Handling and Training of Mice and Rats Results in Calmer Animals During Experimental Procedures

by Camilla Bengtsson and Marie Eriksson 
Researchers/Project Leaders, RISE Research Institutes of Sweden

For most people with pets, handling and training their animals is important. Living with an “undomesticated” pet can be trying, especially when the day comes for a visit to the veterinarian. The same should be true for our laboratory rodents. If we handle and train them well, our work with the animals becomes easier and safer, and we help the animals feel safe in the procedures to which they are exposed. 

We take this very seriously within the in-vivo department of RISE Research Institutes of Sweden. Since 2015, we have actively worked to improve the welfare of mice and rats in toxicology studies in order to reduce stress, anxiety, and fear. By handling and training the animals gently, with respect for individual differences, we have reduced stressful behaviors and shown that collaboration and social contact are possible between laboratory animals and handlers in experimental procedures. 

We handle and train all our rodents from the very first day they arrive at our facility, usually at 4–7 weeks old. All animals are individuals. This becomes very clear when unpacking the animals, who will engage in differing defensive behaviors—in rodents, most commonly flight, freeze, or fight. The unpacking procedure itself, therefore, is very important for our understanding of and continued collaboration with the animals. 

How we handle and train the animals from arrival until the study begins will be the foundation for how well the animals cope with the various procedures they will encounter in the study. Trust is the most important aspect of animal handling and training. We avoid forced restraint and sedation if possible.

We should also think about how the animals perceive their environment. What do they see, hear, smell, and feel? How can we help them get a positive picture of their new situation and of us, and how can we help them have as good a life as possible as a laboratory animal? The cage—their new home—must be designed carefully in order to best meet the animals’ primary needs. 

Most rodents are housed in groups, so we need to ask: Do they have the ability to eat, drink, and rest without competition from other individuals? Are there enough activities to keep them occupied during their waking periods? Rodents need bedding material, chew sticks, multiple levels, and room to stand up straight and climb. 

The environment outside the cage is also important. Light, temperature, and humidity need to be optimal. Rodents are very sensitive to noise, so it is important to consider how they perceive potentially disturbing noises such as ventilation and the noise we make when we work in the room. 

Our rats live in groups of 2–10 in modified rabbit cages, but upon arrival they are first placed in traditional cages in smaller groups. They stay in the smaller cages during the first two handling sessions. The reason for this is to avoid having to chase rats in the big cages before they have become used to us and the environment. We want to avoid inducing defensive behaviors and keep them as calm as possible. 

When the animals are ready to move to their big cages, they go out in our observation boxes. In these boxes, we can observe them easily and evaluate the progress resulting from our previous contact. We always want the animals to feel safe approaching us. 

We handle and train all our animals approximately five times before the study begins during the acclimatization period, regardless of the length of the planned study. Our goal is to build trust and create recognition in the procedure(s) the animals will be exposed to in the study. We want them to trust us, our hands, and a Vetbed (a plush mat designed for animals to rest on) that we always use during handling and training and in the study. The training is documented, and the observations we record mainly relate to the animals’ defense and stress behaviors.

During the first training session, the most common behaviors we see are freeze and flight (seldom fight), vocalization, defecation, urination, back flipped ears, eyes half shut or shut, stiff body and tail, and agitated tails. We can also see if there are any outliers in stress reactivity. Some animals are simply more scared than others, and this can be good to know before the study begins, especially when it comes to making relevant observations concerning what can occur in the study. Although the training may be conducted every day, we prefer handling mice—who, in our experience, are more easily stressed than rats—every second or third day. Early on, we focus on calm handling and cuddles, just to let the animals realize that we are friendly, our hands are safe, and that the Vetbed is nice to sit on. One session takes 1–2 minutes and can be done individually or with cage mates on a table or in the lap.

During session 2 through 5, we focus more on the training for upcoming procedures. If the animals are to be dosed orally, we train the dose grip. At session 5, we give them a little bit of water through a soft tube. We also train different sampling procedures. If the sampling is to be done by the tail, we handle the tail more, and pick at it gently with our nails. If we are to sample via saphenous vein, we train to familiarize them with the grip and with the noise of the shaving machine. If the animals must be put in restrainers, e.g., for inhalation studies, we train the animals to freely enter the restrainer by putting a treat in the front of the restrainer. 

All training is reward based, and the reward can be something good to eat, gentle touch, an activity (e.g., climbing), or voice reward. We aim to always end a training session with something positive; the same applies after procedures in a study. All our animals seem to enjoy going out in the observation boxes (see photo, page 6), so this can also be used as a positive reinforcer. 

The training and handling protocols are general and flexible and could easily be transferred to other research areas, facilities, or even breeders. Our documentation, photos, and films help us to learn more about “best practices” for different individuals and strains, and we can use them to create educational materials for others. 

Handling and training rodents before a study begins can seem time-consuming, but the truth is that it saves time. When we start our studies, we never have problems with dosing and sampling procedures due to stressed and struggling animals, and we minimize stress-related mistakes. Most important of all is that we have calm animals who collaborate with us in all situations even though it is not all pleasant, and we can do our work with great comfort knowing we have done everything possible to create a good welfare situation for our animals during their stay here with us. 

It also allows us to get to know our animals and their behavior well before the study, which results in us making much more accurate observations of them in the actual study. It is easier for us to see if a behavior is due to the compound or stress. Stress affects the whole-body system, so we also believe that the test results are more reliable if the animals are calm and happy. We see so many advantages of handling and training the animals that it has become a standard procedure, documented in all our study files. 

Looking back at our careers working with laboratory rodents, we regret that for so many years we didn’t consider these factors. Cognitive ethology wasn’t so accepted years ago, but today most people have a different view of animals in general, and more and more people in a variety of fields see the advantage of working with unstressed and cooperative animals. It’s timesaving, educational and, most importantly, better welfare for the animals and the personnel (no animal lover wants to distress animals in their daily work). It’s also better for scientific outcomes, since calmer animals are more “normal” physiologically and behaviorally, and therefore more representative of the humans for whom they serve as models. 

We have produced two short videos showing our work, available for viewing at https://bit.ly/3e5M1DW. We also hope to get funding to produce a one-hour educational film, explaining in detail how and why we train and work with our animals, for those who want to apply this process to improve welfare for their laboratory animals in their own circumstances and environment.

Small changes often lead to bigger ones, and when a high culture of care has been accepted, there is no turning back. All animals, regardless of their situation in life, always should be treated with love and handled with respect for the individual. Our laboratory animals should be looked upon as our companions and heroes. Without them, we would not be where we are today. If we really need to use them in our science, we should do this with great care!

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