If their mature liveweight is 550kg, this means the calves should be 128kg today. March-born calves are more than likely to be underweight at this time. The best policy is to weigh all calves and separate the ones that are under target weight and give them special treatment. Special treatment could be extra meal and/or preferential access to quality grass. This might mean grazing them ahead of the main bunch or the maiden heifers and not asking them to clean out paddocks.
The most amount of meal I feed young calves is 2kg/day. For the calves that are on target, if grass quality is good, (1,000kg/ha to 1,200kg/ha with high perennial ryegrass content) then meal feeding is not necessary, although some farmers like to feed a small bit (less than 0.5kg/hd), to assist with herding.
Calves should be moved on to a fresh break every three days to keep grass intakes high, this is the key to maximising daily liveweight gain. Bulling heifers should be 63% of their mature liveweight (around the 350kg mark).
Simplifying the calf-rearing system