You should try some Apple cider vinegar & that does exactly what you just mentioned & also helps clear there gut...
Its a really old wifes tale used in conditioning olden day pitbulls for the ring.
The Encyclopaedia of Natural Pet Care describes Apple Cider Vinegar as: 'Long a folk remedy, cider vinegar has been shown to improve the health of dairy cows, horses, dogs and other animals. It reduces common infections, aids whelping, improves stamina, prevents muscle fatigue after exercise, increases resistance to disease and protects against food poisoning. Cider vinegar is rich in the vitamins, minerals and trace elements found in apples, especially potassium; it normalizes acid levels [pH] in the stomach, improves digestion and the assimilation of nutrients, reduces intestinal and faecal odours, helps cure constipation, alleviates some of the symptoms of arthritis and helps prevent bladder stones and urinary tract infections.' Birds are no exception in the animal world. ACV, and we point it out that it is made of the whole red sweet apple, provides enzymes and important minerals, such as potassium, calcium, magnesium, sulphur, chlorine, phosphorous, iron, silicon and other trace elements. The vitamins contained in ACV are bioflavonoids (vitamin P), beta-carotene (precursor to vitamin A), vitamin C, E, B1, B2 and B6. Tannins from the crushed cell walls of fresh apples as well as malic acid and pectin and other powerful nutrients