Disease definitely can have a direct effect on heifer performance. The two most common diseases to affect heifers is respiratory disease and scours. Respiratory disease can be controlled through good environment and a scheduled vaccination program. Scours can also be controlled via good colostrum feeding and a clean environment. In the USA, there are many good vaccines available to prevent scours in dairy calves.
Management seems to play the biggest role in all disease prevention programs.
Research has shown that animals that have been affected by respiratory disease will never catch up to herd mates. Most studies show that sick heifers fall 3 to 6 months behind healthy calves of the same age. In fact, sick calves are 2.5 times more likely to die at a later date than healthy calves. Diseases do have a permanent negative effect on heifer growth and the only way to handle a disease properly is to prevent it. I like to keep heifer nutrition easy so it gets done.