[mixmastamyk]

I was thinking about that myself and came up with the idea that perhaps their diet is changing.

I wouldn't be surprised if laboratory food was centralized around corporations just like human food. Meaning, I bet cheaper ingredients (more wheat/corn) have made their way into it over time. I can't imagine such peripheral industries not being affected.

[nwhitehead]

This is an interesting hypothesis. It wouldn't even have to be changing percentages of ingredients, it could simply be the result of increased agricultural efficiency and yields. 100 calories worth of corn feed is quite likely to be subtly different in composition today than decades ago.

[mixmastamyk]

Yes, pesticides and packaging are thought to be possible factors too.

[boneheadmed]

I think that what you're saying is most likely what is happening.