Production and quality of milk were determined for 18 successive years according to different supplements, in an experimental farm in Asturias (Northern Spain; Atlantic Arc), provided with Lolium perenne and Trifolium repens sown meadows, used for rotational grazing and silage by a herd of Friesian dairy cows with grouped winter calvings. The concentrate used for supplementation varied according to dose (depending on yield or fixed contribution) and concentrate type (rich in starch or digestible fiber). Different grazing plots were assigned to each dairy group, maintaining the same stocking rate of 2.2 UGM/ha. Parallel to these long-term trials, energy and nitrogen balances were carried out on individualized cows in a metabolic house. The results in this regard were used to model milk production and composition by lactation week using the incomplete gamma function with concordant results. Forage‑based cows produced 4,221 kg milk/cow·year with 3.68 % fat and 3.01 % protein. The heifers could not remain without supplementation and the response to it was between 1.55‑1.82 kg milk/kg DM concentrate. The concentrate dose had more influence on milk production than the nature of this. The most effective supplementation was the fixed concentrate intake of 5 kg/head·day and the highly digestible fiber concentrate increased the milk fat content.

de la Roza‑Delgado B., Martínez‑Fernández A., Modroño M.S., Argamentería A. (en prensa). Pradera de Lolium perenne L. y Trifolium repens L. en Asturias. IV. Producción y composición de la leche en vacas Holstein en pastoreo (con y sin suplementación): análisis de 18 años. ITEA‑Información Técnica Económica Agraria. Vol. xx: YY-YY. https://doi.org/10.12706/itea.2024.012