The potential of diverse swards on herbage production and animal performance, economic and environmental sustainability, and nitrogen excretion in a dairy-beef system

The beef industry in Ireland and elsewhere is facing many challenges including those related to the economic viability and environmental sustainability of pastoral-based production systems. Therefore, there is a need to investigate different pastoral production systems which have the potential to reduce the environmental burden and nitrogen excretion in a dairy-beef system. The overall aims of this thesis, carried out in two experiments, were: 1) to evaluate the effects of sward type on herbage production, animal performance, carcass traits, profitability and Greenhouse gas emissions, as well as evaluating the daily methane and carbon dioxide emissions and rumen fermentation parameters of a dairy calf-to-beef production system, 2) investigate the impact of conserved forages from different sward types on dry matter intake, apparent digestibility, and nitrogen balance of growing dairy-beef heifers. From the first experiment, diverse swards produced higher annual dry matter yields with 55% less inorganic nitrogen fertiliser. Animal performance was also improved on the diverse swards, with animals reaching slaughter 30 days earlier compared to animals on the grass only forage. Carcass output, as well as gross and net margins were also increased with diverse swards. The GHG emissions per ha were lower for the diverse swards, while live weight per animal per ha were higher for these swards. In the second experiment, dry matter intake and nitrogen intake was higher for animals offered a diverse sward as a conserved forage relative to perennial ryegrass. Total nitrogen output was lowest for the grass only forage, with no difference between the diverse forages. Between the diverse swards, there was a tendency for animals offered the multispecies forage to have a higher faecal nitrogen output and lower urinary nitrogen output relative the perennial ryegrass white clover forage. Retained nitrogen was highest for animals offered the diverse forages, compared to the grass only forage. In conclusion, diverse swards offer the potential to improve the efficiency and economic sustainability of pasture-based beef production systems, as well as producing lower total GHG emissions expressed on a per ha basis, per livestock unit, per animal finished, per kg beef carcass, and per kg meat yield, compared to perennial ryegrass monocultures.