From my personnel experience, dont ever give beef to lab, it will cause loose stool and stomach upset for them. Chicken, Duck, and Turkey are best for them. As chicken liver is an organ, this should be included in food as minimal quantity, more liver will also cause loose stool for them. Happy to see that you are shifting from processed to home made food. I introduced barf to my lab by giving him one packed food meal on morning and night i gave chicken. After one month, i gave him only chicken.