The transfer of passive immunity in calves is well understood to be vital for the health and future performance of dairy and beef calves. It is also crucial for the future sustainability of the industry. Up until now, options for testing IgG levels in calves were limited to the first week of life and the only affordable tests were indirect and lacked accuracy. Recent research into a penside direct quantitative Lateral Flow Test for IgG has shown a strong correlation with morbidity and performance when used in calves entering rearing units up to 6 weeks of age. This expands the assessment of calf immune status beyond the farm of origin and incentivises the pre-conditioning of calves before sale, improved management but also the transfer of these benefits down the supply chain. Improved management of calf immune status will lead to better welfare, reduced use of antibiotics, improved lifetime performance and lower carbon intensity of beef and milk.