In an experimental farm located in Asturias (North of Spain; Atlantic Area; 43° 28' 50" N, 5° 26' 27" W, 10 m above sea level), with sown meadows of Lolium perenne and Trifolium repens, in a system of rotational grazing and silage for Friesian cows with winter calving, was determined along eight consecutive years the chemical composition of offers and refusals, the in vivo digestibility of the forages, as well as the effect of different supplementations on the total diet digestibility. Each year, the herd was distributed in three groups: a control group without supplementation and another two treatments to contrast different doses (according milk yield or flat rate) and modalities of concentrate (two concentrate rich in starch and another one in digestible fiber). Two cows of each groups were allocated into metabolic stalls to control of voluntary intake of forage, concentrate dose, excretion of feces, urine and milk, plus live weight and body condition score control. Samples were taken daily for nutritive analysis and estimation of in vivo digestibility. It was detected that the evaluated grass from North of Spain has a nutritional limitation due to organic matter digestibility loss in summer (59.4 % in August, respect 74.4‑77.5 % in spring and 73.2‑78.3 % in autumn, p < 0.001). Nevertheless, it was surprising the high neutral detergent fiber digestibility results (annual range 51.8‑76.0 %). The in vivo organic matter digestibility of concentrates values ranged from 85.5 % and 74.4 % for starch‑rich concentrates and 71.5 % for the concentrate rich in high digestibility fiber.

de la Roza‑Delgado B, Martínez‑Fernández A, Modroño MS, Argamentería A (2022). Pradera de Lolium perenne y Trifolium repens en Asturias. I. Evolución de la composición química y de la digestibilidad in vivo sobre vacas frisonas a lo largo del año. ITEA‑Información Técnica Económica Agraria 118(1): 48-68. https://doi.org/10.12706/itea.2021.013