Lambing Percentage Calculator NZ
Lambing percentage is lambs divided by ewes, and almost every part of that is contested. The lambs can be the ones docked or the ones weaned. The ewes can be those put to the ram, those wintered, or only those that actually lambed. Each combination is a real measure that real people use, and they give materially different answers from exactly the same season, which is why two farmers quoting lambing percentages over a fence are quite often not comparing the same thing. Rather than pick one and present it as the answer, this calculator gives you all of them from one set of numbers, each labelled with the denominator it used, so you can see the spread and quote whichever your comparison needs. The one that flatters is lambs weaned over ewes that lambed, because it has already excluded every ewe that failed to produce. The one that is hardest on you is lambs weaned over ewes to the ram, since it counts the dry ewes, the ewes that died and every lamb lost from mating through to weaning. Both describe the same flock. If you are benchmarking against anyone, agree the denominator before you compare the number.
| Measure | What it counts | Result |
|---|---|---|
| Docked over ewes to the ram | Everything from mating on, including dry ewes and ewe deaths | 138.0% |
| Docked over ewes wintered | Measured against the flock you fed through winter | 135.3% |
| Docked over ewes that lambed | Litter size among the ewes that produced, dry ewes excluded | 145.3% |
| Weaned over ewes to the ram | The hardest measure, and closest to what you have to sell | 133.0% |
| Weaned over ewes that lambed | The most flattering, since the failures are already out | 140.0% |
| Lamb survival, docking to weaning | Losses in that window alone, separated from the rest | 96.4% |
The five lambing measures span 12.3 percentage points from the same season. All six describe the same season. Quote the denominator alongside the number, because the number does not identify itself.
How it works
Each row is the lamb count divided by the ewe count, multiplied by a hundred. Nothing more complicated than that is going on, and that is exactly the point: the arithmetic is trivial and the ambiguity is entirely in which two numbers you picked. Lamb survival is the one row that is not a lambing percentage at all, being weaned lambs over docked lambs, and it will sit below a hundred percent in any normal season.
Why the denominators differ
Ewes to the ram is the largest denominator and so gives the lowest percentage, because it includes ewes that did not get in lamb and ewes that died before lambing. Ewes wintered can be larger or smaller than that depending on when you count and whether hoggets went to the ram. Ewes that lambed is the smallest denominator and gives the highest percentage, because every failure has already been taken out of it; what it measures is really litter size among the ewes that succeeded, which is a useful number but a different question from how the flock performed.
Worked example
A flock with 1,000 ewes to the ram, 1,020 wintered and 950 that actually lambed, docking 1,380 lambs and weaning 1,330 of them, produces six defensible figures. Docked over ewes to the ram is 138.0 percent, which is the one most likely to be quoted. Docked over ewes wintered is 135.3, docked over ewes that lambed is 145.3, weaned over ewes to the ram is 133.0 and weaned over ewes that lambed is 140.0. Lamb survival from docking to weaning was 96.4 percent. The spread between the lowest and the highest of the five lambing figures is 12.3 percentage points, from one season on one farm, and every one of them is honestly calculated.
Related calculators
- Herd Replacement Rate: how many of them you need to keep.
- Stock Units: what the flock and lambs demand in feed.
- Kill Sheet: what the lambs returned at the works.
- Wool vs Shearing: the other thing the flock produces.