Differences in circulating corticosterone levels associated with elevation of breeding sites in Rufous-collared Sparrows Zonotrichia capensis

To facilitate breeding and any energetically costly activity, individuals of the same species can substantially vary their circulating corticosterone (CORT) levels to cope with local environmental conditions at different elevations. We compared baseline and the stress-induced plasma CORT levels during the parental care stage between free-living Rufous-collared Sparrows (Zonotrichia capensis) that breed at high (~ 2500 m) and low (~ 500 m) elevations in central Chile. We found that baseline CORT levels at different elevations were similar and that stress-induced levels were significantly lower in birds breeding at high elevation; however, we detected no sexual dimorphism in CORT levels related to elevation. We found that larger individuals had higher stress-induced CORT levels at low elevation regardless of sex. Our results show that environmental conditions at high elevation seem to be not severe enough to promote more elevated baseline CORT levels. However, breeding Rufous-collared Sparrow must still deal with both shorter breeding seasons and increased exposure to unpredictable events. Thus, a reduced stress response during the parental care stage would be more favorable for supporting breeding activities at high elevations. Future studies should focus on describing the life-history traits of these populations and the effects that other stressors, such as predation pressure and food availability, may have on the adrenocortical response in these environments to evaluate the consequences for survival and reproductive success. This information is important for enhancing our understanding of the ecological and evolutionary mechanisms that modulate variation in the adrenocortical response among populations of the same species.

90 Evaluation of transport duration on immune response and blood parameters in sedentary horses

Transport has cogent effects on the physiological and immunological welfare of horses, resulting in inevitable stressors regardless of adaptation or conditioning. We hypothesized transporting sedentary horses would yield allied results to studies using transport-conditioned horses. Mature stock-type horses (n = 4) were subjected to three transport durations (0.25, 3 and 6 hours) with 7–8 days between transport. All subjects were transported simultaneously for all durations of transport. Blood samples were collected before, post-transport and 24 hours post-transport and analyzed for complete blood count (CBC). Body weight (BW), rectal temperature (RT), blood glucose (GLU) and blood lactate (BLA) were recorded before and post-transport. All data (p<0.05) were analyzed using PROC MIXED (SAS © 9.4). Transport duration did not influence CBC, BLA or other physical measurements. Resulting GLU increased after 3 (158.5±8.5 mg/ dL) and 6 (147.50±8.5 mg/dL) hours of transport compared to 0.25 hour of transport (117.8±7.2 mg/dL). Weights decreased after transport; however, this was likely due to eliminative behavior during transport. Total WBC tended (P = 0.06) to increase before transport (7.71±0.6 K/µL) than post (5.64±0.59 K/µL) and 24 hours post-transport (6.14±0.06 K/µL). Percent neutrophils (N) increased post-transport (66.8±2.5%) compared to before transport (55.7±2.6%) and 24 hours post-transport (57.2±2.5%). Neutrophil to lymphocyte ratio (N:L) tended (p= 0.07) to increase post-transport (66.7±2.7%) than before (55.7±2.7%) and 24 hours post-transport (57.3±2.6%) regardless of duration. Increases in N are consistent with previous research indicating a short-term stress response. Previous research measuring adrenocortical response reported elevated N:L ratios indicating stress; our results suggests transport, even minimal, may stimulate a stress response in rarely-transported horses. Elevated GLU after transport may further support an adrenocortical response as cortisol can influence blood glucose concentrations. Findings indicate even short-term transport elicits an immunological stress response and may be intensified in rarely transported horses compared to seasoned travelers.

Programming of the Hypothalamus-Pituitary-Adrenal Axis by Very Preterm Birth

Background: Many very preterm (i.e., <32 weeks of gestation) newborns fail to mount an adequate adrenocortical response to stress or illness, termed relative adrenal insufficiency. Conversely, later in life these infants show features of increased glucocorticoid bioactivity, such as abdominal adiposity, insulin resistance, raised blood pressure, shorter stature and internalizing problem behavior. Summary: Studies suggested that very preterm newborns have impairments along multiple levels of the hypothalamus-pituitary-adrenal (HPA) axis. Among the impairment were defects in: (1) the pituitary responsiveness to exogenous corticotropin-releasing hormone, (2) 11β-hydroxylase activity, and (3) the interconversion between cortisol and inert cortisone. There is some evidence suggesting that later in life these infants have an increased basal secretion rate of cortisol and adrenal hyperandrogenism. However, the response to acute (psychosocial) stress was blunted rather than enhanced in them. The mechanisms explaining this switch in HPA axis activity are complex and not yet fully understood. Key Messages: Very preterm newborns have several impairments along the HPA axis that could impede an adequate adrenocortical response to stress or illness. Later in life, these infants are predisposed to increased HPA axis activity, which could partially explain their phenotype.