Efficient, innovative and sustainable heifer rearing systems: improving efficiencies through the utilisation of precision technologies and an enhanced understanding of the nutrient requirement of dairy youngstock    Background   Recent CAFRE analysis has estimated heifer rearing to cost £2,000/heifer or 6ppl of milk produced.  Calving at the optimum weight and age has shown previously (Pirlo et al., 2000) to result in improved fertility, longevity and potential lifetime performance.  However, the average age at first calving in Northern Ireland dairy herds is still estimated to be...