sward quality throughout the grazing season, and it can achieve a balance of desirable traits. When varieties with close heading dates are sown together, this increases compe- tition between varieties, resulting in an increase in DM yield compared with the average yield of the component varieties sown separately. In contrast, mixtures with a wide heading date range have a lower yield than the corresponding weighted average of their components. In the first year after sowing, most mixtures are likely to change in their composi- tion from what was sown. Early studies suggest that, in mix- tures managed for grazing, later-heading varieties become more dominant, while in silage mixtures, the contribution of earlier-heading varieties tends to increase. In addition, mix- tures with a greater heading date range will change more than those with a smaller heading date range. Tom Niehof, the product manager for forage at Barenbrug, outlines the key benefits achieved using grass seed mixes. “For farmers it’s better to use a mixture because of several reasons,” he said. “The main reason is spreading risks in terms of growing conditions, harvest flexibility and persis- tence, for example, with drought resistance and winter hardiness being important. “The result in your pasture should be a balance between yield potential, animal productivity and climatic or soil ad- aptation. Every single grass species and/or variety has its own characteristics. “That’s why we make specific mixtures into a concept to combine the benefits and eliminate possible risks. Normally we combine three to five varieties into a mixture. Depending on purpose, it can be also up to five species. “When farmers use grasses as forage for ruminants in ani- mal production the main reasons are as a source of protein, energy and digestible fibres. They also need it to stimulate animal health and as a source of palatable feed. “With this in mind, you can imagine that using a mix will fit better in someone’s strategy than using a single variety,” adds Niehof.


Clover inclusion Using white clover in mixtures with perennial ryegrass in a farm system can boost sward production and lead to higher milk solids production. Previous research has shown that white clover use can reduce the need for chemical nitrogen inputs due to a process called biological nitrogen fixation, which occurs in the root nodules of the white clover plant. However, despite these benefits, white clover is still not being fully exploited on many dairy farms. In other research over a three-year period, diploid and tetraploid swards produced the same amount of grass, but when white clover was included there was an extra 1.5t of herbage DM produced each year (17t compared to 15.5t DM/ ha/year). The white clover content declined from 36% to 18% over the three years but this still maintained higher sward DM pro- duction than swards without any white clover. Overall, for every 1% increase in clover content there was an increase in herbage production of around 40kg DM/ha. In addition, swards containing clover were grazed out more efficiently, as shown by a decrease in post-grazing height from 4.32cm in pure grass swards to 3.91cm in grass/ clover swards. The grass/clover swards also had improved nutritive value in terms of digestibility and protein content.


Managing white clover swards White clover is clearly a very different plant from perennial ryegrass, with a different growing habit. It has a lower winter growth rate but has a much higher growth rate in summer and autumn. This means grass/clover swards often have a lower opening farm cover in spring but shorter rotations in summer, due to the extra forage being produced. As white clover has high protein and is highly digestible, there is a risk of bloat, but only when sward clover content is high (typically over 40%).


▶ DAIRY GLOBAL | Volume 8, No. 1, 2021 17


Cows can be picky eaters in- deed. This taste preference can be boiled down to the choice of grass variety used to seed the field.


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