Abstract:
Genetic selection for rapid growth in
broilers has inadvertently resulted in increased susceptibility to heat stress, particularly in male birds. Increased
oxidative stress associated with hyperthermia may be
reduced by avian uncoupling protein (avUCP), which
has been proposed to modulate free radical production.
However, the relationship between avUCP expression
and current heat stress management strategies is
unclear. Embryonic acclimation or thermal manipulation (TM) and dietary fat source are 2 heat stress interventions that may alter avUCP expression and
oxidative stress, but the literature is inconclusive. The
objective of this trial was to investigate the effect of TM
and dietary fat source on avUCP gene expression and
oxidative damage in the breast meat of market age
broilers before and after acute heat challenge. The influence of bird sex was also evaluated as broilers exhibit a
high degree of sexual dimorphism in growth and stress
susceptibility. Concentration of thiobarbituric acid reactive substances (TBARS) was measured as a marker of oxidative damage. Embryonic TM occurred from incubation d 7 to 16 for 12 h daily at 39.5°C. Dietary treatments were applied during the finisher period using
either poultry fat, soya oil, or olive oil supplemented at
4.5% in the diet. Acute heat stress (AHS) occurred on d
43 at 32°C for 4 h. Bird performance was decreased by
TM, but no significant differences were noted between
dietary fat source treatments. Neither avUCP nor
TBARS concentrations were significantly influenced by
TM or dietary fat source. Downregulation of avUCP
was observed following AHS, concurrent with an
increase in TBARS concentration. Male birds exhibited
higher levels of both avUCP expression and TBARS
compared to females and a significant interaction was
noted for heat stress by sex, with avUCP expression
being greatest in males prior to AHS. The increase in
avUCP expression and TBARS concentrations in male
birds may be associated with an increased susceptibility
to stress arising from the increased growth rate noted for
male broilers.
