Complex sentence: A "trencher-fed pack" is a pack of foxhounds or harriers in which the hounds are kept individually by hunt members and only assembled as a pack to hunt-usually, such dogs are maintained together as a pack in kennels.
Split into simpler sentences: A "trencher-fed pack" is a pack of foxhounds or harriers in which the hounds are kept individually by hunt members and only assembled as a pack to hunt. Usually, a pack of hounds are maintained together as a pack in kennels.