Four factors can be considered to determine if a feed additive should be used: anticipated response, economic return, available research, and field responses (Hutjens, 1991). Response refers to expected performance changes the user could expect or anticipate when a feed additive is included. Several examples are listed below.
- Higher milk yield (peak milk and/or milk persistency)
- Increase in milk components (protein and/or fat)
- Greater dry matter intake
- Stimulate rumen microbial synthesis of protein and/or volatile fatty acid (VFA) production
- Increase digestion in the digestive tract
- Stabilize rumen environment and pH
- Improve growth (gain and/or feed efficiency)
- Minimize weight loss
- Reduce heat stress effects
- Improve health (such as less ketosis, reduce acidosis, or improve immune response)
If milk improvement is the measurable response, a breakeven point can be calculated. For example, a consultant recommends an additive that raises feed cost 10¢ per day. If milk is valued at 12¢ per .45 kg, every cow must produce .38 kg more milk to cover the added cost associated with the additive. Another consideration is if all cows receive the additive, but only cows fresh less than 100 days respond. Responding cows must cover the additive costs for all cows (responsive and non-responsive cows). One guideline is an additive should return two dollars or more for each dollar invested to cover non-responsive cows and field conditions which could minimize the anticipated response.
Research is essential to determine if experimentally measured responses can be expected in the field. Studies should be conducted under controlled and unbiased conditions, have statistically analyzed results (determines if the differences are repeatable), and have been conducted under experimental designs that would be similar to field situations.
Results obtained on individual farms are the economic payoff. Dairy managers and nutritionists must have data to compare and measure responses. Several tools to measure results (to evaluate responses on a farm) include DHI milk records (peak milk, persistency, milk components, and milk curves), reproductive summaries, somatic cell count data, dry matter intake, heifer growth charts, body condition graphs, and herd health profiles which will allow critical evaluation of a selected additive.