Briefly, the National Sheep Improvement Program, or NSIP, is the organization charged with calculating and providing sheep producers with Estimated Breeding Values (EBV's) for traits of interest to those producers.

An Estimated Breeding Value, or EBV, is a measure of the genetic merit of an animal for a given trait.  Computers use a statistical method developed in the 1950's called Best Linear Unbiased Prediction, or BLUP for short, to separate environmental factors from genetic factors.  This allows producers to compare the relative genetic merit of animals, especially between flocks where different feeding systems can skew appearances.

EBV's are derived, not only from data provided by the animal in question, but also data gathered from his/her relatives in flocks across the country.  Connectivity between flocks and contemporary groups is key.  Exactly how the computer does all that may not be important, but the result is.  A breeding animal won't pass its environment on to its offspring; what it does pass on is genetic merit for given traits.

At this time, we use  the following EBV's:

Maternal/Milk (MWWT) estimates genetic merit for mothering ability.  This primarily indicates milking ability, but also includes other maternal abilities.

Pre-Weaning Growth (WWT) estimates genetic merit for pre-weaning growth other than that included in MWWT.

Post-Weaning Growth (PWWT) estimates genetic merit for post-weaning growth.

Number of Lambs Born (NLB) estimates genetic merit for number of lambs born.

Number of Lambs Weaned (NLW) estimates genetic merit for number of lambs weaned.

Parasite Resistance (PWEC) estimates the genetic merit for resistance to parasitic worms.  A lower number is better.

U.S. Maternal Index (USMI) This is not technically an EBV, but is an index constructed from the EBV's.  It is indicative of pounds of lamb weaned, which is what we're all looking for on the income side of the profit equation.  Because of the importance of the USMI, we use this index in pricing our rams.