You really can’t compare unless you have a feed tag from the Purina product (and even then you might not be able to compare because Purina often lists ingredients in AAFCO categories rather than actual ingredients).
Purina had something like 91 mills to my knowledge (not all of them make horse feed), and they do not use fixed formulas. Their formulas vary regionally. They use low-cost formulations so for example, they may use things like citrus pulp as forage products in the southeast, whereas the ingredients in the same product made out west would have totally different ingredients, even though the guaranteed analysis for protein, fat and fiber are the same. Some people may love and swear by Purina Senior while others hate it…they are both feeding purina senior but what is in the bag is not the same.
Tribute feeds are made in one new, clean and ionophore free facility in Ohio. Their quality control is the best I’ve seen. Their products typically have higher guaranteed levels of amino acids (lysine, methionine, threonine) than competitors. They also have higher guaranteed levels of pre and probiotics, and I’ve seen better results with their EquifermXL than with other brands of probiotics. They use chelated minerals for better absorption, and they use quality ingredients.
There are other companies out there that have great products too. I have fed many of them over the years. I’m married to a feed dealer so I’m lucky in that I’ve been able to feed my horses the best feeds over the years. I’ve fed everything from Nutrena, Buckeye, Triple Crown and even grain mixes milled by my husband. Triple Crown is one of the few in my opinion that compares to Tribute. However, Triple Crown products cost a lot more money, and they aren’t made in one single ionophore free facility.
I’ve fed Tribute for at least 5 years now. My horses look and feel great and I think it’s a great company. Those are the reasons I chose and recommend Tribute.