According to scientist Dr. Marianne Dawkins, animals in captivity are considered to have good animal welfare if they are healthy and get what they want. Since animals can’t tell us what they want, how do we figure it out? One way scientists study this is by seeing if animals are willing to “pay a price” for something they value. For example, a rat can be trained to push a lever to get food. Over time, the number of lever presses required to access the food increases, meaning the “price” goes up. If the rat is willing to push the lever many times, they are believed to be highly motivated to access it. Providing a valued resource in a captive animal’s enclosure may improve their welfare. One drawback of this method is that the “price” may have a physical limit. For example, the rat wants to access the food, but the number of lever presses required exceeds the animal’s physical capabilities. Now scientists cannot be sure if the animal gave up pressing the lever because they didn’t want the food or because the price became too physically demanding. An alternative strategy is to make the “price” something unpleasant. Instead of completing a task that requires physical exertion, the animal must overcome a situation they would otherwise avoid. For example, an aversive or unpleasant “price” would be interacting with a mild electric current to access food. Now, the shocking sensation would become increasingly irritating over time until the animal stops attempting to access the food. This strategy was used in Dr. Rachael Coon’s research.
During her PhD in the Animal Biology Graduate Group at UC Davis, Rachael, now a postdoc at the University of Calgary, measured how much feedlot cattle (beef cattle raised for human consumption) wanted to access hay using an electrified barrier as a “price”. This research was conducted under the supervision of Dr. Cassandra Tucker and was approved by the University of California Davis Institutional Animal Care and Use Committee (Protocol #: 21195). In North America, feedlot cattle are usually fed a diet consisting of more than 76% grains, which is very different from the grass they evolved to eat (USDA, 2013). This grain-heavy diet makes them gain weight faster but can cause health problems, like an increased acidity in their digestive systems, particularly in their rumens, the main compartment of their stomachs. The healthy rumen pH range for cattle is between 5.5-7, but cattle are diagnosed with acidosis if pH falls below 5.8 for multiple hours per day and persists over time. Prolonged high acidity can lead to stomach ulcers and liver abscesses.
Rachael was interested in knowing if feedlot cattle fed a high-grain diet would pay a “price” to access additional hay, which might help slow digestion and reduce acid build-up. She set up an experiment with an electrified barrier in front of the hay bin (Figure 2).
Steers (young, sterile male cattle) had to push against the electrified barrier with their noses to get to the hay (Figure 3). Each day, the electric current on the barrier increased, making it harder for the steers to get to the hay. Steers always had unlimited access to the high-grain diet in another bin, so pushing against the electrified barrier was completely voluntary and not because they were hungry. There were two groups in the experiment. One group had access to a small amount of hay behind the electrified barrier, and the other group had access to more of the high-grain diet behind the electrified barrier.
Besides checking how much steers wanted more hay or grain, Rachael also measured the acidity in their rumens. She thought that if steers experienced more acidity in their rumens, they would be willing to touch a higher electric current to get hay compared to healthy steers that had lower acidity in their rumens. Interestingly, Rachael found that steers were more willing to touch a higher current to eat extra grain than hay. This may have been because the high-grain diet was higher in calories than hay and likely tasted sweeter, making it more enjoyable. Another reason could be that the steers were used to eating grain, while hay was a new food for them. Steers often fear new foods, so the unfamiliar hay may not have been as attractive. When looking at rumen pH levels, steers appeared more motivated to get hay as the acidity in their rumens increased. However, overall, steers were more willing to touch a higher current to eat extra grain (Figure 4).
These findings were surprising for a couple of reasons. First, steers were more motivated to get grain than hay. Second, they were willing to pay a “price” to access grain even though they already had free access to it. This behavior is known as contrafreeloading, where an animal works for a resource it can get for free. The reason for this behavior is unknown–one theory is that the animal might be bored and finds the challenge of working for the resource interesting.
In an earlier experiment, Rachael demonstrated that steers wouldn’t interact with the electrified barrier if there was no food behind it. This means that the electrified barrier alone isn’t enough of a stimulating challenge. However, the combination of the electrified barrier and the possibility of getting food seems to be enough to motivate steers to work for more grain, even when it’s freely available elsewhere.
The fact that steers are willing to contrafreeload, to “pay the price” for extra food, shows that they value the food resource and the act of searching for and eating it. Future research should explore why feedlot cattle such as steers choose to work for food they can get for free, and what this behavior means for their welfare.
This research was recently published in the Journal of Animal Science and an open-source version can be found here.
1USDA. 2013. Feedlot 2011, part I: Management practices on U.S. Feedlots with a capacity of 1,000 or more head. Report No. 626.0313. UDSA-APHIS-VS-NAHMS, Fort Collins, CO.
Rachael acquired her MSc in dairy behavior and welfare at the University of Guelph before completing her PhD in feedlot cattle behavior and welfare at UC Davis. She is now a post-doctoral associate in the Faculty of Veterinary Medicine at the University of Calgary, where she studies the behavior of rangeland beef calves and the welfare of rodeo animals at the Calgary Stampede.
[Edited by Isabelle McDonald-Gilmartin and Nicole Rodrigues]