I just measured the sugar content of the whey being expelled from a two gallon goat loaf that is currently fermenting (heh, goat loaf), and the reading came out to 6brix. That means that whey from coagulated goat (heh, coagulated goat) has 10-15% less lactose it looks like than raw moocow milk.
From Wikipedia, "In use, a sample is placed between a measuring prism and a small cover plate. Light traveling through the sample is either passed through to the reticle or totally internally reflected. The net effect is that a shadow line forms between the illuminated area and the dark area. It is where this shadow line crosses the scale that a reading is taken."
The refractometer I use looks similar to the one pictured on the right, but is used to measure sugar levels, in this case lactose. It is highly likely that I'm misinterpreting some crucial point here, but through tasting the samples and measuring them I am pretty confident that there is indeed a lower amount of lactose in goat milk.
The reason why this is important is fundamental--the more lactose (i.e., the sweeter the milk), the higher the potential acidification (sharpness), which directly affects flavor and texture. That is why washed cheeses are usually milder, since the washing removes lactose, thus removing the potential for excessive acidification. Over acidified curds also can cause corky textures which are generally considered defects.
Cheese A Day by Jeremy Pickett is licensed under a Creative Commons Attribution-Noncommercial 3.0 United States License.
Based on a work at cheeseaday.blogspot.com.