Understanding EPD's

1. The 60-Day Weaning Weight EPD provides an estimate of preweaning growth potential.

2. The 120-d Postweaning Weight EPD combines information on preweaning and postweaning growth to

 predict genetic merit for postweaning weight at 120 days.

3. The Maternal Milk EPD provides an indication of the genetic merit for mothering ability.  This EPD

primarily reflects genetic differences in ewe milk production potential as realized in her lambs. 

The maternal milk EPD is thus expressed in pounds of lamb weaned, not pounds of milk

produced.  It is derived by evaluating if individual ewes produce lambs that do better or worse

than expected based on the weaning weight EPDs of the parents.  Ewes whose lambs grow faster

to weaning than predicted are assumed to be better milk producers whereas ewes whose lambs

grow more slowly than predicted to weaning are assumed to produce less milk.  This relationship

between maternal milk EPD and actual milk production has been validated in beef cattle and is

assumed to be similar in sheep, although other elements of maternal behavior may also be

included in the maternal milk EPD.  Selection for high maternal milk EPDs is anticipated to

improve milk production and mothering ability in the flock.

4. The Milk plus Growth EPD combines information on weaning weight and maternal milk EPDs to provide an index of the total

 anticipated contribution of an animal's daughters to lamb weaning  weight.  The milk plus growth EPD is calculated as the sum

 of the maternal milk EPD plus one half the weaning weight EPD.  It recognizes that the genetic contribution of a ewe to the

 weaning     weight of her lambs combines the effects of her milk production (measured by the maternal milk  EPD) and a sample

 one half of her genes for preweaning growth potential (measured by the  weaning weight EPD).  Because the milk plus growth

 EPD is calculated from two other EPDs, an accuracy value is not reported for this EPD.

5.  The Number Born, or Percent Lamb Crop, EPD evaluates genetic potential for prolificacy.  This

EPD is expressed as numbers of lambs born per 100 ewes lambing.  An EPD of +5.0 for percent

lamb crop thus indicates that an animal is expected to produce daughters who will have an average

of .05 more lambs at each lambing, or 5.0 more lambs per 100 lambings, than an average ewe. 

Selection on percent lamb crop EPD is expected to increase prolificacy in the flock

.

6.    The Number Weaned EPD evaluates the genetic potential for prolificacy and maternal genetic effects on lamb survival.

  This EPD primarily reflects the ability of animals to have and raise lambs and is expressed as numbers of lambs weaned per 100

 ewes lambing.  An EPD of +5.0% indicates that an animal is expected to produce daughters who will wean an average of 0.05

 more lambs at each lambing than a ewe with an EPD of 0.0.

7.    The Total Pounds Weaned EPD provides a combined measure of genetic merit for prolificacy, rearing ability, and growth. 

 An EPD of +10.0 lb indicates that an animal is expected to produce daughters who will, on average, wean 10 lb more lamb at

 each lambing than the daughters of an average animal. This EPD should be used to select animals to improve total pounds

 weaned in the next generation.