By: Dr. Joseph McFadden, associate professor of dairy cattle biology in the Department of Animal Science at Cornell University
In 1991, Dr. Mike Hutjens, emeritus professor in the Department of Animal Sciences at the University of Illinois, defined four key factors for evaluating feed additives: Response, Returns, Research and Results (Hutjens, 1991). Dr. Hutjens later added 3 additional Rs for industry professionals to consider: Repeatability, Reliability and Relativity. Feed additives that claim to reduce methane emissions from cattle will emerge as potential tools to mitigate climate change. The pressure to consider their use will be significant. However, we must consider these seven Rs when evaluating the efficacy, economics and safety of feed additives to inhibit enteric methane emissions from cattle without impacting animal performance, farm profitability or consumer acceptance of the technology.
Responses are performance outcomes producers, nutritionists and veterinarians expect to observe in livestock fed a feed additive. The response variable that some might consider as being of paramount importance is a feed additive’s ability to inhibit methane yield (e.g., g/kg of dry matter intake) or methane intensity (e.g., g/kg of milk yield). But we need to be cautious because inhibiting ruminal methanogenesis (i.e., the formation of methane by microbes known as methanogens) has the potential to impact other biological responses. We would prefer to also observe improved feed intake, fiber digestibility and/or feed efficiency in response to supplementing diets with feed additives; however, these outcomes are never guaranteed and shouldn’t be ignored. Depending on the mode of action for a feed additive, which may be unknown, the inhibition of ruminal methanogenesis has potential to compromise rumen digestion or the conversion of feed nutrients to meat or milk. Therefore, we must consider the effects of a feed additive on the complete animal system to avoid net gains in methane emissions.
Returns represent the projected or actual profitability of a feed additive. Unless producers are incentivized or regulated to use feed additives that only reduce enteric methane emissions, which is yet to be proven, such a feed additive would also need to ensure additional benefit to animal performance. This could be in the form of enhanced feed efficiency, energy-corrected milk production, health or fertility. Moreover, understanding the true return for feeding an additive is complicated because outcomes, including the inhibition of methanogenesis, may not be responsive in cattle at all stages of growth or lactation. Animals that respond to a feed additive will need to cover the cost of non-responders.
Research aimed at defining the efficacy of feed additives to inhibit ruminal methanogenesis in the cow is critical. This said, our scientific approach for studying feed additives that may inhibit methanogenesis requires refinement. Controlled and unbiased independent studies with adequate replication, accurate quantitation of methane output and statistical inference are needed. Scientists need to characterize methane inhibition efficacy of feed additives at various stages of growth or lactation, as well as their interaction with diet, environment and genetics. But, we cannot solely focus on methane yield and intensity. We must consider the impact of the feed additive on other greenhouse gasses (e.g., nitrous oxide), energetic efficiency, nutrient digestibility, nitrogen and phosphorus excretion, and meat and milk composition as well as other important outcomes such as health and reproduction. The presence of compounds in meat and milk that may have human safety concerns (e.g., nitrate or bromoform) also deserves consideration to ensure the parallel development of consumer support for the science and technology.
Results obtained by producers and nutritionists for individual farms is critical to confirm a desired feed additive response. Tools to measure animal performance responses include milk records (major components and fatty acids), reproductive reports, somatic cell counts, dry matter intake and growth and body condition charts. But approaches to measure methane emissions are urgently needed. Research has explored the use of drones, lasers and satellites at the farm level and spot sampling methods at the cow level (e.g., GreenFeed). Other efforts are focused on whole-farm modeling of environmental impacts including methane emissions (e.g., Ruminant Farm Systems [RuFaS] model). The use of milk fatty acid data obtained using mid-infrared spectroscopy as a predictor for methane output is also being considered.
Repeatability represents the statistical results that define the efficacy of a feed additive to inhibit methane (or enhance performance outcomes). Feed costs are the largest input in the cattle industry. Every farmer or nutritionist that chooses to include a feed additive that inhibits methane is accepting a certain amount of risk that it won’t be effective. This decision should be based on statistics and return on investment.
Reliability refers to how predictable a response is across a variety of management scenarios. Repeated testing of a feed additive, independent research and validation, and the continual monitoring of efficacy on individual farms is required. It can be argued that that we don’t have a feed additive that reliably inhibits methane at the present time; however, reliable feed additives will emerge in time.
Relativity refers to the comparison of products that claim to inhibit methane. Although we should consider the type of methane inhibitor, and relative degree of methanogenesis inhibition, we must also consider the aforementioned performance outcomes in tandem. If two products inhibit methanogenesis to a similar extent, the product with the superior effect on animal performance and profitability should be accepted.
The renaissance of feed additives may be upon us, but stay ready with the 7 Rs of feed additives.
Dr. Joseph W. McFadden is an associate professor of dairy cattle biology in the Department of Animal Science at Cornell University. He studies dairy cattle nutrition including the impact of feed additives on nutrient digestibility and bioavailability, and milk production with funding from the U.S. Department of Agriculture, National Science Foundation, Foundation for Food & Agriculture Research, industry, and Cornell. McFadden is actively leading the development of a national center for testing feed additives for their ability to modify methane output and other biological responses using a team-based holistic approach.