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Litter size vs age in guinea pigs

Post Number:#1  Unread postby Ghost » Sun Sep 16, 2018 3:10 pm


As guinea pigs age do they tend to produce fewer or more births/litter?

As it turns out, David's heard is not producing as much as it once did. The boars are all younger, many less than 1 year. It seems that he had quite a few producing sows, but recently he lost a number of older sows. I can definitely find pregnant sows, however the over all birth rate seams less. I don't see that many sows that balloon up prior to a litter as I use too. My guess is that there are less offspring per birth. Has anyone here notices a correlation between size/age of the sow and litter size. I'm guessing that boar's size/age has little to do with the litter size.
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Re: Litter size vs age in guinea pigs

Post Number:#2  Unread postby michaels4gardens » Sun Sep 16, 2018 4:14 pm


I noticed reductions in fertility, and litter size as they age.. [same as rabbits]
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Re: Litter size vs age in guinea pigs

Post Number:#3  Unread postby akane » Sun Sep 16, 2018 6:00 pm


It used to be that with more litters and a few years guinea pigs would produce larger litters instead. It was not at all uncommon to start having consistent litters of 5-7 with occasional 8-9 after the first year or 2 of breeding. That would often continue right up until they died of complications or no longer were able to keep condition between litters at what is a pretty old age for a guinea pig.

The fact litters over 4 end up with smaller pups and litters of 7 or more frequently have runts led to all show breeders and many others selecting guinea pigs for 3-4 pups a litter. Despite large litters of small pups usually making up the size difference within a couple months. I now find it rare to have a sow start producing larger litters with age when it used to be practically guaranteed 10 years ago. I have not seen they decline much though. I've had them produce litters right past 5 years old if they don't die of something first and with no extra skipping of pregnancies. They consistently produce until they reach the point that age starts impacting their weight and coat quality even between litters. Usually it starts with signs of vit c deficiency during pregnancy such as thinning hair or odd movements from painful joints. They have an increased need for supplementation despite no drop in the available vit c. I was steadily culling the ones that went that way out of my herd so I would see even fewer have any issues as they aged. Majority I've had run into complications and be lost giving birth before they ever slow down production. Often after 3-6years of breeding.

When more recently raising for meat though I rarely had a reason to keep a sow 3+ years like I used to. I no longer have 6-8year old pigs producing litters. Within a year or 2 you have more than enough quality offspring to move on with the breeding program. Breeding the same ones for an extra 2-4years doesn't really make any progress toward larger, hardier, and better producing stock. The giant cuy breeds have all been selected for only about a 3 year lifespan for that reason. You have plenty of cuy to establish the next generation by then so having them grow faster, produce quicker, but not live as long ends up being perfectly acceptable.
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Re: Litter size vs age in guinea pigs

Post Number:#4  Unread postby Ghost » Wed Sep 19, 2018 4:23 pm


I suppose it all comes down to the fact that David does not track his herd. This is very much a free breeding herd. If you watch this https://www.youtube.com/watch?v=H_TUBzkwlM8 video, you get a good what David's herd is. David's herd has a smaller space and fewer numbers (compared to the vid), but that is what you get. I have taken more a personal interest, than David does. David's only real concern is, "Do I have enough rodents to feed my other creatures?" And to be truthful, I do want his herd to produce. When his larger crocodilia become less active (in the winter) I would like a few more rodents to eat for myself.

David killed off his entire rat colony, I did not urge him to do it, but I feel good that it is gone. It was smelly and gross, I think the GPs have a more humane existence compared to the rats. I am very comfortable with his guinea pig colony, even though he kills GPs on a regular basis, to provide for other creatures.

Now that he does not have a rat colony, the production of the GP colony is more an issue.

akane wrote:It used to be that with more litters and a few years guinea pigs would produce larger litters instead. It was not at all uncommon to start having consistent litters of 5-7 with occasional 8-9 after the first year or 2 of breeding. That would often continue right up until they died of complications or no longer were able to keep condition between litters at what is a pretty old age for a guinea pig.


How does the size of first litter compare to the second and third litter?

In a herd situation the young sows will breed at the youngest time biologically possible, because they are not separated from the males. The sow "Skunk Face" has a unique marking so that I know she had her first litter a few weeks ago. There was only two in the litter. Is it possible that Skunk Face can have a bigger litter next time?

There was once a sow I called Mane Girl who I noticed would balloon-up before every litter (I assume she had a lot of offspring per litter). One day Mane Girl had a severely infected eye, so she was euthanized and fed to a large snake. I think something also happened to the other large sow.

I also know two sows that have been producing for over a year. They do produce, but I haven't seen them balloon-up. I would hesitate to suggest killing-off those two, but if it would lead to a more productive herd then perhaps it would be worth it.

akane wrote:I now find it rare to have a sow start producing larger litters with age when it used to be practically guaranteed 10 years ago. I have not seen they decline much though.


I assume you are talking in the context of guinea pigs that you purchase from other breeders. I haven't gotten very many details from David about how he started his colony, however, he is adamant that he has a closed colony. (closed colony) Meaning that once it was started, he has not added any new GPs. I don't know exactly when his colony started, but I am thinking the colony was started a few years prior to 2010. He has not told me where he got his foundation stalk. I suppose that with a genetic bottle neck, that herd could have lost some valuable gene in the last eight years.
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Re: Litter size vs age in guinea pigs

Post Number:#5  Unread postby akane » Wed Sep 19, 2018 5:39 pm


All sources of US guinea pigs seem to have lost litter size over the years. No matter where we got them growing up until I went off to college we always ended up with litters of consistently 5 or more after their first year of breeding. Around 5 years or so later I started keeping guinea pigs again and have gotten show culls, random craigslist postings, other breeders, etc... with none producing more than 3-4 their entire lives except very random litters of 5. In the lifetime of our very first pair I saw more litters of 8 than I could count and a couple litters of 9 with various guinea pigs from other sources producing much the same. The most recent 5 years I raised far more guinea pigs at a time and never even saw a litter of 6. Maybe only 2 litters of 5 that entire time. I would assume the mass production from single sources being spread by chain pet stores has played even more part in that than show breeders. Many of the animals sold across the country by places like petsmart and petco are from only 1-3 mass breeders and distributors. Then those are crossed into the local pets and you end up with very little local variation compared to other animals. Since the goal of different breeds in guinea pigs is mostly the same you also don't have breeders trying to preserve different characteristics like you do with rabbits and it's far easier to simply lose the genetics for something from the entire population.

1 litter doesn't prove much. Some go from having 2 the first liter to 4 every litter after. Overall most US guinea pigs these days will stay around 3 with some leaning toward 4 and occasionally 2 or occasionally 5. However, it's a good idea to cull sows having 1 or 2 very large pups because oversized pups will increase sow deaths. Large singleton pups that are born alive have higher odds of dying to their own oversized singleton or 2 pup litter. In situations where they are not heavily supervised and given veterinary care for stuck pups they will mostly cull themselves out after enough generations. It would be unlikely to keep having oversized pups in an established herd that does not have new individuals being added very often so the odd litter of 2 is less likely to be an issue.

If you wanted to try to slightly increase litter sizes and consistent production you'd have to keep better track of each sow and prioritize those that produce 4+. It is easier to cull out the ones that don't produce well frequently or for as long since you can easily pick out and remove any not holding condition for whatever reason. Keeping track of those that lose production sooner would still allow culling their offspring as well but like I said age is not really prioritized by most given guinea pig reproduction speed. The ones leaning towards meat production usually end up with even shorter lifespans rather than being selected to breed for more years. You just have to keep enough young every year to replace those sows.

Many of these things will cull themselves out if you aren't trying to save their offspring on purpose because those sows will not have as many years or as many overall offspring that might not end up as feeders. There are lots of ways humans end up unintentionally influencing things in bad directions though. That's one reason many of the best meat production animals are a singular color. What offspring are kept has not been influenced by interesting colors resulting in people acting closer to natural selection in the wild instead of keeping offspring from poor producers on purpose. Even if someone is not paying close attention to each breeding animal the odds of offspring removed at random will favor those that produce better. The less random the selection the more you have to pay attention to details to avoid accidentally culling for less production instead of better.

Such as the current giant cuy species were actually selectively bred and developed to save the failing domestic guinea pig population in South America. People had been eating the largest ones and ignoring the smallest since they made the largest meals without thought to producing more large cuy from them. There's also a superstition against eating dark colored cuy in much of South America so on top of that any dark cuy were culled regardless of size or production before they could reproduce. South American cuy were actually quite small for awhile from people neither randomly culling or paying attention to keeping good traits. Luckily some very dedicated groups bred the size back into them plus some extra to make the 3 major breeds of 4-8lb cuy being exported today.
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Re: Litter size vs age in guinea pigs

Post Number:#6  Unread postby Ghost » Wed Sep 19, 2018 7:12 pm


Thanks Akane for your input. I guess one thing that happens when you don't keep records is that the whole thing becomes one big guessing game. It's like there is an effect (or just a perceived effect without proof) and then the breeder just starts grasping at straws to figure out why.

Another guess as to what caused a slow down in production is the heat. Here in Zone 8 Texas we had lots of 100+ Fahrenheit days. It is still hitting in the 90s. David has an air conditioning unit in the indoor portion of the GP habitat. He seems to think that heat could be an issue.

The third largest male had to be euthanized for fight injuries. Three weeks earlier, I noticed scratches on the GP. At that time scratches were not bad, but I was sure that if that male was not culled it would only get worse. David culled many large males back in March (that is why I eat a female in April). David is now reluctant to kill-off the large males. I was able to show David that we still had two larger males. With that and the worsting condition the scratched up male was finally culled.

I am thinking that the maturity/size of the males are not an issue when it comes to the production rate of the herd. I'm guessing that as long as you have a few males ready to do the job :mrgreen: that you generally don't have to worry about that.

I don't think I will be in it to get greater record kipping. I'm only there once per week and I have other things to do other than the GPs. Many times there are multiple births and I can't relate sows to litters. The only reason I caught Skunk Faces's litter was, she was the only sow that went from plump one visit to less plump on the next visit, and there was only one litter on the day I was there.

My guess is that David will either start a new rat colony, or start a second GP colony by splitting the current colony. I don't think he will give more floor space to the current colony. At one time the current colony had more floor space, but due to circumstances beyond his control he had to reduce the outdoor portion of the colony. I think it would be cool if he imported super cuy to start a second colony. He is in touch with animal importers, but I don't know what he think of the cost of the deal.
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Re: Litter size vs age in guinea pigs

Post Number:#7  Unread postby akane » Wed Sep 19, 2018 11:15 pm


You don't need to import them yourself. You can contact some of the larger west coast breeders and they'll ship them by ground transports, they also go to major rabbit shows, and have even shipped some on airlines to alaska. Odds are there is even someone closer and often traveling to your local arba shows but they can be hard to find without using the FB group. Most of the major breeders are in Oregon and some have consistent shipping routes by now they send throughout the western and southern US. Really the only problem is it's still about $100 a sow but they often do trio specialty sales at times and even a $50 giant cuy boar to american sows will increase the growth rate considerably. The size of crosses is not fully predictable but I found the growth rate increase is worth it by itself even if the offspring stop at an only marginally larger 3lbs over typical guinea pigs. I didn't lose a single regular size american sow I bred to my boar that eventually reached 6lbs but after the first generation I crossed the 50/50 sows back to their sire.

Tracy Iverson in Cottage Grove, OR is the main original importer of the peru giant strain, runs the peru giant FB group, and an ARBA judge mostly for cavy. Karyn Fegles is another major breeder involved in importing the first pure giant cuy. Aside from ARBA having their info there is also an old but the only currently functional directory by the oregon cavy breeders http://ocbsociety.tripod.com/BreedersDirectory.htm A handful have imported them since then and someone was setup to import the Andina and Inti lines of giant cuy but it looks like they just posted that the shipping service refused and are looking into their policy.
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Re: Litter size vs age in guinea pigs

Post Number:#8  Unread postby michaels4gardens » Thu Sep 20, 2018 5:19 am


makes me want to get more GP.. I really did enjoy them.. When I had them --I had them in a "colony" situation until the sows began to get plump, I then moved the sows to individual cages.. I recorded the birth / growth info-- and selected stock from the best- I did have a few surprise litters in the colony...
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Re: Litter size vs age in guinea pigs

Post Number:#9  Unread postby akane » Thu Sep 20, 2018 8:56 pm


With how badly they do alone I never separate sows individually. I always do at least 2 and just stick a young female I am planning to sell and don't want bred in with the other. Usually small herds can be kept track of pretty well. Particularly if you at least know basic color genetics or things like coronets (the forehead swirl) being dominant and don't have all the same color. Also easier to figure out with a single boar but you don't usually attempt 2 boars with less than 8-12 sows. My herd that included 4 red sows with a cream boar (dilute red) was a bit harder since all they produced was red with the occasional cream but odds 2 would birth the same 12-24hrs between checking them was low.

They also make tags for guinea pigs. It's not very expensive or difficult to tag a guinea pig. Just keep them firmly still because if they manage to jump forward or scoot back before you release the clamp the ear will easily rip and generally never heal. One of mine mostly healed but it was still hard to put a new tag in due to the giant ridge of scar down the middle. I'm not sure I have a pic of a tagged guinea pig but it's the same tags we use on the chinchillas as well. If they aren't in huge groups to have multiple litters at the same time or have enough color/coat variation you just have to scoop up the suddenly skinny one to write down her litter quantity and date under her tag the same as tattooing rabbits. Condition during pregnancy or after birth would be even easier to keep track of than hoping they don't pop out a same color litter on the same day. 3 herds of 6-10 along with the smaller pair/trio cages for separating sows there were maybe 3 times I couldn't tell who had what over several years. Mostly after I got 2 groups of show cavy with one being all silver solid and one being all red. Color genetics are bred very pure in show cavy so a given color should always produce itself or close to it if they have any quality.

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Re: Litter size vs age in guinea pigs

Post Number:#10  Unread postby ohiogoatgirl » Thu Jan 03, 2019 2:50 am


something to consider is that the female decides how many babies by the number of eggs produced in a cycle. More viable eggs = more eggs available to be fertilized. Low birth rates due to the male animal is usually quite abrupt but much easier to spot when breeding in defined groups or tracking when sows birth. Low birth rates due to the male would be low sperm production or malformed sperm, which is heritable. A male with malformed sperm has something going on in the production and formation of the sperm. If he managed to get any live offspring they too will produce poorly or not at all. I recently learned about this in sheep where someone bought a super amazing show ram and got 3 lambs from him over many years and many many ewes. Even then the offspring never produced at all and when the offspring ram was tested his malformed sperm was just like the sire's.

This also goes for females though. Females producing low numbers of eggs will produce daughters with low egg production. This is a long term breeding goal though. In goats number born is only 15% heritable, birth weight is 30-40%, mature weight 65%.
In sheep number born 10% heritable, birth weight 15%, mature weight 50%.
I would suspect the rabbits and GP are not terribly far off. I would definitely operate under the assumption that years of pet and show breeders selecting for small number litters, and often larger birth weight, intentionally or not this is the result. Heck even within NZ rabbits which are a meat breed a lot of breeders will go for smaller litters. While in rabbits there doesn't seem to be much difference in birth weight, excepting the odd huge single, at least in my experience, with GP being geared to fill up the available uterus space with babies ready to hit the ground running... We end up with large pups and birthing issues.
I didn't think about this when I still had my GPs but starting over I would definitely breed for larger litters and the smaller birth weights.

However it's a careful line. In sheep birth weight is a big topic because small lambs are significantly more prone to dying in the first week of life. Once you get to the 'decent sized' lambs, about 8lbs, the lambs do fine. And as birth weight gets higher the mortality rate doesn't really take a hit until the huge 13+lb lambs. But going smaller than 8lbs and the lambs mortality rate is crazy.
Being contained and small as they are I think 'too small' babies won't be as big a problem as sheep. Plenty of people pasture lamb in low temps which won't be an issue for GPs, stuff like that.

__________ Thu Jan 03, 2019 2:43 am __________

The simplest way to see who is producing and who is not.. I think I would keep a notebook in/near the GP area. Prepare a smaller area you can put really heavily preggo sows. When the colony has sows looking bred make note (black American sow 1/3/19 bred?) something like that. Maybe get a livestock breeding crayon to temporarily mark the ones looking bred, to easier spot and note if they get real big or not.
The big preggo sows can go into the maternity ward smaller pen. Then you can easily see who popped and has babies following.
If a marking crayon would work (or you go into ear tags) you can mark or tag the ones from bigger litters. IE, the singles, twins from the maternity pen don't get tagged.. the 4+ litters get tagged and that sow gets tagged. Now when returned to the colony at large you can see the tagged ear GP should not be pulled for feeding/culling etc. The young ones without tags can be pulled. Thus you select for larger litters.

If it were me and I really wanted to make sure I'm going to be able to continue I would actually start another colony or divide off a small second colony. In the new one would go sows that litter 4+. (If I am getting mostly singles and twins I'd even start with keeping the sows and offspring that have triplets and go from there.) I would tag the boars from these litters and when of-age weaned to the main colony. As the 'littering sows' are sorted they will get put in the main colony for periods of time to get bred back.
After some time with the secondary colony growing (and pups grown into breeding age young sows).. I would go to the main colony and choose some of the best looking ear tagged boars. The more the better to combat inbreeding %. (inbreeding also being a factor to fertility issues) Say I got up to 25 or 30 sows I'd want to chose about 8 of the very best of the tagged boars. And hopefully the sows and daughters not being all sired by the same one or two boars, then we can increase the variety of genetics. Also by this time assuming I've built up a good number of ear tagged boars in the main colony I would probably cull all non-tagged boars. This way I can increase production in the main colony by selecting boars but not culling all of the genetics from the whole rest of the colony. As the main colony production goes up I can add 4+ litter sows into the second colony. Thus keeping genetics from becoming bottlenecked.
Eventually the first colony will be smaller in number. And I hypothesize it would become obviously not as productive as the second colony. I would then just cull the remaining of the 'first' colony. From here I could select more from within the colony or begin again by separating out sows who produce 5+ or 6+ etc.

__________ Thu Jan 03, 2019 2:50 am __________

I've attached a graph I saved from a very long detailed break down about inbreeding percentages and calculating for wild flocks or things like fish breeding where you don't have "male A breeds females 1-15" but a huge tank with appx 200 female fish and appx 50 male fish. And multi sire breeding in sheep/cows.
percent inbreeding chart.png
percent inbreeding chart.png (92.04 KiB) Viewed 589 times


I know this is getting real long now :roll: but I've been watching tons of webinars about breeding systems and haven't thought about the GPs in ages.. Now my wheels are all a'turnin'! :mrgreen: that's what ya get pokin' the bear :roll: :lol:
Can I get back all that spare time I used to have?

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