Effect of dairy cattle stocking rate and degree of defoliation on herbage accumulation and quality in ryegrass — white clover pasture

Abstract

Herbage accumulation rates were measured on rotationally grazed ryegrass - white clover swards during five regrowth periods (two in spring and one in each other season). During each regrowth period equal numbers of 3 m² plots were located on farmlets stocked with dairy cows at 2.77 or 4.28 cows/ha. Exclosure cages were placed on the plots during the grazing immediately preceding each regrowth period so that 10, 35, or 60% of the pre-grazing herbage mass was consumed by the cows. The mass of grass leaf, stubble, white clover, dead, green, and total herbage was measured after grazing and every 14 days thereafter for 8 -10 weeks. The rate of green herbage accumulation was not significantly influenced by the degree of defoliation for the 28-day period immediately following grazing. The rate of dead and total herbage accumulation increased as the degree of defoliation decreased, although significance was rarely reached. This was reflected in in vitro digestibility of late spring, summer, and autumn swards. With long regrowth intervals (56 -70 days) swards had the opportunity to reach ceiling herbage mass, and as a result herbage accumulation was affected. Green herbage accumulation was greater and dead herbage was less in hard than in lax grazed swards. Differences in the rate of accumulation of total and green herbage accumulation between stocking rates were positively associated with differences in tiller density. Ceiling herbage mass was reached in late spring, summer, and autumn, and varied with season (6.5, 5.8, and 3.8 t DM/ha respectively).

Keywords:

• grassland management
• dairy cattle
• herbage accumulation
• perennial ryegrass
• white clover
• tiller density
• botanical composition