Stock Selection
Variation
To make changes within a breed individual differences such as height, length, depth, muscling and fleece cover are necessary. However, each animal should have a sound mouth, fleece and be able to walk freely.
Fertility
Select replacements from those lambs born during the first 42 days of the lambing season. Ewes that naturally breed in the autumn and lamb in the spring are more fertile. Testicle size in rams is important, for there is a positive correlation between diameter of the testicle and fertility in the ram and his daughters. Ewe lambs that breed or cycle during the autumn, age 9 to 12 months, are more fertile than those ewe lambs that do not.
Lambing rate
Keep replacements from lambs born of multiple births from ewes 1 – 3 years old. This age group of ewes has not reached its peak production years for multiple birth, which occur at 4 – 7 years of age. Preference for season of birth would be autumn, winter and spring, because multiple births occur less frequently in the autumn and most frequently in the spring.
Longevity
Retain replacement from lambs produced by ewes or sired by rams which are seven years old or older. The presence of breeding animals in the flock at the age would indicate they were productive and healthy.
Milk Production
Body weight of lambs 60 days of age is an indicator of milk production in their mother. Peak milk production occurs about 40 days after lambing. It has been found that ewes with a longer muzzle and a more open face produce more milk.
Body Length
The length of the head is correlated to the body length. However, the length of the ear has also been found to be correlated to the body length.
Growth Rate
Birth weight is associated with growth rate. Lambs heavier at birth reach market weight earlier. Direct selection for birth weight can result result in lambing difficulties because of lamb size. Overfeeding of ewes during the last 4 – 6 weeks of gestation can result in a giantism occuring in lambs. Gains in body weight after weaning is a measure of the gaining ability inherited by the individual sheep.
Ram weight at 12 to 16 months is an indicator of growth rate for lambs sired by the ram. Extremely wide-
fronted and deep-
bodied sheep gain weight rapidly, but present serious problems at lambing time. Composition of gain, fat or muscle, is more important than just total gain. Attempts to obtain large body weight in replacement ewes by overfeeding encourages excessive fat deposits and results in reduced fertility and milk production. Some large mature sheep do not reach sexual maturity early and some reach sexual maturity early but do not attain sufficient growth. Ideally one should select for early sexual maturity and growth.
Structural Correctness
Cull for slaughter individuals which have produced lambs with a deformed jaw, are coarse and open in their shoulders, stand too straight on their back legs, and are very weak in their pasterns. Selecting and using structurally sound breeding sheep is more rewarding than trying to selectively breed out of an unsound situation.
Environmental Adaption
Adapted sheep will reproduce and grow at the rate they are genetically capable of when adequate nutrition and protection is available. A deeper than wide body shape along with a thicker skin is characteristic of an animal adapted to a hot environment.