I've noticed that in some maternal separation papers, it is specified whether rat pups are cross fostered at birth, while in others it is not mentioned. Is cross fostering important when examining early life stressors in later life behaviours? If it is, can anyone provide me with some tips for successful cross-fostering?
Thanks!
Hi Sarah,
I’m not an expert in maternal separation but I think it would depend on the question you’re asking. In genetic studies, for example, cross-fostering to uniform genotype mothers is vital, because otherwise any results may be due to maternal effects.
I’ve done cross-fostering in mice, but the principles will be the same. I found the best way was to remove the two mothers from their nests, remove the pups from the nests (weighing/sexing/marking/etc them depending on your needs), change gloves (to avoid the ‘wrong’ mother’s smell), take some of the bedding material from the nest the pups are going into and put it in the palm of your hand, put the pups on top of it, cover them with more of the bedding material from the nest, and gently rock them back and forth. This helps to get them smelling as much as possible like their new mother, and helps to avoid her cannibalising the pups. Put the bedding material and the pups back in the nest, then reintroduce the mother. Change gloves and repeat for the other direction of fostering. We then tried to give the mothers minimal disturbance for the next ~6 days (e.g. not changing cages), as again, stress can cause her to cannibalising the pups.
Also, remember to keep the pups warm while they are away from the mother, we had a heated mat that we put their container on. Apart from that, just general animal handling things, e.g. having everything set up so you can do it as quickly and quietly as possible.
Hope that helps,
David
Hello Sarah,
manipulations in post-natal environment are able to produce long term effects on behavior and its underlying circuits, and among these critical different experimental procedures there is cross fostering.
If you aim to foster pups with mother appertaining to different strain, I think you should evaluate differences in maternal behavior (both quantity and quality) also at the moment of reunification of mother-pup dyad, that has been indicated to be a key element in influencing mother-pups bond (in different procedures, like maternal separation and social isolation) and thus produce long lasting effects on pups.
Moreover the life period when you decide to apply this manipulation it should depend on what you aim to model in your pre-clinical study.
Finally be careful in producing your Control groups, as puzzling results are derived from handling procedures.
Hope I have been helpful to you
Best whishes,
Matteo
Hello Sarah
I can only confirm what Mattep and David wrote. It is important for the reasons they give but also to get to uniform litter sizes. Normally those will vary from 5-14 and this will certainly affect eg body weight development and behaviour.
One other point that Matteo also mentioned: be sure how to treat your control group. I would recommend not to handle them too much and potentially reduce the cage cleaning to a minimum as well as keeping those at a really isolated place.
Best regards
Thomas
I learned from Harry Broadhurst that cross-fostering was vital for the studies of classical genetics such as development of the Maudsley reactive and non-reactive rats. The main disadvantage was the amount of time and grant money needed to do the extra work. Although I did not engage in genetic studies myself the cross-fostering control was also important for studies of manipulations of maternal history by prenatal exposure to drugs. It was at that point that I realised that countless numbers of studies refer to strain differences in rats without cross-fostering controls and cannot therefore be interpreted as establishing genetic effects. Most people don't seem aware of that. It seems to cast doubt on many studies of genetically manipulated animals (e.g. knock-outs and knock-ins) where cross-fostering appears to be very rarely done. Do the others who have responded to you question agree? If I am right then it is a matter that deserves a public airing.
Thank you everyone for your responses! And thank you David for your cross fostering pointers, I will definitely be applying them when it comes time for me to run the maternal separation study!
Hi Sarah J Baracz ,
I have been practiced what David Ashbrook explained nicely. It works.
Thank you,
Good luck
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