The ferrets at NMBU work in shifts, and when they are “on duty,” their job is to eat experimental feed and produce feces. During their time off, they spend time with their companions in a shared enclosure, where there is plenty of activity, play, minor squabbles, and the characteristic sounds of ferrets.
The reason the ferrets are employed in this eating job is that they serve as model animals for determining the digestibility of protein ingredients used in feed for other animals, such as dogs, cats, pigs, chickens, and fish.
Professor Øystein Ahlstrøm at the Norwegian University of Life Sciences (NMBU) is responsible for these unusual assistants, and there are 19 of them in total.
To ensure that a feed provides the nutrients required by the animal species that will consume it, it is important to measure the feed’s digestibility. In other words, researchers need to determine how much of the nutrients are absorbed in the intestine.
In the digestibility trials involving the ferrets, both animal-based and plant-based protein ingredients are examined, including fish meal and soybean meal.
Protein is an essential feed ingredient, and its quality has a major impact on how much of it is digested. If a protein ingredient is found to have a digestibility of 50 percent, it means that half of the protein is not absorbed during digestion and instead passes out in the feces.
“However, if a test feed shows that 80 percent of the protein is absorbed and digested in the intestine, then the protein ingredient has a higher nutritional value,” says Ahlstrøm.
Established as a Standardized Method
The method for which the ferrets are used has been employed since the 1970s. Previously, mink were used in these experiments, but since mink farming is no longer permitted, ferrets have taken over the role. Both mink and ferrets belong to the mustelid family and produce very similar results when it comes to protein digestibility.
“Over time, the method has become established as a standardized and broadly applicable approach, serving as a model for measuring biological digestibility in vivo, that is, digestibility measured in living animals,” says Ahlstrøm.
Do Ferrets, Fish, and Dogs Digest Protein in the Same Way?
“No, ferrets do not have exactly the same protein digestibility as salmon, cats, dogs, chickens, or pigs, but the ability to digest protein is quite similar across these animal species.”
Ferrets are particularly valuable as model animals for salmon because both are carnivores with relatively short and simple digestive tracts. Many of the studies focus specifically on fish meal and other protein ingredients intended for use in aquaculture feeds.
“Collecting uneaten feed and feces from fish is complicated because they live in water. Using ferrets is both simpler and more reliable.”
Watch the video clip "Ferrets in playland"
Also Used to Test Novel Feed Ingredients
According to Ahlstrøm, around 80 percent of the assignments received over the past two years have come from ingredient suppliers, particularly from the fish meal industry and producers of fish feed and pet food in Norway and abroad. In most cases, the purpose is to obtain digestibility data in order to assess the quality of a protein source.
“We have also conducted tests as part of research projects in which we evaluated new protein ingredients such as insect meal, tunicate meal, oyster meal, mussel meal, poultry meal, and feather meal.”
Feathers themselves are completely indigestible, although they contain protein. In other words, if you eat feathers, they pass through the digestive system largely unchanged. However, when feathers are treated with enzymes that break down their proteins, the resulting feather meal becomes digestible. In Europe, approximately seven million chickens are slaughtered each year, and feathers currently have limited commercial use.
Intestinal Length Makes the Difference
The fact that ferrets have such a short and simple digestive tract is one reason why they provide reliable digestibility results. In fact, estimating protein digestibility for dog food can be more accurate using ferrets than by analyzing dog feces directly.
“In dogs, microorganisms in the large intestine consume some of the remaining protein, making digestibility appear higher than it actually is. What really matters is small-intestinal digestibility. Proteins and amino acids are not absorbed in the large intestine, so what happens there only interferes with the results,” says Ahlstrøm.
A ferret’s intestinal tract is only three to four times its body length, and microbial activity in the large intestine has little influence on the outcome.
What Are the Advantages of Ferret Trials?
One major advantage of using ferrets is that a trial can be completed in just seven days. In addition, only one to two kilograms of the protein ingredient are normally required to carry out a test. The test diet is prepared as a wet feed with a high moisture content. When formulating the experimental feed, the protein ingredient being evaluated is used as the sole source of protein.
The feed also contains cellulose powder, corn starch, and soybean oil, all of which are protein-free. Four ferrets are fed the diet for seven days, receiving carefully weighed daily portions, for example 160 grams per day.
“The first three days are an adaptation period, allowing the ferrets to clear any previously consumed feed from their digestive systems. We also observe whether they find the diet palatable,” says Ahlstrøm.
The animals’ feces are then collected for four days. The samples are freeze-dried, weighed, and analyzed for their protein content.
Why Are Only Males Used?
“Protein contains a great deal of nitrogen, so it is important that the ferrets do not urinate on their feces, because urine also contains nitrogen. And males have a greater distance between... well, you understand. If too much urine gets onto the feces, the results become inaccurate,” says Ahlstrøm.
Department Engineer Mette Henne is responsible for the daily care of the ferrets and the practical execution of the trials.
“Ferrets are very interested in people, and we see that whenever we enter the room or step into the group enclosure. They are curious, enjoy playing, and are not afraid of humans. They also like collecting things and always seem to want more of just about everything,” says Henne.
In the wild, ferrets are essentially solitary animals, meaning that they normally live on their own. However, when they are semi-domesticated, they become more social, although they may occasionally fight or bite one another when housed together. Their main activity is sleeping, which they do for 18 to 20 hours a day. The rest of their time is spent eating 10 to 12 small meals and playing with enrichment objects and with each other.
Photo: Janne Karin Brodin
We Know Them All by Name
All of the ferrets have names, and since they come from a Danish breeder, one of them is named after King Frederik of Denmark. Others bear the names of well-known Danes such as entertainer Eddie Skoller and rock musician Kim Larsen.
“But we still haven’t managed to get them to respond to their names,” Henne says with a smile.