Sheep flock productivity: know your own numbers

Lamb marketing is the main source of revenue for most sheep operations, and every decision that protects that revenue — how many lambs you will have, when they will be finished, what they will weigh on the rail — rests on the same thing. Your flock's own numbers. The breed averages and provincial benchmarks are a starting point, and they describe nobody's flock.

Consider lamb mortality. A Quebec survey of thirty flocks put average pre-weaning mortality at 15.8% per flock, with a range from 6.8% to 31.7% (OMAFRA, Forecasting Lamb Production). Ontario's GenOvis performance program lands at almost exactly the same average — 15.3% across all breeds. The flock losing 6.8% of its lambs and the flock losing 31.7% are not running the same business, and the average hides both of them. The number that sets your breeding, feeding, and marketing is the one from your own records — not the one printed in a table.

The sheep twin of knowing your cost to keep a cow: a short list of numbers separates a flock that improves year over year from one that runs on memory. None require a research trial — they require records, kept through the season against each ewe and lamb.

The numbers worth knowing

Five numbers. Each is only as good as the records underneath it. Take them in the order the lamb crop moves through the year.

1. How many lambs — from your breeding records

Everything downstream depends on this. The number of market lambs available comes from a chain of four factors, each one readable from a different record:

ewes bred × conception % × lambs born per ewe × survival % − replacements = market lambs

Each link varies, and each variation is a record. Gestation averages 147 days across breeds, but Rideau flocks may lamb closer to 142 and Suffolk closer to 150 — recording ram turn-in and turn-out dates against first and last lambs born gives your flock's real window, which sets every due date that follows. Conception runs above 90% for in-season breeding but falls to a variable 50–60% for out-of-season breeding in Ontario. Prolificacy differs by breed: on GenOvis, Rideau ewes averaged 2.35 lambs born per lambing, Suffolk 1.64, and Dorset 1.55 (OMAFRA, Forecasting Lamb Production). Survival is where the mortality range above lives.

The records behind the chain are written per ewe: bred or open, lambs born alive, lambs born dead, assisted or not. Run those across the flock and you get lambing percentage and weaning percentage — and the gap between them is your death loss, located at the stage where it actually happens instead of a feeling that the year was rough.

OMAFRA's production targets are a useful mirror, not a verdict: non-prolific breeds benchmark around 165% lambing and 150% weaning, prolific breeds around 240% and 210% (OMAFRA, Measuring Productivity of the Sheep Flock). Your flock sits somewhere on that line, and only your records say where.

2. When they will be finished — from your growth records

A breed table will tell you that GenOvis lambs gain around 0.29 kg per day between 50 and 100 days, with Suffolk faster (0.37) than Dorset (0.30) or Rideau (0.29). It cannot tell you when YOUR lambs will reach market weight, because that depends on your feed, your health, your season, and your management. That number comes from your records: lambing dates, periodic weights after weaning, and the sale date and weight of each market group.

Days to market is marketing date minus lambing date. Average daily gain is weight gained divided by days. Neither exists without the weight written against the tag at a known date. A flock that knows its real post-weaning gain can plan for a holiday market or a forward contract; a flock running on the breed average is guessing at the calendar. And because feed is the largest cost on a sheep operation, the number of days a lamb spends growing before it ships is the number that decides whether that lamb made money or just consumed it.

The same growth records, taken monthly after weaning, are what let you spot a set of lambs falling behind before they fall out of the target weight window.

3. What they will weigh — from your dressing records

Selling on the rail, or into a value chain with a target carcass weight, turns dressing percentage into money. Dressing percentage is carcass weight divided by live weight, and it moves with gut fill (10–22% of pre-fast live weight), fleece moisture and dags, breed and muscling, gender, fatness, and time off feed (OMAFRA, Predicting lamb carcass weight). A fat-score-4 lamb can dress nearly six points higher than a fat-score-2 lamb at the same live weight. A table cannot set your target live weights from that, because your flock's dressing percentage is your flock's.

The record is short and per animal: the tag, the live weight taken before slaughter, and the carcass weight that comes back on the kill sheet. Add the fat score you estimated live against the actual millimetres of fat at the GR site (11 cm off the midline at the 12th rib), and over a season you learn what live weight and score produce the carcass your buyer wants. Miss the target weight range in a value chain and there is a price penalty; hit it, and you capture the premium. The difference is whether the rail data was recorded against the tag or lost on a scrap of paper.

What this looks like to keep

OMAFRA publishes a flock productivity workbook that lays these calculations out in a spreadsheet, recorded by hand or in Excel (OMAFRA, Measuring Productivity of the Sheep Flock). The shape of it is small and the same on paper, in a spreadsheet, or in an app:

• At breeding — ewe or group ID, ram or breeding group, turn-in and turn-out dates.
• At lambing — per ewe: lambs born alive, born dead, assisted or unassisted, lamb IDs.
• After weaning — periodic weights per lamb or group, to read average daily gain.
• At marketing — per market group: sale date, average weight, and the carcass data when it comes back.

Four touch points, written against the animal's ID, on whatever survives the barn. One season of this lets a flock compare itself to last year and to the benchmarks; three seasons show the trend — which ewes, which sires, which stages, which seasons — and turn guessing into decisions.

Where records earn their keep

Records inform decisions. They do not make them. The lambing percentage will not tell you which ewe to cull; it tells you which ewes came up open or weaned a single off a twin, so the cull list builds by reason before you walk to the chute. The dressing percentage will not set your live-weight target; it tells you what your lambs actually dress, so the target is yours instead of the province's. Days to market will not write your forward contract; it tells you when your lambs finish, so the market you aim at is real.

The numbers here describe what productive flocks measure, drawn from OMAFRA's sheep specialists and performance programs — not a prescription, and nothing in it is veterinary, nutritional, or marketing advice for your operation. The decisions stay with you and your advisors. The job of the records is to put your own number in front of you — computed from your ewes, your lambs, and your rails — rather than the one you remembered or the one that describes nobody's flock.

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