As most dairymen and dairy nutritionists know, efficient milk production is largely a matter of managing rumen function and the fermentation process.

It is a function of providing the correct amounts of fermentable components (feedstuffs) in the right combination so the products of fermentation meet the nutrient or molecular needs of the cow, and specifically the mammary gland, in accordance to the animal’s genetic potential.

Anyone who has fed and milked dairy cows for more than about a day knows this can be an incredibly complex process, particularly when we consider the variables in forages, byproducts, environment, management conditions and the cow itself.

Given the research and development of the computer models that help the nutritionist predict fermentation profiles and performance, we have an unprecedented ability to manipulate rations more effectively than ever before.

Of course, this comes with a list of complicating factors, but producers have an uncanny knack of working through these challenges.

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In addition to coming closer to optimizing rations, science and the industry have provided an ever-developing and expanding list of additives and nutritional tools that can be used to change the rumen environment in some manner to improve the products of fermentation – hopefully, with a positive result.

One of the more recent classes of dairy feed additives are referred to as plant extracts or essential oils (EOs). Numerous products have entered the market in recent years, and a substantial amount of research and experience with these various products have emerged.

Some has been positive, others only marginally so. This article will pursue a straightforward evaluation of these products and a number of their iterations.

A crash course: What is an essential oil/plant extract?

EOs are molecular compounds extracted from specific plants, generally through a steam distillation process. They are characterized by an oily consistency and generally are at least somewhat aromatic – in some cases, very aromatic.

Over the years, a long list of these extracts have been discovered that have interesting properties medicinally, some of these having been known and used for literally thousands of years. Most commonly, these products have antimicrobial or antiseptic properties.

Certain compounds are known to affect only specific microbial organisms. Because of this effect on various microbial species, these compounds have gained the attention of scientists wishing to modify the microbial population of the rumen and subsequent rumen fermentation characteristics.

Examples of these substances include capsaicin from various hot peppers, cinnamonaldehyde from cinnamon, allicin derived from garlic, thymol from thyme and oregano, eugenol from cloves, pinene from juniper berries and limonene from dill, to name a few.

Jim Paulson with the University of Minnesota has published an article on several websites providing a detailed table of many EOs, the organisms they affect and the identifying researchers.

As mentioned, EOs have been identified and are currently being used in some capacity as a means to potentially improve or alter rumen fermentation. A significant degree of hope is placed on these naturally occurring compounds as a replacement for some of the chemically created commercial additives – in particular, antibiotics.

Much of the earlier research with these products has been done in a controlled lab setting and helped identify very specific results when introducing these products into a microbial population in the rumen. The effects of EOs seem to be diet-dependent (specific forage or carbohydrate profiles) and pH-dependent, and thus need to be evaluated in the cow.

Certain products seem to work better with a particular diet and not as well in others. There is still limited data available from trials with lactating cows feeding EOs. Many of the products currently being sold in the U.S. dairy market have only very limited domestic research (one or two trials), with limited types of rations or forage and feed ingredient sources. The body of existing research, as a whole, remains limited.

Of the research that has been pursued, some interesting results have been noted. A trial at the University of Wisconsin in 1997 involved 33 multiparous mid-lactation cows. The supplemented cows showed increased milk production, increased components and increased fat-corrected milk yields. Cows were fed a common 50-50 forage-to-concentrate diet with corn silage and alfalfa as the forage.

On a larger scale, researchers at Penn State conducted a production field trial involving 170 cows fed a 42-58 forage-to-concentrate ration where corn silage made up greater than 66 percent of the forage, and the concentrate was largely composed of byproducts.

As in the first trial noted above, cows receiving the essential oil blend produced more milk and more fat-corrected milk. Components in milk were similar but numerically higher in the treatment cows.

In another study at the University of Wisconsin, researchers completed a trial with dairy cows prefresh to 105 days into lactation. A total of 40 cows were used, with 20 cows as control and 20 cows receiving 1.2 g of an essential oil blend (CRINA).

There was no observed benefit to the treatment-fed prefresh cows. However, dry matter intake and fat-corrected milk production increased the longer cows received the additive.

It has been theorized from the results seen here that a potential adaptation period may be required to fully realize the benefits of feeding these products.

Additional research has yielded a variety of results, including increased total-tract acid detergent fiber and starch digestibility, increased ruminal true organic matter and nitrogen digestibility, and improved dry matter intake, milk yield and milkfat yield in dairy cows reported when feeding various EO compounds or commercial products (blends).

On-farm trials have reported varying returns on investment ranging between 2 to 1 and 6 to 1.

Conversely, numerous studies have shown little or no effect. This seems to illustrate the effect noted above, that the effectiveness of EOs are highly diet- and animal-specific.

Over time, hopefully, different EOs or EO blends will be identified as more effective in specified diets, perhaps to the point where some degree of predictability can be anticipated when a specific EO is used with a specific ration or forage type.

Please note that most, if not all, commercial EO products are actually blends of two or more individual EOs. For instance, Vigortone (Cargill) produces an EO product known as Cinnegar, which is a blend of extracts from cinnamon and garlic.

Other existing products are much more complex, with proprietary formulas developed from an anticipation of the effects on specific microbial species in the rumen by each component of the product.

Interestingly, there is a fairly wide range of these blends when it comes to the different EO components included. As with many other classes of additives where a given class has multiple competitive parties, very little, if any, head-to-head research has been run in an effort to evaluate who has the best product.

However, it should be noted that for such research to be meaningful, it would have to be replicated under a variety of dietary and animal conditions.

Conclusions

Hopefully, this discussion highlights at least a few of the important factors in evaluating EOs. In summary, EOs and the commercial blends of EOs have shown promise as a means of modifying rumen fermentation with concurrent positive results in terms of feed efficiency, overall animal performance and income over feed cost. There are reported health benefits as well, but that’s another article.

Secondly, because of the many variabilities, the industry is still at a point with this class of additives that a certain amount of trial and error will have to be employed on the farm in deciding which EO product should be selected, or if an EO has any place at all in the feeding management program.

Starting with the current research, as always, is obviously step one, particularly the work that matches a given farm’s feeding and management practices as closely as possible. Review as many of the products as is feasible. Finally, consider the cost of each product and understand that it has to perform financially as well as biologically.  PD

Stephen B. Blezinger