Browsing by Author "Arjona, Anibal Augusto"

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    Effect of neonatal heat stress on growth, mortality and blood characteristics of juvenile broilers exposed to high ambient temperature
    Arjona, Anibal Augusto (Virginia Polytechnic Institute and State University, 1988)
    Previous studies indicated that exposure of broiler cockerels to acute heat for 24 hr at five days of age increased their survivability when exposed to high ambient temperature prior to market. Since they were conducted at low relative humidity, the aims of the present study were to determine if higher relative humidity affected the response and to investigate the physiological basis of the response. The early, neonatal, heat stress consisted of increasing ambient temperature to between 35.0 to 37.8 C for 24 hr at five days of age in half of the pens (early heat stress) while the remaining pens were kept at 29.4 C (early control). At 6 wk of age a second, late, juvenile, heat challenge was administered. Ambient temperature in half of the early heat stressed pens and early control pens was gradually increased to between 35.0 to 37.8 C for 8 hr on two consecutive days. Significantly lower mortality during the second heat challenge was observed in the early heat stressed birds. This reduction in mortality ranged from 75 to 90% of that seen in the early control birds. Additionally, there were no deleterious effects on body weight, body weight gain or feed efficiency caused by exposure of birds to early heat stress. Feed restriction or administration of a commercially available electrolyte package to the water had no effect on the ability of the birds to withstand high ambient temperature. Water consumption, core and surface body temperature were increased upon exposure to late heat; however, there were no significant differences between the early heat stressed and early control groups. There was a significant reduction in plasma T₃ concentration in the late heat stressed birds. No significant differences in plasma glucose were observed among the heat treatment groups. A significant increase in total plasma protein occurred during the first sampling period during late heat stress, with values returning to control levels during the second sampling period. No significant differences between the early heat stressed and early control groups were observed in plasma T₄ and total plasma protein during late heat. Heterophil to lymphocyte ratio was lower in the early heat stressed group than in the early control group during the second day of late heat exposure These results indicate that thermotolerance can be induced by exposing broiler chicks to 35.0 to 37.8 C for 24 hr at 5 days of age with no adverse effects on performance. Although the mechanism by which Early, neonatal, heat exposure induces thermotolerance is unknown, it is clear that it does not resemble acclimation.
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    Molecular responses of neonatally heat stressed broilers exposed to acute heat stress
    Arjona, Anibal Augusto (Virginia Tech, 1991-08-07)
    Exposure of broiler cockerels to between 35.0 to 37.8 C for 24 hr at 5 days of age increases their survival when exposed to a heat challenge at 6 weeks of age (35.0-37.8 C; RH 50% ). This' phenomenon does not resemble acclimation since the physiological changes known to occur in acclimated birds exposed to heat have not been observed in the neonatally stressed birds. A series of experiments were conducted to elucidate the mechanisms of neonatally induced thermotolerance. In Experiment 1, the erythrocyte protein profile of control and 5 days heated birds prior to and during exposure to acute heat were determined. Prior to juvenile heat exposure no differences in the erythrocytic protein profile of neonatally stressed and control birds were observed at any age (10, 17, 24, 31 and 38 days of age) when maintained under control conditions. However, upon exposure to an acute heat challenge (40.5 C; 52 days of age) temporal and differential expressions of proteins similar in molecular weight to heat shock proteins (HSPs) were observed between the neonatally stressed and control birds. In Experiment 2, the effects of neonatal heat stress at various ages (5, 8, 12, 16 days of age) on the protein synthesis profile of heart, brain (telencephalon, diencephalon, brain stem, cerebellum) and liver tissues during exposure to an acute heat challenge were studied. In addition, body temperature during neonatal heat exposure was monitored. A significant increase in body temperature was observed during neonatal heat stress. A steady increase in the magnitude of the temperature change was noticed up to 12 days of age. Body temperature of birds exposed to neonatal heat at 16 days of age was similar to that of birds heated at 5 days of age.