How Many Sows Do You Need?

15 New Born Piglets

This is one of our Mainline sows who recently had fifteen live piglets and two dead. That’s an excellent piglet count and an excellent live birth rate. Not every ovum fertilized gestates. Not every fetus gets born. Not very born piglet lives. Most deaths happen in the first 48 hours as the piglet switch over from live support by their mother to having to breath and do other vital things on their own. Not everyone is born perfect.

In the picture above they’re just born. Three days later they’re all doing great. That too is unusual and most excellent. With a large litter like that it would not be surprising to have some deaths during the first two days as the piglets have to live in the outside world and compete with each other.

We don’t crate our sows. Not during gestation and not during farrowing. Good sows nest well, lay well, farrow well, milk well and mother well. I select hard for these traits. This lady has proven herself so she will see many more years on our farm and it is likely some of her daughters will too.

This is her third litter so she is called a parity three sow or P3. As a general rule gilts, new mothers, have fewer piglets and then they go up about half to one piglet with each parity. Eventually when they get old and near the end of their fertility their litters drop to four, then two or one piglet. Then they stop heating and stay open. That is the end of the breeding line – generally around four to six years, sometimes longer, in exceptional cases much longer. This is with big farm pig breeds that can break the 1,000 lb barrier with little fat on them. The old saying is that dogs age about seven times faster than humans. From my observations I would say that pigs age about ten times faster.

A more typical count of piglets for a gilt is six to eight piglets and then rising into the low teens. We’ve seen many in the high teens and even 23 in a litter. That is extremely unusual!

Don’t count your piglets before they are weaned. For that matter, don’t count your pigs before you get them to butcher. Gestation takes four months (114 days) to get to this stage where the piglet emerges into the outside world. About another six weeks to gets it to weaning. Weaning is a stressful time for piglets as they transition off their mother’s antibody rich milk. Then there is another five months to get to market weight when they find out if their in the breeder track (5% of gilts, 0.5% of boars) or the feeder track in the school of life. Those are actually better odds then out in the wild (perhaps 2% for gilts, 0.1% for boars). It’s hard being a guy either way.

Johan on the post Wee-Wee-Weaning All the Way Home asked:
Lets say you need to produce 25 piglets per week throughout the year, how many sows and boars will you use?

You might figure:

P = number of pigs you want to sell annually

L = Litter count born alive (e.g., 8 piglets per farrowing)

Y = Litters per year per sow (2 is a good figuring number)

D = Survival rate from birth to market (most congenital deaths are in first 48 hrs, most survive post weaning acclimatization)

S = number of sows you need

C = sow to boar ratio = 10 is a good number to use

B = number of boars you need unless you’re doing AI.


S = -Int(-P/D/L/Y)

B = -Int(-S/C)

For example:

P = 25 piglets/wk x 52 weeks = 1,300 piglets/year

=> 91 sows and 10 boars

There are fractions in there but partial pigs are not very useful. The rounding up by negated Int gives you a margin of error. e.g., 5.5 becomes 6 and 0.5 becomes 1.

D, the survival rate to market, is the biggest variable. That’s mostly you managing the herd. Good genetics, biosecurity, feeding, health, protection from predators are all factors that will make a difference.

L, litter count, makes a big difference too. Research I’ve read suggests that litter count is strongly controlled by environmental and management factors such as good diet, low stress, not getting diseases, etc.

Plug this into a spreadsheet and you have the barest start of a business plan. Careful not to use too sharp a pencil. Reality will be different.

There’s another variable T, Time to Market, to consider of how fast the animals get to market. Balanced commercial hog feeds and top genetics generally get you there the fastest at the highest cost. The commercial hog feed of corn/soy grains also tends to produce a lower quality pork higher in Omega-6 fatty acids and lower in the heart healthy Omega-3 fatty acids.

Pure pasture is the slowest, leanest and lowest cost route. The meat will be good but lean with not a lot of marbling due to the low calorie nature of most pastures. There are many good feeds that can supplement or replace grain bringing pasture growth rates up on part with grain diets and boost calories to give marbling. Boosting the meat with dairy in particular, such as the whey we use, seems to give a superb flavor. Some supplements to consider that you might be able to produce yourself or obtain locally: dairy, eggs, apples, spent barley, pumpkins, turnips, etc. See the Pig Page and follow the feed links.

Time to market tends to be critical to minimize for confinement operations and less of an issue for pasture based farms. Some mix between the extremes is a good place to end up. It all depends on your speed and quality goals for your farm.

See, algebra’s fun!

Also see:
Dipping Your Toes into Breeding
Have You got the Right Stuff to be a Breeder
Keeping a Pig for Meat
Breeders Page

Outdoors: 4°F/4°F Sunny
Tiny Cottage: 66°F/62°F

Daily Spark: Genetics are where the math meets meat.

Before you get a boar ask yourself, farmer, “Do you need a boar?” Getting a boar for a single sow is rather expensive. In fact, these big boys eat a lot of food so it takes a lot of piglets to justify a boar. I figure one per three sows if by land (pasture) and six sows if by seed (grain fed) makes him economical. Do your figuring to check with your situation. One boar can service up to about 15 sows with ease depending on the timing of their heats.

About Walter Jeffries

Tinker, Tailor...
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7 Responses to How Many Sows Do You Need?

  1. Johan van der Merwe says:

    Walter, thank you for the feedback.

    How will you divide the 100 pigs in groups for pasture? Will it be 10 camps with each a boar and 10 sows. Or 50 sows with 5 boars in one camp?


    • How we divide the groups of depends on the genetics, breeding goals, seasons and pasturing. It’s not a fixed thing. You could do it in all sorts of groupings. Generally I like to keep the number of big breeders in a group under 50 and even under 30. This is because when you walk through a field and have 50 animals each of around 500 lbs come thundering up to you to see if you have a treat it can be, well, challenging. Don’t trip. That’s 25,000 lbs of pork on the hoof and they will trample you if you fall down. Thus for practical purposes it is better to divide the herds into smaller groupings. On the other hand, 100 piglets is not quite so over whelming.

      I would suggest running the boars in pairs, one much larger than the other. Thus you might have two boars, two boars and one who would later get a follower boar making six down the road. Very young boars can get introduced to the larger boars just fine in my experience. Even do a few roaster boars into the big breeder boar groups.

      Then run sows through their herd groups in sets of ten to fifteen with at least 30 days in with the boars to catch a second possible heat if they miss. One hundred sows farrowing twice a year is 200 / 12 months or 17 sows a month. That could be manageable with even a single boar set but I like having more boars as I am working on developing our genetics so this lets me run more gene lines. As you do it you’ll find your comfort zone.

  2. Dawn Carroll says:

    I had a Middle White sow that continually farrowed 15 with her highest 23. She raised all of her babies even the 23 count. But I did bottle feed her babies to help her out. I would have to take water based markers with me to mark the babies that I had fed. I would mark each one. I had to do this because they were all white babies and hard to tell apart. Not only were they hard to tell apart but I also found that piglets (and adult pigs) lie about having just sucked down 6 oz of milk replacer.
    She was the best producing sow that I kept daughters from for breeding. The daughters highest number in their litters was 19.
    If I was able to, I think, I would like to look into reviving the Middle White breeds as I found them quite docile and to be good mothers. She crossed well with all my purebred boars of different breeds.

  3. Aidan Hamilton says:

    Would you be willing to share the numbers you plug into your formulas so we can see how it runs and what kind of numbers are attainable?

    How do you know which boar mates with which sow? Do you run brothers together when possible to mitigate genetic variance or is it the piglets they produce that matters more to you?

    • If I’m running two identical brothers together I am not worried about differentiating who’s the sire. I’ve done that on occasion. Usually though the father’s are different enough that I can tell at a glance which sired what piglet, this is part of how I organize our boar herds as that makes it easy. I like having multiple boars together because then there is a lead boar, a sub-boar and small upcoming testing boars. This makes it so the sows get better mated and produce larger litters and I can run more sows together reducing the total number of groups we manage which can be as high as 25 or so different groups at times. Every time we create a new group it increases our work load so I’m sure you can understand the desire to have fewer groups.

      As to numbers, I’m very conservative. I figure two litters a year and six piglets a litter. It is not too uncommon to wean 10 to 14 piglets and for some of the sows to do three litters a year, especially from the Blackie line, but I like to be low in my estimates and pleasantly surprised. We increase our sow numbers in the spring and then cull back in the fall. That ebb and flow may change a little when we get our large open greenhouse built which will give us more sheltered winter paddocks that the pigs can choose to go into. We’ve been testing things out with small temporary greenhouses and the south field shed for years along this line. In fact, back just before we started the Butcher Shop adventure we were about to build the large greenhouse when we realized the butcher shop, which had been planned to start construction in 2014, was going to have to take priority. Sometimes plans get shifted.

  4. Farmer Justice Kwersy says:

    I very much appreciate the projection in your write up, but I’m curious on the actual figures you plugged into the equation

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