Essential oils have proven efficacious in some feeding trials, but more research is needed, say researchers at the University of Wisconsin-Madison.

The researchers conducted a feeding trial on transition and early-lactation cows and found that cows receiving essential oils had lower milk yield than control cows in weeks 1 through 5 postpartum and similar milk yield in weeks 6 through 10. The treatment cows did start to show a milk-yield advantage as they approached mid-lactation. However, the feeding trial did not continue past week 15.

 Another paper on essential oils was presented in the December Journal of Dairy Science. That study, conducted by the University of Delaware, found that mid-lactation cows fed essential oils produced 5.9 pounds more 3.5 percent fat-corrected milk per day than cows fed the control diet.

The Wisconsin researchers say more research regarding potential interactions between basal diet, stage of lactation and dietary essential oil supplementation is needed before essential oils can be used with confidence in commercial practice.