Perennial ryegrass (Lolium perenne) is the most common grass on New Zealand farms. Its main advantage is its ability to keep growing over many years. In Europe some perennial ryegrass pastures have been growing for centuries – hence the name.
Perennial ryegrass needs moist fertile soils to grow well and struggles during hot dry summers because of its shallow roots. In wet winters it can recover well from treading and hard grazing by stock.
The feed quality is better if it is grazed every three to four weeks during spring and autumn to remove emerging flower heads and encourage leafy, resilient regrowth.
Endophyte and stock health
Perennial ryegrass usually contains a fungus called endophyte, which lives inside the plant and is transferred to the next generation through seed.
Endophyte produces toxins that can make grass less palatable, but also benefits the grass by deterring insect pests and over-grazing by animals. Plants with endophyte are especially resistant to Argentine stem weevil, a major cause of ryegrass plant loss in pastures. Ryegrass types with little or no endophyte are used in the southern South Island, where pasture pests are much less common.
In the early 1980s endophyte in ryegrass was found to be the cause of ryegrass staggers, a summer-to-autumn disorder in stock. Endophyte can also reduce milk and beef production in summer and early autumn. Perennial ryegrasses are now available with endophyte types that do not produce the animal toxins, but still deter insects.
Italian ryegrass (Lolium multiflorum) is erect and large-leafed, and grows a large amount of high-quality forage for up to three years. Some types survive for only a year (annuals) and are usually sown in autumn, between other winter feed crops.
Italian ryegrass needs highly fertile soils. Its endophyte content is seldom a problem to livestock.
Hybrid ryegrasses are widely used to boost winter pasture in cooler regions. They combine the best features of perennial and Italian ryegrasses, and are sown alone or mixed with perennial ryegrass.
They range from ‘short-rotation’ ryegrasses similar to Italian ryegrass, which have high yields of leafy forage over one to four years, to long-rotation ryegrasses that survive longer. Some contain the same endophyte as perennial ryegrass.
By using drugs to double the sets of chromosomes, researchers have created modified Italian and perennial ryegrasses that are larger, establish faster, are more drought persistent and hardier in winter. They are also preferred by stock because of their high sugar content; and so animals eat more and grow faster.