Heart rate, blood pressure, cardiac output, and total peripheral resistance of single comb White Leghorn hens during an acute exposure to 35 C ambient temperature

Genomic basis of insularity and ecological divergence in barn owls (Tyto alba) of the Canary Islands

Islands, and the particular organisms that populate them, have long fascinated biologists. Due to their isolation, islands offer unique opportunities to study the effect of neutral and adaptive mechanisms in determining genomic and phenotypical divergence. In the Canary Islands, an archipelago rich in endemics, the barn owl (Tyto alba), present in all the islands, is thought to have diverged into a subspecies (T. a. gracilirostris) on the eastern ones, Fuerteventura and Lanzarote. Taking advantage of 40 whole-genomes and modern population genomics tools, we provide the first look at the origin and genetic makeup of barn owls of this archipelago. We show that the Canaries hold diverse, long-standing and monophyletic populations with a neat distinction of gene pools from the different islands. Using a new method, less sensitive to structure than classical F_ST, to detect regions involved in local adaptation to insular environments, we identified a haplotype-like region likely under selection in all Canaries individuals and genes in this region suggest morphological adaptations to insularity. In the eastern islands, where the subspecies is present, genomic traces of selection pinpoint signs of adapted body proportions and blood pressure, consistent with the smaller size of this population living in a hot arid climate. In turn, genomic regions under selection in the western barn owls from Tenerife showed an enrichment in genes linked to hypoxia, a potential response to inhabiting a small island with a marked altitudinal gradient. Our results illustrate the interplay of neutral and adaptive forces in shaping divergence and early onset speciation.

The effects of early age thermal conditioning and vinegar supplementation of drinking water on physiological responses of female and male broiler chickens reared under summer Mediterranean temperatures

The effects of early age thermal conditioning (ETC), vinegar supplementation (VS) of drinking water, broilers' gender, and their interactions on respiratory rate, body temperature, and blood parameters (biochemical, hematological, and thyroid hormones) of broiler chickens reared under high ambient temperatures were determined. A total of 1100 1-day-old chicks were divided into four treatments: the "control" which were non-conditioned and non-supplemented; "heat-conditioned" which were exposed to 38 ± 1 °C for 24 h at 5 days of age; "vinegar supplemented" which were given drinking water supplemented with 0.2% of commercial vinegar from 28 to 49 days of age; and "combined" which were both heat conditioned and vinegar supplemented. All groups were exposed to the natural fluctuations of summer ambient temperature (average diurnal ambient temperature of about 30 ± 1 °C and average relative humidity of 58 ± 5%). ETC and broiler gender did not affect the respiratory rate or body temperature of chronic heat-exposed chickens. VS changed the body temperature across time (d35, d42, d49) (linear and quadratic effects, P < 0.05) without changing respiratory rate. Heat-conditioned chickens exhibited lower levels of glycemia (P < 0.0001) and higher hematocrit and red blood cell counts (P < 0.05). Furthermore, the greatest effects of VS, alone or associated with ETC, were the lowering of cholesterol and triglyceride blood concentrations. A significant (P < 0.05) effect of ETC, gender, and ETC×gender on T3:T4 ratio was observed. Finally, some beneficial physiological responses induced by ETC and VS, separately or in association, on chronically heat-stressed chickens were observed. However, the expected cumulative positive responses when the two treatments were combined were not evident.

Broiler survivors of intravenous micro-particle injections: evaluation of growth, livability, meat quality, and arterial blood gas values during a cyclic heat challenge

When broilers are exposed to high ambient temperatures, their cardiac output can increase by 20 to 50%. Previously, we developed an intravenous micro-particle injection technique to select broilers having a cardiopulmonary capacity capable of accommodating increases in cardiac output associated with fast growth and cool temperatures. In the present study, male broilers were injected at 18 to 20 d of age with cellulose micro-particles sufficient to trigger >50% mortality by 35 d of age. The survivors of micro-particle injections (cellulose survivors) and saline-injected flock mates (control group) were exposed to a moderate cyclic heat challenge (peak temperature of 35 to 37 degrees C) beginning on d 36 and continuing through d 57. We tested the hypothesis that if the cellulose survivors represent the population cohort having the most robust cardiopulmonary capacity, then during a subsequent heat challenge these survivorspotentially may perform better than their unselected flock mates. Based on data combined from two independent experiments, the cellulose survivors exhibited improved livability and body weight gain when compared with their unselected flock mates during the cyclic heat challenge. Meat quality characteristics did not differ between the groups. In a third experiment, cellulose survivors and saline-injected male broilers were reared at thermoneutral temperatures or were exposed to a cyclic heat challenge beginning on d 36. Arterial blood samples were collected from unanesthetized birds at 47 to 49 d of age and were analyzed for pH, partial pressure of CO2, bicarbonate, partial pressure of O2, and saturation of hemoglobin with O2. The blood gas values for the cellulose survivors and saline-injected broilers did not differ within a temperature regimen, regardless of whether the broilers were chronically acclimated to heat or were exposed to an acute heat challenge at the end of the experiment. The cellulose survivors did not differ in susceptibility to panting-induced respiratory alkalosis or hypoxemia when compared with their saline-injected flock mates. Overall, these observations indicate that selection for a robust cardiopulmonary capacity can confer advantages in growth and livability without affecting meat quality when broilers are exposed to a moderate heat challenge.

Potassium chloride improves the thermotolerance of chickens exposed to acute heat stress

Experiments were designed to test the hypothesis that chicks that drank an electrolyte solution containing K prior to and during an acute exposure to heat would have greater thermotolerance than chicks that consumed only water. In three experiments, 5- or 7-wk-old male chickens drank distilled water (control), or .3, .6, or .9% KCl solutions (Experiments 1 and 2), and .6 or .9% KCl or .8% KHCO3 solutions (Experiment 3) for 48 h before acute heat stress (HS) and during HS. Body temperature (Tb), blood pH, partial pressure of blood carbon dioxide (pCO2), ionized Ca (Ca2+), plasma Na, K, Cl, total Ca, inorganic P (Pi), and osmolality (Osm), and water consumption were determined. Water intake increased with the concentration of KCl. Before HS, .6% KCl increased plasma K and Ca2+, whereas .9% KCl resulted in a marked increase in K, Ca2+, Na, Cl, and Osm and a decrease in pH. During HS, .6% KCl-birds had lower hyperthermic Tb and pH values and higher Ca2+ and K concentrations than controls. Plasma Na and Osm of .6% KCl birds decreased whereas those of the control birds remained unchanged. Providing K as KHCO3 aggravated respiratory alkalosis and failed to influence either Tb or plasma electrolytes, suggesting that the beneficial effect of .6% KCl may in part be attributed to the accompanying Cl. Hyperthermic Tb and Ca2+ values were highly correlated. The results showed that .6% KCl solution reduced HS-related responses and indicated a relationship among supplemental KCl, blood Ca2+, and Tb.

Acute heat acclimation and kidney function in broilers

Broilers previously exposed to high environmental temperatures (heat-acclimated) are more resistant to heat stress and consume more water during heat stress than nonacclimated controls. Two experiments were conducted to determine whether heat-acclimated broilers conserve body water by reducing urine and solute (Na) excretion. In the first experiment, renal function studies were conducted at an ambient temperature (Ta) of approximately 21 C using anesthetized 7-wk-old male broilers. Control birds reared at a constant Ta of 24 C (Group N: noncycled Ta) were compared with birds that had been heat-acclimated by exposure for 3 to 6 d to a daily sinusoidal cycle of 24 to 35 to 24 C (Group C: cycled Ta). In the second experiment, renal function studies were conducted on anesthetized 5-wk-old control and heat-acclimated male broilers while they were exposed to a Ta of 21 C (Ambient Ta: Groups NA, CA), or to a Ta of 32 C (High Ta: Groups NH, CH). When high intravenous infusion rates (.37 mL/kg body mass per min) were used to simulate the volume expansion caused by thermogenic polydipsia, urine flow rates were significantly lower in Groups C and CA than in Groups N and NA, osmolal clearances were lower in Groups CA and CH than in Groups NA and NH, and all heat-acclimated groups in both experiments (Groups C, CA, CH) had significantly lower glomerular filtration rates (GFR), filtered loads of Na, and tubular Na reabsorption rates than the respective control groups (Groups N, NA, NH). These changes in kidney function potentially would minimize urinary fluid and solute loss when heat-acclimated broilers consume large quantities of water to support evaporative cooling. Reductions in GFR, filtered loads of Na, and tubular Na reabsorption rates also may help heat-acclimated broilers reduce the metabolic heat load associated with active (energy requiring) recovery of solute (Na) from the glomerular ultrafiltrate.

Research note: Maxiban effects on heat-distressed broiler growth rate and feed efficiency

One study was conducted utilizing 192 male broilers, at 4 to 7 wk posthatching, to evaluate a narasin-nicarbazin drug combination (Maxiban) for effects on bird growth rate, feed efficiency, and survivability during cycling ambient temperature (24 to 35 C) distress. Maxiban did not impact (P greater than .1) live weight gain, but reduced (P less than .05) gain:feed ratio (unadjusted for mortality), from .29 for controls to .21 as bird survivability declined (P less than .05) from 87.5 to 69.8%. Adjusting feed efficiency by adding the gain of birds dying of heat prostration to that for birds surviving the experiment resulted in feed efficiency for Maxiban-supplemented birds being similar (P = .48) to birds not consuming Maxiban. Under the conditions of the present study, Maxiban increased the mortality rate of male broilers exposed to cycling ambient temperature of 24 to 35 C during 4 to 7 wk posthatching.

Effect of peripheral foot cooling on metabolic rate and thermoreregulation of fed and fasted chicken hens in a hot environment

An experiment with a factorial arrangement of treatments was conducted to determine the effect of ambient and water-cooled roost temperatures on metabolic rates of fasted and fed Columbian Plymouth Rock hens. Indirect open circuit calorimetry was used to determine oxygen consumption and carbon dioxide production rates by the hens. Experiments during the thermoneutral period were conducted at 25 +/- 1 C for both ambient and roost temperature treatments. Experiments during the heat-stress period were conducted at an ambient temperature of 35 +/- 1 C. Roost temperatures of 20 +/- 1 (water-cooled roost) and 34 +/- 1 C were provided. Fasting was for at least 40 h; fed hens were fasted, then gavaged with 20 g of sucrose dissolved in 20 mL of distilled water. The metabolic rates were consistently higher in fed than fasted hens for all temperature treatments. The respiratory quotient responses were significantly influenced by feeding status of hens but not by ambient or roost temperature treatments. Cooled roosts in the 35 +/- 1 C environment provided metabolic rates 19% lower. The rectal temperatures of heat-stressed fasted and fed hens with a 34 +/- 1 C roost were elevated 1.20 and 1.32 C, respectively, whereas those of hens with the 20 +/- 1 C water-cooled roosts increased only .22 and .28 C during the heat-stress period, respectively. Hens on the 20 +/- 1 C roost did not initiate thermal panting, whereas those on the 34 +/- 1 C roost panted vigorously. It is concluded that the water-cooled roost partially alleviated heat stress by lowering metabolic rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of fasting and acute heat stress on body temperature, blood acid-base and electrolyte status in chickens

1. The tolerance of chickens to acute heat stress, evaluated by the time required to reach the critical body temperature (Tr) of 44.5 degrees C, was markedly enhanced as the period of fasting was extended. 2. Fasting reduced the rates of heat-induced changes in blood acid-base and electrolyte status. 3. Changes in Tr were correlated with changes in blood pH, pCO2, [Cl-] and [Pi] but not with changes in [Na+] or [K+]. 4. Blood acid-base and electrolyte status were related to Tr rather than time of exposure to heat stress.