Thirty years of plant breeding has evolved modern ryegrasses to provide nutritious feed for animals, including more ryegrass dry matter (DM) available on a seasonal basis.

The range of different heading dates of modern perennial and hybrid ryegrasses drives the between-cultivar variation of the seasonality of DM yield and feed quality. Defined as the time in spring when 50 percent of ryegrass plants have emerged seed heads, the heading date influences the timing of the spring flush of ryegrass DM production. This flush of production occurs approximately six weeks before the heading date. 

Until the late 1990s, most perennial ryegrasses had similar heading dates, offering few management options to manipulate the timing of the spring and summer DM flush, and the onset of seedhead production. Choosing modern ryegrasses with different heading dates offers the opportunity to manage the timing of the flush of spring pasture DM production, and the timing of the onset of a drop in pasture feed quality.

Early to mid-heading ryegrasses produce more DM earlier in spring, but lose feed quality earlier, than later-heading ryegrasses.

Mid-heading ryegrass cultivars such as Excess (+7) perennial ryegrasses drive early spring DM production to support the demands of spring lambing ewes and calving cows.

Figure 1: Average daily growth rates of Vast tetraploid perennial ryegrass compared with other ryegrass cultivars across four trials in Canterbury (2) and Waikato (2) run for three years from 2017.

Note: Data is the combined mean of 4 three year trials completed in Canterbury (2) and Waikato (2). The value in brackets beside each cultivar name is the cultivar's heading date relative to Nui.

Late-heading ryegrasses produce less DM earlier in spring but deliver more quality, late spring and summer feed. These are available as both diploid and tetraploid perennial ryegrass types such as Expo (+21) and Base (+22) respectively. Vast Tetraploid perennial ryegrass, with its late heading date (+36 days after Nui), provides improved spring and summer DM yield and summer feed quality, both of which support a slower post-peak decline for spring-calving dairy herds, better ewe lactational performance, and weaned lamb growth rates (see Figure 1).

When developing regrassing plans, include ryegrass cultivars with a range of ryegrass heading dates as shown in Table 1. Peak spring and early summer DM yield will be more evenly distributed, as will the timing of seedhead production, simplifying the task of keeping on top of late spring and early summer pasture quality.

Contact your local PGG Wrightson Technical Field Representative for assistance developing a re-grassing plan for your farm.

Table 1: Categories of ryegrass and hybrid cultivar heading dates, defined as relative to well-known, older cultivar Nui ryegrass, heading at day zero.