By having his animals' DNA scanned by a gene-testing firm, Mr. Gardiner, a Kansas cattle breeder, can tell nearly from birth how many pounds they are likely to pack on per day and how much rich, marbled beef their carcasses will yield. U.S. cattle ranches, using technology developed by companies including food-safety firm Neogen Corp. and animal-drug maker Zoetis Inc., are conducting more-sophisticated genetic tests like the ones that give Mr. Gardiner a glimpse of his animals' future.