The questions, "What's a better animal (or seed) worth?" and "What makes one animal (or seed) worth more than another?" are faced regularly by animal and plant breeders when they select animals or seeds to use in breed improvement programs. Answering the question is complicated by two I facts. (a) A strain of animals or seeds that is superior in some of the traits it will pass on to its offspring may be only average or inferior in other traits. (b) Because some pairs of traits have negative genetic cor relations, breeding to improve one trait may degrade another trait. The breeder needs to make trade-offs. How much can he afford to degrade one trait while improving another?