Agronomic Performance of Perennial Ryegrass ( Lolium perenne L)—Ribwort Plantain ( Plantago lanceolata L) and Perennial Ryegrass Swards Under Intensive Dairy Cow Grazing

ABSTRACT This study investigated the agronomic performance and root characteristics of perennial ryegrass and mixed perennial ryegrass–plantain swards under intensive rotational grazing by dairy cows in Northern Ireland over two full grazing seasons (2023–2024). Key objectives were to evaluate herbage yield, growth dynamics, utilisation, botanical composition, forage quality and root morphology. Total seasonal yield PRG and PRG‐PL were 11,683 and 11,766 kg DM ha −1 , respectively. The PRG‐PL swards exhibited greater herbage utilisation (80.5% vs. 76.7%). Herbage quality analyses showed mixed perennial ryegrass–plantain swards had higher ash ( p < 0.001) and acid detergent fibre ( p < 0.01), but lower neutral detergent fibre ( p < 0.001), water‐soluble carbohydrates ( p < 0.001), digestibility ( p < 0.001) and gross energy ( p < 0.001) compared to perennial ryegrass. Botanical composition remained consistent across years, with mixed perennial ryegrass–plantain swards averaging ~29% plantain. Root assessments revealed perennial ryegrass swards had significantly greater fine root development ( p < 0.001), biomass ( p < 0.001) and surface area ( p < 0.001) to 30 cm soil depth, whilst mixed perennial ryegrass–plantain sward roots were fewer in number but exhibited slightly thicker diameters in deeper layers. Plate metre calibration showed no significant difference ( p > 0.05) between sward types, validating the use of a common equation. Notably, mixed perennial ryegrass–plantain swards ( p < 0.05 ) showed increased growth during periods of low rainfall, suggesting enhanced drought resilience. These findings indicate that incorporating plantain into perennial ryegrass swards can enhance utilisation efficiency and potentially improve resilience under variable climatic conditions without compromising annual productivity. This research provides robust, year‐on‐year data supporting the agronomic viability of moderate plantain inclusion in temperate grazing systems.