Pellet variability

[Matias Andina]

Hello all,

I was reading this paper https://www.science.org/doi/10.1126/science.abk0297 which uses another feeding device but explain the choice of pellet formulation as follows:

To select the diet for the longevity studies, we first compared standard lab chow (Teklad Global 2018) with two different precision food pellets with similar caloric content but different compositions: a grain-based diet that we used previously (F0170) (7) and a purified diet (F0075) (fig. S1A). We found that mice fed the purified diet showed similar body weight gain to the standard lab chow; however, the mice fed grain-based pellets gained significantly more weight (fig. S1B). Because the composition of grain-based diets is known to vary by batch and by season of the year (23), and because longevity experiments require at least 4 years duration, we chose the purified diet that can be completely defined and maintained over the entire duration of the lifespan experiments, and did not cause excessive weight gain compared to lab chow.

The diet they are referring to is the same formulation as the Bio-Serv F0163 (20 mg version) that we use for our FEDs. I don't think I can do a thorough analysis about lots and seasonality, but I am curious about whether people found something or can relate. Just trying to gather some thoughts from the community.

Best,

Matias

[Lex Kravitz]

Interesting question Matias! 

We have done months of mice eating only 20mg grain pellets from FED3 and have never seen obesity like they observed.  We have found that our mice prefer the little 20mg grain pellets over their laboratory chow.  We know this because if we leave regular food in the cage they tend to ignore it and only eat from FED3.  But they do not over-eat pellets or gain weight on grain pellets. 

We mostly use TestDiet 5TUM pellets but have used Bioserv before too. Both suppliers have a very similar nutritional profile, and given that they are both low fat (~10% fat by calories) I'm surprised that these researchers saw so much weight gain (Figure from the supplement below, their mice ended up at 50g on average!).  Their rationale for choosing a purified diet to obtain more consistency across a 4 year study seems sound though.   I'm curious if anyone else has seen weight gain with grain pellets?