Plasma corticosterone responses to handling in Japanese quail selected for low or high plasma corticosterone responses to brief restraint.

1. Plasma corticosterone responses to handling in Japanese quail selected for low or high corticosterone responses to brief mechanical restraint (low and high stress lines) were measured in this study. 2. Initial corticosterone concentrations did not differ between the two lines. Corticosterone concentrations increased 15 min after handling began in quail handled for 5 or 15 min, with greater increases in quail from the high stress than the low stress line. Integrated corticosterone responses were higher in high stress than low stress quail, although the difference between the lines was not significant in quail handled for 5 min. 3. Patterns of plasma corticosterone after 15 min differed between quail handled for 5 or 15 min. Corticosterone increased further or did not change from 15 to 30 min then decreased from 30 to 60 min in quail handled for 5 min, whereas corticosterone decreased from 15 to 30 min then did not change in quail handled for 15 min. Corticosterone concentrations at 60 min remained elevated above initial concentrations, and were similar in quail handled for 5 or 15 min. Corticosterone concentrations at 15 min were more than twice as high in quail handled for 15 min compared with quail handled for 5 min. 4. Although the lines of quail have been selected on the magnitude of corticosterone responses, there was still marked variation in responses between birds within each line. Some quail in the high stress line showed little or no corticosterone response to handling, whilst large responses were seen in some birds of the low stress line. The lines of quail differ in characteristics other than corticosterone responses, including fear behaviour and reproductive development, so the lines provide valuable opportunities to investigate the potential significance of differences between individual birds in their corticosterone responses.

Maternal corticosterone further reduces the reproductive function of male offspring hatched from eggs laid by quail hens selected for exaggerated adrenocortical stress responsiveness.

Activation of the hypothalamic-pituitary-adrenal (HPA) axis can depress the hypothalamic-pituitary-testicular axis. Male quail cloacal gland (CG) size and foam production shows androgen dependency, and males selected for exaggerated [high stress (HS)] rather than reduced [low stress (LS)] plasma corticosterone (B) stress response exhibit reduced CG and testes development. High stress hens also deposit more B into egg yolks than LS ones, and quail hens given B produce chicks that have a reduced growth rate and adults with heightened HPA responsiveness. Herein, we gave LS and HS hens no B [empty implants, control (CON)] or B-filled implants and assessed the reproductive performances of these hens and their male offspring. Mortality was similarly elevated in LS and HS B-treated hens, but only HS B-implanted hens showed reduced egg production. In male offspring, CG volume (CVOL), intensity of CG foam production (CFP), and the proportion of individuals that produced CG foam were measured from 4 to 11 wk of age. At 6 wk, BW, and at 15 wk, BW, testes weight (TWT), and TWT relative to BW were also determined. Hen treatments did not affect male chick CVOL at 4 wk, but CVOL differed thereafter as follows: LS CON > LS B = HS CON = HS B at 5 and 6 wk and LS CON > LS B > HS CON = HS B from 7 to 11 wk. By 8 wk, and thereafter, CFP differed as follows: LS CON > LS B > HS CON > HS B. Group differences in the proportion of individuals that produced CG foam generally supported CFP findings from 4 to 8 wk of age. Body weight did not differ by treatment at 6 wk of age. By 15 wk, TWT were similarly depressed in both HS groups. However, similarly higher 15-wk BW in the LS-CON and HS-B groups contributed to TWT relative to BW differences as follows: LS-B > LS-CON > HS-B; LS-CON = HS-CON; LS-B > HS-CON; and, HS-CON = HS-B. Both selection for exaggerated HPA responsiveness and maternal B treatment negatively affected the reproductive function of HS male offspring.

Cloacal gland growth differences in high and low plasma corticosterone stress response line male quail reared under short daylengths.

Mail quail selected (generation 32) for reduced [low stress (LS)] or exaggerated [high stress (HS)] plasma corticosterone stress response to brief mechanical restraint (5 min of immobilization) were studied for differences in the growth of their cloacal glands when reared essentially lifelong on short day lengths of 8L:16D. Post-brooding, at 4 wk of age, 96 quail (48 LS+48 HS) were housed in cages (1 LS and 1 HS male/cage), and the short day light treatment was instigated. Using a digital caliper, cloacal gland (CG) size measurements (length and width, mm) were made biweekly beginning at 42 d of age and ending at 196 d of age (28 wk old). The CG volume (CVOL) was calculated from these measurements using a literature-proposed formula. The CVOL in both lines increased similarly with increasing age from 6 to 12 wk of age. However, beginning at 14 wk of age and thereafter, LS males showed greater (P<0.05) CVOL than HS ones. No further increases in CVOL were observed in either line at 24 wk of age beyond that seen at 22 wk. This study demonstrated that although both lines show CG development under short days, eventually CG growth becomes comparatively stymied in the HS males. Furthermore, the maintenance of similarly lower CVOL in HS than LS males, CVOL that showed no further increase from 22 to 24 wk of age, suggests that holding these quail lifelong on short days results in, comparatively, yet another permanent negative reproductive consequence in quail selected for exaggerated plasma corticosterone stress responsiveness.

Cloacal gland and gonadal photoresponsiveness in male Japanese quail selected for divergent plasma corticosterone response to brief restraint.

Corticosterone is linked to testicular depression, and in Coturnix, a relatively photorefractory species, day length and androgen dependency in cloacal gland development and foam production are evident. Furthermore, male quail selected for reduced (low stress, LS) rather than exaggerated (high stress, HS) plasma corticosterone stress response show more photo-induced reproductive development, greater resistance to reproductive declines induced by exposure to very short days, and a quicker recovery to a higher reproductive level upon return to long days. To determine whether a milder reduction in day length would also influence stress line reproductive photoresponsiveness, and perhaps photorefractoriness, males grown on 16 h of light were given 13 h of light for 4 wk followed by a return to long days for 12 wk. Cloacal gland measurements were made following the initial stimulatory photoperiod and weekly thereafter during the 2 light treatments. Plasma testosterone was determined initially, after 4 wk of light reduction, and at the end of the study, along with BW, testes weight (TWT), and TWT relative to BW. Cloacal gland volume (CVOL) was greater in LS than HS males grown on long days. Whereas exposure to 13 h of light reduced CVOL in both lines, line differences (LS > HS) persisted during the first 3 wk of light reduction. Moreover, by 2 wk of rephotostimulation, and weekly thereafter, line differences (LS > HS) in CVOL reemerged. Cloacal gland foam production and the proportion of individuals that produced cloacal gland foam responses reflected changes in CVOL. The BW did not differ by line, yet LS males had a higher TWT and TWT relative to BW than HS ones. All individuals, however, exhibited relative photorefractory responses. Whereas none of the LS males completely resisted reproductive regression induced by a 3 h light reduction, LS males showed other reproductive benefits upon mild photocastration and subsequent rephotostimulation (e.g., greater resistance to CVOL and cloacal gland foam production losses during a mild light crash and quicker restoration to full reproductive potential upon relighting).

Active immunization of broiler breeder cockerels against chicken inhibin accelerates puberty and prevents age-induced testicular involution.

Injection of quail and breeder hens with a recombinant protein antigen (MBP-cINA521)--a fusion of the bacterical maltose-binding protein (MBP) and a fragment of the alpha-subunit of chicken inhibin (cINA521)--accelerates puberty and enhances lay. Herein, the effects of this immunogen on reproductive responses in broiler breeder males were assessed. Cockerels were subcutaneously injected with 0 (vehicular controls), 1, 3, or 5 mg of MBP-cINA521 at 13 wk of age and with one-half of these dosages (boosters) at 18 wk. Bird subsamples were weighed, blood sampled, and killed at 24, 28, and 39 wk of age to assess age and vaccination effects on BW, testes weight (TWT), TWT relative to BW (RTWT), TWT > or = 20 g (TWT20; theoretical threshold TWT for maximum fertility), and plasma testosterone. Breeder males are sexually developing, reach peak sexual activity, and show age-related reproductive decline at these ages. Because vaccine gonadal effects at 24 wk appeared to be dramatic, the size of the left testis was also scored to see if size differences could be detected by mere visual inspection. Male fighting increasingly reduced sample sizes beyond 24 wk. Because mortality was unrelated to the treatments and to insure meaningful statistical comparisons, MBP-cINA521 data were pooled. Body weight (P < 0.04), testis score (P < 0.02), TWT (P < 0.03), RTWT (P = 0.06), and plasma testosterone (P = 0.08) were elevated in immunogen-treated males at 24 wk of age, and more (P < 0.05) MBP-cINA521-treated birds than controls achieved a TWT20 at this time. These variables did not differ by treatment at 28 wk. However, by 39 wk, treatment effects reemerged as follows: TWT (P < 0.04), RTWT (P = 0.06), and TWT20 (P < 0.01) were increased in vaccinated males who also showed nearly 3-fold higher levels of plasma testosterone. We conclude that immunoneutralization of inhibin accelerates puberty and retards age-related sexual senescence that typically occurs in broiler breeder males.

Early T-maze behavior and broiler growth.

In the laboratory and at a commercial farm in Argentina, chicks that showed a short latency to exit a T-maze (LEX) (HP, high performance) gained more weight than those with a longer LEX (LP, low performance). The present study re-examined this relationship and evaluated additional T-maze measures using broilers reared in quasi-intensive, environmentally controlled conditions. In the T-maze, a mirror strategically placed at the end of a corridor stimulates the test chick to leave the isolation chamber (start box) and to move toward its reflection. Having done so, it can then see other birds and thereby be further stimulated to completely exit the maze. However, when a test bird hesitates or stops at the mirror, its performance categorization may be confounded. Herein, the T-maze performance of 3-d-old broiler chicks was assessed using three different measurements: 1) the latency to exit the start box (LEB), 2) the latency to reach the mirror section of the maze (LRM), and 3) LEX. The fastest (top 25%) and slowest (bottom 25%) of the birds within a sex and within each of the three T-maze criteria were classified as HP and LP chicks, respectively. The relationships between these measures and body weight were examined in 4-, 42-, and 56-d-old males and females. Irrespective of the T-maze classification criteria used, HP and LP chicks had similar body weights at 4 d of age. However, chicks classified as HP according to LEB or LRM measures were heavier at 42 and 56 d of age than LP ones (P < 0.02 for all comparisons). These differences were apparent in both sexes. On the other hand, there were no detectable differences in body weight at the latter ages between chicks categorized as HP or LP according to their LEX scores. The present results indicate that 1) broiler chicks that exit the T-maze start box and reach the mirror quickly subsequently grow faster than their slower LP counterparts and 2) LEB and LRM are better predictors of growth than the LEX value used in previous studies.

Struggling behavior in shackled male and female broiler chickens.

Anecdotal evidence suggests that the struggling behavior of shackled broiler chickens may be positively related to compression of the shank and the probable associated discomfort: birds with large shanks tend to struggle more violently than do those with smaller shanks. Males are generally heavier and have thicker shanks than females. Therefore, we tested the hypothesis that, because the leg gaps of shackles are fixed in size, male broilers would struggle more than females. At 42 d of age, 264 floor-reared broilers were cooped in groups of 12 (six males and six females) and were transported from the university farm to the abattoir. Eighty of these served as test birds (n = 40/sex) and were shackled on a moving processing line with a bird of randomly selected sex on either side. Upon shackling, the latencies to struggle, numbers of struggling bouts, and total time spent struggling were recorded during a 1-min test period. Subsequently, the BW and circumference of the right shank (CRS) of each test bird were measured. Male birds were heavier and had thicker shanks than females (both P < 0.0001); they also struggled sooner (P < 0.01) and longer (P < 0.008). When data from males and females were pooled, CRS was negatively correlated with latency to struggle (r = -0.30; P < 0.006) and positively associated with SB (r = 0.23; P < 0.04) and total time spent struggling (r = 0.23; P < 0.04). However, there were no detectable correlations within sex. Body weight was not significantly correlated with any of the struggling behavior measures. Although other gender-related factors may be influential, an interpretation of our findings based on sex differences in CRS seems the most parsimonious. We conclude that use of shackles of fixed leg-gap size may contribute to increased struggling behavior in male broilers.

Fecal corticosterone metabolites and plasma corticosterone in Japanese quail selected for low or high plasma corticosterone responses to brief restraint.

Fecal corticosterone metabolites and plasma corticosterone in Japanese quail selected for low- or high-plasma corticosterone responses to brief mechanical restraint (low- and high-stress lines), and in a line of unselected quail, were measured in this study. No line differences were observed in baseline plasma corticosterone concentrations, but fecal corticosterone metabolite concentrations and daily fecal corticosterone metabolite production were 20% higher in quail of the high-stress line than in unselected or low-stress quail for males and females living together in group cages (P < 0.05). No differences were observed between lines in corticosterone metabolite concentrations and production for male birds in individual cages. Baseline plasma corticosterone concentrations, fecal corticosterone metabolite concentrations, and production appeared to be higher for males and females in group cages compared with males in individual cages. This difference might have been because of greater corticosterone secretion by male quail living in mixed sex groups than living individually. Correlations between baseline plasma corticosterone concentrations and fecal corticosterone metabolite concentrations in low-stress and high-stress quail, and for all birds combined, were r = 0.521 (P = 0.038), r = 0.604 (P = 0.013), and r = 0.431 (P = 0.002), respectively. The low- and high-stress lines that have been selected for low- and high-corticosterone responses differ in other characteristics, including growth and reproductive performance, and the current results are consistent with the assumption that these other differences are a consequence of greater daily corticosterone secretion in quail of the high-stress line.