You know much theory, but demonstrate zero practical knowledge:

0. There is near-zero risk of prion disease from cows in the US considering they're domesticated, not wild. There is no recent history of it either in the US. Collagen hydrolysate is highly processed to be short-chain.

1. As one gets older, vitamin C, no matter how much of it is consumed, is useful but insufficient for collagen synthesis.

2. You're right in theory about chicken/fish/pork collagen, but the commercial availability of their derived collagen hydrolysate is terrible or contaminated. Only bovine collagen hydrolysate has excellent and contaminant-free commercial availability.

3. You're measuring the wrong thing. It is not isolated amino acids have the resulting healing effects. It is only peptides, and these are poorly synthesized from plain amino acids.