Current Cow Breeding Methodsbr Could Lead to Their Extinction In the United States, there arebr more than nine million dairy cows. A majority of these cows are large bovines withbr black-and-white markings, known as Holsteins. Researchers have found that more thanbr 99 of these male Holsteins trace backbr to one of two cows from the 1960s. This means that only two Y chromosomes existbr among all male Holsteins in the United States. Female holsteins haven’t fared well either,br with the population’s genetic similarities makingbr the effective population size less than 50. This amount of inbreeding leads tobr genetic homogeneity, which increasesbr the risk of inherited disorders. The “inbreeding coefficient” for Holsteinsbr is currently about 8 and has continuedbr to increase by around .4 every year. Inbreeding reduces the population’s abilitybr to evolve, inhibits fertility and lessens theirbr ability to fight diseases in the future.