Feed efficiency from day 21 to 43 was improved by 7.1 percent in ADEB birds and by 6.5 percent in ADEB+El birds compared to the controls; there was also a numerical improvement in feed efficiency for B+El birds. Measured over the length of the study, the improvement in feed efficiency over control birds was 5.6 percent for both ADEB and ADEB+El groups.
To assess immunocompetence, the researchers subjected the birds to an immune assault of sheep red blood cells. Compared to control birds, there were significantly higher titers for total and immunoglobulin (Ig) G antibodies in the B+El birds during the primary antibody response seven days later. During the secondary antibody response (14 days after immunization), the B+El and ADEB groups both exhibited significantly higher IgG levels than controls.
In a follow-up experiment comparing the performance of ADEB and control birds, the researchers found a 4 percent increase in average weight gain and a 3 percent improvement in feed conversion for supplemented birds. When birds were subjected to heat stress from days 37 to 41, supplemented birds had 62 percent fewer deaths than unsupplemented birds.
The improvements in productive performance in this study may be related to enhanced metabolic efficiency and stress resistance, the researchers suggest. They also note that many of the vitamins in the B complex have unique effects on immunocompetence and that submarginal levels of fat-soluble vitamins have been found to impair immunocompetence. The results of this study "clearly show the advantages of supplementing the drinking water of broilers with vitamins," the researchers write.
Another study (Deyhim and Teeter, 1993) assessed performance traits with and without heat stress when vitamins and (or) trace minerals were withdrawn from days 28 to 49. Several studies have suggested that the vitamin requirements of poultry increase with heat stress. Furthermore, reduced consumption during such times will limit vitamin intake.
In this study, Deyhim and Teeter found statistically significant reductions in weight gain and feed efficiency in unsupplemented birds in both environments, but they saw only a numerical difference when assessing the interaction between heat stress and supplementation.
Feed efficiency was 5.4 percent worse and weight gains were 2.9 percent lower when vitamins and trace minerals were both withdrawn. Withdrawing only the trace minerals had no effect on performance traits. However, when vitamin supplementation was discontinued and trace minerals remained in the diet, the effects on feed efficiency and weight gains compared to fully supplemented birds were even more pronounced--declines totaled 8.3 and 6.1 percent, respectively.
"The data indicate that the 28 to 49 day combined vitamin and trace mineral withdrawal does not occur without consequence," the researchers write. "Significant economic loss can occur when supplemental vitamins and trace minerals are withdrawn from the diet during 28 to 49 days posthatching."
Revisiting this same study, the researchers (Deyhim et al., 1996) recently assessed the effects of vitamin withdrawal on the nutritional composition of meat. Measuring thiamin and riboflavin concentrations, the researchers noted that heat and withdrawal each had a marked effect on breast meat concentrations of the vitamins. There was no interaction, however. Following the 21-day withdrawal period, muscle concentration was 45 percent lower for thiamin and 31 percent lower for riboflavin than in the controls. When birds were heat stressed, breast meat concentrations decreased 23 percent for thiamin and 37 percent for riboflavin compared to unstressed birds. The researchers note that such dramatic reductions in vitamin levels, especially when the effects of vitamin withdrawal and heat stress are combined, have the potential to affect consumer perception of the nutritional value of the meat they buy.
References:
- Deyhim, F., and R.G. Teeter. 1993. Dietary vitamin and/or trace mineral premix effects on performance, humoral mediated immunity and carcass composition of broilers during thermoneutral and high ambient temperature distress. J. Appl. Poultry Res. 2:347.
- Deyhim, F., et al., 1996. Vitamin and trace mineral withdrawal effects on broiler breast tissue riboflavin and thiamine content. Poultry Sci. 75:201.
- Ferket, P.R., and M.A. Qureshi. 1992. Performance and immunity of heat-stressed broilers fed vitamin and electrolyte supplemented drinking water. Poultry Sci. 71:88.
