The temporary ley of Lolium perenne and Trifolium repens is widely used for milk production in temperate-humid areas. Its nutritional value depends on its chemical composition, ingestibility and subsequent digestive and metabolic use. On the central eastern coast of Asturias, data are available on the evolution of its chemical composition and digestibility. The general objective of this paper was to obtain information on the use of energy and nitrogen ingested. The specific objectives were to determine, throughout the year and for a period of 12 years, the evolution of the energy units, the urinary losses of nitrogen and the recovery of the same in milk, with forage as a single diet or supplemented with different scales and modalities of concentrate. During spring, metabolizable energy at maintenance level (MJ), milk forage units according to INRA 2018 and net lactation energy at feed level 3 (Mcal), per kg of dry matter, ranged respectively between 11.1‑11.7; 0.93‑1.01 and 1.31‑1.49. In summer, they were reduced to 10.2‑8.9; 0.87‑0.69 and 1.18‑0.84. In autumn, spring values gradually recovered. The grass silages had values similar to those of summer grass. Energy supplementation with concentrates significantly elevated metabolicity, feeding level and recovery of raw energy ingested in milk. Nitrogen supplementation significantly increased the recovery of nitrogen ingested in milk and with 15 % crude protein on dry matter, the excretion of nitrogen into the environment was reduced. The evaluated pasture has high potential for milk production in compliance with EU regulations.

de la Roza‑Delgado B, Martínez‑Fernández A, Modroño MS, Argamentería A (2022). Pradera de Lolium perenne y Trifolium repens en Asturias. II. Balances nutricionales sobre vacas frisonas en producción a lo largo del año. ITEA‑Información Técnica Económica Agraria 118(4): 530-546. https://doi.org/10.12706/itea.2021.039