.…”

“…These results suggest that territorial aggression in chickens is T-independent, because the plasma concentration of T in male chicks is reported to be low until 28 days of age ( Tanabe et al , 1979 ). In addition, our latest results showed that the chicks which were castrated and reared in isolation for more than two weeks expressed high frequencies of aggressive behavior ( Yan et al , 2019 ), suggesting that isolation-induced aggressive behavior is also T-independent in chickens. However, the concentration of blood nontesticular T in the castrated chicks, probably derived from the adrenal gland ( Tanabe et al , 1979 ), is approximately 24 pg/ml ( Yan et al , 2019 ).…”

“…In addition, our latest results showed that the chicks which were castrated and reared in isolation for more than two weeks expressed high frequencies of aggressive behavior ( Yan et al , 2019 ), suggesting that isolation-induced aggressive behavior is also T-independent in chickens. However, the concentration of blood nontesticular T in the castrated chicks, probably derived from the adrenal gland ( Tanabe et al , 1979 ), is approximately 24 pg/ml ( Yan et al , 2019 ). Therefore, it is impossible to completely exclude the effect of a lower concentration of blood T on chick aggressive behavior by castration alone.…”

“…The R-I and SI tests were used to quantitatively monitor territorial and isolation-induced aggressive behavior, respectively. The total aggression frequencies (TAFs) and aggression establishment rate (AER) were used as indices of aggressive behavior of the chicks ( Raihan et al , 2017 ; Yan et al , 2019 ).…”

Influence of sex hormones on the aggressive behavior during peck order establishment and stabilization in meat and egg type chickens

“…Hormones are known to influence the performance of mating behavior ( Schumacher and Balthazart, 1983 ) and aggression and vary at the individual level, as higher concentrations of endogenous testosterone were observed in quails performing more aggressive behaviors ( Maekawa et al, 2018 ). Aggressive behaviors have been stimulated by the administration of exogenous testosterone ( Erpino, 1975 ; Fernald, 1976 ; Finney and Erpino, 1976 ; Barfield, 1979 ; Ogawa, 1998a ; Graham and Wells, 2001 ; Yan et al, 2019a ), exogenous estradiol ( Grelk et al, 1974 ; Barfield, 1979 ; Trainor et al, 2008 ; Heimovics et al, 2015 ), and the estradiol-testosterone combination ( Archawaranon and Wiley, 1988 ). The hypothalamus is a well-known brain region involved in the performance of aggressive behaviors.…”