In the animal kingdom the cow is the only animal bestowed with subtle body. She can do wonders beyond imagination that benefit mankind. A healthy cow means the gross body of a cow is well protected. When her subtle body is rightly awakened she becomes a holy cow, "kamadhenu". Puranas tell us about kings gifting away 'healthy cows' to spiritual masters, who in turn processed them into 'holy cows'.
Fire ritual viz.YAJNAM makes a healthy cow as a holy cow. Cow has a built in software that can store, process and release solarenergy. The key to activate that software is gayatrimantra. The solar energy released by a cow has a distinct quality. Cow actually process sun rays before releasing them through her breath, urine, dung etc, and more significantly her "voice".