What is a breeding calendar?

A breeding calendar is a schedule that combines a species' oestrous cycle with its gestation length, so you can see when an animal can be bred, when to re-check for a return to heat, and when young are due if the service held.

How do you calculate a due date from a breeding date?

Add the species' average gestation length to the service date, then note the normal range around it. For example, a cow served on 1 May is due about 7 February (283 days), with a normal window of 3 to 11 February.

How many cycles should a breeding window cover?

Two or three. A 42 to 63 day window in cattle, sheep or goats keeps births compact enough to manage in batches while still giving females that miss the first service another chance.

Do breeding calendars work for seasonal breeders?

Yes, with one extra check: the planned service date must fall inside the breeding season. Sheep cycle in autumn, mares in spring and summer, so a target birth month outside those constraints cannot be met without light programmes or hormonal management.

Breeding planning · 7 min read

Animal Breeding Calendar: Gestation Lengths and Due Dates by Species

Updated 7 August 2026

A breeding calendar answers two questions at once: when an animal can be bred, and when the young arrive if that breeding takes. Both come down to two numbers per species — the oestrous cycle length, which sets how often you get a chance, and the gestation or incubation length, which sets the due date.

This page collects those numbers, then shows how to work backwards from the date you want young on the ground. Every species listed has its own calculator if you would rather type a date in than count days.

How often does each species come into heat?

Cycle length decides how long you wait for a second chance if a service does not hold. Seasonal breeders add a second constraint: outside their season there is no cycle at all.

Species	Cycle length	Heat lasts	Season
Cattle	21 days (18–24)	12–18 hours	Year-round
Sheep	17 days (14–19)	24–36 hours	Autumn (short days)
Goats	21 days (18–24)	24–48 hours	Late summer to winter
Pigs	21 days (18–24)	2–3 days	Year-round
Horses	21 days (19–22)	5–7 days	Spring and summer
Dogs	6–8 months	5–9 fertile days	Year-round
Cats	14–21 days while in season	4–7 days	Spring to autumn
Rabbits	Induced — receptive most of the year	—	Year-round indoors

Ranges reflect published reference values; individuals and breeds vary.

How long is gestation for common breeding animals?

These are the averages a breeding calendar is built on. The range matters as much as the average: plan attendance around the earliest date, not the mean.

Species	Average	Normal range	Young
Cattle	283 days	279–287	Calf
Horse	340 days	320–370	Foal
Donkey	365 days	340–385	Foal
Pig	115 days	112–120	Piglets
Sheep	147 days	142–152	Lambs
Goat	150 days	145–155	Kids
Dog	63 days	58–68	Puppies
Cat	65 days	61–70	Kittens
Rabbit	31 days	28–33	Kits
Chicken (incubation)	21 days	20–22	Chicks

How do you plan breeding dates backwards from a target birth date?

Most planning is reverse arithmetic. Decide the month you want young born in — grass availability, market dates, staffing, weather — then subtract the gestation length to get the breeding window.

Example: lambs wanted from 20 March means tupping around 24 October, because 147 days back from 20 March lands there. Add a second cycle of 17 days and you know that ewes not held by 10 November will lamb into April.

Target birth date − average gestation = first service date.
Add one cycle length for each repeat opportunity you want inside the window.
Keep the group's breeding window to two or three cycles so births stay compact.
For seasonal breeders, check the target service date still falls inside the breeding season.

What should a breeding record actually contain?

Two dates are worth writing down that most people skip: the expected return to heat, and the earliest end of the due-date range. The first catches failures three weeks early; the second stops late-night surprises.

Service or mating date, and the sire used.
Method: natural service, AI, or embryo transfer.
Expected return-to-heat date, so a missed heat is noticed instead of assumed.
Pregnancy diagnosis date and result.
Calculated due date plus the earliest date of the normal range.
Actual birth date and outcome, which is what improves next year's calendar.

Why do due dates drift from the calendar?

Litter size: large litters often arrive slightly early in pigs, dogs and cats.
Parity: first-time mothers commonly go a day or two either side of the breed average.
Breed: draught cattle and some dog breeds run longer than the species mean.
Fetal sex and singles versus twins shift equine and ovine dates by days.
Counting method: canine gestation measured from ovulation is far tighter than from mating.

Which calculator should you use next?

More species are listed on the full gestation chart and in the guides index.

Common questions

Figures here are published reference ranges for planning, not veterinary advice. Confirm pregnancies and health decisions with your own vet.