Frequently asked questions 

What are EPDs?

"EPD" is short for "Expected Progeny Difference." An EPD is an estimate of the genetic merit of an animal for a single trait. Specifically, the EPD of an animal is the expected difference between the performance of that animal's progeny and the average progeny performance of all the animals in the breed, for that trait.

How are EPDs Calculated?

NSIP collects recorded performance data from purebred producers such as weights, number of lambs born, wool characteristics, etc. This information is entered into an Excel Spreadsheet provided by NSIP. The spreadsheets are sent to the Data Coordinator via e-mail.

Each breed group has a Data Coordinator who checks the data for errors and forwards the spreadsheets to the NSIP computer. For each breed, NSIP collects these performance records from purebred flocks across the country, breed by breed. This data comes from sheep reared under many different management systems, year after year after year.

The NSIP computer then identifies the genetic linkages between these flocks and across years — like when rams are sold or traded, or when progeny are distributed into many flocks — and puts this data into one massive calculation for each breed. The NSIP dataset for a breed also includes all the data from previous years, for all the relatives, across generations. The EPD calculations even include data from related traits, because an animal's performance in any trait gives information on how it will perform in a similar trait (for example, a good preweaning weight for a fast-growing lamb suggests it will also have a good postweaning weight). These calculations produce EPD values on every trait for every ram, ewe, and lamb in the system. And these EPDs are recalculated annually (or more often for accelerated flocks), after the performance records from each new production cycle are entered into the computer.

How are EPDs reported?

An EPD is reported in the normal units of a trait, such as +0.5 pounds (for weights) or -0.3 microns (for wool diameter). It's important to note that an EPD value is not a ratio or an index. EPDs are expressed as deviations (+ or -) from the average population value, which is considered to be zero. Therefore, EPDs always have a positive (+) or negative (-) sign in front of them. The positive and negative symbols don't always mean better or worse — it depends on the trait. For example, an Weaning Weight EPD of +0.5 pounds is good (i.e. more weight of lamb at weaning), but an Fiber Diameter EPD of -0.3 microns can also be good (i.e. smaller diameter fiber, which is more valuable to fine wool producers). Not only can we compare sheep with positive and negative EPDs, but we can also use EPD values to compare animals who both have positive EPDs. For example, a ram with a Weaning Weight EPD of +1.0 is good, but a different ram with a Weaning Weight EPD of +2.0 is better. EPDs may take a little getting used to, but once you get the hang of them, they give the most objective and reliable estimation of genetic value possible.

What Traits Does NSIP Evaluate?

Maternal Traits - NSIP evaluates all individual animals within a flock for three very important maternal traits: (1) number of lambs born per ewe lambing, and (2) maternal milk, and (3) Milk+Growth. To obtain an accurate evaluation of genetic merit for each of these traits, producers record information on all ewes exposed for breeding and all lambs born in each production cycle.
Growth Traits - NSIP evaluates growth for three possible weights: weaning weight, postweaning weight, and yearling weight. Farm flocks and range flocks are analyzed differently because their weighing schedules are so different. Farm flocks receive 60-day weaning weights and 120-day postweaning weights. For farm flocks, the cutoff point between weaning weight and postweaning weight is 90 days. Range flocks receive 120-day weaning weights and yearling weights. Some range flocks also chose to take 60-day preweaning weights, and those weights are used in their genetic analysis. NSIP accepts generous time windows around each age to weigh lambs, so that any flock can arrange convenient weigh dates to fit its management schedule.
Wool Traits - NSIP calculates EPDs on three wool traits: grease fleece weight, fiber diameter, and fiber length. These measurements only need to be taken once during an animal's lifetime, usually at a year of age. These measurements must be taken on a full year's growth of wool. A producer can also record codes for face cover and skin folds, although no EPDs are calculated on these traits.
Carcass Traits - Carcass traits are still under development but will be incorporated into NSIP very soon. These traits will be fat thickness, ribeye area, and an index trait called the "Carcass Value Trait", which will be calculated from the age of a lamb, the weight of the lamb, ribeye area, and fat depth between the 12th and 13th ribs. Producers will record values for these traits either from direct measurement of the carcass or from ultrasound measurements on the live animal.
Accelerated Traits - For those breeds using accelerated lambing systems, NSIP is working on two important traits: date of first lambing, and lambing interval. Currently, implementation of these two traits are still under development.

How Does NSIP Work?

NSIP works hand-in-hand with the breed associations. Performance data flows from farms and ranches to the breed association offices and then to Virginia Tech University, where the actual EPD calculations take place. The EPD results then flow back to the breed association offices and then back to the individual farms and ranches. This means that there is no central do-it-all NSIP office. (This style of organization is similar to the well-known DHIA system that has been functioning successfully in the dairy industry for many years). Specifically: Purebred breeders collect performance data on their farm or ranch and enter that data into data-entry spreadsheets on their own computer, or have someone else enter it for them. These spreadsheets have been developed by NSIP and are supplied to all the breed association offices and breeders. Producers then send their completed spreadsheet to their respective breed association. People at the breed association office combine all the files into a single large spreadsheet file. They do additional checking of the data (especially registration numbers) and then send the breed data on to Virginia Tech for genetic evaluation. At Virginia Tech, geneticists run the complex software to calculate EPDs. They also archive all the NSIP databases in a secure mode. The specialized EPD software (BLUP = Best Linear Unbiased Prediction) calculates the genetic values for each animal and each trait. After these EPDs are calculated, the results are sent back to the breed associations. The breed office then uses these results to publish the breed sire summary and other genetic documents for the breed. It also sends genetic reports back to the individual breeders. Most of this work is done over the Internet. NSIP oversees and coordinates the entire process. NSIP also develops new procedures and traits; it tests improved data collection and data evaluation techniques; it maintains the databases for security and archival purposes, and it coordinates genetic research with the data. The NSIP main office is located at the ASI headquarters in Englewood, Colorado. NSIP clerical and bookkeeping tasks are performed there.

Does NSIP Accept Electronic Data Entry?

Yes. In fact, NSIP only uses electronic data entry. All producers enter data onto specially designed, easy-to-use spreadsheets. These spreadsheets look very much like the traditional paper forms — i.e. they have rows and columns. However, these computer forms also do automatic error-checking, so that the spreadsheet catches typos and other data errors when they are first entered, which makes these errors very easy to correct. If a producer doesn't have a computer or prefers to avoid doing data entry, they can have a friend/relative/neighbor do it or make arrangements with the personnel at the breed association office to do this for them. After producers enter their data, they send the file via the Internet (or just mail a diskette) to the Breed Association office or the Breed Data Coordinator.

Can Rams Be Compared Under Different Management Conditions?

Yes,across-flock EPDs are designed to allow this comparison. The calculation of EPDs uses data from many different flocks, and this procedure is mathematically valid across flocks. This means that a range operation in dry country can use rams from a Midwestern corn-soy crop farm, and that a Midwest farm can identify top-quality range rams reared on sagebrush and rattlesnakes. Of course, on each farm, the groceries and health still have to be good enough to permit good performance, and in particularly stressful environments (such as desert range) there may be unique genetic adaptations that affect performance. But at least EPDs give a producer a clear and reliable report about an animal's genetic potential.

Can Rams Be Compared Between Different Breeds?

No, An EPD in one breed cannot be compared to an EPD from another breed. Across-flock EPDs are calculated only within a breed. Each breed database is independent from all other breed databases, and the numbers are not commingled.

What About Commercial Producers?

EPDs are only calculated on purebred animals. EPDs are not calculated for commercial flocks. Commercial producers do not join NSIP directly. Commercial producers, however, can really benefit from NSIP because they can purchase rams (and ewes) from NSIP purebred flocks that have precisely the improved traits that they need. Because EPDs are provided on a trait-by-trait basis, commercial producers can decide what traits they need for their operation and then use NSIP to find rams and ewes that excel in those specific traits. The Breed Associations publish "Sire Summaries" — in printed form and on their websites — which are genetic catalogs that list all the NSIP sires in that breed, trait by trait. These sire summaries often include lists of "trait leaders," which is convenient for quickly identifying top genetics. Commercial producers can study these sire summaries and easily find the best sires and dams which carry the improved traits for their own operations

How Much Does NSIP Cost?

The NSIP fee structure is very simple and reasonable. Annual fees are based on two things: (1) a flock charge plus (2) a charge per each breeding animal in the flock. The flock charge is an annual fee per flock. An animal is defined as an adult ewe or a ewe lamb that will be part of the breeding flock or a ram that will be used to sire lambs. On the Enrollment Form, a producer counts all animals, male or female, that were used in breeding during the past year. Producers enroll only purebred animals with registration numbers. They also enroll any ewe lambs or ram lambs used for breeding that will be registered but have not yet been assigned registration numbers. For example, a purebred producer with 97 breeding ewes and three breeding rams would pay a total NSIP fee of $175.00. (= $50 flock charge plus $1.25 x 100) This producer would send a check for this amount together with the completed Enrollment Form to the NSIP office.   In some cases you are billed by the Data Coordinator who will send your EPD report upon  receipt of payment.

How Can A Producer Join NSIP?

Simple. A producer submits an Enrollment Form to the Breed Association Office or Breed Data Coordinator. This Enrollment Form is a very easy-to-fill-out form that asks a few questions about contact information, breed, and flock size.  All purebred producers with registered animals can join NSIP. Calculation of across-flock EPDs, however, is dependent on the establishment of good across-flock genetic linkages. NSIP is currently working closely with six breeds to calculate across-flock EPDs. These breeds are Targhee, Suffolk, Polypay, Dorsets, Hampshires, and Columbia. Producers in other breeds will receive across-flock EPDs if enough flocks join NSIP so that good genetic linkages can be established. NSIP will help facilitate this. If the breed association office cannot act as a collection point for data, then the group of breeders needs to find someone else to do this role. Again, NSIP will facilitate this. There are people in the sheep industry already doing these tasks