DOI: 10.11648/j.bio.20261404.15 ISSN: 2328-5893

Enhancing Nitrogen Utilization in Dairy Cattle by Precision Protein Feeding: A Systematic Review

Genet Hailu
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Improving nitrogen utilization in dairy cattle is increasingly important due to rising feed costs and the environmental burden associated with nitrogen losses from livestock systems. This systematic review evaluated evidence on precision protein feeding strategies aimed at enhancing nitrogen use efficiency (NUE) in dairy production systems. A total of 1,124 records were initially retrieved from major databases, including Web of Science, Scopus, PubMed, CAB Abstracts, and Google Scholar, alongside supplementary grey literature sources. After duplicate removal and multi-stage screening, 58 studies met the eligibility criteria and were included in the final synthesis. Across the reviewed literature, a consistent pattern emerged showing that excessive crude protein supplementation does not proportionally improve milk production but instead increases nitrogen excretion and feed costs. In contrast, metabolizable protein supply derived from rumen microbial protein, rumen-undegradable protein, and endogenous nitrogen—provides a more functionally relevant indicator of protein availability for productive use in dairy cattle. The synthesis further shows that nitrogen efficiency can be substantially improved through coordinated nutritional interventions. These include balancing limiting amino acids such as lysine and methionine, synchronizing rumen-degradable protein supply with fermentable energy availability, and reducing unnecessary crude protein intake. In addition, controlled-release nitrogen sources such as Optigen® were identified as effective tools for stabilizing ruminal nitrogen availability and improving microbial protein synthesis. Evidence across studies indicates that these precision feeding strategies enhance nitrogen capture in productive pathways while maintaining or improving milk yield and milk protein output. At the same time, reductions in environmentally reactive nitrogen forms—particularly ammonia (NH 3 ) and nitrous oxide (N 2 O) were consistently reported. Overall, the findings demonstrate that improving nitrogen utilization is less dependent on increasing protein supply and more dependent on improving nutrient synchrony and protein quality. Precision protein feeding therefore represents a practical and scalable approach for improving both the economic efficiency and environmental sustainability of dairy production systems.

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