Very few cattle were kept. No more were kept because there was no way of keeping them. In the fields wheat, rye, oats, barley and beans were raised, but no hay and no turnips. Field grasses and clover which could be introduced in the course of field crops were unknown. What hay they had came entirely from the permanent meadows, the low-lying land bordering the banks of streams. "Meadow grass," writes Dr. Simkhovitch, "could grow only in very definite places on low and moist land that followed as a rule the course of a stream. This gave the meadow a monopolistic value, which it lost after the introduction of grass and clover in the rotation of crops."[42] The number of cattle and sheep kept by the community was limited by the amount of forage available for winter feeding. Often no limitation upon the number pastured in summer in the common pastures was necessary other than that no man should exceed the number which he was able to keep during the winter. The meadow hay was supplemented by such poor fodder as straw and the loppings of trees, and the cattle were got through the winter with the smallest amount of forage which would keep them alive, but even with this economy it was impossible to keep a sufficient number. The amount of stall manure produced in the winter was of course small, on account of the scant feed, and even the more plentiful manure of the summer months was the property of the lord, so that the villain holdings received practically no dung. The villains were required to send their cattle and sheep at night to a fold which was moved at frequent intervals over the demesne land, and their own land received ordinarily no dressing of manure excepting the scant amount produced when the village flocks pastured on the fallow fields. The supply of manure, insufficient in any case to maintain the fertility of the arable land, was diminishing rather than increasing. As Dr. Russell suggested in the passage referred to above, the continuous use of pastures and meadows causes a deterioration in their quality. The quantity of fodder was decreasing for this reason, almost imperceptibly, but none the less seriously. Fewer cattle could be kept as the grass land deteriorated, and the small quantity of manure which was available for restoring the productivity of the open fields was gradually decreasing for this reason. Soil exhaustion went on during the Middle Ages not because the cultivators were careless or ignorant of the fact that manure is needed to maintain fertility, but because this means of improving the soil was not within their reach. They used what manure they had and marled the soil when they had the time and could afford it, but, as the centuries passed, the virgin richness of the soil was exhausted and crops diminished.