As the temperature falls below the LCT, short term and long term responses are activated. The goal is to feed the calf so that it will maintain its own body heat and still have enough reserves left over for growth. Death will occur if the calf remains unable to maintain its core body temperature for an extended period of time. Cheating on quality at this stage of growth will not only decrease your feed efficiency, it could also lead to death in a cold weather feeding environment. The starter ration is fed primarily for rumen development.
Energy is the engine that drives growth and development.
Protein and fat should be separated by a 4-5 part spread. Protein is meant to drive calf growth. Fat must be present in adequate amounts to generate body heat, thereby freeing up protein for growth. In order to provide the calf with the excess energy it needs to maintain body temperature and growth during the winter, the diet becomes the first line of defense. A high quality milk replacer made from milk proteins and animal fat is ideal.