Investigating the effect of legume and herb inclusion in combination with perennial ryegrass on pasture-based sheep production systems

There is a constant pressure, nationally and internationally to reduce methane (CH4) emissions from ruminant livestock, coupled with the necessity to enhance production efficiency. Diverse pastures containing clovers and herbs offer the potential to deliver enhanced animal and sward performance, coupled with environmental benefits. However, questions remain unanswered regarding 1) The factors driving improvements in animal performance, 2) The ability of clover and herb inclusion to mitigate CH4 emissions and N output and 3) The impact clover and herb inclusion has on meat-eating quality. This research considers these concepts through monitoring various animal performance factors in an intensive pasture-based sheep production system implementing binary sward mixtures of perennial ryegrass (Lolium perenne L.) and one companion forage. The five sward treatments investigated were: Perennial ryegrass (PRG), PRG plus white clover (Trifolium repens L.;PRG + WC), PRG plus red clover (Trifolium pratense L.;PRG + RC), PRG plus chicory (Chicorium intybus L.;PRG + Chic) and PRG plus plantain (Plantago lanceolate L.;PRG + Plan). Chapters 3 and 4 were conducted with wether sheep (n = 20) housed in metabolism crates. Sward treatments were offered as zero-grazed herbage at a ratio of 75% PRG and 25% of the respective companion forage and 100% PRG for the grass only treatment, on a dry matter (DM) basis. Results show that the inclusion of any companion forage increased dry matter intake (DMI) (P < 0.001). Sward crude protein concentration was increased and neutral detergent fibre content was reduced in all binary sward mixtures while organic matter digestibility was generally enhanced with companion forage inclusion (P < 0.001). Animals consuming PRG + WC ranked 14% lower for CH4 g/day than sheep offered PRG, while the addition of any companion forage ranked CH4 g/kg DMI lower (P < 0.001). There was a greater abundance of the rumen archaea Methanobrevibacter in sheep consuming the PRG diet (P < 0.001). On average, herb diets (PRG + Chic or PRG + Plan) reduced urinary nitrogen concentration by 34% in comparison to legume diets (PRG + WC or PRG + RC) and 13% relative to the PRG diet (P < 0.001). A two-year grazing study, employing a randomised block design was then conducted to determine the effect of the same five sward treatments, with a primary focus on lamb performance during the post-weaning period (Chapters 5 and 6). Results indicate that lambs grazing any binary sward exhibited superior growth performance compared to those grazing PRG. Improvements were reflected in an increased post-weaning average daily gain (ADG) of 29-58 g/day, leading to a reduction in age at slaughter by 16-50 days, over PRG lambs (P < 0.001). Companion forage inclusion ranked CH4 production in growing lambs 6-13% lower than lambs grazing PRG (P < 0.05). There was a lower abundance of Methanobrevibacter in lambs grazing PRG + RC (P < 0.001). The evaluation of meat-eating quality included assessments by both trained and consumer sensory tasting panels. Meat produced from lambs grazing PRG + Plan exhibited reduced tenderness, with flavour and overall liking scores also generally lower for meat from these lambs (P < 0.05). Findings suggest that the incorporation of legumes and herbs alongside perennial ryegrass can improve the production efficiency of pasture-based sheep production, primarily during the summer period, enhancing pasture digestibility and nutritive value facilitating an increased DMI. Clover and herb inclusion improved lamb performance and had a positive impact on CH4 mitigation. However, findings highlight the need to consider diet type in tandem with meat-eating quality when selecting finishing systems for pasture-fed lambs. Correct implementation of binary sward mixtures can serve as a practical and feasible CH4 mitigation option, while also providing enhancements in animal and sward performance in pasture-based sheep production systems.

2025-11-17 JG: Author's signature removed from PDF