How many cows can one bull cover?

It depends heavily on the bull's age. Commonly quoted figures are about 10 to 12 females for a 12 to 15 month old bull, 12 to 18 for a 15 to 18 month old, and 18 to 25 for an 18 to 24 month old, with most recommendations keeping mature bulls to no more than 25 cows. Individual bulls vary widely in their ability to cover cows, so these are starting points to adjust from rather than a capacity to rely on.

Why carry spare sires?

Because a sire that goes lame, gets injured fighting or turns out to be infertile takes his whole share of the mob with him, and you often do not find out until scanning. Carrying a spare or rotating sires through the mating period protects against that. The cost of one extra ram set against a group of ewes that come up empty is usually a straightforward comparison, which is what the cost per female mated figure here is for.

Mating Ratio Calculator NZ

This works out how many rams, bulls or stags a mating mob needs at whatever ratio you decide to run, how many spares to carry on top, what ratio you actually end up working at once the spares are out there, and what the whole team costs per female mated. The ratios in the picker are starting points with sources attached, not standards, and the difference matters. Beef and Lamb New Zealand puts one ram to 100 to 150 ewes as a guideline for fit mixed-age ewes on flat to rolling country, reduced to around one to 100 for ewe hoggets or when using ram hoggets, and reduced again on steep country where the work is simply harder. For cattle the spread is wider still and driven mostly by the age of the bull, from about 10 to 12 females for a yearling up to around 25 for a mature bull. Individual sires vary enormously inside all of those numbers. The spares question is the one worth taking seriously, because a sire that goes lame, gets hurt fighting or turns out infertile takes his entire share of the mob with him, and you usually find out at scanning when nothing can be done. One extra ram against a group of empty ewes is normally an easy comparison to make.

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Females to mate

Starting point

Females per male

Spares to carry

Cost of each male

males to put out, including spares

At the ratio8

Spares1

Ratio you actually run1 to 111

Cost per female mated$10.80

If one of the 9 fails, the rest are covering 1 to 125, which is still inside the ratio you planned. Without the spare it would be 1 to 143. Starting points, not standards. A young sire covers fewer females than a mature one, steep country is harder work than flat, and individual animals vary widely inside every figure here.

Situation	Commonly used range	For your mob at that ratio
Mixed-age ewes, flat to rolling	1 ram to 100 to 150 ewes	8
Ewe hoggets, or using ram hoggets	about 1 to 100	10
Mature bull, natural mating	no more than 1 to 25	40
Bull, 12 to 15 months	1 to 10 or 12	91

Every row is worked against the same mob you entered, so the ratios can be compared directly. Use the row that matches your stock: the cattle rows against a mob of ewes are showing you the arithmetic, not a recommendation. Sheep ratios follow Beef and Lamb New Zealand guidance for fit mixed-age ewes, reduced for hoggets and for steep country. Cattle ratios are the commonly quoted figures by bull age and are widely described as starting points to adjust from, since individual bulls vary widely in how many cows they can cover.

How it works

The number of males at your ratio is the females divided by the females per male, rounded up, because two thirds of a ram is not a thing you can put in a paddock. Spares are that number multiplied by your spare percentage, also rounded up, so a small mob still gets one spare rather than a fraction of one. The ratio you actually run divides the females by the total males including spares, which is always tighter than the ratio you planned, and that is the point of showing it: carrying spares is not just insurance, it lowers the working ratio for everybody. Cost per female mated spreads the whole team across the mob, which is the figure to set against a scanning result.

Why the working ratio matters as much as the planned one

Because sires do not divide the mob up between themselves neatly. In a mob run with several males they will compete, some will do far more work than others, and the quietest one may do almost none. So the planned ratio describes an intention and the working ratio describes the paddock. Running slightly more males than the guideline is the usual way of covering that unevenness, alongside making sure they are sound and fit before they go out, which does more for a mating than any arithmetic on this page.

Worked example

A thousand mixed-age ewes at one ram to 125 needs 8 rams. A 10 percent spare allowance adds 1 more, so 9 go out and the working ratio is one to 111 rather than one to 125. At $1,200 a ram that is $10,800 of rams, or $10.80 for every ewe mated. If one of those nine turns out to be infertile, the eight left are covering one to 125, exactly the ratio that was planned in the first place, which is the whole argument for the spare. Without it, eight rams becomes seven and the ratio slips to one to 143.

Related calculators

Lambing Percentage: what the mating produced.
Calving Date Planner: when the mating has to start.
Herd Replacement Rate: how many females to keep.
Stock Units: what the mating mob demands in feed.

Data sources: sheep mating ratios follow Beef and Lamb New Zealand mating management guidance. Cattle ratios by bull age are the commonly quoted extension figures and are presented as starting points rather than standards, because individual bulls vary widely. Every ratio here is editable.