Including white clover in nitrogen fertilized perennial ryegrass swards: effects on dry matter intake and milk production of spring calving dairy cows

The current experiment was undertaken to investigate the effect of including white clover (Trifolium repens L.; WC) into perennial ryegrass (Lolium perenne L.; PRG) swards (PRG/WC) receiving 250 kg nitrogen (N) per hectare (ha) per year compared with PRG only swards receiving 250 kg N/ha/year, in an intensive grass-based spring calving dairy production scenario. Forty spring-calving cows were allocated to graze either a PRG/WC or PRG sward (n = 20) from 6 February to 31 October 2012. Fresh herbage was offered daily (17 kg dry matter (DM)/cow) supplemented with concentrate in times of herbage deficit (total supplementation 507 kg/cow). Pre-grazing herbage mass (HM), sward WC content and milk production were measured for the duration of the experiment. Herbage DM intake was estimated in May, July and September. Pre-grazing HM (+/- s.e.) was similar (1467 +/- 1731 kg DM/ha) for both treatments, as was cumulative herbage production (14 158 +/- 769 kg DM/ha). Average WC content of the PRG/WC swards was 236 +/- 30 g/kg DM. The PRG/WC cows had greater average daily milk yield and milk solids yield from June onwards. Cumulative milk yield and milk solids yield were greater for the PRG/WC cows compared with the PRG cows (5048 and 4789 +/- 343 kg milk yield/cow, and 400 and 388 +/- 187 kg milk solids/cow, respectively). Cows had similar DM intake in all measurements periods (151 +/- 042 kg DM/cow/day). In conclusion, including WC in N-fertilized PRG swards increased milk production from cows grazing the PRG/WC swards compared with PRG, particularly in the second half of the lactation.