The productivity and nutritive value of multispecies swards compared to perennial ryegrass only and perennial ryegrass-white clover swards

Multispecies swards have been shown to increase dry matter (DM) production from lower nitrogen (N) inputs, compared to Lolium perenne swards (LP). However, there is limited understanding of how these swards perform under bovine grazing, and how best to manage them. The aim of this thesis was to quantify the DM production, botanical composition, nutritive value and morphology of a six-species multispecies sward (MSS) and an LP-Trifolium repens (LP-TR) sward. Both MSS and LP-TR were subjected to reduced N fertilisation compare to LP, while MSS underwent less intensive grazing compared to LP and LP-TR. In order to achieve the aim, two experiments were established. The first was a farmlet experiment intensively grazed under a dairy-calf to beef system. At 92 kg N ha-1 a-1 MSS had greater annual production than LP-TR receiving 92 kg N ha-1 a-1 (+ 1,950 kg DM ha-1 a-1) and LP receiving 205 kg N ha-1 a-1 (+ 2,650 kg DM ha-1 a-1) and did not have a greater weed burden. Both LP-TR and MSS had higher crude protein concentration (+ 28 and 37 g kg DM-1, respectively) and lower neutral detergent fibre concentration (- 31 and 41 g kg DM-1, respectively) than LP swards. The relative ranking of the swards in terms of water soluble carbohydrate and DM concentration was LP > LP-TR > MSS. Despite the leaf component of LP contributing more to herbage DM compared to LP-TR and MSS, the organic matter digestibility of the three different sward types did not differ. The second was a plot scale cutting experiment. Annual herbage produced by both LP and LP-TR was not significantly affected by defoliation frequency. However, LP-TR did produce an additional 802 kg DM ha-1 a-1 when managed on a 28-day rotation vs. 21-day rotation, while MSS produced significantly more herbage (+1,923 kg DM ha-1 a-1) when harvested less frequently. Increasing post-cutting residual from 4 cm to 6 cm had no effect on the quantity of herbage DM produced, the botanical composition, the nutritive value or the morphology of the swards. The contribution of unsown species to herbage DM was significantly lower in MSS than LP and LP-TR under all cutting management. Although lengthening the rotation interval resulted in reduced organic matter digestibility in LP, neither legume containing swards were affected. Furthermore lengthening rotation interval reduced the crude protein and dry matter of LP and the crude protein of LP-TR, while it had no impact on MSS. The findings from this highlight the potential of multispecies swards in intensive beef grazing systems and underscore the importance of optimising sward management practices based on sward type. It is important to note that the study recognises the need for further research in this area. Nonetheless, the results demonstrate the considerable performance of the evaluated swards, specifically in terms of defoliation frequency and height. Although cutting height and defoliation length did not have a significant impact on the yield of the LP sward system. These findings carry practical implications for farmers, suggesting that LP swards can be grazed more frequently without sacrificing yield, potentially leading to increased livestock weight gain per hectare. Further exploration of the practical and systemic implications of these results is crucial to fully understand their significance in enhancing beef production profitability.