A Review of Nitrogen Use Efficiency of Dairy Replacement Heifers: Improving Management Practices and Minimizing...

Within the agricultural sector, dairy cattle farming systems are of the main ammonia emitters contributing to nitrogen (N) pollution. As a main strategy to mitigate N pollution, increased N use efficiency (NUE) of dairy cattle farms has been proposed. Dairy replacement heifers are an important aspect of dairy herds, and improving their NUE is a step toward addressing the issue holistically. The aim of the current review was to describe and assess heifer nutritional practices that affect NUE and examine protein supplementation to minimize N excretion in the environment. Heifer management practices related to growth and nutrition appear to have an important role on improving overall farm NUE. In particular, age at first calving, dietary crude protein level and rumen degradable protein level appear to be among the factors that affect N losses during the growth period. From a management point of view, frequent body weight monitoring at growth benchmarks and the use of mechanistic nutritional models are highly desirable to increase NUE under on-farm conditions.