Resource centerGrowth & weights4 min read
Birth weight and weaning weight
The two weights that anchor every growth figure, and what happens when one is missing.
The question
Why does BreedIQ keep asking for a birth weight, and why does a weaning show up as "deduced" when nobody recorded it?
The concept
Birth weight is the first point of the growth curve and a trait in its own right: too light and the lamb struggles to survive, too heavy and the lambing gets harder. Weaning weight is the kilos the ewe produced through milk and care; it is the main measure of maternal ability and the basis of "kg weaned per ewe".
Why it matters
Every ADG from birth, every adjusted weight and every maternal EBV depends on these two points. A missing birth weight removes the lamb from the birth→50-day calculation; a missing weaning weight removes the lamb from its dam's kg weaned.
The data behind it
Birth weight is recorded per lamb in the lambing form (sex, ear tag, kg, alive or stillborn) or later from the profile. The flock average in the demo is 4.31 kg over 90 birth weights, and the Lambing statistics page shows 4.29 kg over 96. Weaning is recorded in the Chute (Weight › "Mark as weaned on this date") or in the profile. If nobody records it, BreedIQ deduces a weaning at the species' cutoff age (120 days by default, configurable in Settings › Weights) with the date it passed and without a weight. It never invents kilos, and a weaning you record yourself always wins over the deduced one.
- 1Record lambing form
- 2One row per lamb: sex, ear tag, birth weight, alive/stillborn
- 3Difficulty: unassisted, easy pull, hard pull, cesarean
- 4Sire (or unknown)
- 5Observations about the ewe (official management codes)
- 6Seen at the lambing: udder, milk, mothering 1–5 (descriptive; not in EBVs)
- 7Add another lamb
- 8Save the lambing
- 9Record abortion (separate event)
How to read it in BreedIQ
The profile's Performance card shows birth weight, weaning weight, weaning date, age at weaning and ADG to weaning. The Weights tab marks each row as "Real" or deduced and lets you correct the weaning. The Weaning analysis page (Productivity › Weaning) reports the observed average weaning weight and age for the selection and separates lambs with a valid weight from weanings without one (45 of 98 in the demo), which are left out of the average rather than counted as zero.
Decisions it supports
Set the weaning date for a lot, decide which ewes repeatedly wean light lambs, and complete missing birth weights while the lambs are still young enough for the data to be useful.
Limitations
Observed weaning weights are not standardized: two lambs weaned at 90 and 110 days are averaged as they are. For a comparable figure, use the adjusted weights and the EBVs, which correct for age and birth type. The deduced weaning also stops lot protocols from asking for a weaning the system has already assumed.