Cover photo: Martin Dawes (CC BY-SA 2.0, cropped) · Source
A practical UK guide to breeding cattle: bulling heifer targets, heat detection, AI or the bull, bull fertility tests, calving interval and sexed semen.
A way through this story
Cattle breeding targets at a glance
- Heifers: first service at about 15 months and 65% of mature weight, calving at 24 months (the Agriculture and Horticulture Development Board suckler targets)
- Oestrous cycle: a cow comes back into heat roughly every 21 days if she is not in calf
- Breeding season: bulls in with cows for nine weeks and with heifers for six weeks
- Compact calving: more than 65% of cows calving in the first three weeks, with the whole calving period under 12 weeks
- Calving interval: 365 days is the usual ideal
- Bulls: fertility test about 10 weeks before he goes in with the cows
- Gestation: roughly 280 to 290 days for common terminal sires
Why breeding performance drives herd profit
Every cow that fails to get in calf, or calves late, costs money: a barren cow still eats for a year, and a late calf is lighter at weaning or sale. The Agriculture and Horticulture Development Board’s suckler fertility manual (2017) recorded 88 calves born per 100 cows or heifers put to the bull in 2016, against an industry target of more than 95. It puts the value of a 2% improvement in fertility in a 100 cow herd at £1,000 to £1,200 a year in extra sales.
Rearing bulling heifers to target
Heifer rearing sets up the whole breeding life of the cow. The Agriculture and Horticulture Development Board targets for suckler replacements are puberty at around 12 months, first service at 15 months and first calving at 24 months. At service a heifer should weigh 65% of the herd’s mature cow weight, rising to 85% at the start of her second breeding season and 95% at the start of her third.
For a herd of 650 kg cows, that means a bulling weight of about 423 kg, and the manual works out the growth needed as around 0.85 kg a day up to service. Dairy guidance is similar. The Royal (Dick) School of Veterinary Studies advises bulling dairy heifers at 60% of adult weight at 13 to 15 months, with calves averaging 0.7 to 0.8 kg a day, to calve down at 22 to 24 months.
Weigh heifers rather than guess, at weaning and again a few months before bulling, while there is still time to change feeding. Heifers that are well grown should get in calf within two cycles, and a short, tight bulling period makes them easier to manage at calving.
- Serve heifers at the start of the breeding period so they calve early and have longer to recover before their next service
- Use an easy-calving bull or AI sire on heifers
- Keep heifers on a shorter mating period than the main herd
The oestrous cycle and heat detection
A cow that is not pregnant comes into heat about every 21 days. First heat after calving can come from around 30 to 60 days, usually within 40 days according to guidance from Farm Advisory Service Scotland, and recording that first heat helps you spot cows with problems early.
The one reliable sign is standing heat: the cow stands still to be mounted by another animal. Secondary signs help you pick out cows coming into or going off heat:
- Mounting other cows
- Clear mucus from the vulva, and a swollen, reddened vulva
- Bellowing and restlessness
- Resting her chin on other cows
- Rubbed tailhead hair and dirty flanks
- A drop in milk yield or feed intake
- Bloody mucus a day or two after heat, which means you have probably missed her this time
Watching is the expensive part of AI. Without synchronisation, the Agriculture and Horticulture Development Board manual suggests observing natural heats for about 20 minutes three times a day. Tail paint, scratch cards and activity collars help, but do not replace watching.
AI or natural service?
Artificial insemination gives you access to top quality, high accuracy genetics without the cost of buying and keeping a bull, and it avoids the disease risk of bringing a bought bull onto the farm. The drawback is labour: you need good heat detection, or you need to synchronise cows for fixed-time AI, which adds drug costs and extra handling. The Agriculture and Horticulture Development Board puts conception rates to AI at typically 50 to 60%.
Natural service takes the heat detection job off you, but everything then depends on the bull being fertile and working. Many suckler herds use both: AI on heifers or the best cows for a few weeks, followed by a sweeper bull. Whichever route you take, handle cattle quietly around service, because stress lowers the chance of a cow holding.
Bull fertility testing and bull-to-cow ratios
Few bulls are completely infertile, but many are sub-fertile, and a sub-fertile bull usually shows up as a spread-out calving and more empty cows rather than as an obvious failure. The University of Edinburgh’s Farm Animal Practice says 20% or more of unselected breeding bulls may be classed as sub-fertile.
A breeding soundness examination by your vet covers:
- History and health status, including vaccinations and past performance
- A physical check of condition, feet, legs, eyes and the reproductive tract, including scrotal circumference
- Collection and microscopic examination of semen for motility and shape
- A final report on whether the bull is a satisfactory potential breeder
The Agriculture and Horticulture Development Board advises testing about 10 weeks before the bull is needed, because sperm takes around 60 days to produce, which leaves time to source a replacement. Aim for the bull to be at body condition score 3, and quarantine a new bull for four weeks before he joins the herd.
On numbers, the Edinburgh practice says a fully fertile bull running with 40 to 50 normally cycling, disease-free cows should get 95% of them pregnant in a 9 to 10 week mating period. Young bulls and bulls on big or hilly ground should be given fewer cows; agree a figure with your vet.
Compact calving, gestation and calving interval
A tight breeding season gives a tight calving period, which makes batches of calves more even and makes feeding, health jobs and selling simpler. The Agriculture and Horticulture Development Board targets are more than 65% of cows calving in the first three weeks and the whole calving period under 12 weeks. Our post on managing a compact calving pattern in suckler herds goes into the detail of how to tighten one up.
Gestation for common terminal sire breeds runs at roughly 280 to 290 days. Rather than counting days by hand, use our cattle gestation calculator to work out calving dates from service dates.
The usual ideal calving interval is 365 days, a calf every year. CAFRE suggests that 75% of a suckler herd should ideally have calved again within 390 days. Cow condition plays a big part: in the Agriculture and Horticulture Development Board manual, cows calving at condition score 2.5 to 3.0 had an average calving interval of 364 days, against 418 days for cows at score 1 to 1.5.
Sexed semen and beef-on-dairy
Many dairy herds now use sexed dairy semen on their best heifers and cows to breed the replacements they need, and beef semen on the rest so that surplus calves are worth more. The Agriculture and Horticulture Development Board figures for the 12 months to March 2022 showed sexed semen made up 70.5% of all dairy semen sales, up from 17.9% in 2017, and beef semen made up 48% of semen sales to the dairy herd.
For the beef sire, look for calving ease on heifers and on smaller cows, and for growth and carcase figures that suit the buyer of the calves. Agree the breed and sire type with your calf buyer if you sell on contract. A vet-led fertility plan, covering heat detection, pregnancy diagnosis and herd health, is the best place to tie these choices together.
Frequently Asked Questions
At what age should heifers be bulled?
Suckler targets are first service at about 15 months to calve at 24 months. Dairy heifers are usually bulled at 13 to 15 months to calve at 22 to 24 months. Weight matters more than age: aim for 60 to 65% of mature cow weight at service.
How often does a cow come into heat?
About every 21 days if she is not in calf. The clearest sign is standing to be mounted by another animal.
How many cows can one bull serve?
University of Edinburgh vets say a fully fertile bull running with 40 to 50 healthy, cycling cows should get 95% of them in calf in a 9 to 10 week season. Give young bulls fewer cows and agree numbers with your vet.
When should a bull be fertility tested?
About 10 weeks before he is due to go in with the cows. Sperm takes around 60 days to produce, so this leaves time to retest or find another bull.
What is a good calving interval for cattle?
The usual target is 365 days, so each cow calves once a year at about the same time.
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Source: AHDB Beef BRP Manual 8: Optimising suckler herd fertility for better returns
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