Ratty Corner

What am I Breeding Towards?

Happy, healthy rats!


This is the temperament bit. I've realised that although I love a rat who will come and settle on my lap, the ones I love best are those that are happy to say hi and have a little fuss but have more interesting things to do; the rats that get into mischief and make me laugh; the ones that are nosy and get into scrapes. So that's what I aim to reproduce. Um. Naughty rats? Bold, inquisitive, cheeky, friendly rats.


It goes without saying, doesn't it? OK, I'll say it anyway. I'm not expecting my rats never to have a day of illness because sometimes infections happen, but I am expecting them to recover quickly and completely from any infection, not to have any chronic illness, not to get tumours at a young age nor have parents with tumours at a young age, and not to have repeated attacks of respiratory problems. Unfortunately I've not arrived at this goal yet, so although we're finding a very low incidence of mammary tumours there are still some rats in each generation who go on to suffer from chronic respiratory disease.

Long Lived

The tricky one. I'd really like to make a difference here too, but this is definitely a work in progress as it takes a ratty lifetime to see the results. It will be interesting to see if the Essex markings have an effect on the lifespan, and an interesting ethical dilemma for me if they do. I'm also getting British Blues popping up at the moment, which are stunning in Essex markings but the colour does have a small effect on lifespan and I don't plan to intentionally continue it. Having said that, I've bred from a blue agouti Essex girl, Blythe, in spring 2009 because she had the best temperament of herself and her sisters. So difficult to balance everything.

There's also the nature vs nurture question. Studies have shown that having a diet 80% of the volume of a free-feeding diet can help to extend lifespan. I have begun restricting the feeding of my rats to prevent obesity, but am reluctant to restrict their food to a great extent as they enjoy their food so much. I am currently allowing a dry mix base of 20g per day for bucks and 17g per day for does, with adjustment judged by the weight and condition of the rats. This is in addition to their fruit and/or veg daily. Their food is scattered into the cage litter to promote natural foraging behaviour. At the moment this is having positive results, with no obese rats and only two or three chunkies in a population of 37, and no visibly underweight rats. My rats have half an hour of freerange for each group (more would be ideal, but there are usually six or seven groups), and those groups which show willing have wheels installed. This allows opportunity for exercise which also extends lifespan. Food restriction and exercise are, of course, a nurture advantage so would not be expected to pass down to future generations, unless I can count on an epigenetic effect:
"an epigenetic trait is a stably inherited phenotype resulting from changes in a chromosome without alterations in the DNA sequence." Science Daily
Brilliant video on YouTube: The Ghost in Your Genes

There is also research which concludes that neophilic rats, ie those which enjoy new experience, have longer lives than neophobic rats. The question is whether this can be worked backwards so that breeding for neophilic rats will extend the lifespan generation by generation, or whether neophobia/neophilia is an on/off condition. I'm planning to make neophilia a major selection point for my breeding rats in the hope that this will show lifespan benefits. I'm also planning to select for rats that remain active and trim as they age.

Rats which grow and mature slowly tend to have longer lifespans. Because of this I am trying to stop myself automatically selecting larger rats over smaller ones. I also intend to push back my breeding age for does and accept those who will not breed at an older age as casualties of my selection methods, and to breed second litters some months later from does who have a successful first litter. In this way I hope to reduce selection for faster maturing rats and increase selection for more slowly maturing rats with longer fertility and lifespan. This may or may not impact on the suitability of my rats for showing, but that's less important to me than encouraging my furry friends to stick around for longer. It's a good excuse to keep more rats from each litter; how can I select if I don't have a choice to breed from?

Is this all going to show results? I don't know. It could all go completely pearshaped. Maybe I'm just crazy and have the wrong viewpoint. We'll have to wait and see. You have my thanks if you're willing to come along with me for the ride and ask for my kittens.

Colours, Markings and Coat Type

I began with the plan to breed for Essex markings in four main colours, agouti, cinnamon, mink and black. My main focus is on the Essex gene, simply because it makes the most beautiful rats I've ever seen. I'd like to always pick the best marked for breeding, but if there's a compromise to be made it will be on markings and colour rather than on temperament, health and lifespan.


In my fourth and fifth litters which were my first inbred matings, the Russian blue gene from my foundation doe, Kitty, reappeared. I was completely and utterly bowled over by the Russian blue kittens' looks, type and personalities, so much that I changed my plan to keep mink and cinnamon from the litter and switched my attention to the Russian blue and Russian blue agouti. This isn't a point of no return, as I still have the option to switch back later if this doesn't work out.

Russian blueRussian blue agouti

I am no longer planning to breed rex coated rats, as I don't feel completely comfortable with passing on the temperament of my inital rex buck and have not bred down from his litter. His sons are much better, but still have their moments.

The Essex Variety Standard

"To be recognised in any standard colour, remembering that the effect of the gene responsible is to lighten the top colour. The darkest area is along the spine, becoming less intense down the sides of the animal. The gradual fading of colour continues onto the belly which is off white, with no spotting of darker colour. When viewed from above, the fading effect should be symmetrical, having no clear demarcation. The fading effect also to be seen on the legs so that the feet are also off white. There should be no obvious patches of contrasting colour. Pied tails not to be penalised. A head spot or blaze is essential; this must be well defined, centrally placed on the forehead and symmetrical." Marked Varieties, NFRS

The Essex Gene

The present day Essex marking was discovered in a pet shop in 1996, the rats being called 'Roberts' after the first rat bred for this marking. It is now known by the name of the county in which it appeared. The gene sits on the hooded locus, so is known as Hro. It is dominant and thought to be a lethal homozygous version of the gene (allele), which means that all surviving Essex rats are heterozygous, Hro/H, with homozygous Essex being reabsorbed in the uterus.

In plain English this means that any rat with one copy of the Essex allele (and no other markings to complicate things) will be Essex. Essex rats all have one copy of the allele for Essex markings and one copy of a non-Essex allele, because any that had two Essex alleles would not be born. Essex litters are always expected to give a mixture of Essex and non-Essex rats. My litters to date have been bred from one Essex and one unmarked parent, but I haven't discounted using two Essexes as a way of producing smaller litters. I just need to be absolutely sure first that it wouldn't cause any welfare issues.

Brandywine Essexes

Because I've been selecting strongly for the temperament I prefer and for health, I managed to lose the show quality Essex markings for a while. The Barnaby x Blythe mating had some does with nice markings, but I've not bred down from that litter due to health issues in their ancestors. On the other side I bred down from Sherbourne who was far from well marked but a very nice buck, and to my delight after a couple of generations the 'to standard' markings made a reappearance.


Pro-rata (NFRS club magazine) issue 99, May/June 1997 - The Robert gene by Sheila Sowter
Pro-rata (NFRS club magazine) issue 117, May/June 2000 - Essex rats by Joanna Holmes and Anne Foster
Rat-A-2-E (MRC club magazine) issue 30, Feb/Mar 2006 - The Varieties by Graham Mobbs

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Last modified: Saturday, 18-Oct-2014 19:02:32 BST

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