Known environmental effects

Differences in performance are a reflection of both the genetic merit of the animal (the genes it carries and passes on to progeny) and environmental factors. Some of these environmental factors are known and highly repeatable, meaning the evaluation can account for them. These known environmental, or fixed, effects include information such as date of birth, birth and rear type, and dam age, as well as management groups.

The more you record about how animals were born, raised and managed, the better the evaluation can account of these differences between animals and the more reliable their breeding values will be, particularly for early in life traits.

Birth date

When you tag lambs at birth, the birth date is most accurate because you are recording the exact date of birth of each lamb.

If you do not tag at birth, there are alternative ways to record date of birth which include:

Record lambing date from a distance. You will see (and record) which ewe lambed on which date. If you then mother up later, you already have the birth date for that lamb.
Drift lambing – separate ewes which have lambed from pregnant ewes throughout the lambing period to get a better estimate of lambing date.
Early, mid and late-foetal ageing – lambing dates estimated from pregnancy scanning.
Use the middle date of your lambing period (all lambs are given the same date). If you do this, Sheep Genetics recommends a short lambing period of five weeks to minimise the bias due to age
Use Artificial Insemination and provide a single date of birth for the AI program. Ewes tend to lamb over 10 days. Make sure you leave at least 10 days between AI and using backup sires if using lambing date to determine sire pedigree.

Sex of animal

The sex of an animal should be recorded as male (1) or female (2).

Note: Both rams and wethers are recorded as male (1), however if wethers continue to be recorded following castration, they must be management grouped separately to their ram contemporaries for these measurements (see Management Group section).

Birth type and rear type

Birth type refers to the size of the litter the ewe gave birth to (lamb was born into). Rear type refers to the number of lambs the ewe reared.

Birth type is recorded at birth or informed through pregnancy scanning, however must be recorded for each lamb. Rear type is recorded at weaning. Each of these should be submitted as numbers in the birth type and rear type fields, 1 = single; 2 = twin, 3 = triplet, 4 = quadruplet etc.

Lambs which are tagged but die before weaning will have a rear type of 0. It is important to adjust any sibling’s rear types to reflect how the litter was raised.