Research Note

Tightening Safety Factors (Safely)

Reduce the risk of underfeeding? Or, reduce the risk of overfeeding? Which better supports the dairy producer’s IOFC (income over feed cost)?

Underfeeding lowers feed costs but fails to optimize a cow’s genetic potential to make milk and milk components and remain productive. Overfeeding wastes nutrients and can over-condition the cow while generating environmental headaches. Both underfeeding and overfeeding can cause health problems.

Safety factors (SF) in diet formulation increase nutrient inclusion above published or recommended requirements  to minimize the risk of underfeeding without overfeeding.

“The best dietary safety factors,” says Emeritus Professor Bill Weiss at the Ohio State University, “take into account variability in the nutritional requirements of cows in a group or pen as well as variability in the nutrient composition of their ration.”

However, Weiss cautions that the SD in nutrient composition in tables consists of both “true variation” and sampling and analytical variation (aka “observer variation”).

“Based on limited data,” Weiss says, “we suspect that for many feedstuffs observer variation may exceed true variation.

“Forages have both high sampling and true variation, which means these feedstuffs must be sampled on each farm and you should take duplicate independent samples and average the lab results. To get an accurate SD to use for developing forage SF, you would need to take multiple, duplicate samples and calculate the SD from the averages of the duplicates.”

Most concentrate feedstuffs, Weiss adds, have low sampling and true variation, so the mean and SD can be obtained from good feed composition databases for calculation of feedstuffs-specific SF. However for wet feedstuffs, such as high moisture corn, wet corn gluten feed, or wet brewers grain, true variation is high and sampling is necessary to get an accurate mean while using the SD from the database.

“You should take duplicate independent samples and average the lab results. This will result in more accurate diet formulation.”

Grouping 

Weiss also notes that grouping cows by milk yield for diet formulation may improve IOFC, based on research from Ohio State and the University of Wisconsin. The cost savings from grouping occurs mostly because, with less variation among cows in a pen, the SF can be reduced.

Weiss says simulation studies point to the optimal SF for metabolizable protein as the mean milk yield plus 1 SD, assuming the SD is known. The SD within a group is less, so the SF for the group’s diet is tighter, which can improve IOFC.

Questions?

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