"Globulin" = immunoglobulin... essentially part of the immune system responsible for recognizing pathogens, and specific to certain pathogens. For instance, you vaccinate the cow for Rotavirus a couple weeks prior to calving, she makes extra immunoglobulin to Rotavirus and that ends up in colostrum. The calf drinks colostrum, immunoglobulins (Ig) are absorbed through the intestine, and the calf is protected for several weeks against Rotavirus. Ig is made of protein, so your cows need an adequate level of protein in their diet the last few weeks/months prior to calving to produce high quality colostrum.
How much is in the old bag? ie new bag as 150g Ig per 500g bag, does the old bag have 55g Ig per 500g bag? Make sure you're comparing apples to apples.
"Colostrum supplement" means it's given in addition to the dam's colostrum. Maybe you think the calf needs a little extra colostrum since his dam doesn't have much milk or is uncooperative; you supplement him. "Colostrum replacer" is what OptiPrime is; it's designed to be given in place of the maternal colostrum. You have an orphan calf, cow died, cow has no milk, calf is a twin, etc. That's what OptiPrime is for (or use half the bag for supplemental purposes).
A calf needs 100g IgG at birth - your job is to figure out how to make that happen.
Re the link:
OptiPrime is guaranteed free of all major colostrum transmissible diseases including Johne’s.
Unless the old colostrum supplement has the same statement, that by itself would make me use OptiPrime. You really don't want to take the chance of Johnes in your herd.