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deer’s belly contains a mandala of its own, an intricate dance of lives, sustained by hungry lips and teeth. Young ruminants must build their rumen community from scratch, a process that takes several weeks. During this time, they nibble their mother, the soil, and the vegetation, gathering and swallowing the microbes that will become their helpers.
    The rumen’s ecosystem is a self-sacrificing mandala, embodying endless change. Microbes are carried out of the rumen along with digested plant cells. They travel to the second part of the deer’s stomach and are swamped with acid and digestive juices. For these microbes, the gut’s hospitality has ended. The innkeeper kills and digests them, pocketing their proteins and vitamins along with the liquefied plant remains.
    The rumen retains plant solids and the microbes that cling to them, ensuring both the complete digestion of the plant and the continuity of the rumen’s microbial community. The deer hastens the breakdown of these solids by bringing them back into its mouth, chewing the cud, then swallowing the pulverized remains. This rumination allows the deer to “wolf” down its food, literally on the hoof, then chew it in a safe hiding place, away from real wolves.
    As the seasons change, the deer’s browsing moves from one part of the plant to another. The woody food of winter will change to springtime greenery, then autumn acorns. The rumen adapts to these changes through the gradual waxing and waning of the members of its community.Bacteria suited to digestion of soft leaves increase through the spring, then taper away in winter. No top-down control by the deer is needed to direct this change; competition among the rumen inhabitants automatically matches the rumen’s digestive capabilities to the food available. But sudden changes in diet can disrupt this elegant molding of the rumen community to its environment. If a deer is fed corn or leafy greens in the middle of winter, its rumen will be knocked off balance, acidity will rise uncontrollably, and gases will bloat the rumen. Indigestion of this kind can be lethal. Young ruminants face a similar digestive problem when they suckle their mother’s teats. Milk would ferment and create gas in the rumen, especially in immature animals whose rumens have yet to be fully colonized by microbes. The sucking reflex therefore triggers the opening of a bypass that sends milk past the rumen, into the next part of the stomach.
    Nature seldom throws rapid dietary change at ruminants, but when humans feed domesticated cows, goats, or sheep, they must address the rumen’s needs. These needs do not necessarily conform to the desires of human commodity markets, so the rumen’s balance is the bane of industrial agriculture. When cows are taken from pasture and suddenly confined to feedlots to be fattened on corn, they must be medicated to pacify the rumen community. Only by stamping down the microbial helpers can we try to impose our will on the cow’s flesh.
    Fifty-five million years of rumen design versus fifty years of industrial agriculture: we face questionable odds.
    The deer’s effects in the mandala were subtle. At first glance, shrubs and saplings appear unmolested. Only close observation reveals the missing tips of branches and the short, amputated stubs of side shoots. About half the dozen shrub stems in the mandala have been trimmed, but none of them have been cut back to stumps. I infer that deer and their microbial companions are frequent visitors to the mandala, but the deer are not starving. They can afford to nibble the succulent endsof twigs, leaving the woody stems behind. This choosiness is becoming a threatened luxury among white-tailed deer in the eastern forests. Across much of the deer’s range plant defenses are deployed in vain: deer populations have expanded rapidly, and the teeth and rumens of these growing hordes have sterilized the forest of saplings, shrubs, and wildflowers.
    Many ecologists