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

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 approxi-mately) 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 < 0.001) compared to SIL, with intakes during weeks 8-12 of the experiment lower with SIL compared to ZG (P < 0.001). Cows on ZG had a higher milk yield, milk protein concentration, milk fat plus protein yield and energy-corrected milk (ECM) yield (P < 0.001) than cows on SIL. With the exception of milk yield (where the difference was primarily observed during weeks 8-12 of lactation), these differences were observed most weeks during the study period. Milk fat concentration was unaffected by treatment (P > 0.05). Milk of cows on ZG had higher concentrations of total monounsaturated fatty acids (P < 0.001), total polyunsaturated fatty acids (PUFAs, P < 0.001) but lower concentrations of saturated fatty acids (SFAs, P < 0.001) compared to cows on SIL. Diet had no effect on cow BW or condition score. This study has shown that when harvested from the same sward, milk yield and ECM yield were improved when cows were offered zero-grazed grass compared to grass silage. This difference in perfor-mance was likely due to the lower forage intake observed with the grass silage-based diet.(c) 2023 The Author(s). Published by Elsevier B.V. on behalf of The Animal Consortium. This is an open access article under the CC BY license.

Automated summary

Comparing the effects of zero-grazing and grass silage on dairy cow performance, the study found that cows offered zero-grazed grass had higher milk yield and milk protein and fat yield. In addition, zero-grazed grass had higher concentrations of monounsaturated fatty acids and polyunsaturated fatty acids, but lower concentrations of saturated fatty acids. Grass silage, on the other hand, showed lower forage dry matter intake.