An alternative strategy for supplementing ruminants fed low-quality roughages is discussed. In this strategy, the quantity and quality of supplement are adjusted to constrain mass-loss to a limit compatible with the productive function of the animal. The limits to mass-loss for survival, reproduction, and wool growth are discussed in relation to winter mass-losses of unsupplemented animals in South Africa . The consequences of nutrient imbalances on feed utilization are discussed in the light of the requirements of the ruminant for individual nutrients. Possible benefits of manipulating the ratio of glucose: acetate in absorbed nutrients with rumen-stimulating supplements, bypass starch and protein, and protected fats are discussed.