Be aware that there are two different body types for chins that correspond to the two types, or species, of chinchillas: Chinchilla lanigera and Chinchilla brevicaudata. The chinchillas living in captivity today, whether as ranchies or pets, are a mix of both types but often a chin will strongly manifest the attributes of one species over the other.


For instance, the brevicaudata body shape and features (photo of brevi traits in domestic chin) are more puggish, blocky and stout, and brevis are usually larger and heavier than C. lanigera. Lanigeras have a body shape and features (photo of lanigera traits in domestic chin) that are more pointed, narrow and slender and they are usually smaller and lighter than C. brevicaudata. The two species are described in detail on Species Description.


Pet breeders strive to develop more brevicaudata traits in their offspring because that look is considered more attractive and appealing to pet owners (actually, the brevicaudata bias began with the fur industry's value of larger fur-producing animals). Brevi traits receive the most attention in the pet community, they're regularly focused on and praised as the ideal.


Unfortunately, some people get obsessed with the idea that they might be able to control their chinchilla's appearance and they begin to micromanage their chin's diet and constantly weigh them in an effort to fatten their (smaller, slimmer) lanigera type or, in some cases, to make their (larger, heavier) brevi type lose weight through "dieting." The latter usually occurs when the chinparent has only seen the lanigera species type and consequently believes that their larger brevi type must be obese.


But a chin's body size and shape aren't "problems" to be corrected, they're completely normal attributes of the particular species type. Manipulating a chinchilla's nutritional intake to achieve some presumed ideal is as dangerous to a chin's health as it is useless: Weight gain or loss will not fundamentally alter genetically assigned attributes, and a lanigera type chin will not transform into a brevi type by gaining weight. Note, for instance, how the extra weight on this lanigera type domestic chinchilla hangs around the underarm area rather than creating a more round or blocky appearance. Thus, larger is NOT always better, and extra fat can negatively affect health (liver disease) as well as appearance!


Under normal circumstances an adult chinchilla's ideal weight (which is genetically determined, mainly by species type) is maintained within what can be considered a healthy weight RANGE that can vary by as much as 50 grams, plus or minus. In other words, there is no one perfect, absolute weight number that a chinchilla must maintain at all times throughout his life. Where a chinchilla is at within his healthy weight range at any given time is determined not only by his genetics and species type, but also by the influence of other routine circumstances: change of seasons or change in diet, current stress level, the amount of exercise the chin has been getting, etc.


Unless something exceptional occurs, like the chin suddenly gains or loses weight by a significant amount or other symptoms accompany the weight gain/ loss, there is no need to obsess about weight. Instead, be proactive, ensure your chinchilla has a healthy lifestyle that includes regular exercise and unlimited access to fresh, high quality hay, pellets and distilled or filtered water, with treats given in strict moderation.