How to make best use of zero-grazed grass

Fresh grass, including zero-grazed forage, is the cheapest feed source available to dairy cows.

Increasing its inclusion in dairy cows’ diets presents farmers with opportunities to reduce feed costs.

To achieve this, significant numbers of Irish farmers are turning to zero-grazing to make use of fragmented or far-away land, lower the feed costs of housed cows or simply improve grassland utilisation.

Recent Agri-Food and Biosciences Institute (AFBI) research 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 of dry matter per hectare (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 (>3,500kg 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 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 the parlour at a rate of 6.4 and 4.7kg DM/day for cows and heifers respectively. Grass utilisation, 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; an increase in acid digestible fibre (ADF) and a reduction in metabolisable energy (ME) content were observed.

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

Cow performance was also impacted by pre-cutting sward cover; daily milk yield increased by 1.8kg/cow/day when cows were offered grass from low grass cover swards (compared with those on the high cover treatment).

An uplift of 0.2kg/cow/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.