A common post I often see on social media is,
“I have a small baby in this litter, could it be a dwarf?”
Most likely not. If the baby has always been small, hitting all the milestones as it’s litter mates, such as pigment showing around same day and eyes opening, you most likely have a runt on your hands. Often a dwarf rat will not slow down in growth until around weeks 3 - 4 in an average litter. (It was recently brought to my attention by someone that had a smaller litter that their difference was more obvious much earlier.) Sometimes you won’t notice a runt until the first week passes. Sometimes there are more than one in a litter. Runts will often catch up to their litter mates by weeks 9-12. However, if you have a little one that is skinnier than it's litter mates, lagging, not hitting their milestones, you may have FTT (Failure to Thrive also known as 'ill thrift' by veterinarians.) They are often very skinny and weak; not able to absorb all the nutrients needed to meet those milestones. Most often FTT will not survive into adulthood. Either the mother will push them out of the nest, sensing something not right, or they will pass on their own before 2 weeks. There are exceptions, my 939 gram boy, CRUS Bennet, being one of them. He was FTT, ½ the size of his siblings and too weak to be able to push them off so he could nurse. If his breeder didn't make sure he latched on and supplemented him with extra formula he most likely would have never survived past 2 weeks. He was one of my biggest boys and lived to just shy of his 2nd birthday.
As with CRUS Bennet (mentioned above), I have become known as 'The Collector of Runts'. I have a soft spot for the lil guy in a litter. This is simply as a pet lover, not a breeder. Wanting to keep runts or adopt runts from others, fills up the mischief rather quickly. This limits my space so I am not able to work with all the varieties I want. Often a breeder will have what they call a 'bucket list' of rats they would like to someday work with. My list of those that I would like to someday have would include: Harvel, Roan, Whiteside, & Rex. I also love a beautiful Self rat. (All one color). I am trying to get the pigment of my lines all the way down to their toes. There will sometimes be an odd recessive blaze, or variegated popping up, keeping the litters even more entertaining. The most recent marking surprise in a litter happened at the end of last year, in the 2016 Winter All Science Litter, appearing at 4 ½ weeks. OCRA Inertia was our very first Himalayan and OCRA Tesla ended up being a beautiful Burmese! Up until she showed up, I had never even seen a Burmese. WOW! I must say, my favorite look for sure. Currently we are working with Standard & Satin coats in Burmese, Himalayan, Siamese, Mink, Russian Blue, Agouti, Blue, Chocolate, Black and all of their dilutes. I also loved our pets that were Hairless and enjoy the Drex but do not want to work with those as a breeder. Hairless often have lactation issues that would mean doubling up on my breeding so I would need a foster mother for the babies. With my 2 Drex rats that I love as pets, I have found a lot of issues such as the eyelashes growing wrong and extra pory due to the irritation. The constant shedding from coarse broken hairs also drives me batty but they are worth it. I love them dearly.
Study of growth hormone in spontaneous dwarf rat
Great pictures for comparison
More information on dwarf rats
Below are a few interesting things I have found online about overweight babies and basic litter size. (Warning some of the scientific studies can get graphic in their descriptions of their testing and how they cull) Often in scientific studies they will want to have same numbers of offspring and equal sex ratio to help them get to the outcomes for their studies. As a pet breeder I do not see the necessity to do this. Though I love a squishy fat baby, I do not want to simply focus on having equal sized litters to have the fat babies but rather overall healthy babies thinking of the long term health of the rat.
- Long-term effect of early postnatal overnutrition on insulin resistance and serum fatty acid profiles in male rats
- Developmental programming in skeletal muscle in response to overnourishment in the immediate postnatal life in rats
- Increase of Long-Term ‘Diabesity’ Risk, in Neonatally Overnourished ‘Small-For-Gestational-Age’ (SGA) Rats
- This one says though weight smaller in larger litters the brain development was greater in the larger litters than small