You cannot let just anyone feed and tend calves (read orphan lambs/goats/wildlife into much of this). The person must be of the right patient temperament and they must have a passion for cleanliness and detail. Wash your hands and boots before handling baby stock and going into the shed or shelter area and also when you leave. Never ever mix batches of calves of different ages or put young ones into an area that older ones have just vacated unless a total cleaning and disinfection has occurred. There are appropriate disinfectants and you do need correct advice as to which ones... but none of them work well in the presence of persistent organic matter. (Poo and dirt). After cleaning and disinfecting a liberal sprinkling of white slaked lime (Limil) left in place for a few days will help finish off. Cover, wash or broom it away before introducing more animals. If using straw bales then they must be fresh and new. Nothing kills/sets back new calves faster than being raised in the faecal organics (shit) of those that went before them...shed or paddock. I often see a person raise their first batch well and then think that they are good at it, only to have subsequent batches "crash" or do poorly.
Despite the best laid plans, things will go wrong, especially with later batches of calves raised in the same areas as the first.

