Resource centerGenetics & selection4 min read
The Flock Index
Which ewes will raise more lambs, heavier, for more years.
The question
A ewe lamb grows fast. Will she also be a good mother, lamb regularly and wean heavy lambs? Growth alone cannot answer that.
The concept
The Flock Index is the maternal selection index. Like Growth it is unitless and built from EPDs times published factors, but it spreads its emphasis across twelve traits that describe a productive ewe: maternal weights, survival, litter size, lambing interval and total weaning weight.
What it weighs
Declared emphasis shown in Sires › Indexes: 50-day weight (maternal) 22%, gain 50–100 (direct) 18%, 50-day weight (direct) 14%, lamb survival (maternal) 10%, birth weight (maternal) 9%, number born in later lambings 6%, lambing interval 6%, birth weight (direct) 4%, lamb survival (direct) 4%, number born at first lambing 3%, total weaning weight in later lambings 2% and at first lambing 1%.
"Maternal" traits are the part of a lamb's performance that comes from its dam's milk and care, separated from the lamb's own genes. A ewe with a high maternal 50-day weight makes her lambs heavier regardless of who the sire is.
Why it matters
Replacement ewes stay in the flock for years; a wrong choice costs several lambings. The Flock Index puts most of the weight on the lambs she weans and keeps enough on growth so her lambs still sell well.
Where you see it
The Dashboard's "Productive ewes" panel ranks the 44 ewes by Flock; the Replacements page shows each candidate's maternal percentile with the Flock value; and the profile shows "Flock 1.78 · P98 · 99% of its weights", where the last figure says how much of the index's emphasis is covered by traits with data.
- 1Proven sires ranked by the chosen index
- 2Productive ewes ranked by Flock (Flock Index)
- 3Growing ram lambs ranked by Growth (Growth Index)
- 4Index selector: Flock, Growth or Prolific Flock
- 5Open the full ranked list
Decisions it supports
Choosing which ewe lambs to keep and which maternal-line rams to buy. The Replacements page combines a maternal and a growth percentile into one score with a configurable split (by default 50% maternal, 50% growth, retain 70%) and suggests Keep or Cull. The suggestion is a ranking; the producer decides.
Limitations
Young ewes have no lambing records yet, so their Flock rests mostly on pedigree and is flagged as partial with a lower accuracy. The "Observed at lambing" scores (udder, milk, mothering 1–5) are descriptive and do not enter the EBVs; maternal ability in the Flock Index is measured through the lambs' weaning weights.