Your yearling is too young to be fed Integrity Performance.
While the differences between the two products appear minimal, the importance of those differences are in the relationships of nutrient-to-nutrient and nutrient-to-calorie relationships.
The feed sources of the nutrients are critical. While some commercial feeds primarily focus on the guaranteed analysis (GA), Integrity’s focus is not only on the GA but what ingredients are providing those nutrients and how they affect the two critical relationships mentioned above.
For example, gut health is a primary focus of Integrity which is why beet pulp is the first ingredient in both Growth and Performance. However for a growing youngster, protein and particularly the amino acid lysine are critical to the growth phase which is why soybean meal is the second ingredient in Growth. Granted working horses need protein to add & rebuild muscle fiber but that relationship in nutrient to nutrient and nutrient to calorie is different than a growing horse which is why soybean meal is the fifth ingredient in Performance.
In Performance, rice bran is the second ingredient because fat is a major fuel source for a working horse. Keep in mind you are working a yearling that is still growing and building the foundation from his genetic makeup; an adult performance horse has already reached his growth potential.
If you want higher fat during work sessions, you can add oil or Integrity Rice Bran to the meal prior to work. I would need to know more about your yearling and the type of work to recommend amounts. Usually feeding 1.5 hours prior to a work session will allow fatty acids to circulate and provide added fuel and dietary fat, reducing the lactic acid levels for moderate-to-intense work sessions.