In the group facing moderate antigen exposure, pigs receiving 370 percent of NRC requirements had 21 percent greater gain than those receiving 70 percent of NRC requirements. In the high-antigen exposed group, the corresponding increase in gain with optimum vitamin intake was 19 percent. However, total gains were consistently greater for the moderate-antigen exposed pigs than for the high-antigen exposed pigs because of greater feed intake (P < 0.01). Feed intake increased quadratically (P < 0.01) with increased vitamin fortification as well.
There was also a significant linear improvement (P < 0.05) in feed efficiency with increased vitamin fortification. For both antigen levels, feed efficiency was best in diets with vitamins added at 370 percent of NRC requirements. At that level of vitamin intake, efficiency was improved by 10 percent for the moderate-antigen exposed pigs and 6 percent for the high-antigen exposed pigs, compared to their counterparts receiving 70 percent of NRC requirements. There was no significant difference in feed efficiency by antigen exposure.
The fact that the optimum vitamin allowances for both levels of antigen exposure were the same did not support Stahly and Cook's expectation that optimum allowances would rise as antigen levels decreased and performance potential increased. This expectation is contrary to the hypothesis that challenged animals have higher vitamin requirements, but it is based on the earlier Iowa State study of lean growth potential, which had suggested that vitamin requirements remain fairly constant per pound of lean gain. Stahly notes, however, that the differences in antigen exposure between the two groups in this study were much less than in previous work with the same two management systems.
Although the less-than-expected difference in antigen exposure did not allow the researchers to confirm their theory that vitamin requirements increase as the potential for gain increases, the results did reconfirm these two points from the earlier study:
First, current NRC requirements should be reconsidered--not because they risk clinical deficiencies in today's swine, but because they do not meet requirements for optimum performance, regardless of genetic potential or health status. In both of these studies, it was not until the pigs received roughly four or five times the NRC requirements that their performance reached its optimum and, thus, enabled producers to maximize profits.
Second, any hypothesis that healthy animals have lower vitamin requirements than sick or stressed ones is a simplification, and possibly a fallacy. Granted, disease and stress do increase basic requirements for some vitamins, such as E, that are closely linked to an animal's ability to mount an effective immune response. Furthermore, the reduced feed intake that accompanies stress and disease suggests the need for greater vitamin concentrations in the feed to ensure enough total vitamin intake to meet the animals' basic requirements.
However, as both of these studies show, reducing vitamin allowances for animals with less disease pressure can reduce gains and feed efficiency. In fact, optimum vitamin allowances resulted in greater returns for the healthy pigs than the challenged ones, as measured by gains and feed efficiency.
References:
- Stahly, T. et al., 1995. Dietary B vitamin needs of high and moderate lean growth pigs fed from 9 to 28 kg body weight. Iowa State University Research Report, ALS-R1263.
- Stahly, T., and D. Cook. 1996. Dietary B vitamin needs of pigs experiencing a moderate or high level of antigen exposure. Iowa State University Research Report, ALS-R1373.
