Cattle and other ruminants produce highly digestible human food from materials that are largely inedible by the human population, including grasses, milling residues, oilseed crushing byproducts, etc. This is accomplished through rumen microbial fermentation, which produces usable energy compounds and excellent quality protein. This miraculous anaerobic fermentation process, however, contributes to the production of unwanted greenhouse gases (GHG), in particular methane (CH₄) which can trap atmospheric heat.

Many GHG mitigation strategies have been studied, with the goal of reducing GHGs and CH₄. While reducing GHG production can be readily accomplished, doing so and maintaining production and feed efficiency has been much more difficult to achieve. Roque et al. [1] determined that seaweed (Asparagopsis) reduced CH₄ production by 67% when fed at 1% of the diet, but this substance also reduced intake and milk production. In the study of van Zijderfeld et al. [2] nitrate reduced CH₄ production by 40% but has the potential to be toxic.

Plant bioactive compounds have been extensively studied, but most lack consistent results, or have unwanted side effects. Tannins, as an example, have been demonstrated to reduce CH₄ production, but also bind feed proteins, reducing intestinal digestibility [3]. Goel and Makkar [4] reviewed saponins as compounds to reduce CH₄ production and concluded that these reduce protozoa, but this may or may not translate into reduced GHG. Many essential oil compounds have demonstrated potential in vitro, but limited in vivo testing has been much less promising [5].

Agolin, an essential oil blend has been shown to alter the rumen biota leading to greater energy efficiency as well as reductions in CH₄ and NH₃ output. A meta-analysis based on 23 studies demonstrated a 4.1% improvement in energy corrected milk yield after a four-week adaptation period, with no change in dry matter intake. In addition, methane intensity (g/kg ECM) was reduced by 9.9% on average and CH₄ output was reduced in all trials in which it was measured [6]. A subsequent feeding experiment [7] further confirmed the methane intensity reducing potential for Agolin at 11.1%, along with a reduction in NH₃ intensity of 16.0%.

The purpose of this study was to evaluate the essential oil blend Agolin in a high producing herd that would be representative of high concentrate feeding and management practices and determine if improvements in yield and efficiency were measurable.

The ingredient composition of the diet used during the study period is given in Table 1. The diet contained 59.6% forage with 70% of the forage as corn silage, with a grain content of approximately 40% of the total dry matter.

The nutrient composition of the diet is shown in Table 2. The composition clearly shows that the diet was a high concentrate diet and would be expected to represent the type of diet typical for high producing dairy cows in the United States.

Pen selection was based on the level of production and average days in milk for all cows available in the pen at the time that the trial was started. While the numbers of animals remained consistent within the pen, some cows were removed, and others were placed in the pens. There were 184 control and 146 test cows that were in the same pens, receiving the correct diets for the full duration of the trial (Table 3). The pre-trial data for these cows showed that they remained well matched across treatments.

Results for milk yield and milk composition were based on cows included in the analysis (Table 4). Milk yield did not change with the inclusion of Agolin, but fat and protein percentages were elevated (P < 0.05). There was a significant improvement in fat yield per cow/day (P < 0.05) resulting in a tendency for FCM and ECM to be greater for the treatment group (P < 0.10). Increased milk fat yield was also found in a California Agolin feeding trial [9] involving very high producing cows receiving high energy diets.

Efficiency was calculated by pen. There was a tendency (P < 0.10) for both FCM and ECM to be improved when the additive was included in the diet. This is in also agreement with the California Agolin feeding trial [9].

¹Values for all cows in pens when pen allocations were made; ²Pretrial values for cows that remained in the pens for the duration of the trial were used in the statistical analysis.

¹P < 0.05 differences are significantly different: P < 0.10 there is a tendency for differences to be significantly different.

Agolin has been demonstrated to significantly increase FCM and ECM in mid-lactation cows producing more average levels of milk of approximately 30 kg [10] [11] but prior to conducting the current experiment, it was questioned if the product could improve performance in very high producing cows. During ruminal methanogenesis, CO₂ and H⁺ react to form methane, representing a loss in energy to the host animal. If methanogenesis is inhibited and H⁺ accumulates, rumen pH declines, and fiber digestion can be reduced. Reducing CH₄ production in the rumen without reducing organic matter digestibility requires the H⁺ to be utilized in the production of volatile fatty acids, mainly propionic acid. This results in the energy being available to the host to use for productive purposes.

Knapp et al. [12] categorized CH₄ mitigation strategies into three categories: 1) Feeding diets to reduce the acetate/propionate ratio, to decrease H⁺ to be used in the formation of CH₄. 2) Improving animal productivity to dilute maintenance and improve feed efficiency. 3) Provide rumen fermentation modifiers. All three strategies were evidently in practice for the test pens of animals as reported here.

This feeding study compared the lactational performances of high producing cows receiving the rumen modifier Agolin® to cows receiving the same diet without the feed additive. The results provide further evidence that Agolin has the potential to increase fat and protein corrected milk in high producing dairy cows. Other trials have also demonstrated the ability of Agolin to reduce enteric methane production. With a combination of improved energy corrected milk and feed efficiency in addition to a decrease in enteric methane emissions Agolin Ruminant shows potential to be of benefit not only to dairy profitability but also to the growing demand for reducing the carbon footprint of dairying.

The authors would like to thank Mr. Doug Young, Spruce Haven Farm, Union Springs, NY, 13160, USA for providing his facilities, expertise and enormous assistance in running this trial. The authors also wish to acknowledge Dr. Essi Evans, E+E Technical Advisory Services, for sorting and compiling data and providing all statistical analyses.

Mr. John Clark and Mr. Peter Williams market Agolin in the United States of America. Both were involved in the design but not the analysis of data or interpretation of results.

Williams, P., Clark, J. and Bean, K. (2021) Evaluation of Agolin®, an Essential Oil Blend, as a Feed Additive for High Producing Cows. Open Journal of Animal Sciences, 11, 231-237. https://doi.org/10.4236/ojas.2021.112018