Requirements Of Future Grass Based Systems (Dairy)

Dairy Production Systems

Table 2 outlines the overall changes in and impact of management practice at Curtins Farm, Teagasc Moorepark over the last 25 years, from 1984 to current management. The overall objective of the farm systems research is to increase farm profitability per ha by implementing practices to increase the quantity of grass harvested per ha for milk solids production, whilst improving nutrient use efficiency. As illustrated in Table 2, the SR on the farm increased from 2.5 LU/ha in 2005 to 2.8 LU/ha in 2009, while at the same time both concentrate use and inorganic fertiliser use decreased.

Improved grazing management practices have resulted in total pasture production increases of 25 per cent, from 12.5 t DM/ha on grazing paddocks in the 2001 to 2005 period to 15.7 t DM/ha in 2009. This increase in total growth resulted in a surplus of 1.6 t DM/ha.

Milk solids production per cow fell from 500 kg to 430 kg (2001-2005) due to increased grazing intensity and reduction in concentrate use. The focus of the research in more recent years has been to identify significant quantities of extra feed within the system which, when coupled with a further increase in overall farm SR to 3.3 LU/ha, will facilitate the realisation of increased milk solids production per hectare from home grown feed in future years.

Source: McCarthy (1984); McCarthy et al. (2005); McCarthy et al. (2007); Coleman et al. (2009)

When capturing the maximum benefits of grazed grass, a key management practice is to have the correct number of cows calving compactly at the beginning of the grass growing season. Stocking rate, traditionally expressed as cows per ha, is the major factor governing productivity from grass. A recent review of SR experiments reported that an increase in SR of 1 cow per ha will result in an increase in milk production per ha of 20 per cent (McCarthy et al., 2010).

With a current average national mean SR of 1.9 LU/ha, mean calving date of mid-March and calving rate of 59 per cent in first 42 days, the Irish dairy industry is missing out on significant milk production and grass utilisation potential. From a grassland management perspective, recommended best practice is to have a SR of 2.5 to 3.3 cows per hectare on the grazing area platform, with 90 per cent of the herd calving in the first 42 days after calving start date. The focus of efficiency in dairying must target higher grass utilisation per ha. Shalloo (2009) has clearly set out the gains that can be achieved from this.

These efficiencies are necessary if swards with high growth capacity are to have a realistic impact in grazing systems. Key targets for the success of this system are to increase grass production to 18 t DM/ha and grass utilisation to 90 per cent; the ultimate output target of the dairy production system should be the production of 1400-1500 kg milk solids/ha.

Silage production on Irish farms

Apart from providing feed primarily for the winter, the production of grass silage also facilitates efficient grazing management, recycling of nutrients from slurry and biological control of internal parasites. Just over 1 mn of ha Irish grassland is harvested for silage at least once during the year (CSO, 2001), and grass silage is made on 87 per cent of Irish farms (Table 11). The average proportions of this total area harvested for first, second and subsequent cuts of silage were 78, 21 and 1 per cent, respectively. These proportions vary among enterprise, with dairy farms placing the highest emphasis on taking a second cut (69:30:1) and sheep farms the least (92:8:0). The emphasis on second and particularly on third harvests of grass for silage has declined in recent years, and this trend is likely to continue as the length of the grazing season increases into the shoulders of the grazing season.

At least twice as much land is used for silage-making on farms involved in dairying (20 ha or more) compared to other enterprises, with the smallest areas being on cattle rearing (7.9 ha) or sheep (7.1 ha) farms (Table 11). Round bale silage (99 per cent of all baled silage) is made on 74 per cent of all farms, and although it is popular across all enterprises (Table 11) and farms sizes, it is particularly common (and often the primary silage-making system) on cattle rearing (84 per cent) and sheep (81 per cent) farms, and smaller sized (82 per cent) farms. In many cases where it is a secondary system (usually dairy farms), it is used tactically to remove grass from paddocks that are surplus to the short-term needs of the herd (thereby facilitating improved grazing management and overall animal nutrition) or to remove small yields that would be difficult or expensive to successfully ensile.

Most estimates of silage digestibility during the past few decades have shown annual national average DM digestibility’s between 630-700 g/kg. Grass for silage preservation should always be of good quality and, on average this has been the case (Wilson and O’Kiely, 1990; Keating and O’Kiely, 1997). However, these national averages masked a proportion of unsatisfactorily preserved silages which were more frequent when grass was harvested at an early stage of maturity during wet weather conditions.

Table 11: Scale and characteristics of grass silage production in Ireland within different farming enterprises

Due to the emphasis on grazing silage swards early in spring, crops used for silage production need to grow rapidly between spring grazing and the first silage harvest, and to re-grow rapidly where a second harvest of silage is required. It is desirable that grass cultivars be developed that use soil N more efficiently and/or have a lower requirement for N input. Optimal seed mixtures that boost yield and persistency due to synergies between compatible grasses (Helgadóttir et al., 2008) must be identified. Grasses in a mixture should have similar heading dates to make it easier for a farmer to estimate the optimal growth stage at which to harvest the crop.

Grass clover systems

Current grazing systems employ management practises which are optimised for grass growth, with minimal focus on clover. Grass clover swards are not regularly used despite the low national average SR in Ireland. In New Zealand, despite higher stocking rates, clover is an integral component of grazing dairy systems (Woodfield, 1999). The challenge is to integrate clover more into grazing systems and to develop an understanding of the interactions between grass and clover under grazing. Humphreys et al. (2009) reported high levels of milk solids output (1000 kg/ha) from a reasonable SR (2 cows/ha) in high clover content systems. Genetic improvements in white clover have resulted in 1 per cent annual improvements in herbage yield, N fixation and resultant animal performance (Woodfield, 1999). Recent innovations in New Zealand using semi hybrid clover in grazing systems are encouraging. A recent evaluation of semi hybrid clover showed that it produced 50 per cent more DM than conventional clovers over three years. The need for clover is clear in grazing systems, but its successful integration into these systems on farms has yet to be achieved.