Effects of Supplemental Ascorbic Acid on Energy Conversion and Performance of the Domestic Fowl Exposed to High Ambient Temperatures

191 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997.A series of experiments was conducted to elucidate the effects of providing supplemental ascorbic acid (AA) on energy conversion and performance of the domestic fowl exposed to high ambient temperatures. Energy conversion and growth of heat-exposed chickens were similar regardless of supplemental AA. However, the substrates utilized to achieve this were different as indicated by the AA-induced shift in the respiratory quotient towards 0.70. Further experiments need to be conducted to determine whether this shift in the respiratory quotient reflects an increase in gluconeogenesis and uric acid formation or lipid utilization or both. Supplemental AA also maintained plasma triglycerides during acute feed deprivation. This finding may suggest an increased availability of lipid for utilization in extrahepatic tissues and may explain, in part, the difference in the respiratory quotient between unsupplemented and AA-supplemented birds. A similar situation may exist during heat exposure because the metabolic effects of acute feed deprivation and heat exposure are similar. These data indicate that supplemental AA influences body nutrient stores that are used for energy purposes during periods of reduced energy intake. Supplemental AA also appears to influence nutrient utilization in ad libitum fed birds maintained under thermoneutral conditions. Supplemental AA increased (7.8%) the percentage of whole carcass protein in 35-day-old birds. This was accompanied by a substantial reduction (4.3%) in the percentage of whole carcass lipid. Supplemental AA does not appear to influence heat loss in heat-exposed birds, as estimated from weight gain, feed consumption, body core and buccopharyngeal temperatures, and heat production, based on O$\sb2$ consumption and actual respiratory quotients. In fact, supplemental AA exerted a thermogenic effect in older birds maintained under both thermoneutral and high ambient temperatures. This suggests that the response to AA-supplementation on body temperature is age dependent and in older birds, environmental temperature independent. This may explain the variability in the literature regarding the benefits of AA-supplementation. The results regarding the effects of exogenous nitric oxide on weight gain, advocate the use of antioxidant supplements in humans as a preventative measure against metabolic free-radical damage as well as supplemental therapy in treating conditions that promote free-radical formation such as smoking and exposure to xenobiotics.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD