Significant numbers of dairy farmers are turning to zero-grazing to make use of fragmented or far away land, lower the feed costs for housed cows, or simply to improve grassland utilisation.

Fresh grass is the cheapest feed source available to dairy cows across the UK and increasing its inclusion in dairy cow diets presents farmers with opportunities to reduce feed costs.

Recent research from the Agri-Food and Biosciences Institute (AFBI) has indicated an increase of 15% in grass utilisation in zero-grazing systems, compared to conventional grazing systems.

This improvement often comes from the ability to achieve consistent residuals of 1,600-1,800kg DM/ha, alongside reduced rejection sites in swards associated with excreta or urine spots in conventional grazing systems.

Zero-grazing also provides the opportunity to cut at higher grass covers (>3,500 kg DM/ha) which would otherwise be challenging in a grazing system.

But what impact does using these covers have on animal performance and grass utilisation?

During the summer of 2017, AFBI compared animal and sward performance in two groups of housed cows; one offered fresh grass harvested from low cover swards (3,500kg DM/ha) or high cover grass swards (4,500kg DM/ha).

Cows were housed full time and offered fresh grass twice daily, with additional concentrate feeding in parlour at a rate of 6.4kg and 4.7kg DM/day for cows and heifers respectively. Grass utilisation, grass intake and animal performance were measured over a 110 day period.

Results showed that feeding grass from the high cover swards had a negative impact on grass production, with an average reduction of 14kg DM/ha/day in grass growth rate when compared with the low cover swards.

Grass utilisation and quality were also reduced in the high cover swards, with an increase in acid digestible fibre (ADF) and reduction in metabolisable energy (ME) content observed.

This impacted on grass intake, with animals on the low grass cover treatment consuming 0.9kg DM/day per cow more than the animals on high grass cover treatment.

Cow performance was also impacted by pre-cutting sward cover, with daily milk yield increasing by 1.8 kg/cow per day when cows were offered grass from low grass cover swards, compared with those on the high cover treatment. An uplift of 0.2 kg/cow per day in milk fat plus protein yield was also evident on the low cover treatment.

Both improvements in milk yield and quality contributed to higher profitability from the low grass cover treatment.