Increase intake and up milk yield with later grass variety
USING late heading grass varieties in intensive grazing systems increases grass intake and boosts milk yield by up to 180kg during the early grazing season, according to Irish research.
Its widely believed that intermediate varieties of ryegrass provide a timely surge in growth during late April and May, says Teagasc grassland researcher Michael ODonovan. "But this additional grass production is not being converted into extra milk within intensive grazing systems."
To find out why milk yield was unaffected, a study at Teagascs Moorepark Research Centre investigated the sward structure of different ryegrass varieties and its effect on cow performance.
When swards are managed at a height of 8cm, late maturing varieties have 20% more leaf than intermediates due to the higher position of grass leaves on the stem.
This led to an average drymatter intake of 16-18kg/dayfor cows grazing intermediate heading varieties, nearly 2kg/day less than for later headingpaddocks resulting in 180kg extra milk over 180 days. Milk fat and protein yields were also higher with later heading swards.
One reason for these responses is that more than 55% of dry matter yield is stem for intermediate heading varieties compared with 45% for late. Dr ODonovan believes there is no point having a grass variety with a higher dry matter yield when 60% is stem, which is less digestible.
"In later season, intermediate heading varieties have the advantage in terms of grass intake over later heading ones, but this cannot compensate for the loss in milk production during the early grazing season."
Many Irish producers are now taking on these findings with many opting for late heading varieties when reseeding grazing fields, he adds.