Here is my take on this subject.
I now have 3 deppei and one jani, and every breeder I have purchased from have all said the same things, in one way or another, when I asked this same question about growth rates in deppei. While some deppei may grow " normal " compared to other pines, some may take up to at least 5 years to be full or mature adults. Sometimes they can have the potential to be slow growers. Not all of course, but some can.
Deppei are also prone to regurge, especially in the first year, and they like to be in cooler temps. Food items should be smaller than say what you would feed a bull or bigger pine. I was told by many breeders that they fed their baby deppei not every 7 days but every 8 or 9 or even 10 days in their first year, due to them being prone to regurge. I lost my first deppei due to a powerful regurge. After that, the next one I got, which was the most beautiful baby deppei I had seen to date, as it was born with its' adult colors, I made sure that I would not feed it anything I felt would be too big. Looking back, I probably was a little TOO careful, but nevertheless, the snake seems fine, eats great, does grow, but I am also experiencing slow growth in him as well. He is four years old, and is at least 3 1/2 feet. Right now, I am experiencing somewhat of a good growth spurt with him though, as he sheds more frequently than some others, and is growing steadily now. But like yourself, I did experience slow growth the first few years with him. Now, whether that was my doing in feeding smaller meals or him just being a slow grower, I am not sure, but I just have to also go by what I was told by those with more experience than myself with deppei. My two year old hypo deppei is the same size as yours as well, being at least 2 1/2 feet.
One thing you have to remember is that each snake is an individual, and that plays a part in its' individual growth. Some deppei will grow fast, and some, like our examples, do grow slower.
Also, another thing that may play an important part in the size and growth factor of deppei is this one simple thing, and that is the size they are when they are born. In my experience with checking out babies at shows, and from what breeders have told me, most of the time, baby deppei are smaller than other pits, like northern or southern pines, Tx. bulls, etc., when they are born. In that aspect, if they are smaller at birth, the possibility of them taking longer to get the same size as other pits may be a real factor. To me, that only makes sense.
Now, whether or not if they are slow growers or if they didn't grow a lot in their first few years, and if that makes a difference in them reaching breeding size in the future, my first thought would be no, it shouldn't make a difference, but I honestly could be wrong, as again, snakes are individuals. I have had great success though in buying or receiving, for example, older adult pits, and having them grow significantly more after receiving them. One example, my hypo northern pine, was 4 1/2 feet when I got him, and very stocky. He was, I believe, 4-5 years old ( Meltzer, correct me if I am wrong! ) when I got him, and he is now at least 6 feet. Same with my white bull. He was four feet when I got him, and now is between 6 and 7 feet.
So, that is my take, and I hope this helps! Anyone else that has deppei or breeds deppei, please chime in!! I love learning about them!!
Billy
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Genesis 1:1