Assessing the Impacts of Ractopamine and Parasiticides on the Environment

Project Title

A Comprehensive Risk-Benefit Analysis of Ractopamine and Common-Use Parasiticides: Co-Occurring Impacts on Microbial Communities, Non-Target Environments, Chemical Fate, and GHG Emissions from Manure


Jonathan Challis (AAFC Lethbridge)

Tim McAllister (AAFC Lethbridge), Kevin Floate (AAFC Lethbridge), Trevor Coates (AAFC Lethbridge), Stephanie Terry (AAFC Lethbridge), and Mark Hanson (University of Manitoba)

Status Project Code
In progress. Results expected in March, 2028 ENV.09.21C


Previously funded work by this team (ENV.09.17) evaluated synthetic hormones used in beef production and how they moved through the environment once excreted by cattle. What they found was that most of these hormones broke down quickly in the pen floor with minimal risk of contaminating areas outside of the feedlot environment.  The exception was ractopamine, which could be found in the pen floor and catch basins, and persisted for up to 5 months post application. Manure composting was found to increase the rate of degradation of ractopamine.

Since numerous products are used in the feedlot to promote optimal animal health and welfare and enhance productivity many of these biologically active compounds can occur simultaneously  in pen floor manure and may influence further product breakdown and other important processes occurring in manure.


  • To provide a holistic and comprehensive risk-benefit analysis for a number of important and representative co-occurring veterinary-use drugs commonly used in the beef-cattle industry.

What they will do

These researchers want to further evaluate how ractopamine (RAC) behaves in the feedlot environment when other cattle-use parisiticides are present, and assess the formation and degradation of specific metabolites . Specifically they will examine if the presence of  ivermectin (IVM) or fenbendazole (FBZ) and oxfendazole (OFZ) impact the degradation of RAC and major RAC metabolites and if these compounds alter manure microbial communities and manure greenhouse gas emissions. First they will determine concentrations of RAC, IVM, and FBZ in manure from commercial feedlots , water from catch basins and in water, air, and soil samples from surrounding environments

Next this team will conduct a feeding trial at the Lethbridge research centre where they will assign 200 steers to 20 pens with the following treatments: control; no IVM,  FBZ, or RAC (control), RAC only, IVM and RAC, FBZ and RAC, and FBZ and IVM and RAC. Cattle will be monitored for health and performance. They will sample fresh feces, pen floor, soil, water, and air throughout the feeding trial.

Following the feeding trials they will conduct lab scale composting studies where they measure breakdown of all 3 products as well as manure microbial communities and methane emissions associated with composting. Manure will be collected from pens containing the controls, just RAC, and RAC+IVM +FBZ to be used directly in the composting studies.

In the next study they will use artificial wetland tanks to simmulare a wetland/catchbasin environment in close proximity to a feedlot. They will add low vs high concentrations of RAC, IVM, and FBZ mixtures and conduct chemical analysis to determine their degradation..

Finally they will develop a risk benefit analysis to evaluate the potential risks and benefits of using the products mentioned.


This project will give us a better understanding of the fate and effects of veterinary products in feedlots and surrounding environments. Risk-benefit analysis using the information gained from this work will help identify if mitigation is needed and how and where those steps can be applied.