Effect of spring grazing on the yield and quality of perennial ryegrass (Lolium perenne) and cocksfoot (Dactylis glomerata) cut for conservation

Two early perennial ryegrass varieties (Cropper and RvP Hay Pasture), an intermediate perennial ryegrass (Talbot) and an early cocksfoot (Roskilde) were grazed fortnightly by sheep, mown to simulate grazing or left undefoliated from January to May. The effects of spring management on ear emergence, D-value ( in vitro ) and conservation yields were assessed in each of the 2 years 1976 and 1977. Grazing and mowing had a similar effect on date of first (5%) and 50% ear emergence of the ryegrass varieties; the effect was an average delay of 2 d in both stages of growth over the 2 years. Defoliations significantly (P<0·001) delayed the fall in D-value with no significant differences between grazing and mowing in the ryegrass varieties, nor in cocksfoot in 1977. The occurrence of a D-value of 67 was delayed by between 3 and 8 d for the ryegrasses and 9 and 11 d for the cocksfoot. The early ryegrasses produced stemmy regrowths and fell to 67 D-value about 4 weeks after the final defoliations in 1976 and after 5–6 weeks in 1977. The fall in D-value took 7–14 d longer in the intermediate ryegrass. Yields were significantly ( P < 0·001) reduced by grazing and mowing, particularly in 1976. The DM yield reductions in mid June averaged 25% for the ryegrasses and 41% for the cocksfoot.
The results indicate that either first or 50% ear emergence may be used to indicate times when a D-value of 67 will be reached in grazed or ungrazed swards but further work is required to determine the effect of weather conditions on the accuracy of this prediction. An early fall in D-value of early perennials after spring grazing, and a marked reduction in yield of cocksfoot, suggests that these grasses should be used sparingly where spring grazing of fields set aside for conservation is a feature of the farming system.