Lack of water is another reason. The stress of acclimating to new surroundings could be a factor. A lot of times goats in a new environment don't eat as well as they would if they are comfortable in their surroundings.
Goats that dont eat all the time, like here, twice a day, can look alittle skinny in that area coming up on their next feeding. The gut doesnt tell health of an animal, over all condition does. Do they have a good coat, do they have meat over their bones and is the area around the spin filled out and not boney? Typically this can be more pronounced with age or with a goat that has a large amount of body capacity.