Performance of dairy cows offered either zero-grazed grass or grass silage prepared from the same sward

•Ensiling herbage at an early growth stage may offer an alternative to zero-grazing.•Wilting young leafy herbage in later season was a challenge.•Resulting silage had a lower DM content and poorer fermentation characteristics.•Intakes and energy-corrected milk yield were improved when cows were zero grazed.•Offering silage reduced cow performance compared to the same herbage zero grazed. Daily harvesting of fresh grass for housed livestock when its nutritive value is high (Zero-grazing) is a labour-intensive process which requires a consistent supply of grass at the optimum growth stage. An alternative approach which may save on labour and require less time spent on grassland management each day, involves harvesting and ensiling herbage on a number of occasions (every 4 weeks approximately) during the growing season when it is at the same nutritive value as herbage used for zero-grazing. This study examined the impact of these two approaches to dairy cow performance. Thirty-six mid-lactation Holstein-Friesian dairy cows were offered either zero-grazed fresh grass (ZG), or grass silage (SIL) prepared from the same sward harvested at a similar growth stage, over a single season. Fresh grass was harvested daily and offered to ZG cows for a 12-week period. During this period, the same sward was harvested once weekly and ensiled in round bales. Following a five-week ensilage period, the silage was offered to cows on SIL for a 12-week period. All cows were also offered 8.0 kg concentrate per day. Zero-grazed grass and grass silage had a mean metabolisable energy content of 11.0 and 11.3 MJ/kg DM, respectively. Mean forage DM intake (DMI) and total DMI were greater for cows on ZG (P