Other Rodents (Guinea Pigs and Hamsters)

Guy Mulder: Alright so there’s an unfortunate
title in the agenda there. When we first started talking about this, I was, they said can you
just talk about something other than, and I thought they said mice and rats because
I know Joe was going to speak and he talks very well obviously about mice, and I thought
oh he must be doing rats, I’ll just do other rodents and they, and I said, what other rodents,
and they said, you pick. So I thought over the next month or two I, I would remember
and actually send a more, more descriptive title, so it ended up in the agenda as other
rodents. So what I decided to uh, pick here, let me find the clicker, to talk about today,
is guinea pigs and hamsters and the reason I picked those is, once you get away from
mice, which is, and Joe or actually you may know, AAALAC’s counted this once, how many
mice are used in research every year? Yeah, I don’t know if it’s tens of millions or hundreds
of millions, but it’s multiples of millions, and then you probably drop down to rats and
maybe it’s in the neighborhood of one or two million, I don’t really know, and then you
get down to the guinea pig and hamsters and they’re significantly smaller numbers, but
they certainly still play important roles in research, so, according to the USDA that
collects this data yearly, and this is data from 2009 and 2010 averaged together, there’s
about, a little over 200,000 guinea pigs used annually in the US and about 150,000 hamsters.
Interestingly when I went back and tried to find more recent data to see if this is still
trending downward or if it’s flat, I, I was gonna ask AWIC later I can’t find that data
anywhere on the web more recently than 2010, so we turn this in annually, I think it’s
2014, so you’d think, 11, 12, or 13 would be floating out there somewhere but I couldn’t
find it. So today we’re gonna review some of the natural environment and behavior of
these guys, and much like Joe pointed out and, and Bernie on the first day, the natural
behavior, the telos, the uh, guinea pigness of a guinea pig. It’s important to understand
that as we look at how we’re gonna house them in the laboratory, how we’re gonna meet those
needs, natural needs or innate needs that they seem to have, that are beneficial. How
to let them control their environment in some fashion and, and, is there data out there
to show that’s actually beneficial for research? Both of these species, there’s certainly not
as much data as Joe just reviewed briefly about the mice, but there’s a little bit.
We’ll talk about a little bit about their social structure and behavior, both in the
wild and laboratory setting, and then, a couple recommendations for laboratory housing. So
we’re gonna start with guinea pigs, if you guys are taxonomists and you’re interested,
the taxonomy is here, Cavia porcellus is the common guinea pig. I’ll give you a little
anecdote here. We, we, Charles River produces both hamsters and guinea pigs in the US and
in Europe we also produce guinea pigs in a facility near Montreal, Canada and roughly
50% of that production in Canada sources down to the US to support biomedical research.
And twice now in the last year and a half, the fish and wildlife at the border has stopped
our trucks and said, you need a wildlife permit to bring a guinea pig into the United States,
and if you look at US fish and wildlife guidelines on what’s a wild animal, a wild animal is
all those sorts of things we think of, tigers and lions and elephants, but it specifically
says white rats are not wild animals, white mice are not wild animals, and white rabbits
as well as sheep and goats and the common livestock. So, occasionally we get border
inspectors that say, wait a minute, I have to adhere to the rule, directly, specifically,
technically, and I can’t use judgment here, so um, we had to get special permits twice
and then they changed their minds twice, so right now we’re in that process again actually
appealing it up through the fish and wildlife service in Washington D.C., asking for an
exemption that guinea pigs really are not wild animals. We’ve pointed out, um, this
made us go back and look at the natural history of the guinea pig. Turns out there’s actually
no free living guinea pigs, Cavia porcellus, anywhere in the world right now. There are
probably one, between one and three strains that were probably the derivative or the origin
of our research and pet guinea pig, but natural free living guinea pigs as we know them here,
um, actually this is a capybara, so they don’t really look like that, but um, do not exist
in the wild. They originated in South America, the Andes, mountainous areas, primarily Peru.
They’ve been domesticated an awfully long time, as early as 5000 B.C. and they were
domesticated primarily as a food source, so they were raised and guinea pig, varieties
of guinea pigs are still raised for food. And guinea pigs have been proposed actually
as a, as a uh, species that under developed areas could raise them, they have a fairly
fast reproductive rate, they produce decent size litters, and they, and they’re a size
that could be a food source. So they’ve actually been talked about as, should they be introduced
to areas where they’re having trouble, having a, um, an easy to raise, small-scale farming
that could produce some meat, a meat source. They were introduced to Europe somewhere in
the neighborhood of 1500, mid-1500s to the early 1600s. There was actually the earliest
dated European guinea pig comes out of a little town in Belgium and with carbon dating they
showed that it was probably a pet in a wealthy household. So it dates back as a pet a couple
hundred years as well. First described in research in the 1700s, and again as we know
the guinea pig there are no free living ones in the wild in the world. So laboratory stocks
and strains they’re all, they have a pretty uniform body, confirmation and size, they
all look very similar, with the difference of coat coloration. The primary guinea pig
used in research are out breds in a particular Hartley or Dunkin-Hartley, and you see the
top pictured here is an albino shorthaired animal, the one down below is a hairless,
euthymic or normal immune system but a hairless guinea pig, those are the two that Charles
River produces. There are other vendors that produce the haired guinea pig also in the
US. There is an NIH outbred, to my knowledge it’s not commercially available, I think there
are one or two academic colonies in the country, so they’re probably available in very small
numbers somewhere but I don’t know where that is. And then there’s inbred strains, strain
2 and strain 13, and again to my knowledge there is no commercial colonies for these,
so they may be available from a small academic or research facility somewhere. So their natural
behavior. Wild cavies are group living animals. They tend to live in small groups, the description
in the literature vary anywhere from 5 to 8 to as many as 15 to 24 but small groups
usually one adult male and one or several females and their unweaned offspring. They’re
described as active both day and night in that they don’t sleep but they nap. I think
in a laboratory setting they are certainly more active during the day than perhaps mice
and rats, um, uh, whether or not they sleep, I don’t know. Uh, they don’t dig burrows,
but they will uh, they, they move, they move through underbrush and tunnels, um, uh, either
created by other game or, or, or that they can create, so that they do hide under structures,
under, under, underbrush and I’ll show you later how, how we’re trying to use that and
we’re investigating that, is it one way to provide them an enriched environment without
giving them a true hut. So they’re born precocious and nearly self-sufficient and actually we
recently did a pilot project to rederive guinea pigs and we simply did C-sections and raised
them without, uh, nursing, and put them on a moist diet at the time of birth. And about
60% survived, so they, they, um, they do not need to nurse, in a commercial setting we
wean them between one and two weeks of age, if you let them wean naturally, it’s somewhere
between 25 and 30 days of age. The females are readily, readily accept fosters of, of,
other females’ pups and so group rearing is certainly possible. Females reach sexual maturity
very early, around 30 days, in males it’s closer to 2 months. And at least in captivity,
mature pups are rarely accepted into domestic groups, but in the wild the males will injure
or kill sons, um, uh, their own sons or unrelated sons as, as they mature. If you guys have
ever worked with guinea pigs or had a child that had a guinea pig in their bedroom, these
guys are vocal. They’re vocal in our auditory range, you certainly know when they’re happy,
sad, upset, it’s, there’s been 11 different calls described for these guys, everything
from a chutt to a chutter to a whine to a purr to a scream, uh, okay my screen just
went black. Touch the screen itself or the keyboard, there we go. Um, It was what I thought
was interesting is they were described as having the first tweet before um, um, uh,
before the internet was, was, was, uh, developed. So it’s a very complex repertoire vocalizations
and in particular between the moms and the pups that if you remove a mom, uh, with the,
with the youngers in the cage, they will emit a very, uh, distress-oriented sound that the
mothers respond to and the mothers can pick out distress sounds of their pups versus distress
sounds of other pups. So it’s certainly very important part of their socialization with,
with each other. It’s been described that their behavioral repertoire really hasn’t
changed much with domestication and that’s from looking at what wild cavies are, are
still uh, running around, uh, the behavioral frequencies of some of those behaviors are
different and in general it’s been described that they’re more sociopositive or less aggressive
towards each other. So by bringing them into captivity and either through selective breeding
or just a captive setting, um, over the years, um, they seem to be a less aggressive in a
breeding, um, in a breeding area there are large rooms where we have, we have thousands
of these cages, breeding groups of animals, fighting is almost unheard of, uh, and I very
rarely hear concerns from research institutions that deal with fighting. So again, social
structure, small groups primarily, five to ten individuals. They will actively seek contact
with one another, they, they, they certainly are a social species. Interesting though when
they’ve, when they’ve either produced large mixed sex colonies or in the wild, within
a large mix-sex colony, they will break off into those, there will still be one dominant
male for the group, but they will develop small groups of, uh, males and females with
subordinate males over those small groups, uh, that can also co-exist within the same
general space, so, um, uh, Joe can comment if mice will do that in those large settings
he described but to me this was, was interesting. I hadn’t seen this described before. And when
in the wild they don’t seem to maintain an exclusive territory. I think they spend a
great deal of time foraging and, and moving about but they’re not as strictly territorial
as perhaps some of the other, some of the other rodents. They do have a complex social
interaction. Each sex has its own linear dominance hierarchy. In the wild, subordinate animals
will retreat or attack when the, primarily when the dominant male is involved. And there’s
a well described repertoire of aggressive behaviors with stand-threats and head-thrusts
and attack, should be attack lunges, um, so much like the other rodents. But the domesticated
guinea pig that we use in research, those aggressive behaviors seem to be dramatically
absent or at least dampened and the primary aggressive behavior we’ll see at least in
our breeding colonies and sometimes in a research setting is hair pulling and, and, ear-nibbling.
Doesn’t usually escalate to frank fighting. And again in mixed groups in the laboratory,
males will form these small harems and it’s been described as a bonding or an attachment
like social bond between the males and the females that can be long lived and fairly
strong and when these familiar partner males are available to the females they’ve also
showed that they can buffet the cortisol responses in the blood to females that are exposed to
novel environments, so it seems to be comforting or, or supportive to uh, to guinea pigs. So
I think that, what drives the message home is that these really are social animals. They
do well with uh, certainly, uh, in the wild and the laboratory. Um, they’re uh, um�
should, should be housed, socially whenever possible. Ear-,early experience, uh, it certainly
matters and there’s, there’s been studies with males, not a great deal with females,
but males reared in isolation, so right after weaning, show aggression when they’re introduce
to other single males, so there’s a, there’s a learning and, and behavioral repertoire
that they learn when they’re with one another as they’re, as they’re, uh, as they’re maturing,
and that, and that affects absent, um, they are more aggressive towards one another, and
when you introduce one of these isolated males into a colonies of multiple um, other guinea
pigs, not only does the male that was raised in isolation suffer and have aggressive behavior
directed toward it, it aggressive towards the others. But there can actually be effects
throughout the, that larger group of animals showing reduced weight loss, and in one publication
described actually death of the animals when you introduce this, this novel or a strange
male into a stable group. Females tend to be more adaptive, so they, and they don’t
tend to, tend to show this um, uh, effect of isolation and then being put into a larger
group or a group of unfamiliar, they seem to adapt readily to it. And this, this graph
over here is simply trying to show that, that isolation, these animals, when you take an
isolated male and drop it into a larger group or expose it to a, um, to another um, male
it hasn’t met before, you will see increases in serum cortisol. In addition to the aggression.
Guinea pigs don’t handle novelty well, but they also seem to be easily startled or threatened
by both novelty noise and in one of our facilities where we use quite a few guinea pigs, we were
having guinea pigs that were stampeding and injuring each other’s people, walk by as a
stranger such as myself, if I go in the room as the vet, in my white jacket, they would
freak out and run around the cage and stampede, when the normal husbandry staff came in, they
were fairly calm. So we actually ended up putting up what we call visual barriers so
that as I walked down the hallway and they saw my flash of white, uh, the guinea pigs
wouldn’t react and stayed calmer based on observational studies that we performed in
the room. They really have two reactions when they’re startled or threatened and it’s either
to freeze which sounds just like you’d expect, they hold still. Or stampede, and this stampede
is really the more worrisome in a research setting. It can certainly cause trauma to
themselves, especially if you’re on a wire-bottom flooring caging system, such as a tox setting.
They can entrap limbs in that wire floor and injure themselves. They can trample young
and end up killing young. Years ago we bred animals at a higher density than we do now,
and one of the reason we’ve reduced the uh, the density is we were having trampling of
animals and the young were suffering in these cages and when we dropped, simply pulled one
female guinea pig out of the group housed breeding cage, uh, our infant mortality or
neonatal mortality essentially went to zero. So it was as simple as one too many animals
in this, in this, um, uh, relatively large group cage. And it’s been described to lead
to abortions in pregnant sows. One way to combat that is certainly provide them with
shelter and they will retreat into a shelter, uh, if it’s provided. So as Joe pointed out
earlier, you really can’t talk about social housing as an isolated, uh, parameter when
we’re talking about any of the species that we’re dealing with. You have to look at the
overall cage or living environment and for guinea pigs, shelters are very important.
In the wild, they run under underbrush, they follow tunnels under underbrush to stay away
from predation, um, stay out of view. If you provide guinea pigs a shelter and actually
these guinea pigs that we, um, perform cesarean rederivations on, at, um, several hours old,
we put in an inverted mouse cage in a large group cage with the sides cut off so it was
more like a garage where they could enter and leave, and that age they were migrating
into the shelter, so it’s certainly very strong natural draw they have. Um, they don’t dig
so giving them nesting material, they may burrow into or push under it, but they won’t
build a nest, they won’t build a tunnel through that material. They will use burrows excavated
by other animals, which is hard to mimic in a research setting but in the wild they will.
So certainly it’s important to provide these guys with some kind of shelter, some kind
of protection from, um, and their, I guess, native behavior, some kind of, some kind of
protection from predation. So there have been studies that have showed the benefits of shelters,
it’s not just a common sense, there’s some data behind all this that if you provide paired
guinea pigs with a hut it lowers daily fecal cortisol concentrations, um, and, if you compare
types of shelters, I know it’s, uh, there are uh, the top picture here is a through
and through shelter so the animal can enter one side and leave the other, and at least
there’s some evidence that suggests maybe they like a one way tunnel where they come
in and back, back out or turn around and come back out versus a through and through tunnel.
So the recommendation here I think is pretty simple. We should socially house whenever
possible. If you do need to isolate guinea pigs, especially if you’re gonna isolate guinea
pigs right after birth, you’re probably gonna change their behavior repertoire later on
when they’re introduced to others, certainly males. And certainly from a commercial standpoint
we raise them as groups so they’re coming in pre-conditioned to being group housed,
and that’s certainly gonna be the uh, the um, setting that they would probably prefer
in a, in a research setting. But we also have to remember that the overall housing environment
is also important. You should provide some kind of a solid floor with bedding, it’s gonna
minimize, uh, limb injuries, photodermititis, broken, broken legs which still occur in tox
settings. Provide some, some kind of shelter or hut, and if possible, put them in a low
traffic, low noise area. They do startle, they can become accustomed to noises. We actually
um, uh, will play radios in the housing rooms during the light time when the uh, staff members
are in there and we’ve seen that if the radio breaks for some reason and we haven’t replaced
it yet, the general excitability of the animals goes up when there’s not that background level
of, of low noise going on. This picture here was to show something that um, I think is,
this is um, when you look at their native behavior in the wild, they like to hide under
things. Bushes, brush, etcetera. This is one of our large breeding pends, so this is in
one of our commercial breeding rooms, and it’s a large bedded cage with a group of females
and a male, and a feed hopper over here. It’s very difficult to put a tunnel in there, or
a tunnel, a hut that can accommodate all those guinea pigs. So we wondered, well can we just
give them a shade, a sun awning. If in the wild they will retreat under things because
that gives them comfort or, or protection, is it as simple as doing that in a large cage?
And that’s what you’re seeing here is a black piece of um, rigid plastic laid over the cage
and we have actually observational studies that will be published soon, uh, showing that
they will spend a great deal of their time under this, under this shadow area, or under
cover. So in our, and we haven’t adopted this across the board yet but if this looks like
a way that we can meet their need to provide some kind of shelter without putting a shelter
in every one of these cages. The problem with a shelter in every one of these cages. You
see this little food hopper back here, some of these guinea pigs, there’s not very many,
the young ones can use this food hopper as a launch pad, squeeze through those bars,
jump up on the cage and they go shooting across the room on top of the cages, and so anything
we put in there as a launch pad just gives them a stepping stone to get out of the cage,
and we’d have to modify several thousand cage tops with more bars, whereas something as
simple as this may suffice to give them a shelter and um, and, and give them that behavioral
need without uh, just giving them all ladders to escape and run around the room. And of
course the day they do that is typically when the USDA inspector is on site, which happened
once a couple years ago so it was, I thought it was pretty funny. The plant manager wasn’t
so, uh, didn’t find it so humorous. And actually I think to the USDA’s credit, they were, they
certainly understood what was going on, it was the first time in 30 years they’ve ever
seen it, it wasn’t written up as an issue, but we certainly found it funny. Alright.
So we’re gonna move to hamsters. Any of you ever seen this? I saw it last week just surfing
the web. So back in the, in the 40’s when hamsters became um, a more common pet in North
America, this was a little company down in Alabama that, that put this ad out in Mechanics
Illustrated, probably other publications as well. Well there was a, um, teenager, and
I don’t know where he’s from, that purchased six of these and set them up as a breeding
colony. He worked for the local A&P. After about two years he quit his job at the A&P
and the local manager for the store said I’m gonna keep your job open because this hamster
thing is never gonna work. Well he ended up turning this little hamster colony into a
colony that he sold to Harlan um, at one point, and this, this was the origin of the Harlan
hamster colony, uh, I don’t know when they bought it but I think he did just fine for
himself. He actually, he and his two brothers ended up running this colony and ultimately
selling it to a commercial vendor, so. Uh, I just think it’s funny, it talks about they’re,
they’re cute, they’re cuddly, they’re delightful. If you pick up any pet, any book on hamsters,
at Amazon or any lab animal on text in hamsters, within the first couple of sentences it will
say they’re aggressive and they bite and so this is what we decided was the great pet
for our, for our kids. So they certainly are a rodent, um. The Syrian golden hamster, the
one that we commonly use in research is Mesocricetus auratus, the picture here. There are a number
of other hamsters, I’ll show you pictures in a moment, um, that you’ll certainly see
in pet stores and that are used in research in smaller numbers. So laboratory hamsters
are believed to have originated from a single group of four litter mates that were imported
into the US in the 1930s. I can’t find evidence that there were subsequent infusions, it’s
hard to imagine there wasn’t over, over those years, but if this is literally true, then
it certainly tells us there was a bottleneck in their genetics at some point. They’re considered
an outbred now and they’re maintained as an outbred, but if they really came down to one
litter of four individuals, they’re probably not as diverse as their wild counterparts
would, counterparts would be. These are some of the other hamsters you’ll see in research
once in a while, the European hamster, the Chinese hamster and the Siberian hamster.
And if you go to Petco and wander the isle you’ll see all sorts of these pet, or fancy
hamsters that are usually just described as being derivatives of the Syrian hamster. So
their natural environment is an arid dry area, Syria, um, the rocky plains and light vegetation
with very sparse resources. Although this is, this is about social housing and we often
house these guys socially, in, in nature these guys live in burrows as solitary animals.
Males have their burrow, females have their burrow and when the two meet they fight. Um,
they’re more omnivorous in the wild than, than uh, we treat them in captivity. They’ll
eat insects, um, fruit as well as, you know grains and plant roots. This is kind of interesting
that in, in, in a lab, most of us would describe them as nocturnal. They’re active during,
during the dark cycle. Studies that look at them out in the wild describe them as either
diurnal or crepuscular in the wild so we certainly have changed their, at least their activity,
um, budget by bringing them into the laboratory. And something that I don’t fully understand
is that they tell you to approach with caution a sleeping hamster during the light cycle.
I can’t imagine that if I’m a 1500 gram animal and someone picks my cage up, pulls it out
of the rack, puts it on a table and then opens the top, I’ve probably woken up. But, every
text out there says, when they’re sleeping, don’t bother them. I don’t know how you don’t
not bother them if you have to do something with them. I don’t think they’re as, as, as
aggressive if you’re, if you’re, if you’re, if you’re um, not overly aggressive with handling
them. There’s ways to pick them up so you don’t have to cup them in your hands necessarily,
but they’re always described as being this very aggressive, difficult to deal with animal.
And I know in our setting where we use relatively large groups of hamsters, bite wounds with
the hamsters are extremely unusual, so it’s probably a combination of acclimation of the
staff on how to work with them and acclimation of the animals to the setting. Unlike the
guinea pig, these guys do live in burrows, they’re very fastidious and if you’ve worked
with hamsters for long, you’ll notice in the cage there’s usually an area where they horde
the food in one corner. If you give them nesting material they build a nest in another corner
and often the predominant amount of feces and urine is in a third spot. And this is
their native behavior in the wild, they’ll usually have a, a burrow with multiple, um,
sections or sub-burrows where they’ll devote one to defecation and urination or the toilet
area, another one for food storage and then one where they nest and sleep. Again they
are solitary in the wild, females, there’s one female and her litter. And the males live
alone, um, almost exclusively with the exception of the, of the brief interactions when they
mate. And they will hibernate when temperatures drop, drop low enough. Woops. Hit that too
many times. So communication, they may be a solitary animal but certainly they need
to communicate with each other and scent is one communication means for them. This picture
on the top is showing you the uh, flank scent gland and then there’s a ventral scent gland
on the belly as well. We occasionally get calls from clients that order these that aren’t
familiar with them and they’ll report that they have tumors on their flanks and tumors
on their abdomens. Uh, they’re not tumors, they’re a natural scent marking gland so don’t
be surprised if you see them. In males the ventral gland gets quite, um, uh, enlarged,
uh, as the animals go into sexual maturity. And this, the use of scent is, is as important
as the hamster as it’s been described with uh, with mice. It’s used, um, they, they can
leave scent both in urine and feces and these, and these glandular secretions, and it, it
communicates things like dominance rank, territory resource marking, uh, the females will um,
they have a vaginal discharge that also has a scent to it and that will identify to males
that the female is receptive and willing to mate. It’s used as territorial marking, especially
the flank gland. Communication and vocal communication is also important and what’s important to
remember here is these guys vocalize or communicate at a, at a level, at a frequency well above
our usual ability to hear. And what this is showing, this is the hamster here and if you
look at this as human, um, human hearing range and the dark bar is what can, is soft noises
that can be detected so you, and if really loud noises, your frequency grows in both
directions. So we stop, um, we overlap with the hamster a little bit. As we age, this
side of the bar starts shrinking back. So these guys, they’ll certainly make noises
that we can hear, fighting, that sort of thing, but there’s probably lots of ultrasonic communications
going on that we have no, um, no easy way to understand or even measure, unless you’re
in there with some kind of a measuring device that can get up into the ultrasonic frequencies.
It’s certainly surrounding mating behavior. They are ultrasonic range in this 32 to 42
kilohertz, there’s ultrasonic vocalizations going on and these vocalizations seem to both
influence both the male and, and the female, as well as odor and estrous cycle. Um, and
somehow facilitate mating, so. Much like the other rodents we work with, we need to remember
the guinea pig, much of, although, it, they certainly emit noises above what we can commonly
hear, we certainly are, very rich repertoire that we can hear. These guys probably have
a somewhat rich repertoire that we have no easy way to understand or, or ascertain. And
its social interactions, these guys fight. Everything you pick up talks about their fighting,
their territorial behavior. They come together for a couple of reasons, fighting over territory
or mating as adults. The females attract the mates by leaving this vaginal scent trail
when they’re fertile. If males try to interact with the female when they’re not in this fertile
state, the females will fight and sometimes fight to the point of killing the male. They’re
receptive to the uh, male, for about a week period and they show the classic lordosis
um, right around estrous. And interesting, at least in the wild, following mating, the
female will chase the male from her nest, retrieve his food and take it. So� um, we
don’t see that in commercial breeding area, but again, uh, I think the cage is small enough,
there’s, there’s not two dens to worry about, but, um, it’s a pretty aggressive behavior.
There are social interactions prior to sexual maturity so the adolescents will play fight,
right around 15 days of age and this peaks out around 35-40 days of age, and its things
like tumbling and pinning without establishment of dominance, without actful damage or injury
to each other. And then this tends to decrease as they get older than roughly 40 days and
they reach sexual maturity in that neighborhood of 40-50 days and at that point, uh, it can
transition over to actual fighting. Particularly if you mix males that haven’t been around
each other. So this is where it becomes confusing. It’s that hamsters are certainly aggressive.
There are studies out there that have looked at co-housing of hamsters, both those that
have been isolated prior and those that have been group housed all along, and up to 40%
of group housed hamsters show some degree of evidence of fighting in, in at least this
one study. Sorry, I lost my screen again. Certainly female hamsters become aggressive
at puberty, both towards females and certainly towards males and separation may be necessary
if you’re co-housing them. And in, in forced group housing of adult females has shown to
result in, in increased heart rate, core body temperature, activity in the adrenal grand,
weight. So there’s certainly, um, they certainly may be intolerant depending on probably their
early experiences on how they handle group interactions as they mature. But despite being
a solitary species in the wild, and despite being aggressive and they do fight, most laboratory
hamsters are group housed. For anyone in here that has hamsters, do you group house them?
Someone, yep, I see a couple hands go up. We certainly do in our research settings and
we certainly do in our, in our breeding setting. And it appears that prior experience can be
really important in hamster behavior as it relates to social housing. And when given
a choice, hamsters have shown preference for social housing, so this has been shown a couple
different ways and I’ve highlighted one here. If you take animals at weaning and either
isolate them or group house them, group housed male hamsters will spend more time in social
proximity or social contact than singly housed hamsters. 71% of their awake time, they’ll
be in close proximity to other hamsters and 100% of their sleeping time in this particular
study, but even singly housed hamsters that are isolated at weaning, if you provide them
the opportunity, and these were cages that were connected with tunnel arrangements so
the animals could get closer to one another if they wished, 50% of the awake time, hamsters,
animals were in close proximity to, um, hamsters they hadn’t met before. It dropped down a
little bit about sleeping but roughly 47%, so we’re looking at about 50% of the time
they would at least seek out close proximity to other hamsters even if they were raised
in isolation. And there’s been some work that shows socially housed hamsters show submissive
behavior at closer proximity, so their, their tolerance of another strange male seems to
be improved, uh, if they’re, if they’re group-housed from, from weaning. And the commercial breeders,
house hamsters in same-sex groups post-weaning, so when you order hamsters, you receive hamsters,
you’re receiving preconditioned hamsters that have been in a group setting, so they should
be amendable to group housing at your end if they’re, if they’re kept in stable groups.
So the recommendations are pretty simple. Young, young litter mates can and should be
housed together. We certainly do that in a commercial breeding setting and we certainly
do it in our research settings as well at Charles River. Group housing of adult animals
is generally successful, again if you bring them in as, as, uh, as, preconditioned groups
where they’re used to one another, they know each other, it can be successful. But certainly
mixing strange, meaning novel or unknown sexually mature hamsters with one another, uh, certainly
raises the risk of fighting, can lead to fighting and those guys probably need separation if
you see aggression. And just like the guinea pig and mice earlier that Joe talked about,
the rest of the environment is as important as the social, as the social setting that,
that we have them in. Preference testing in hamsters has showed that they prefer solid
floors with bedding over slotted or wire-bottom floors. I don’t think many of us would have
issue with that. You should provide cage on the, food on the cage floor for hamsters,
and actually the USDA regulations specifically say hamsters can be fed on the cage floor,
and that’s really for two reasons. It allows them to, to um, perform this hording behavior,
so they can move food around and congregate it in one part of the cage, and depending
on the wire bar lid you have, the wire bars can be too thin, and the animals with their
broad snout can actually have trouble eating from the wire bar lid, and it’s been documented
to show weight loss, um, and even death. So feeding on the cage floor is an excellent
idea. And then provide nesting material. They will nest, it’s a hording material, they’ll
interact with it. It’s beneficial for thermal regulation and um, uh, I think from a thermal
regulation in your study endpoint data, it’s certainly important and as Joe pointed out
earlier, we’re housing these guys in an environment that’s much colder than, than their thermal
neutral zone and certainly much colder than their natural habitat and nesting materials
is one way to address that. So I feel a little deficient. I didn’t have nice videos for you,
but um, um, I think guinea pigs, it’s, it’s really pretty simple. Why would we not socially
house them? The hamster literature is a little more confusing. Several of those references
I provided, and if you’re interested, um, uh, I’m happy to share this with you and I
have hamsters, or hamsters and guinea pig references here, several of the references
that talk about social housing, group housing, and isolation, and the downstream effects
of that, make recommendations that we really should only singly house these guys and um,
I don’t think the industry has listened to that, I also think there’s enough evidence
out there both, both seat of the pants evidence that we’ve learned by doing it, as well as
what a few studies have looked at that socially housing of hamsters is fine if we do it correctly,
um, do it in a way where the hamsters have an ability to have a stable group. The cage
should be large enough that if they wanna retreat from one another, they can. We’ve,
you can certainly keep bonded breeding pairs together for prolonged periods of time. The
female will occasionally go after the, after the male, after she’s mated. But we’ve had
success in experimental settings with keeping them together for multiple litters. The literature
would argue that that’s not possible but it certainly is possible. If you have a management
program to identify when aggression occurs and separate them if you need.

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