The most important factor hampering the growth of livestock production, however, is the feed situation—a chronic shortage of sufficient energy feeds and an imbalance among the major feed components, including a serious protein deficit. Soviet livestock feed rations remain deficient in both quantity and quality despite long-standing plans to upgrade animal diets. Data on feed balances for the USSR are more limited than for most western countries, including only concentrates and a few categories of roughages fed, an estimate of pasture "fed", and total feed units used by all livestock. Ambitious plans to increase supplies of livestock feed have consistently fallen far short of target. The strong emphasis on expanding livestock herds and the length of time farms require to bring animals to acceptable slaughter weight have combined to absorb most of the increase in production of feedstuff's. Livestock feed comprises concentrates and roughages.