A step-by-step guide to pig heats and insemination

The performance of a breeding herd can be assessed in many ways – be it pigs born alive, pigs weaned, or litter weight weaned. But whatever the metric, that level of performance will hinge upon successful service in the breeding herd.

During the “Principles of pig production” webinar series run by AHDB, Adrian Cox of Farmvet Integrated Livestock Services told attendees: “Even really small tweaks to service management can have a big impact on herd profitability.”

There were many factors influencing breeding herd performance, he said, but one of the most important was the stock people. “To my mind, the most important aspect of service management is the quality of staff – the level of enthusiasm, the level of training and attention to detail.”

See also: Advice for managing gilts up to service

Mr Cox shared his thoughts on the important stages of optimising heat detection and service to increase the productivity of the breeding herd.

1. Know the farrowing rate

Knowing the farrowing rate enables you to calculate how many sows need service in a given week. And tracking the farrowing rate throughout the year will also highlight any seasonal dips – dips that could be offset by targeting this window for gilts coming into the herd.

The farrowing rate is a percentage that tells you the number of sows that farrow to a given number of services. The calculation is:

(Number of sows and gilts from that service group that farrow divided by number of sows and gilts served) x 100%.

How many sows to serve with a goal of 21 sows farrowing/week

Expected farrowing rate %

Number of sows to serve/week

















The effect of individual staff on live pigs produced

Stockperson Farrowing rate % Total born Number of live pigs produced over 256 sows
1 90.6 11.0 2348
2 89.8 11.1 2413
3 89.1 10.8 2346
4 85.9 11.2 2310
5 81.6 11.0 2153
6 67.8 9.3 1371
Source: Adrian Cox

2. The seven ‘S’s of preparing sows for service

The seven “S”s to remember when preparing the sow for service are:

  • Space: Adequate room
  • Sustenance: Good access to feed and water. The body condition score (BCS) at weaning/service should be 3 (see “Body condition scoring sows” below)
  • Sunlight: Target 250-300 lux for 16 hours a day
  • Snug: A well-bedded, non-slip environment with a temperature ideally around 17-20 C
  • Stimulus: Good boar contact
  • Sized into groups: Ideally, sows would be grouped by physical size and weaning/planned service dates. Placing young weaned sows into pens with larger, more dominant sows will put the former at a significant disadvantage and risk them not returning to heat properly.
  • Stress-free: Calm handling and preferably no group mixing or vaccinations until after 28 days post-service.

Body condition scoring sows

  1. Emaciated, prominent backbone
  2. Thin, prominent backbone
  3. Backbone just palpable. This is the ideal BCS during lactation and at weaning/service
  4. Slightly overweight, cannot find backbone
  5. Rounded body, overfat

3. The heat detection process

Timing Ideally, heat detection should take place twice daily.

Location The optimum is to take the sow to the boar pens to get a good standing heat. The boar should be better at detecting a heat than a stockperson.

Research has shown that:

  • A sow and boar in the same pen is nearly 100% effective in picking up a heat
  • In comparison, the easier option of having a sow in stalls and boar in the alley is 67.5% effective
  • And sows on the outside of the boar pen is 87% effective.

Grouping Groups should be small to allow adequate contact with the boar.

Contact Nose-to-nose contact is key – the pheromones in saliva trigger uterine contractions.

The sow should be with the boar for three to four days after weaning, with the boar removed for 24 hours prior to heat detection to avoid habituation.

Oestrus and ovulation Oestrus is the period of receptivity during which ovulation occurs – the period of standing heat.

Ovulation is the release of the egg from the ovary, which typically occurs two-thirds of the way through standing heat (oestrus) in sows and gilts.

Detecting when oestrus begins is key to targeting the best time for ovulation, which will impact litter size because of the number of eggs fertilised. If service is within oestrus, but not catching ovulation, you can end up with a good farrowing rate because sows are falling pregnant, but a poorer litter size.

So, firstly, the start of oestrus must be identified (see “Signs of oestrus” box) and then sows should be served twice, 16-24 hours apart.

Ideally, a third check 24 hours afterwards the last service would confirm how accurate service was – if there is a good standing response two days after service, it would suggest the first service was a bit soon so the animal could be served again. These learnings can be used for future and oestrus mapping programmes can also be used to improve timings.

Signs of oestrus

  • Swelling/reddening of the vulva
  • Clear discharge from the vulva
  • Standing response to back pressure or a boar
  • Riding behaviours – can often be seen through marks on the back if not witnessed happening
  • Pricked ears
  • Tail pointed up or flicking
  • Hunting for the boar
  • Restlessness
  • Change in appetite.

4. Insemination protocol

To get insemination done correctly and successfully, the environment, routing and procedure are all paramount. The key factors to consider or processes to follow are:

  1. Service should take place in warm, hygienic, well-lit facilities with a non-slip floor. Whitewashing the walls and ceiling in the insemination area can help with lighting. It is important to have all equipment to hand so the process can be done smoothly.
  2. Semen should be stored at 17C and transported to the insemination area in an insulated box.
  3. A calm and quiet environment is key. Anything that increases the adrenaline level in sows will result in deteriorating performance.
  4. Work with a small group of sows at a time – only sows which can be inseminated within 20 minutes should be stimulated by the boar, with nose-to-nose contact.
  5. Once perfectly set up, the sow’s vulva lips should be wiped clean with tissue and parted. The catheter should be inserted upward and inwards, avoiding the bladder, until the ridges of the cervix are felt. A plastic covering on the vulva and use of vinyl gloves here increases hygiene levels. Lubricant can be used if necessary.
  6. The semen container should be attached to the catheter and then the sow allowed to draw the semen in naturally with continued boar contact, in no rush. Stimulation in the form of pressure on her back, rubbing her flanks and devices such as plastic hoops can aid the drawing in of semen.
  7. Once the semen pack is completely empty, the catheter should be slowly and gently removed if not released naturally. The sow should be allowed to rest in front of the boar for at least 15 minutes before being quietly moved to a post-service area.
  8. At this point, service should be noted, so that records are up-to-date and accurate.

5. Post-service management

The job is not done once service itself is complete. The post-service window is important to ensuring the service is successful in establishing a healthy pregnancy.

Comfortable dry sow accommodation should be provided with good access to water and nutrition. Likewise, any disease challenges can cause issues, so animal health remains a priority.

Mixing should be avoided if at all possible and if it is really necessary, it should happen immediately after service or preferably after five weeks post-service, so the pregnancy is fully established. The window of seven to 21 days post-service is the embryo attachment phase, so it is important to keep groups stable.

It is important to identify returns because accumulating non-productive days will be costly to the business, so sows must earn their keep. The boar should be introduced daily from 18-24 days after mating to observe for “not in pigs” (NIPs).

The time frames of identifying NIPs can be telling:

  • Returns at 18-24 days suggest a problem with service
  • Later returns around 28-32 days suggest the loss of an early pregnancy.

The cost of empty days

A sow cycle is 150 days (116 days gestation, 28 days lactation and six days between weaning and heat).

This means in one year the sow can have 2.43 litters (365 days divided by 150 days).

However, the UK average is about 2.3 litters a sow a year

This gap between possible performance and average equates to nine days lost per cycle, which is 21 days lost a sow a year.

Table 3: Lost production costs


Perfect production

Average production

Production (litters a sow a year)



Assumed pigs a litter



Total pigs a sow a year

11.9 x 2.43 = 28.9

11.9 x 2.3 = 27.4

Difference between perfect and average production (pigs a sow a year)

1.5 (28.9-27.4)

Difference in profit a sow a year (based on marginal pig value of £53)

£79.50 (£53 x 1.5)

*This is a fairly conservative figure and actual numbers are likely to be higher on many systems