Js. Mckee et al., EFFECTS OF SUPPLEMENTAL ASCORBIC-ACID ON THE ENERGY-CONVERSION OF BROILER CHICKS DURING HEAT-STRESS AND FEED WITHDRAWAL, Poultry science, 76(9), 1997, pp. 1278-1286
The objectives of this study were 1) to determine the effects of suppl
emental ascorbic acid (AA) on the energy conversion of broiler chicks
maintained at thermoneutral and potential heat stress temperatures usi
ng indirect convective calorimetry; and 2) to determine whether change
s in energy conversion are reflected in changes in lipid metabolism. I
n Experiment 1, 120 2-d-old cockerels, housed in two identical environ
mental chambers, were maintained under constant light (2.0 +/- 0.2 fc)
and recommended thermal conditions (29.6 +/- 0.8 C; 33.4 +/- 8.0% RH)
and consumed water and feed ad libitum. Beginning on Day 8 posthatch,
one-half of the birds inside each chamber were randomly assigned and
received feed supplemented with AA. Beginning on Day 9 posthatch, the
temperature inside one chamber was increased to 34 C whereas the other
chamber remained thermoneutral. This design resulted in four treatmen
ts: 1) thermoneutral (TN: 27.7 +/- 0.8 C; 40.9 +/- 9.4% RH) and 0 mg A
A/kg feed (ppm); 2) TN and 150 ppm AA; 3) heat stress (H: 33.8 +/- 0.5
C; 43.3 +/- 7.4% RH) and 0 ppm AA; or 4) H and 150 ppm AA. Also begin
ning on Day 9 posthatch, birds were randomly assigned to one of three
identical, indirect convective calorimeters designed to accommodate TN
or H. Oxygen consumption, carbon dioxide production, respiratory quot
ient, and heat production were evaluated daily for 8 h, through Day 17
posthatch. Following calorimetric measurement, birds were returned to
their respective caging unit/chamber for the remainder of the study.
Weight gain, feed intake, and gain:feed were also measured over the 9-
d study. Heat exposure depressed (P < 0.05) weight gain, feed intake,
and gain:feed. Ascorbic acid increased (P < 0.10) weight gain. Oxygen
consumption and carbon dioxide and heat production per kilogram(0.75)
decreased (P < 0.05) with age with no change in the respiratory quotie
nt. Heat exposure lowered (P < 0.001) the respiratory quotient. A temp
erature by AA interaction was detected in which heat-exposed birds exp
ressed lower (P < 0.10) respiratory quotients when consuming the AA-su
pplemented diet. In Experiment 2, 18 2-d-old cockerels, housed in an e
nvironmental chamber, were maintained under constant light and recomme
nded thermal conditions (29.3 +/- 0.4 C; 41.4 +/- 3.3% RH) and consume
d water and feed ad libitum. On Day 9 posthatch, birds were deprived o
f feed for 24 h with ad libitum access to water supplemented with eith
er 0 or 400 mg AA/L. Blood samples were obtained from each bird before
and after feed withdrawal and supplementation. Supplemented birds exh
ibited elevated (P < 0.01) plasma AA, levels that were not affected by
feed deprivation. Feed deprivation increased (P < 0.0001) plasma beta
-hydroxybutyrate with no effect of AA, and decreased (P < 0.05) plasma
triglycerides in the unsupplemented birds. A feed withdrawal by AA in
teraction was detected in which plasma triglycerides remained elevated
in birds supplemented with AA. These data suggest that supplemental A
A influences body energy stores that are used for energy purposes duri
ng periods of reduced energy intake.