Body Condition Scores in cattle are very important for monitoring your herd's health. Body condition can effect many things from
You do not want your Dexters to be too thing or too fat. All cattle, especially reproductive cows have ups and downs in their weights. This is a natural process during pregnancy, post-delivery, lactation, breeding back and at weaning time.
You will find a good article, with illustrations below:
ADCA article on Body Conditioning score for Dexters