The y-axis, Average Animal Response, refers to any average productivity or health measure, such as growth rate, feed efficiency, immunity or reproductive performance, as it responds to vitamin allowances.
The x-axis, Vitamin Allowances, refers to the total level of vitamins in the diet, including feedstuffs and fortification:
- Deficient marginal allowances (2) are below the requirements published by the National Research Council, putting the animals at risk of developing clinical deficiency signs and disorders.
- Suboptimum marginal allowances (3) exceed the NRC requirements and thus prevent clinical signs, but they are inadequate to permit optimum health and productivity.
- Optimum allowances (4) permit optimum animal health and productivity.
Note that there is not a single optimum vitamin allowance. Various influencing factors will affect both the animal's requirements and the ability of the diet to meet them. These factors include:
- Stressors on the animal:
- Disease
- Confinement
- Restricted feeding
- Vitamin antagonists
- Air quality
- Temperature
- Variations of vitamin levels in feedstuffs:
- Bioavailability
- Stability
- Quality of feedstuffs
For instance, vitamin allowances that are optimum in a stress-free environment may become suboptimum as the heat stress of summer increases. Thus, Optimum Vitamin Nutrition remains a dynamic aspect of animal agriculture that must be regularly evaluated.
