Weight is often the best indicator of health in an animal. In some species, you will notice a change in their weight way before you notice that they aren't eating as much as they used to. A primary reason for a change in appetite or weight is usually some sort of health issue.
So how do you weigh a porcupine for example? How do you weigh an 800 pound steer? This is an example of a husbandry behavior. You are training the animal to participate in their own health care so that there is as little stress to them as possible. You want for standing on a scale to become an everyday habit.
Let's start with the porcupine. This is actually a multi-step process that I am going to speed through. First of all you need a large scale, but even when you have a large scale it is difficult to ensure that the porcupine is all the way on the scale everytime. You need something on the scale that the porcupine can stand on. We have found that a large dog carrier works well. You put the kennel on the scale and ask the porcupine to step into it. Then subtract the weight of the kennel from the weight of the porcupine in the kennel equals weight of porcupine. Obviously you first have to get the porcupine used to going into the kennel before you ever place it on the scale. You can do this by placing its food inside the kennel for several weeks. Don't mess with the kennel once the porcupine is inside. Let it learn that no harm comes to it while it is in the kennel.
In the image below, the kennel is sitting on the scale and the porcupine is about to crawl into it.
You can also train a steer to walk on a large piece of plywood that is placed over a scale. The steer will most likely be afraid of the large dark thing on the ground. First just place the plywood in the enclosure for several days (make sure to give the animal plenty of room to get away if it wants to). After a few days you can start to throw a few bites of bread on the plywood so that the animal has to touch the plywood to eat it. It will start to learn that nothing bad happens when it is near the plywood. Ask the animal to step on the plywood by targeting over the wood. Step by step the steer will learn that nothing bad happens when it steps on the plywood. You can place the scale under the plywood and make it a daily routine to step on the plywood.
Watch the video below to see an example of scale training.
The steer in the video above was terrified of the plywood. It took several weeks for him to even go near it or to go in the stall with it. The video above shows tremendous progress where he is ready for us to place the scale under the plywood and weigh him.