A lot of uneaten dropped pellets

[Nik Hayes]

Hey y'all,

I'm doing Free Feeding with overnight fasted mice and there tend to be quite a few pellets laying around on the ground after about an hour with the Fed3's, which might hinder nuanced measurements of food intake. I'm using grain pellets. I tried increasing the TimeOut to 5seconds and 10seconds but there were still a lot of pellets laying around on the ground with most of my mice. One idea I had was to introduce one required nose poke to get a pellet so that maybe they stop lazily poking for the new pellets. My PI's concern was that it might introduce too much of a "learned" component into the foraging but I feel like normal feeding also requires learning -- I guess the pellet is not hidden in that case though.

[Lex]

Hi Nik!  How many pellets is a lot? 

We call this behavior of taking pellets without eating them "hoarding", and it seems to be something that some mice do with free feeding sessions on FED3. In our hands ~10% of mice hoard, so it's something to keep an eye on but not super common.  It's interesting because it is a mouse dependent trait - hoarders hoard, non-hoarders don't.

However we have noted that switching hoarders to FR1 (as you suggest) abolishes the hoarding behavior. I've always thought that was interesting from a feeding perspective.  So I'd recommend trying that.  Please post back what happens if you try it!

Another idea is to use "iso-pad" bedding, which are white pads.  This let's you more accurately see (and quantify) hoarded pellets vs consumed pellets.  

On Mon, Oct 3, 2022, 10:39 AM Nik Hayes <nikolash...@u.northwestern.edu> wrote:

Hey y'all,

I'm doing Free Feeding with overnight fasted mice and there tend to be quite a few pellets laying around on the ground after about an hour with the Fed3's, which might hinder nuanced measurements of food intake. I'm using grain pellets. I tried increasing the TimeOut to 5seconds and 10seconds but there were still a lot of pellets laying around on the ground with most of my mice. One idea I had was to introduce one required nose poke to get a pellet so that maybe they stop lazily poking for the new pellets. My PI's concern was that it might introduce too much of a "learned" component into the foraging but I feel like normal feeding also requires learning -- I guess the pellet is not hidden in that case though.

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[Ames Sutton]

Hi all,

As Lex suggested, we use iso-pad bedding and this allows us to count the pellets that mice "hoard." We have a similar percentage breakdown as Lex indicated of those that hoard, though sometimes with food restriction time limits this increases (e.g. some mice learn that they should hoard so that they can have food later - I find it so cool and annoying at the same time!).

I agree it's a huge caveat. In the future I've considered using some wire mesh where the FED is so that the mice can't hoard directly below the FED, but we haven't tried that yet.

Ames

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[Nikolas Hayes]

Sorry for the late reply. I was using a poor man's version of iso bedding before and just used a few paper towels :). It looks like 7/7 mice hoarded after an overnight fast. The feeding period was roughly 1.5 hours and mice that I typically measure food from in this area eat about 600mg to 800mg of normal pellets in 2 hours (when I do our manual method of putting a chow pellet on the wire rack and measuring manually every 15min). We're using Bio-Serv Dustless Precision Pellets Rodent Grain-Based DIet 20mg with the Fed3's

Cages with 5 second delay had this much "hoarded": 184mg, 530mg, 290mg, and 440mg of pellets + pellet dust on the bottom. 

Cages with 10second delay had: 400mg, 280mg, and 50mg

I'll give the FR1 a shot today and hopefully it helps :). What I'll do is just compare the results of that vs fedding results that we get after some other satiety hormones (cck, etc). If we use FR1 and present in a paper, do you think reviewers would have an issue with it? I'll think about the framing a bit more... the mice really don't have to do much more work poking for the food vs standing up to try and get a pellet from the wire rack.. I guess the main difference is the disappearance of the food from view.

Thanks,

Nik

[Lex Kravitz]

Wow that's a lot of hoarding in 1.5 hours!  We don't test mice after overnight fasting, I wonder if you've identified an interaction where a strong hunger drive enhances food hoarding.  That would make sense.  If you're primarily interested in measuring food intake you could count pellets and subtract them from the hoarded ones?  

I'm really curious if the FR1 reduces this behavior in your hands, please send an update when you run it!  For us a FR1 task completely stopped hoarders but we didn't do the overnight fasting.  

[Nik Hayes]

My PI suggested the subtraction approach too but since I typically give the mice hormones/anorectics that suppress feeding for a bit, subtracting out might be a bit weird. I guess it's possible to just assume they only went for pellets when they were back to feeding and subtract after eating initiates.. but still a bit messy I guess.

I did the FR1 this time with the same overnight fasted mice. This time I measured for about 3 hours because I forgot for a bit... the FR1 definitely helped though... caveat was that this was also their first fr1 session. 

Totals below are basically just the pellet # reported from the fed 3 times 20mg. Total food in mg [hoarded in mg]

Mouse 1: 1500mg [0]

Mouse 2: 1660mg [0]

Mouse 3: 960mg [50mg]

Mouse 4: 1180mg [90mg]

Mouse 5: 1440mg [170mg]

Mouse 6: 1320mg [20mg]

Mouse 7: 1800mg [500mg]

Next time maybe I'll try increasing the delay between when the pellet is dropped or maybe I could do FR2. I'd need to ensure that I don't interfere too much with their normal meal behavior though..