A massive study with data collected from numerous commercial feedlots indicates that Zilpaterol increases both death losses and dark cutters. Ractopamine had an effect on death losses, and little or no effect on dark cutters. The study was conducted by Guy Loneragan from Texas Tech Univ. and Dan Thomson from Kansas State Univ.

The detrimental effects of both beta-agonists were greatest in the summer months. The data sets were huge with 79,171 cattle in the ractopomine data set and in two Zilpaterol data sets there was 722,704 and 149,636 cattle. The entire paper is available free online.

The dark-cutter percentages for cattle on Zilpaterol were 0.53 percent for cattle fed regular feed and 1.59 percent for steers fed Zilpaterol. Steers seem to be more likely to have dark-cutter problems on Zilpaterol than heifers. In the ractopomine data set, there was one out of nine feedlots that had 0 percent death losses on both the ractopomine group and the regular feed group. All of the other feedlots had death losses for both groups.

Further investigation

There is a need to find out what this one feedlot was doing differently. I have talked to two feedlot managers who reduced lameness problems with Zilpaterol by adding more light bulky roughage to the rations. Other factors that may increase adverse effects might be poor feed mixing, rough handling or lack of bunk space. Some animals will eat more Zilpaterol feed than others. Dose is a further possible factor. Zilpaterol is fed at a single dose and the label on ractopomine allows freedom to raise or lower the dose.

Epidemiology approach

The ractopomine data was set up as a controlled experimental design. The Zilpaterol data set used the observational approach that was used in epidemiology. Some people in the industry have criticized the Zilpaterol data because the cattle were not randomly assigned to treatment. Dr. Loneragan is an epidemiologist and observational data is a solid scientific approach when the data is carefully scrutinized for confounding factors. Epidemiology is used to track down causes of food poisoning or bovine spongiform encephalopathy (BSE or mad cow disease). It is also the same method that is used by data mining companies to collect customer information. Powerful statistics and computer programs mine data, and when you click on your favorite shopping sites they know what you like.

The first observations I made of lame, heat-stressed cattle were dismissed as anecdotal by many people in the industry. At a packing plant in the summer of 2006, I observed a pen of Brahman cross cattle with strange new problems I had never seen before. Half of the pen of cattle was normal, about one-third of the animals were sore footed and there were a few down with their tongues sticking way out. The sore-footed animals acted like the stockyard floor was red hot. The downed animals showed severe heat-stress symptoms I had NEVER seen before in heat-tolerant Brahman cross cattle. The only new thing that was different in the industry at this time was the use of ractopomine. It is likely that after this incident many cattle feeders lowered the dose and stopped the problem. When Zilpaterol came on the market, I started seeing additional problems with sore-footed stiff cattle during hot weather in other packing plants. I saw it in all types of cattle ranging from Angus, Holsteins and mixed British/Continentals. My observations were treated as anecdotal until the incident in the summer of 2013 when hooves fell off many cattle in a pen fed Zilpaterol.

We should now think again about the epidemiological approach. If I was a medical doctor and I had observed some weird food-poisoning symptoms in people that had stayed at a certain hotel, it is highly unlikely the Centers for Disease Control and Prevention would have treated my observations as anecdotal. To track down the cause of food poisoning, bits and pieces of information are collected until all the pieces of the puzzle are found. That is how epidemiology works and it is a valid component of sound science.

To access the paper online – Loneragan, G.H., Thomson, D.U. and Scott, H.M. (2014) “Increased mortality in groups of cattle administered β-Adrenerger-agonists ractopomine hydrochlonde and Zilpaterol hydro chloride”.

Dr. Temple Grandin operates Grandin Livestock Systems Inc., Fort Collins, Colo., and is a faculty member in the animal science department at Colorado State Univ.